CCA Technical Support CD_2005

Course for Cement Applications 

Technical Documentation 

Version 2005

Guidelines 

This CD rom contains the current version of the 

Technical Documentation developed by Holcim 

Group Support Ltd Divisions on which the Course 

for Cement Applications is based. 

It is divided into 2 sections: 

• Cement Section 

Clicking on the section will link the user to 

the contents page of that section. Chapters 

within each section can be accessed by 

clicking on the chapter title. 

Other sections and chapters can be 

accessed directly by clicking on the 

navigation bar in the header of each page. 

• Concrete Section

Cement 

Concrete 

Cement - Contents 

Chapter No. 

1. CEMENT HYDRATION .................................................................................................... 2 

2. CEMENT PROPERTIES ................................................................................................ 30 

3. CLINKER OPTIMIZATION ............................................................................................. 48 

4. MINERAL COMPONENTS............................................................................................. 67 

5. CEMENT ADMIXTURES.............................................................................................. 121 

6. CEMENT GRINDING.................................................................................................... 125 

7. PROPERTIES AND APPLICATION OF COMPOSITE CEMENTS ............................. 147 

8. SPECIAL CEMENTS.................................................................................................... 177 

9. CEMENT STANDARDS ............................................................................................... 194 

Course for Cement Applications - 2005 Cement Section - Page 1 of 220

Cement 

Concrete 

Cement Hydration 

Author: S. Montani 

1. INTRODUCTION ................................................................................................................... 3 

2. MAIN FEATURES OF CEMENT HYDRATION .................................................................... 3 

3. HYDRATION REACTIONS ................................................................................................... 4 

3.1 ...Hydration of the individual clinker components.......................................................... 4 

3.2 ...Mineral additives ........................................................................................................ 6 

4. MECHANISM AND KINETICS.............................................................................................. 6 

4.1 ...Basic theories............................................................................................................. 6 

4.2 ...Reaction sequence during cement hydration............................................................. 7 

4.3 ...Acceleration or retardation of cement hydration ........................................................ 9 

5. HEAT OF HYDRATION ...................................................................................................... 11 

6. ROLE OF GYPSUM IN CEMENT ....................................................................................... 14 

6.1 ...General aspects ....................................................................................................... 14 

6.2 ...Calcium sulphate modifications................................................................................ 14 

6.3 ...Gypsum and setting of cement ................................................................................ 15 

6.4 ...Effect of gypsum on strength and volume stability................................................... 18 

6.5 ...Gypsum substitutes.................................................................................................. 20 

7. MICROSTRUCTURE AND PROPERTIES OF HARDENED CEMENT 

PASTE .............................................................................................................................. 21 

7.1 ...Basic physical features ............................................................................................ 21 

7.2 ...Morphological features............................................................................................. 22 

7.3 ...Evolution of pastes during hydration ........................................................................ 25 

7.4 ...Influence of the aggregates on the structure............................................................ 28 

8. LITERATURE...................................................................................................................... 29 

8.1 ...General overview on cement hydration.................................................................... 29 

8.2 ...Gypsum and setting of cement ................................................................................ 29 

8.3 ...Microstructure and properties of hardened cement paste........................................ 29 


Cement 

Concrete 

1. Introduction 

The term cement hydration applies to all the reactions of cement with water. These reactions 

determine to a great extent the concrete properties, as it is finally the mixture of cement with 

water which is the binding agent in concrete. With regard to the cement application, it is thus 

essential to have a basic understanding of the processes occurring during cement hydration. 

To a minor extent, hydration reactions can also take place before the cement is applied in 

concrete during the storage of clinker and the grinding and storage of cement. Even this 

minor surface hydration may cause serious changes of the physical properties of cement. 

Table 1 gives an idea of the possible hydration of cement from clinker storage up to cement 

application. 

Table 1: 

Occurrence of cement hydration 

Storage of clinker 0 to 10% 

Grinding of cement 0 to 1% 

Storage of cement 0 to 4% 

Concrete mix 0 to 100% 

Percentage hydration 

The study of the mechanisms and phenomena of cement hydration has a long tradition in 

cement research. First basic theories to explain setting and hardening of cement have been 

established by Le Châtelier and Michaelis at the end of the last century. The actual more 

refined theories still base on the work of these two researchers. The open questions 

remaining are principally related to the reaction of C 3 S and C 3 A at early stages. 

2. Main Features of Cement Hydration 

As for any chemical reaction, main features of interest with regard to the cement hydration 

are the hydration reactions, the mechanisms and kinetics and the heat of hydration. In the 

following, a brief overview on these three aspects shall be given: 

♦ Hydration 

reactions 

The nature of the hydration products is decisive for the mechanical properties of the 

hardened concrete. In Portland cement, the hydration is predominantly a reaction of the 

calcium silicates with water, producing a gel-like calcium silicate hydrate and calcium 

hydroxide: 

Calcium silicates + H 2 O → CSH gel + Ca(OH) 2 

In blended cements, the reaction schemes get more complex. Nevertheless, the 

hydration products are in general quite similar. 

♦ Mechanisms and kinetics 

The understanding of the mechanisms of cement hydration gives valuable indications on 

the reaction behaviour to be expected, including the kinetics. The knowledge of the 

kinetics of cement hydration and the influencing factors is very important for the concrete 

practice. The reaction speed of the cement hydration must be slow enough to allow the 

placement of concrete; after that, a rapid reaction is desired. 


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Concrete 

♦ Heat of hydration 

The heat liberated during cement hydration may improve or impair the quality of the 

concrete. For ordinary Portland cement, the heat of hydration is typically 380 J/g at 28 

days. This value is lower for the other special Portland cements with the exception of 

rapid hardening cement. In case of the blended cements, generally less heat is 

developed. 

Besides the above mentioned chemical aspects, considerable changes in the physical 

properties of the cement are associated with the cement hydration. The principal changes 

are: 

♦ Development of strength 

From the practical point of view of course the most important change. As long as the 

hydration proceeds, the cement is continuously gaining strength. 

♦ Increase in specific surface 

The transformation of the low surface cement to a gel-like hydrated product of extremely 

high surface is one of the most striking changes of cement hydration. After complete 

hydration, typically a 1000 fold increase in specific surface is obtained. 

♦ Increase in solid volume 

The total volume occupied by the hydration products is roughly twice the volume 

occupied originally by the unhydrated cement. That means that 1 cm 3 of cement will give 

more or less 2 cm 3 of hydrated cement. 

More detailed and specific indications on the different aspects of cement hydration will be 

given in the following chapters. 

3. Hydration Reactions 

3.1 Hydration of the individual clinker components 

3.1.1 Calcium silicates 

The hydration reactions of the two calcium silicates in clinker - C 3 S and C 2 S - can be 

represented by the following chemical equations: 

2 (3CaO • SiO 2 ) + 6H 2 O 3CaO • 2SiO 2 • 3H 2 O + 3Ca(OH) 2 

Weight fraction 100 + 24 75 + 49 

(in symbols of cement chemistry: 2C 3 S + 6H C 3 S 2 H 3 + 3CH) 

2 (2CaO • SiO 2 ) + 4H 2 O 3CaO • 2SiO 2 • 3H 2 O + Ca(OH) 2 

Weight fraction 100 + 21 99 + 22 

(in symbols of cement chemistry: 2 C 2 S + 4H C 3 S 2 H 3 + CH) 

The reactions of both silicates are thus stochiometrically very similar and require more or 

less the same amount of water. The main difference between the two reactions is that C 3 S 

produces more than twice as much calcium hydroxide as C 2 S. 

The principal hydration product of the calcium silicates is a gel-like or microcrystalline 

calcium silicate hydrate. The formula C 3 S 2 H 3 is only approximate, because the composition 

of this hydrate is actually variable over quite a wide range. In contrast, the calcium hydroxide 

formed is a crystalline material with a fixed composition. 

It is believed that calcium hydroxide is not significantly contributing to strength and that the 

calcium silicate hydrates are in the first place responsible for the strength development. The 

importance of the calcium hydroxide being a strong base is mainly related to its effects on 


Cement 

Concrete 

the passivation of the steel reinforcement, the leaching of concrete and the reaction with 

reactive silica and alumina from pozzolanic additives. 

3.1.2 Tricalciumaluminate 

The hydration of aluminates is heavily influenced by the presence of gypsum. In the absence 

of gypsum, the reaction of C 3 A with water is very violent and leads to immediate stiffening of 

the paste (known as flash set) due to the rapid formation of hexagonal calcium aluminate 

hydrates (C 2 AH 8 and C 4 AH 13 ). These hydrates are not stable and later convert into the cubic 

form C 3 AH 6 , so that the final form of reaction can be written as follows: 

3CaO • Al 2 O 3 + 6H 2 O 3CaO • Al 2 O 3 • 6H 2 O 

Weight fraction 100 + 40 40 

(in symbols of cement chemistry: C 3 A + 6H C 3 AH 6 ) 

The theoretical capacity of C 3 A to combine with water is such that 100 parts by weight of C 3 A 

combine with 40 parts by weight of H 2 O; it is thus nearly double that of the silicates. 

When gypsum is present in the cement, flash set can be avoided and the C 3 A reacts first with 

the gypsum to form calcium trisulfate-aluminate hydrate (ettringite): 

3 CaO • Al 2 O 3 + 3CaSO 4 + 32H 2 O 3 CaO • Al 2 O 3 • 3CaSO 4 • 32H 2 O 

Weight fraction 66 + 100 + 137 203 

(in symbols of cement chemistry: C 3 A + 3CS + 32H C 3 A • 3 CS • H 32 ) 

This reaction continues until all the available gypsum is used up. After the depletion of 

gypsum, ettringite is converted into the monosulfate: 

3CaO • Al 2 O 3 • 3CaSO 4 • 32H 2 O + 2(3CaO • Al 2 O 3 ) + 4H 2 O 

(3CaO • Al 2 O 3 • CaSO 4 • 12H 2 O) 

(C 3 A • 3CS • H 32 + 2C 3 A + 4H 3C 3 A • CS • H 12 ) 

Calcium aluminate hydrate continues to be formed from any remaining unhydrated C 3 A and 

the final product of C 3 A hydration is generally a monosulphate-calciumaluminate hydrate 

solid solution. 

3.1.3 Ferrite phase 

The C 4 AF forms the same sequence of hydration products as does C 3 A, with or without 

gypsum. The reactions are, however, slower; C 4 AF never hydrates rapidly enough to cause 

flash set and gypsum retards C 4 AF hydration more drastically than it does C 3 A. 

3.1.4 Calcium oxide and magnesium oxide 

The uncombined lime (calcium oxide) and periclase (magnesium oxide), if present in large 

quantities in cement, may cause expansion due to a slow hydration reaction after the setting: 

CaO + H 2 O Ca(OH) 2 ; MgO + H 2 O Mg(OH) 2 

The actual degree of expansion depends on the state and distribution of these oxides in 

cement, in particular the large crystals of periclase or hard burnt free lime produce 

unsoundness. 

3.1.5 Alkalis 

Alkalis are present as alkalis sulphates or are incorporated in the main clinker phases. The 

first type of alkalis go readily into solution upon mixing with water and accelerate the early 

hydration reactions. The effect of alkalis contained in the clinker phases is not well known; 


Cement 

Concrete 

there is at least some dissolution with time which has some effect on later hydration 

reactions. 

The presence of alkalis in the pore solution generally does not give any special problems 

except when certain aggregates are used that can participate in the alkali-aggregate reaction 

leading to expansion and disruption of the concrete. The aggregates giving raise to such a 

reaction contain either reactive silica or dolomite minerals. 

3.2 Mineral additives 

3.2.1 Blast furnace slag 

Granulated blast furnace slag does not hydrate per se in water, but in the presence of 

activators like lime, alkalis, sulphate and Portland cement, it shows hydraulic properties. The 

activators appear to function by the removal of passive surface films that act as a barrier to 

significant hydration. The glass in the granulated slag is the hydraulic component in the 

presence of Portland cement. 

The hydration reactions of blast furnace slag are not easy to follow and it is thus difficult to 

establish clear reaction equations. Studies on slag cements have revealed that the hydration 

products of the slag hydration are similar to those of the calcium silicate reaction. It is 

believed that the main difference to Portland cement hydration is the lower C/S ratio of the 

calcium silicate hydrates and the reduced amount of calcium hydroxide present. 

3.2.2 Pozzolanic additives 

The natural and artificial pozzolans contain reactive siliceous and aluminous materials which 

on their own do not possess cementitious properties. They react, however, in the presence of 

water with dissolved calcium hydroxide released from the hydration of the Portland cement 

clinker. The reaction products are calcium silicate and calcium aluminate hydrates similar to 

those found in the hydration of Portland cement clinker. Favourable for this pozzolanic 

reaction seems to be the presence of alkalis. 

3.2.3 Limestone filler 

Finely ground limestone can react during hydration with the C 3 A from the clinker to form 

monocarboaluminate (C 3 A • CaCO 3 • 11H 2 O). The presence of limestone in the cement can 

thus to a certain extent retard the hydration of C 3 A, but it is by far less effective than gypsum 

and can not avoid flash set. Moreover, fine limestone filler can have an indirect influence on 

the hydration reaction of C 3 S. 

4. MECHANISM AND KINETICS 

4.1 Basic theories 

As mentioned in the introduction, the first theories to explain setting and hardening of cement 

were advanced by Le Châtelier and Michaelis. Le Châtelier attributed the development of 

cementing action to the passage of the anhydrous cement compounds into solution and the 

precipitation of the hydration products as interlocking crystals. In the theory put forward by 

Michaelis, cohesion is considered to be the result of the formation of a colloidal gelatinous 

mass. The formation of the gel may take place without the cement compounds going into 

solution by a direct „topochemical“ or „solid state“ reaction. 

Both hydration mechanisms take place within in the cement paste. Cementitious reaction 

initially takes place by some dissolution and precipitation, whilst the hydrated material formed 

has only a small degree of crystalline order being gel-like and of colloidal dimensions. The 


Cement 

Concrete 

colloidal theory can also explain the phenomena of swelling, shrinkage, creep and 

selfhealing of cracks. 

4.2 Reaction sequence during cement hydration 

Hydration of cement is a sequence of overlapping chemical reactions between clinker 

components, mineral additives, calcium sulphate and water, leading to continuous cement 

paste stiffening and hardening. The hydration reactions described before proceed 

simultaneously at differing rates and influence each other. 

A simplified schematic presentation of the hydration process of Portland cement is given in 

Figure 1. The three main stages which can be distinguished in this presentation are: 

First stage 

In the first stage, ettringite and calcium hydroxide are formed. The ettringite covers the 

aluminate particles and avoids flash set of the cement paste. After these first reactions, the 

so-called „dormant“ period of typically four to six hours starts where no considerable further 

hydration takes place (certain increase in Ca 2+ concentration). 

The dormant period is usually explained by the behaviour of the C 3 S, the main constituent of 

Portland cement. The two principal theories are based on the protective layer and the 

delayed nucleation concept respectively. The first ascribes the „dormant“ period to the 

formation of a protective layer on the C 3 S particles which is destroyed with time and the latter 

regards the retardation in C 3 S reaction as the cause of a delayed nucleation of the 

corresponding hydration phases. 

Still in the first stage, the cement paste is setting. This stiffening is attributed by some 

researchers to the recrystallisation of the initially finely divided ettringite. Others believe that 

the setting is caused by the loss in plasticity due to some first formation of calcium silicate 

hydrate from C 3 S. 

Figure 1: 

Schematic representation of the formation of hydrate phases in Portland 

cement paste 


Cement 

Concrete 

Second stage 

The second stage after the dormant period is characterised by the restarting of the hydration. 

Precipitation of CSH in form of long fibres and calcium hydroxide takes place on the surface 

of the silicate phases and the reaction proceeds rapidly for all clinker phases. This stage 

ends with the termination of the ettringite formation and the development of a basic matrix 

after about 24 hours. 

Third stage 

In the third stage, the spaces between the solid particles are overbridged and filled with short 

fibres of the CSH phase. The initial matrix, formed by first hydrates of the aluminate, ferrite 

and silicates, is thus densified and the strength of the cement paste increases. The calcium 

hydroxide formed in large crystals is built into the CSH gel matrix. At this stage, ettringite is 

converted into monosulfate and corresponding hydration products are formed from the still 

not hydrated aluminate and ferrite phases. 

As the hydration proceeds, the reactions get more and more diffusion controlled and the 

overall rate of reaction is decreasing. Hydration reactions, primarily those of C 2 S, will 

continue as long as the reactants and space permit it; this can go on for years. In practice, 

there is usually never a complete hydration of the cement and unhydrated cement is nearly 

always remaining in the hardened cement paste. 

A good overview on the hydration reactions in Portland cements can also be obtained by 

taking a look at the heat evolution curves. Figure 2 shows such a curve with the indications 

of the main reactions going on in the process of cement hydration. 

Figure 2: 

Heat evolution curve of Portland cement 


Cement 

Concrete 

For blended cements, the reactions sequences get more complex. In case of the active 

mineral additives, the main differences to Portland cement hydration can be seen in more 

formation of CSH phase at later stage and a decrease in the amount of calcium hydroxide 

and the pore space. For the inert mineral additives, the effect will primarily be a „dilution“ of 

the Portland cement matrix. 

A general effect observed in blended cement is a certain delay of setting and hardening at 

early stages. Normally, the active mineral additives start to contribute to cement hydration 

only after more than 3 days, when suitable activation has taken place (blast furnace slag) or 

sufficient calcium hydroxide has been formed (pozzolans) for their reaction. 

4.3 Acceleration or retardation of cement hydration 

The process of hydration can be accelerated or retarded by different factors: 

♦ Use of accelerators and retarders 

Until now, the most efficient accelerator is calcium chloride (CaCl 2 ), but the problem with 

this product is the corrosion of the steel reinforcement. The exact mechanism of 

acceleration by CaCl 2 is not known; it is believed that CaCl 2 is acting like a catalysator. 

Retarders for cement hydration are for instance phosphates, zincates and carbohydrates 

(including sugar). The retarding action is simply explained by the formation of a 

monomolecular protective film around the cement particles which slows down their 

reaction with water. 

♦ Hydration temperature 

The rate of hydration is strongly influenced by the temperature. Rate of hydration at early 

age roughly doubles when the temperature increases by 10°C. The effect of temperature 

on cement hydration is of particular importance in extreme climates and for steam curing. 

♦ Cement fineness 

The higher the fineness of the cement, the more extended is the zone of reaction. This 

leads of course to a higher rate of hydration. 

♦ Cement composition 

The activity of the clinker used in the cement affects considerably the rate of hydration. A 

high rate of hydration can be expected of clinkers rich in C 3 A and C 3 S (see Figure 3) and 

with a high alkali content. 

Important for the rate of hydration is also the content of mineral additives in the cement. 

The rate of hydration generally is the lower, the higher the dosage of mineral additives in 

the cement. 


Cement 

Concrete 

Figure 3: 

Rates of hydration of compounds in Portland cement 

Increasing the rate of hydration, and hence the early strength development, is always done 

at the expense of the ultimate strength. An explanation is that the microstructure formed 

during the accelerated hydration is usually more coarse and less favourable for strength 

development. Contrary to this, retarded, slow hydration leads to the formation of a more 

refined microstructure which results in better final strength. 


Cement 

Concrete 

5. Heat of Hydration 

The hydration reaction is an exothermic process, that means during the reaction of cement 

with water heat is liberated. The quantity of liberated heat is quite appreciable (typically 380 

J/g for OPC at 28 days) and can lead to a significant temperature rise in mass concrete 

construction, where the heat is not allowed to escape (see Figure 4). During cooling of the 

hardened concrete, thermal gradients may develop and give problems with crack formation. 

That is the reason why special low heat cements have to be used for mass concrete 

applications. 

Figure 4: 

Temperature rise in 1:9 (weight) concrete under adiabatic conditions for 

different Portland cement types 

The main measure to control the heat of hydration of Portland cement is the adjustment of 

clinker composition. The clinker minerals contributing most to the heat of hydration are C 3 S 

and C 3 A (see Table 2), so that it is necessary to limit these compounds to reduce heat 

development during hydration. On the other hand, it is also possible to keep the heat 

liberation low by not grinding the cement too fine. 


Cement 

Concrete 

Table 2: 

Heat of hydration of the clinker components at 21°C (J/g) 

Clinker component 3 days 28 days 6 ½ years 

C 3 S 245 380 490 

C 2 S 50 105 225 

C 3 A 890 1380 1380 

C 4 AF 290 495 495 

The effect of clinker composition and cement fineness on the heat of hydration can be well 

seen in Figure 5 which shows the development of heat of hydration for the different Portland 

cement types. The low heat cements used for mass concrete - type II and IV ASTM - with 

low heat of hydration of about 250 to 300 J/g after 28 days contain less C 3 S and C 3 A and are 

fairly coarse. The rapid hardening cement - type III ASTM - with increased heat of hydration 

of about 420 J/g after 28 days is usually richer in C 3 S and C 3 A and of higher fineness, 

compared with the ordinary Portland cement - type I ASTM. 

Figure 5: 

Development of heat of hydration for the different Portland cement types 

cured at 21°C (w/c-ratio of 0.40) 

For practical purposes, it is not only the total heat of hydration that matters but also the rate 

of heat evolution. The same total heat produced over a long period of time can be dissipated 

to a greater degree, consequently producing a smaller rise in temperature in the concrete. In 

ordinary Portland cement about one half of the total heat is liberated between 1 and 3 days 

and about three quarters in 7 days. It is common to specify the heat of hydration after 7 and 

28 days, giving a reasonable indication of both total heat of hydration and its rate of 

liberation. 


Cement 

Concrete 

In addition to the composition and fineness of cement, the rate of heat evolution is also 

greatly influenced also by the temperature of hydration (see Table 3). The ambient conditions 

thus play also a decisive role with regard to the effects of heat of hydration on the concrete 

properties. 

Table 3: 

Heat of hydration (J/g) developed after 3 days at different temperatures 

Cement type 

Temperature of cement hydration 

4°C 24°C 32°C 41°C 

I 154 285 309 335 

III 221 348 357 390 

IV 108 195 192 214 

A very effective means to reduce the amount and rate of heat of hydration of Portland 

cement is the use of mineral additives in the cement (blended cements). By the replacement 

of the clinker by the less reactive or inert mineral additives, the heat development of the 

cement can be easily controlled. As an example, the heat development curves of slag blends 

with different Portland cement contents are presented in Figure 6. The advantage of the 

blended cement over the low heat Portland cements is that the same clinker as for the 

ordinary Portland cement can be used. 

Figure 6: 

Heat of hydration of mixtures of OPC (P.C.) and ground blast furnace 

slag (S); isothermal method. 


Cement 

Concrete 

6. Role of Gypsum in Cement 

6.1 General aspects 

Ever since cement has been produced in greater quantities, gypsum (CaSO 4 •2H 2 O) has 

been ground into the cement. Gypsum is added to the cement mainly for the purpose of 

regulating its setting time. It prevents flash setting and makes the concrete workable for 

hours. 

The gypsum influences not only the setting but also other cement properties such as 

grindability, sensitivity to storage, volume stability and strength. Gypsum is an extremely 

important part of cement. It is, however, often neglected to pay proper attention to it in the 

production of cement. 

Here, only the effect of gypsum on setting, volume stability and strength shall be elucidated 

more in detail. For the better understanding of the influence of gypsum on cement, it is first 

necessary to take a look at the different modifications in which calcium sulphate can be 

present. In a final part of this chapter, the possible gypsum substitutes shall be discussed. 

6.2 Calcium sulphate modifications 

In cement, it is possible to find at least five basic modifications of calcium sulphate (see 

Table 4). The stable modifications, dihydrate (gypsum) and anhydrite II (natural anhydrite), 

can be found in nature and both are used as additives to clinker in the grinding process. The 

metastable modifications, hemihydrate and anhydrite III, are not available in nature, but can 

easily form during grinding and storage of cement at elevated temperatures by dehydration 

of gypsum. The high temperature modification anhydrite I can form during burning of the 

clinker in the cement kiln. 

Table 4: 

Modifications of calcium sulphate in cement 

Designation Formula Crystal 

water 

Density 

Range of 

stability 

Solubility at 

20°C 

Occurrence 

% g/cm 3 °C % nature cement 

Dihydrate CaSO 4 •2H 2 O 20.92 2.32 < 40 0.20 yes yes 

Hemihydrate CaSO 4 •1/2H 2 O 6.21 2.70 metast. 0.95 no yes 

(α,β) 

Anhydrite III CaSO 4 0 2.50 metast. 0.95 no yes 

(α,β) 

Anhydrite II CaSO 4 0 2.98 40-1180 0.20 yes yes 

Anhydrite I CaSO 4 0 -- > 1180 -- no (~clinker) 

The different mode of action of the individual modifications on the properties of cement can 

be mainly attributed to their different solubilities in water. In Figure 7, it can be seen that the 

solubility of the hemihydrate and anhydrite III is appreciably higher than that of dihydrate or 

anhydrite II. The high solubility of hemihydrate and anhydrite III can lead to anomalous 

setting, as discussed later. The solubility of dihydrate and anhydrite II in the ambient 

temperature range is approximately the same, but their effect on properties of cement can be 

very different. The reason for this is the different rate of solubility which is greater for the 

dihydrate than for anhydrite II. 


Cement 

Concrete 

Figure 7: 

The Solubility of gypsum, hemihydrate and anhydrite 

6.3 Gypsum and setting of cement 

The reactions which take place immediately after the addition of water to cement are of 

decisive importance for the setting of cement. Directly after the mixing of cement with water, 

sulphate dissolves and reacts with aluminate to form ettringite. This vigorous initial reaction 

ceases after a few minutes and then the so-called dormant period starts. 

According to the classical theory, the set retardation is due to the fact that the ettringite forms 

a cohesive cover around the aluminate particles and in this way inhibits their further reaction 

(see Figure 8). The reaction inhibiting effect of the ettringite cover is ended only when this 

cover is broken open by the pressure of crystallisation and not sufficient sulphate is left to 

close the burst section. Thereafter, the reaction of C 3 A can continue unhindered until 

complete hydration. 


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Concrete 

Figure 8: 

Schematic description of set retardation due to C 3 A sulfate interaction 


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Concrete 

The reasons for the setting of cement are still not exactly known. Some researchers explain 

the setting of the cement by the recrystallisation of the initially finely divided ettringite into 

bigger crystals which are building bridges between the cement particles. Other researchers 

attribute the initial set of cement as corresponding to that stage in the hydration sequence 

when a sufficient amount of tricalcium silicate has been converted to calcium silicate hydrate. 

This initial removement of water causes a partial loss of the plasticity of the cement paste. 

The setting of cement is mainly influenced by the reactivity of the clinker (i.e. C 3 A and alkali 

content) and by the type and amount of the calcium sulphate added. The cement fineness, 

the dosage of mineral additives, use of chemical admixutres and the hydration temperature 

play also an important role. The effect of C 3 A content, gypsum dosage and hydration 

temperature on the initial setting of Portland cement is illustrated in Figure 9. 

Figure. 9: 

Influence of gypsum dosage, C 3 A content and hydration temperature on 

initial setting of Portland cement 

In order to obtain normal setting, it is essential to adjust the supply of soluble sulphate to the 

reactivity of the clinker during the first minutes and hours of hydration (see Figure 10). If 

there is no proper balance between sulphates and clinker reactivity, abnormal setting can 

occur: 

Flash set is caused by the formation of aluminate hydrate, due to a high content of reactive 

C 3 A and/or a too small amount of easily soluble calcium sulphate. 

False set can be traced back to high temperature in the mill, causing a dehydration of the 

gypsum to an easily soluble hemihydrate and anhydrite III. Hemihydrate and anhydrite III 

recrystallize to gypsum whose crystals grow into each other and form a solid framework 

which affects the stiffening of the cement paste. This framework of gypsum crystals is broken 

down again through reaction with C 3 A. For this reason the cement paste can regain its 

previous plasticity by remixing. 

Quick set: The high content of easily soluble sulphate and reactive clinker minerals can also 

have an accelerating effect on the formation of sulfo-aluminate hydrate and calcium silicate 

hydrate which can likewise lead to early stiffening of the cement (quick set). 


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Concrete 

Figure 10: 

Formation of rigid structure during setting of Portland cement 

Effect of gypsum on strength and volume stability 

The addition of gypsum - in addition to its principle purpose of regulating setting - has a 

significant effect on the strengths and volume stability. Up to a certain limit, which depends 

on the clinker composition, the gypsum addition increases the strengths and prevents 

shrinkage. If the gypsum addition surpasses this limit, it causes considerable swelling which 

can lead to expansion. This is why an upper limit for the SO 3 content is given in the cement 

standards (see Fig. 11). 


Cement 

Concrete 

Figure 11: Shrinkage and compressive strength of cements as a function of the SO 3 

Content 

The gypsum required to obtain optimum strength and volume stability grows with the C 3 A 

content of the clinker, cement fineness, alkali content and application temperature. Other 

variables influencing the optimum SO 3 content are the form (and solubility) of the calcium 

sulphate in the cement, the nature and amount of mineral additives and also the presence of 

chemical admixtures. Often the optimum SO 3 content would be even above the maximum 

value given by the standards. 


Cement 

Concrete 

6.4 Gypsum substitutes 

There has never been lack of effort to substitute gypsum by other set regulators. In particular 

in countries with few natural gypsum deposits, the cement industry is searching intensively 

for alternative materials. The main alternatives up to date are the use of natural anhydrite 

and limestone and the application of by-product gypsum coming form other industries. 

The use of natural anhydrite as partial substitute for gypsum is already well established in 

practice. In general, it appears that blends of 40 to 60 percent gypsum and 60 to 40 percent 

natural anhydrite can be safely used with all clinkers. The advantage of such blends over 

pure gypsum is the reduction of the risk of false setting and the improved storage stability 

and flowability of the cement. 

In some places, limestone is used as replacement for gypsum. For very reactive clinkers, the 

replacement is typically limited to 25%. In cements with less reactive clinkers, replacement 

levels of up 50% may be possible without negative effects on the setting of cement. 

With respect to by-product gypsum, there are a number of commercial processes which 

produce such materials. An overview on the main sources of by-product gypsum is given in 

Table 5; the most important sources regarding quantities are phosphogypsum and 

desulphogypsum. Another type of by-product not mentioned in the table are used plaster 

moulds, which are for instance used in casting certain clay products. 

Table 5: 

Main sources of by-product gypsum 

Product/process By-product % sulphate* % impurities 

orthophosphoric acid phosphogypsum 95-98 (G) 0.2-1.5 P 2 O 5 , up 

to 1.5 fluoride 

hydrofluoric acid fluorogypsum 80-95 (HH or AH) 2-3 CaF 2 , 

unreacted 

silicofluorides 

citric, formic and organogypsum --- --- 

tartaric acid 

boric acid borogypsum 40-50 (G), 20-30 (AN) 7-10 H 3 BO 3 

flue gas SO 2 removal desulfogypsum 90-95 (G), sulfite for mod. --- 

process 

titanium white titanogypsum 90-95 (G) 0.4 TiO 2 

* G = CaSO 4 • 2H 2 0, HH = CaSO 4 • ½H 2 O, AN = CaSO 4 

The main problem for the use of such by-products as subsitute for natural gypsum is the 

presence of impurities, which may have some harmful effect on setting, strength develpment 

or some other property of the cements. Moreover, the amount of impurities can fluctuate 

quite a lot so that the variability in cement properties may also be higher. 


Cement 

Concrete 

7. Microstructure and Properties of Hardened Cement Paste 

7.1 Basic physical features 

In this section we deal with the physical structure of hydrated cement paste (HCP), as well as 

the effect of its morphology on the important properties of hardened concrete. 

We will be concerned with the main chemical reaction taking place during hydration: 

Calcium Silicates + H 2 O ---> C-S-H + Ca(OH) 2 

where C-S-H are the hydrates of the Calcium Silicates (C 3 S and C 2 S), also called "C-S-H 

gel". 

The most important physical aspect of that reaction is the fact that the total volume occupied 

by the hydration products is, roughly, twice the volume occupied originally by the unhydrated 

cement (see Figure 12): 

Figure 12: 

Basic physical feature of cement hydration 

It must be mentioned that, out of that total volume, 28 % are very small pores (gel pores) and 

the rest (72 %) is solid phase: 

Gel pores = 0.28 Vhp 

Figure 13 shows schematically the growth of crystals during hydration of two pastes, one of 

low and the other of high water/cement ratio (w/c). The w/c ratio is a measure of the degree 

of dispersion of the cement grains in water. 


Cement 

Concrete 

Figure 13: 

Structure formation in cement paste during hydration 

High w/c 

Low w/c 

0 h 

No setting 

Setting 

2 - 4 h 

High age 

Cement hydration can be seen as a continuous process by which the capillary pores (space 

originally occupied by water) are being gradually filled with hydration products. 

7.2 Morphological features 

Figure 14 presents a model (Feldman and Sereda) of the general structure of HCP, showing 

its main features. 

In the hydrated cement paste, there are two distinctive phases: 

♦ Solid Phases 

♦ Pores (at least partially filled with water) 


Cement 

Concrete 

Figure 14: 

Model of Feldmann and Sereda for the general structure of hydrated 

cement paste 

Legend 

x Water in interlayer regions 

o Water absorbed on surfaces 

C Capillary 

pore 

— C-S-H sheets 

7.2.1 Solid phases 

7.2.1.1 CALCIUM SILICATE HYDRATES-(C-S-H) 

The C-S-H particles occupy 50 - 60 % of the total solid volume in hydrated paste; it is also 

called C-S-H gel. The particles are very small (colloidal dimensions) and sheet-like shaped 

(see Figure 15) 

Figure 15: 

Basic feature of C-S-H particle 

The C-S-H particles are arranged as a highly disordered layered structure (see Figure 14) 

with very high specific surface ≈ 3.000.000 cm 2 /g. 

The strength of the HCP is attributed to the attraction forces between the C-S-H crystals over 

their enormous surface. 

The space left between the particles is called gel pores; these pores are extremely small 

(about 1.5 nm), of the order or magnitude of a water molecule (0.25 nm). 


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Concrete 

7.2.1.2 CALCIUM HYDROXIDE (CH) 

Compound with a definite stoichiometry: Ca(OH) 2 , forming large crystals (0.01 - 0.1 mm) of 

hexagonal shape (Portlandite). 

These crystals constitute 20 - 25 % of the solid volume in the hydrated paste. 

Their contribution to strength is low (low surface area); however, their presence is very 

important to passivate the embedded steel rebars. 

7.2.1.3 CALCIUM SULFOALUMINATES 

Occupy 15 - 20 % of solid volume in hydrated paste; they only play a minor role in strength. 

There exist two forms: 

Ettringite: Elongated needle shaped crystals 

Monosulfate: Hexagonal plates or "rosettes" 

Iron oxide can replace aluminium oxide in the Crystal structure. 

7.2.1.4 UNHYDRATED CLINKER GRAINS 

Smaller grains react faster and coarser grains (> 30 µm) tend to remain partially unhydrated. 

7.2.2 Pores 

7.2.2.1 LNTERLAYER SPACE IN C-S-H (GEL PORES) 

Occupy 28 % of bulk volume of C-S-H gel 

Size: 0.5 nm - 2.5 nm (H 2 O molecule = 0.25 nm) 

They are always present in HCP but, due to their small size do not adversely affect strength 

and permeability. However, the movement of water - that is firmly held within the gel pores - 

is the main reason for drying shrinkage and creep. 

7.2.2.2 CAPILLARY PORES 

Represent the space originally occupied by water, not filled with hydration products. Their 

size and volume depend on the w/c ratio and the degree of hydration: 

♦ well hydrated paste, low w/c: 10 - 50 nm 

♦ at early ages, high w/c: up to 10 µm 

7.2.2.3 MACROPORES 

Air bubbles naturally entrapped or intentionally entrained during mixing (10 - 100 µm). 

"Compaction" voids: mm or cm 


Cement 

Concrete 

7.3 Evolution of pastes during hydration 

Figures 16, 17 and 18 show the evolution of the structure of cement pastes, made with the 

same amount of cement (1 kg) but with different w/c ratios, during hydration (under water). 

Figure 16: 

Development of Hydration of Cement Paste made with 1 kg of cement; 

w/c = 0.70 

Figure 17: 


w/c = 0.50 


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Concrete 

Figure 18: 


w/c = 0.30 

lnitially, all pastes contain about 320 cm 3 of unhydrated cement (1 kg), but different volumes 

of water, 700, 500 and 300 cm 3 for w/c ratio 0.7, 0.5 and 0.3, respectively. Consequently, 

pastes with higher w/c ratio will have larger total volumes. The volume of water corresponds 

to the initial volume of capillary pores. 

As hydration proceeds, the total volume remains basically constant, but the amount of 

unhydrated cement is gradually reduced. At degree of hydration 0.5, half of the original 

cement has been consumed and replaced by hydration products. The latter occupy a volume 

about double that of the original cement that hydrated, thus reducing the volume of capillary 

pores. From the total volume of hydrates, 72% are solid phase and 28% are gel pores. 

If we compare the pastes with w/c 0.50 and 0.70 we see that, as they contained initially the 

same volume of cement, at any stage both pastes contain the same amount of hydration 

products. However, the paste with higher w/c ratio will contain more pores because the 

cement grains were more dispersed. 

The paste with w/c ratio 0.30 can never reach full hydration because there is no room left to 

accomodate new hydration products. High-strength concretes, with very low w/c ratios 

always contain unhydrated cement for that reason. 

Clearly, pastes and concretes with lower w/c ratios will have less and smaller capillary pores, 

thus explaining why they are stronger and less permeable (more durable), see Figures 19 

and 20. 


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Concrete 

Figure 19: Strength vs. w/c-ratio 

Figure 20: 

Permeability vs. w/c-ratio 


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Concrete 

7.4 Influence of the aggregates on the structure 

Figure 21 shows that the presence of the aggregates distorts the structure of the HCP in their 

vicinity. In this contact or transition zone (about 20-25 µm thick), there exists a higher 

capillary porosity and a higher proportion of Ca(OH) 2 than normal, making it weaker than the 

rest of the paste. This explains why, in the case of rounded and smooth aggregates the 

failure of concrete tends to happen at the interface between the coarse aggregate and the 

paste. 

Figure 21: 

Model of the contact zone between cement stone and aggregate 

To achieve high-strength concretes it is necessary to overcome this weakness of the contact 

zone. The increased porosity has to be compensated by using high dosages of a 

superplastizer and the preferential alignment and presence of Ca(OH) 2 crystals can be 

solved by adding microsilica or fly-ash. 


Cement 

Concrete 

8. Literature 

8.1 General overview on cement hydration 

Author Title, Publisher pp 

Taylor, H.F.W. Cement chemistry, Academic Press, London, 1990 

Jawed, I., Skalny, 

J. and Young 

Mindess, S. and 

Young J.F. 

Lea, F.M. 

J.F, Hydration of Portland cement, in: Structure and 

Performance of Cements, Ed. P. Barnes, Applied Science 

Publishers, Londond and New York, 1983 

Concrete, Prentice Hall, Inc., Englewood Cliffs 

The chemistry of cement and concrete, Edward Arnold Ltd., 

Glasgow, 1970 

237 - 316 

8.2 Gypsum and setting of cement 


Frigione G. Gypsum in Cement, in: Advances in Cement Technology, 

Ed. S.N. Ghosh, Pergamon Press, Oxford, 1983 

307 - 347 

Roy, D.M. and 

Grutzeck, M.W. 

Locher, F.W., 

Richartz, W., 

Sprung, S. et al. 

Gypsum & anhydrite in Portland cement, 3rd Edition, United 

States Gypsum Company 

Setting of cement 

Part I Reaction and development of structure, Zement-Kalk-Gips, 

1976, 10 

Part II Effect of adding calcium sulphate, Zement-Kalk-Gips, 1980, 

6 

Part III Influence of clinker manufacture, Zement-Kalk-Gips, 1982, 

12 

Part IV Influence of composition of solution, Zement-Kalk-Gips, 

1983, 4 

8.3 Microstructure and properties of hardened cement paste 

435 - 442 

271 - 277 

669 - 676 

224 - 231 


Diamond, S. The microstructures of cement paste in concrete, 8th 122 - 147 

International Congress on the Chemistry of Cement, Rio de 

Janeiro, 1986, Vol. I 

Mehta, P.K. Hardened cement paste - microstructure and its relationship 113 - 121 

to properties, dto., Vol.I 

Taylor, H.F.W. Structure and composition of hydrates, 7th International pp 2 - 13 

Congress on the Chemistry of Cement, Paris, 1980, Vol. I, 

Subtheme II-2 

Diamond, S. Cement paste microstructure - an overview at several pp.2 - 30 

levels, in: Hydraulic Cement Pastes: Their Structure and 

Properties, Cement and Concrete Association, Wexham 

Springs, Slough, UK, 1974 


Cement 

Concrete 

Cement Properties 

1. INFLUENCE OF CEMENT COMPONENTS ON CEMENT PROPERTIES ........................ 31 

2. LITERATURE......................................................................................................................47 


Cement 

Concrete 

1. Influence of Cement Components on Cement Properties 

1.1 General 

Due to the great variety of factors involved, it is difficult to describe precisely the relationship 

between the cement components and the cement properties. The available models for the 

prediction of cement performance usually only reflect the general trends. 

The effects on the cement properties are best understood for the clinker and gypsum. Least 

knowledge is available in case of the mineral components and the chemical admixtures, so 

that virtually the only way to assess their influence is to carry out performance tests. 

1.2 Clinker 

The composition of clinker gives some indications on the properties of cement to be 

expected, as it influences the rate of hydration reaction and thus the setting and hardening 

rate of cement The composition of clinkers control the quantity and rate of heat evolved 

during hydration and the resistance of cement to sulphate attack; therefore, limiting values 

are specified. 

In this section, the influence of composition of clinker on the following properties of cement 

shall be discussed: 

♦ water requirement of standard paste and consistency of concrete 

♦ stiffening rate and setting time of standard paste and slump loss of concrete 

♦ heat of hydration 

♦ strength of mortar and concrete 

♦ sulphate resistance 

♦ other properties of concrete 

A summary on the relationship between clinker composition and the principal cement 

properties workability (water demand, setting) and strength is given in Table 2. 

Table 2: Effect of clinker composition on water requirement and setting time of 

standard paste and compressive strength of ISO mortar (general trends) 

Clinker Water 

requirement 

Setting time Strength 

early final 

C 3 S -- -- 

C 2 S -- -- 

C 3 A 

C 4 AF -- -- 

K 2 O -- 

Na 2 O -- 

SO 3 -- 

P 2 O 5 -- -- 

increasing decreasing -- no effect 


Cement 

Concrete 

1.2.1 Water requirement of standard paste and consistency of concrete 

The water requirement of the standard paste of normal consistency depends primarily on the 

aluminate and alkali content of clinker and on the fineness of cement. 

The relation between the water requirement of standard paste and the composition of 

cement cannot be applied to concrete, as there is a rather weak relationship between the 

water requirement of paste and water/cement ratio of concrete (Figure 1) 

Po - Water reducing admixture (Pozzolith) 

Me - Superplasticizer (Melment) 

Lu 2 ... Ho 2 - various OPC 

Gm, Du, etc. - various Group plants 

Figure 1: Water requirement of cement and w/c-ratio of concrete 

The effect of cement on the consistency or water requirement of concrete is rather small 

compared to other factors, such as sand, admixtures and temperature. An exception is 

concrete with a very short mixing time, where cement with false set may seriously impair the 

consistency of concrete. 


Cement 

Concrete 

1.2.2 Rate of stiffening and setting time of standard paste and slump loss of 

concrete 

The stiffening rate or the „Vicat“ setting time of the standard paste is significantly influenced 

by the composition of clinker. The sulphates and phosphates of clinker usually delay, 

whereas aluminate shortens the setting time of cement. 

The relation between the stiffening rate or setting time of standard paste and the stiffening 

rate - expressed as slump loss - of concrete is, just as for the water requirement, rather poor. 

Therefore, it is difficult to estimate the stiffening rate of concrete on the basis of composition 

or fineness of cement. 

1.2.3 Heat of hydration 

The effect of the clinker composition on heat of hydration has already been discussed in 

detail in the paper on cement hydration. The principal way to control the heat evolution of the 

clinker is the adjustment of the C 3 S and C 3 A content. 

1.2.4 Strength of mortar and concrete 

The rate of strength development of mortar or concrete depends on the type (or composition) 

of cement. The general tendency of cements with a slow rate of hardening is to have a 

slightly higher ultimate strength. 

The ASTM type IV cement, with low content of C 3 S, has the lowest early strength, but 

develops the highest ultimate strength (Figure 2). This agrees with the influence of individual 

clinker components on the rate of strength development measured on pure clinker minerals 

(see Figure 3). 


Cement 

Concrete 

Figure 2: 

Strength development of concrete made with different cement types 

Figure 3: 

Compressive strength of cement compounds 

The two calcium silicates develop the highest strength, but at different rates. The aluminate 

develops little strength, despite a high rate of hydration. 

The rate of strength development of mortar or concrete depends on the clinker composition 

as follows: 


Cement 

Concrete 

a) Calcium silicates. The different rates of hydration of C 3 S and C 2 S affect the rate of 

hardening in a significant manner: A convenient rough rule assumes that C 3 S contributes 

the most to the strength development during the first four weeks and C 2 S afterwards. In 

general, somewhat higher ultimate strengths are reached by cements with lower calcium 

content, i.e. rich in C 2 S. This observation corresponds with the assumption that the 

strength of cement depends on the specific surface of its hydration products. C 2 S 

produces more colloidal CSH gel and less of the crystalline Ca(OH) 2 than the C 3 S. 

b) Aluminates and ferrites. The influence of the other two major components on the 

strength development is still controversial. Presumably, the C 3 A contributes to the 

strength of the cement paste during a period of one to three days. In general, both 

aluminate and ferrite contribute to the strength of cement to a minor extent, but 

significantly influence the hydration process of the silicates and thus have an indirect 

effect on the rate of hardening. 

c) Of the minor components, the alkali sulphates exert the greatest influence on the rate of 

hardening. The alkali sulphate - mostly present as easily soluble potassium sulphate or 

calcium-potassium sulphate with a molar ratio of 2:1 to 1:2 - accelerates the rate of 

hardening, improving the early strength and decreasing the 28 day and ultimate strength 

(see Figure 4). Of the other minor components, fluorine accelerates, whereas the 

phosphorous compound delays the rate of hardening. 

d) Clinker characteristics other than chemical composition. Particularly the burning and 

cooling conditions influence the rate of hardening of a particular clinker composition. 

Frequently, clinkers of the same chemical composition have different strengths and 

clinkers of different chemical composition have the same strength. A simple experiment 

proves that the very same clinker composition may have rates of hardening which vary 

considerably. Reburning of a clinker in a laboratory furnace changes the rate of 

hardening, but does not affect the chemical composition of clinker (see Figure 5). 

Figure 4: Effect of soluble K 2 O on the compressive strength of ISO mortar 


Cement 

Concrete 

A = Clinker of high activity 

B = Clinker of low activity 

Maturity ≅ Degree of hydration 

Figure 5: Model of strength development of mortar and concrete made with two 

clinkers of same chemical composition and different activity 

A general guide on the necessary amount of the main clinker phases to achieve optimum 

strength development is given in Table 3. The most essential point is to have a high C 3 S 

content (in the order of 60%) and to adjust the C 3 A content. 

Table 3: "Ideal" composition of the clinker for optimum strength development 

Clinker phase "Ideal" content (%) 

C 3 S 55 - 65 

C 2 S 15 - 25 

C 3 A 7 - 10 

C 4 AF 7 - 10 


Cement 

Concrete 

The influence of the clinker composition on the standard mortar strength is noticeably 

reduced in concrete. Depending on the quality of cement, sand and aggregate, the 

proportioning of concrete or mortar components, curing temperature, specimen dimension, 

the rate of hardening in mortar and in various concrete compositions is quite different. 

Moreover, the use of admixtures in concrete - which is common practice today - makes the 

relation even more complicated. Due to different hardening rates of mortar and concrete, the 

relation between concrete and mortar strength at various ages varies and depends on the 

above mentioned factors. Concluding, the cement properties, as demonstrated through 

standardised testing methods, do not show their effect in the same way in concrete. 

1.2.5 Sulphate resistance 

The sulphate resistance of concrete depends primarily on the C 3 A content of clinker. The 

ferrite phases (C 4 AF) affect the sulphate resistance to a much lesser degree. The higher the 

C 3 A content of clinker, the more susceptible the concrete is to sulphate corrosion (Figure 6). 

E 28 after 28 days of regular curing = 100% 

E 180 after 28 days of regular curing and 180 days of 

exposure to 10% sodium sulphate solution 

Figure 6: Sulphate resistance of cement measured on ISO mortar specimen (55 OPC) 

Influence of C 3 A content on the loss of Young’s modulus of elasticity E (determined 

from ultrasonic pulse velocity measurements) 

The rate of sulphate corrosion depends - apart from the C 3 A content of clinker - on factors 

other than cement: 

♦ composition of concrete, particularly the water/cement ratio 

♦ age of concrete at the time of the first exposure to sulphates 

♦ type and concentration of sulphate solution 

♦ duration and mode of sulphate exposure 


Cement 

Concrete 

1.2.6 Other properties 

The other properties of concrete, such as 

♦ freeze - thaw - resistance 

♦ permeability 

♦ cracking 

♦ shrinkage and creep 

are only slightly influenced by the composition of clinker and quality of cement. Other 

influencing factors, such as air content, w/c-ratio, curing conditions, are decisive. 

The cement exerts only an indirect influence on these properties by its effect on the water 

requirement and rate of hardening. 

1.3 Mineral components 

The effect of the mineral components on cement performance can be related mainly to their 

activity. The three main classes of materials in this respect are latent hydraulic (e.g. blast 

furnace slag), pozzolanic (e.g. fly ash and natural pozzolans) and inert (e.g. limestone). 

In case of the active mineral components (latent hydraulic and pozzolanic), the general 

effects with respect to cement properties are as follows: 

♦ lower water requirement (except for natural pozzolans) 

♦ delay in setting times 

♦ lower heat of hydration 

♦ lower early strength 

♦ higher long term strength 

♦ lower permeability 

♦ improved resistance to sulphate and other chemical attacks 

♦ lower sensitivity for alkali-aggregate reaction 

The actual influence on the cement properties will of course still depend on the individual 

nature of each material. A more detailed comparison on the effects of the main active mineral 

components blast furnace slag, fly ash and natural pozzolan (at same dosage) is made in 

Table 4. 


Cement 

Concrete 

Table 4: Effect of main active mineral components on cement properties (general 

trends) 

Blast furnace slag Fly ash (class F) Natural pozzolan 

Water requirement 0 

Setting time 

Heat of hydration 

Early strength 

Final strength 

Sulphate resistance 

Permeability (chloride) 

Alkali-aggregate 

 

reactivity 

Shrinkage 0 0 

 

 

O neutral effect 

increase 

decrease 

The inert mineral components like limestone do exert similar influences as the active 

materials in terms of water requirement, setting and heat of hydration, but they will not 

improve the final strength and durability characteristics of the cement. 

Other cement properties than the above mentioned are generally not affected to a great 

extent by the addition of mineral components. 

1.4 Gypsum 

The main function of the gypsum in cement is to regulate the cement setting, but the gypsum 

also influences other cement properties such as grindability, flowability and storage stability, 

volume stability and strength. 

The use of anhydrite instead of gypsum helps to reduce the risk of false setting and to 

improve the storage stability and flowability of the cement at high grinding temperature (see 

also chapter 5.6). In case of highly reactive clinkers, proper set retardation may, however, be 

a problem and blends with gypsum have to be used. 

The substitution of natural gypsum by by-product gypsum may sometimes cause problems 

with setting and strength development due to potential presence of impurities in such type of 

materials. 

1.4.1 Specific surface area 

The specific surface area of cement is usually determined by the Blaine method. The Blaine 

value is calculated from the air permeability of a cement sample compacted under defined 

conditions. The resistance to air flow of a bed of compacted cement depends on its specific 

surface. The Blaine specific surface is not identical with the true specific surface of the 

cement, but it gives a relative value, which suffices for practical purposes. 


Cement 

Concrete 

An absolute measurement of the specific surface can be obtained by the nitrogen (or water 

vapour) absorption method - BET. In this method, the "internal“ area is also accessible to the 

nitrogen molecules and the measured value of the specific surface is therefore considerably 

higher than that determined by the air permeability method: 

Method Blaine Nitrogen Absorption (BET) 

Cement A 2’600 cm 2 /g 7’900 cm 2 /g 

Cement B 4’150 cm 2 /g 10’000 cm 2 /g 

The Blaine value can sometimes be misleading, especially in the case of outdoor stored 

clinker, composite cements - consisting of a more easily grindable component - and clinkers 

containing underburnt material which is easier to grind. The properties of such cements can 

often be poorer compared to other ground to the same specific surface. 

1.4.2 Particle size distribution 

Cements of the same specific surface may have different PSD and different properties. Thus, 

the specific surface is not the only fineness criterion determining the properties of a particular 

cement composition. 

The determination of the PSD can be carried out by the following methods: 

♦ mechanical sieving (residues on sieves of a definite size (e.g. 32, 45 and 60 µm)) 

♦ laser and sedigraph (residues over the whole range of particles sizes) 

The mechanical sieving is usually applied in the cement plants. Due to the limitations in sieve 

sizes, this method does not allow to measure the whole range of particle sizes. 

The overall particle size distribution of cement is commonly analysed by means of the 

theoretical distribution according to Rosin-Rammler-Sperling (RRS), which is described be 

the following formula: 

ln [ln (100/R d )] = n [ln (d) - ln (d')] 

being: 

R d = % of particles with diameter greater than d (residue) 

d = particle size in µm 

d' = characteristic diameter in µm (36.8% of the particles greater than d') 

n = slope of RRS straight line 

The data obtained in the particle size analysis is accordingly plotted in a so-called RRSdiagram 

(see Figure 7), having a double logarithmic ordinate (y-axis) and a logarithmic 

abscissa (x-axis). After linear regression of the particle size distribution, the slope n of the 

straight line and the characteristic diameter d' (at 36.8% residue) can be calculated. 

The slope n and diameter d' are the significant values for the particle size distribution. The 

first characterises the degree of distribution (wide-narrow), whereas the second one states its 

location and is an indicator for the overall fineness. High n values results from a narrow PSD 

and low d' values from a high overall fineness. 


Cement 

Concrete 

Differences in the PSD of cement can also be seen in the relation between the traditionally 

measured Blaine values and sieve residues. At same sieve residue, the Blaine tends to be 

lower with higher n values (see also Figure 8). 

Figure 7: Particle size distribution of cement in RRS-diagram 

Figure 8: Correlation between Blaine and residue 32 µm for different n values (data 

FLS) 


Cement 

Concrete 

1.5 Grinding of Portland cements 

1.5.1 Influence of Blaine fineness 

Since the hydration starts on the surface of the cement particles, it is the specific surface 

area of Portland cement that largely determines the rate of hydration and thus the setting and 

hardening rate. To achieve a faster hydration and strength development, rapid-hardening 

cements are ground finer than ordinary Portland cement. It is common practice to produce 

cement of various strength classes from one clinker by altering the fineness to which it is 

ground. The Blaine value of cement varies between 2’500 cm 2 /g for ordinary Portland cement 

(type I, ASTM) and 5’000 cm 2 /g for high early strength cement (type III, ASTM). 

The rate of hydration is slowed down by the presence of cement gel and if a large quantity of 

gel is formed rapidly, because of a large cement surface, the inhibiting action of the gel soon 

takes place. For this reason, extra fine grinding is efficient only for the early strength up to 7 

days. Moreover, the rate at which the strength of concrete increases is substantially lower 

than that of mortar (see Figure 9). 

Considering the energy consumption for grinding, the fine grinding is often not economically 

feasible. In those cases, where high early strength is not required, fine grinding is of little 

value (see Figure 10). A large number of concrete applications are unable to exploit the 

effects of fine grinding. 

The relations between the Blaine fineness of cement and concrete properties can be 

summarised as follows: 

1) Increasing the fineness of cement, reduces the amount of bleeding in concrete (see 

Figure 11). 

2) Increasing the fineness of cement above 3000, increases somewhat the water 

requirement of concrete. Compared to the influences other than cement on the water 

requirement of concrete, the influence of cement fineness is considerably smaller. 

3) The strength of concrete is influenced by the fineness of cement. The early compressive 

strength increases with an increase in cement fineness. The difference in compressive 

strength due to the difference in fineness of cement, is considerably smaller at 28 days 

and at later age (see Figure 9). 

4) The fineness of cement influences the drying shrinkage of concrete. When the water 

content is increased because of fineness, the drying shrinkage is increased. 


Cement 

Concrete 

Figure 9: Effect of cement fineness on strength of mortar and concrete 


Cement 

Concrete 

Figure 10: Relative specific energy consumption and compressive strength 

development 

Figure 11: Effect of cement fineness on bleeding of concrete (non air-entrained concrete, 

w/c-ratio = 0.57) 


Cement 

Concrete 

1.5.2 Influence of particle size distribution 

The influence of the fineness on the cement properties can be described more precisely, 

when taking into account the PSD of the Portland cement. The PSD is of particular 

importance with respect to workability and strength development. 

The workability of Portland cement and concrete may impair when the PSD becomes 

narrower (at constant specific surface). On one hand, the water requirement for a certain 

consistency tends to increase and, on the other hand, the faster conversion of aluminate at 

narrow PSD may lead to early stiffening problems. 

The mentioned stiffening problems may especially occur if clinkers of high reactivity (high 

C 3 A and alkali content) are ground together with the gypsum at low temperatures (little 

formation of easily soluble sulphates), as it is the case in the modern grinding systems. With 

such clinkers, the proper adjustment of the wideness of the PSD and/or of the calcium 

sulphate carrier is therefore important. 

The effect of the PSD of Portland cement on strength development is not always clear. The 

general trends can be summarised in the following way: 

♦ The most valuable particles for early strength are the ones between 0 - 8 µm. The Blaine 

value is thus a good indicator in this respect, as it is proportional to the portion in this 

fraction. 

♦ The 28 day strength is mainly controlled by the amount of particles in the range between 

2 - 24 µm, which is proportional to steepness n of the PSD. 

The increase in the steepness n at a given Blaine is accordingly an effective means in 

improving the strength potential at 28 days as illustrated in Figure 12. The positive effects of 

higher n values are, however, less pronounced on concrete. 


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Concrete 

Figure 12: 2 day and 28 day compressive strength of Portland cement, as a function of 

the specific surface area and the slope of the RRS-distribution of the cement 


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Concrete 

2. Literature 

Cement components and cement properties 

Gebauer, J., Kristmann, M., The influence of the composition of industrial clinker on cement 

and concrete properties, World Cement Technology, March 1979, pp. 46 - 51 

Wolter, H., Production, properties and applications of Portland slag cements and blast 

furnace cements, Concrete Workshop, Queensland Cement Ltd., 1994 

Malhotra, V.M., Ramezanianpour, A.A., Fly ash in concrete, Second edition,CANMET, 

Ontario, 1994, 307 pp. 

Massazza, F., Pozzolana and pozzolanic cements, in: Lea's Chemistry of Cement and 

Concrete, Fourth Edition, Arnold, 1998, pp. 471 - 631 

Cochet, G, Sorrentino, F., Limestone filled cements: properties and uses, in: Progress in 

Cement and Concrete, Volume 4, Mineral admixtures in cement and concrete, ABI, New 

Delhi, 1993, pp. 266 – 295 


Cement 

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Clinker Optimization 

Dr. J.A. Imlach 

1. INTRODUCTION............................................................................................................... 49 

2. CLINKER COMPOSITION ASPECTS.............................................................................. 50 

2.1 Main Elements (SiO2, Al2O3, Fe2O3 and CaO)...................................................... 50 

2.2 Principal Accompanying Elements (MgO, Mn 2 O 3 , SrO, and TiO 2 ,) .......................... 51 

2.3 Alkalis, Suphur and Chloride.................................................................................... 52 

2.4 Disturbing Minor Species P 2 O 5 B2O3, and (F)......................................................... 53 

2.5 Trace Heavy Toxic Elements. .................................................................................. 55 

3. CLINKER PRODUCTION ASPECTS ............................................................................... 56 

3.1 Kiln Type .................................................................................................................. 56 

3.2 Raw Meal Preparation.............................................................................................. 56 

3.3 Alite Size .................................................................................................................. 56 

3.4 Alite Polymorphism .................................................................................................. 57 

3.5 C 3 A Polymorphic Modification.................................................................................. 57 

3.6 Clinker Microstructure .............................................................................................. 58 

3.7 Rate of Clinker Cooling ............................................................................................ 59 

3.8 Reducing Conditions ................................................................................................ 60 

4. IMPLEMENTATION OF FINDINGS.................................................................................. 60 

4.1 Introduction .............................................................................................................. 60 

4.2 Barriers to Implementation ....................................................................................... 60 

4.3 Fine Tuning of Material Aspects............................................................................... 61 

4.4 Fine Tuning of Process Aspects .............................................................................. 62 

5. LITERATURE CITED........................................................................................................ 64 


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As a result of ever increasing environmental and economical pressures, cement companies 

are now producing composite cements, with ever-increasing degrees of clinker substitution. 

Whilst this has many benefits, there are also some drawbacks, one of these being a poorer 

strength development at early ages, e.g. 1 and 3 days. 

As a means of compensating for this reduced early strength performance, one possibility is 

to increase the early strength performance of the clinker being used. The present report is an 

attempt to review, based on a limited number of the many thousands of reports available, the 

influence of those factors which influence strength development. 

The present survey has had to be of necessity limited in scope and is restricted to 

determining the influence of clinker alone on strength development. Other equally important 

and highly relevant aspects such as fineness of grinding, grain size distribution, optimisation 

of set retarder, use of chemical admixtures etc. lie outside the terms of reference. 

It has furthermore been attempted to give priority to that literature concerning clinkers 

produced at least from plant raw meals and preferably in industrial kilns. This has not always 

been possible. Articles referring to clinker or individual clinker phases produced from pure 

oxides in laboratory furnaces have been on the whole not used. 

To bring order into this report it has been necessary to break up the literature review into 

those individual aspects having an influence on early strength development. Thus the review 

of any one paper may lead to entries under several individual topics. 

In the present review the following have been chosen as topics / sub-topics: 

Chemical Composition Characteristics 

♦ main elements (SiO2, Al2O3, Fe2O3 and CaO), with those characteristics derived from 

them such as LSF, SR and AR and the Bogue-calculated C3S, C2S, C3A and C4AF 

♦ 

♦ 

♦ 

♦ 

principal accompanying elements MgO, TiO2, Mn2O3 

soluble, volatile elements SO3, K2O, Na2O and Cl, 

disturbing minor elements B, P2O5 and (F) 

trace heavy elements such as Cr, Ni, Pb, Zn, etc. 

Clinker Production Characteristics: 

♦ kiln type 

♦ raw meal preparation 

♦ clinker microstructure (alite size, crystallisation of liquid phase, etc.) 

♦ 

♦ 

♦ 

polymorphic modifications 

rate of clinker cooling 

kiln atmosphere 


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2. Clinker composition aspects 

2.1 Main Elements (SiO2, Al2O3, Fe2O3 and CaO) 

Many articles exist on the influence of the main oxides on strength development properties 

and so those now quoted are only a selection of those available. 

One of the earliest and still most comprehensive statistical evaluations was performed by 

Blaine et al. (1965, 1968) at the US National Bureau of Standards on 199 commercially 

available Portland cements (Types 1 to 5) in the 1960’s. Here not only the main elements 

were taken into consideration but almost all of the other elements dealt with in Chap. 2. 

From Blaine’s work the most relevant in the present case is the compressive strength 

development at 1 and 3 days according to ASTM specifications. This was based on 2-inch 

mortar cubes that had been stored in water after an initial 24 hrs in their moulds in a moist 

cabinet. For strength development at 1 day Blaine (1968) reported 8 different equations 

which had been drawn up. The most dominant factors which appeared in these equations 

were C3S, SO3, insoluble residue, and K 2 O. For example in his equation 1, the positive 

contributing factors were as follows: 

+ 18.29xC 3 S +225.8xSO 3 + 376.1xK 2 O 

Also included were a negative constant and negative factors for L.o.I., insoluble residues. 

The work of Blaine is so comprehensive that for the full benefit it must be read in its entirety. 

Alexander et al. (1968) performed a statistical investigation into the strength development of 

commercially available Portland cements in Australia. The latter had a wide range of 

chemical composition, surface areas and a wide range of strength development 

characteristics. These authors considered that the main differences in strengths, when tested 

under the following conditions: 

♦ curing time between 1 day and 6 months 

♦ W/C ratios from 0.35 to 0.80 

♦ curing temperatures from 5 to 75 °C 

were most sensitive to the C 3 A content. Other factors such as particle size had a smaller but 

still significant effect, whilst differences in C 3 S were considered to be of minor importance. 

With specific regard to curing times of 7 days and less, Alexander et al. did consider that the 

C 3 S content was of importance. 

Gebauer et al. (1980), on the basis of the “Comparative Study 1976/77” evaluation of 55 

“Holderbank” Group plant clinkers, found that the chemical composition of clinker is the 

decisive factor influencing the properties of cement. The compressive strength development 

of laboratory cements prepared from them is correlated with the quantity of the principal 

clinker phases, and the alkalis and SO 3 as follows: 

CS 2-day (ISO) = -2.3 + 0.22 C 3 S + 0.40 C 3 A + 3.8 KNS (r = 0.839) 

CS 2-day (ISO) = -1.42 + 0.19 C 3 S + 0.35 C 3 A + 8.5 K sol (r = 0.876) 

(KNS represents K 2 O + Na 2 O + SO 3 and K sol soluble K 2 O) 

Stürmer et al. (1990) reported that the C 3 A content of clinker in the range 0 to 13 % had no 

influence on compressive strength development at 1 and 3 days. Only at 28 days was a 

definite strength increase noted up to 10 % C 3 A, thereafter a drop occurred. (Here It must be 


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Concrete 

stated that modification of the original industrial raw mix reduced the original Bogue 

calculated C 3 S from 75 % down to 57 %). 

Munoz et al. (1995), when considering hourly average clinkers from a single plant, found that 

the C 3 A content had a negative influence on strength development and claim that this might 

be due to the hydration products being poorly crystallised. 

Ghosh et al. (1998) investigated the factors influencing variations in day to day strength 

development for two cement plants in India, using quality data gathered over a period of 3 to 

4 months. Here the naturally occurring variations in chemical composition, fineness of 

grinding etc. were taken into consideration. They found that the principal factors influencing 

strength development within each plant were CaO content, fineness of grinding and clinker 

microstructure. For these two plants, the 3-day strength was increased by 15 to 30 % when 

the clinker CaO was increased by 2 %, e.g. from 63.5 % to 65.5 % with the C 3 S increasing by 

15 %-age points. It was reported that plant B exhibited a higher strength not only because of 

a slightly higher C 3 S content, but also due to its microstructure. 

2.2 Principal Accompanying Elements (MgO, Mn 2 O 3 , SrO, and TiO 2 ,) 

2.2.1 MgO 

It is well known that clinker contains varying amounts of MgO, mainly due to the presence of 

dolomite in the raw materials. Up to 2.0 % MgO can be incorporated into the clinker minerals, 

mainly in the alite, before MgO occurs as an undesirable phase, responsible for expansion in 

mature concrete. The presence of up to 2 % MgO in clinker, as a substitute for CaO, can 

thus increase early strength development in that its presence increases the effective LSF 

and hence the quantity of C 3 S actually present. In clinkers with very high LSF values in the 

order of 100, the presence of MgO can lead to over-saturation and the presence of free CaO. 

Blaine (1968) did not consider MgO to influence strength development at early ages. 

2.2.2 Mn 2 O 3 

On average Mn 2 O 3 is present in clinker at about the 0.1 % level. Unlike the other transition 

elements V, Cr, Co, Ni and Cu, Mn along with Fe and Ti is one of the transition elements not 

associated with toxic properties. From an environmental viewpoint no reason is present to 

limit the quantity of Mn 2 O 3 and in previous years one Group plant (Westport) produced a 

clinker with up to 1.2 % Mn2O3. This was due to the high natural level of this element in the 

quarry materials. 

As presented by Moir (1992), Mn 2 O 3 is mainly located in the ferrite phase and so its presence 

in large quantities would increase the quantity of ferrite and decrease that of aluminate. It 

thus in general reduces early strength development as reported by Knöfel et al. (1983) 

although these authors did indicate that a strength increase was obtained for 0.5 % MnO 2 at 

up to 28 days. Although Knöfel’s work was based on cements produced from pure oxides, 

Alexander et al. (1968) found, on the basis of a statistical evaluation of industrial clinkers, 

that a significant correlation existed between compressive strengths at less than 7 days and 

the level of Mn 2 O 3 up 0.28 %. The statistical work of Blaine (1968) indicated that Mn 2 O 3 

negatively influenced strength development at 3 days but not at 1 day. 

2.2.3 SrO 

According to Group plant data SrO is on average present in clinker in concentrations of 0.11 

%, but can be as high as 0.51 %. Evidence is available (Bürki 1993) that SrO at higher levels 

can reduce early strength development potential of Portland cement clinker. At Italcementi’s 

Vibo Valenta plant, the limestone contains SrSO 4 , which is limited so as to result in a 

maximum of 1.5 % SO 3 in clinker. With increasing quantities of Sr the alite becomes unstable 


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Concrete 

and results in CaOf that cannot be reduced by harder burning. By the addition of fluorspar to 

the raw mix it is possible to compensate for the presence of SrO and obtain a normal free 

CaO level. According to Blaine (1968), SrO is associated with lower strengths at 1 and 3 

days when present in the range up to 0.4 %. 

2.2.4 TiO 2 

The average level of TiO 2 in clinker is about 0.28 %, but values of up to 0.75 % have been 

found at the Joliette plant. TiO 2 is preferentially located in the ferrite phase (up to 2. 0 %, but 

can be found at lower concentrations in belite (0.75 %) and at the 0.4 % level in alite and 

aluminate. 

With regard to its influence on phase development and compressive strength development 

Knöfel (1977) reported that for laboratory produced clinkers increasing the TiO 2 content up to 

1 % increased compressive strengths did cause an increase in strength in spite of a 

decrease of C 3 S, but only at 7 days and more. At 2 days no increase was observed. 

Blaine (1968) does not report an influence of TiO 2 on strength development at 1- and 3-days. 

2.3 Alkalis, Suphur and Chloride 

According to the statistical investigation of Blaine (1968), K 2 O and SO 3 are principal factors 

contributing to early strength development at 1- and 3-days. Na 2 O was not considered to 

have an influence. Osbaek (1979) determined the strength development characteristics of 

laboratory cements having the same fineness and gypsum content, produced from industrial 

clinkers from 31 plants. He found a better correlation between soluble alkalis than the total 

alkali content. Whereas alkalis have a positive influence on 1- and 3-day strengths, they 

have a negative influence at 28 days where a 1 % soluble K 2 O eqvt decreases compressive 

strengths by 10 MPa. When 2 % K 2 SO 4 was added to a chosen cement the strength 

developments changed as follows: 

♦ 

♦ 

♦ 

♦ 

1-day: increase from 10 to 16 MPa 

3-day: increase from 22 to 30 MPa 

7-day: no change 

28-day: reduction from 50 down to 40 MPa. 

Strunge et al. (1985) investigated the influence of higher levels of SO 3 in clinker on clinker 

mineralogy and strength development. Both laboratory and industrial clinkers were 

examined, with SO 3 contents ranging around 3 % by weight. On the basis of their 

investigations they found that: 

♦ 

♦ 

♦ 

increasing SO 3 levels in clinker results in lower alite and higher belite contents (at same 

LSF) 

higher SO 3 levels reduce compressive strengths, but less than expected from the 

reduction of the alite content 

at more than 2 % SO 3 in clinker and alkalis > 1 %, a normal setting behaviour can be 

obtained without the addition of a retarder. 


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2.4 Disturbing Minor Species P 2 O 5 B2O3, and (F) 

2.4.1 P2O5 

P 2 O 5 can occur in some areas (e.g. Uganda) in limestone and other natural raw mix 

components as well as in industrial by-products. When present in clinker in sufficient 

quantities P 2 O 5 has a deleterious effect on early strength development. 

The explanation, as reported by Gutt (1968) and Moir (1992), is that P 2 O 5 preferrentially 

enters the belite lattice and forms a complete solid solution series with C3P (3CaO.P 2 O 5 ), but 

is only incorporated to a minor extent (1.1 wt. %) into the alite lattice. With increasing 

quantities of P 2 O 5 in a raw mix, the amount of alite is reduced by approximately 10 % C 3 S for 

every 1 % P 2 O 5 in the clinker. This effect can be partially compensated by increasing LSF. 

Moir (1992) quoting unpublished Blue Circle data, shows the influence of P 2 O 5 content on 3- 

day compressive strengths. Basically in a cement with a Na 2 O eqvt of 0.8 % compressive 

strengths of approx. 20 N/mm 2 were observed up to 1 % P 2 O 5. At 2.0 % P 2 O 5 the 3-day 

strength had dropped to only 10 N/mm 2 . Increasing the Na 2 O eqvt resulted to 1.5 % results in 

the 3-day strengths increasing to about 15 N/mm 2 . 

According to Blaine (1968) small quantities (< 0.5 % P) can have a negative influence on 

early strength development. 

2.4.2 B 2 O 3 

No information is currently available at present on the levels of B 2 O 3 naturally present in 

clinker, but it is assumed that these are quite low That B 2 O 3 cannot be determined by XRF is 

perhaps one reason why this should be the case. 

From phase diagram studies it is known that B 2 O 3 is similar to P 2 O 5 in that with increasing 

quantities it influences phase equilibrium and reduces the quantity of C 3 S (Fletcher and 

Glasser 1993). It hence reduces early strength development. Again B 2 O 3 is appreciably 

soluble in C 2 S (17 mole %), but only poorly soluble in C 3 S. The presence of B 2 O 3 is therefore 

not compatible with the production of high alite, high early strength cements. 

According to Moir (1992) the presence of 2.8 % B 2 O 3 results in alite becoming so unstable at 

increasing temperatures that at 1700 °C it has no primary phase field in the phase diagram. 

On the basis of it being a well known flux in the ceramic industry it was hoped that it must 

also have the same effect on clinker burning. Tests at CTS/MT laboratories (Imlach 1994) 

showed that whilst the use of colemanite (2CaO.3B 2 O 3 .5H 2 O) did improve burnability, as 

determined by the size of the alite crystals, it did result in increasing quantities of free CaO 

and a corresponding reduction of C 3 S. 

The use of borate glasses as “alkali correctives” is therefore not to be undertaken without 

previous evaluation of the expected reduction of C 3 S. 

2.4.3 Fluoride 

The influence of fluoride is much more complex than that of P 2 O 5 and B 2 O 3 and depending 

on the amount present - and on burning conditions - can have the following effects on early 

strength development: 

♦ 

Increase strength by acting as a flux and hence enabling manufacture of high alite 

clinkers 

♦ Increase early strength development by the production of clinker containing C 11 A 7 CaF 2 

as aluminate phase (Jetset cement) 


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♦ Offset strength reductions due to B 2 O 3 and P 2 O 5 

♦ Reduce early strength development by acting as a powerful set retarder 

2.4.4 Use as Burning Flux 

This is the effect that is presently being used by a few plants of the “Holderbank Group”, 

(Apasco Group and Cerro Blanco). Here the use of fluorspar, which results in clinker levels of 

0.22 to 0.28 % F, is being used to manufacture products with LSF’s in the range 101 to 103, 

which contain about 75 % alite and no belite as calcium silicates. Burning and cooling 

regimes are normal. 

2.4.4.1 PRODUCTION OF JETSET CEMENT 

The addition of fluorspar to raw meals rich in Al 2 O 3 can, under some circumstances, result in 

a clinker containing C 11 A 7 CaF 2 , and not the normal C 3 A, as aluminate phase. This change 

was made use of in a 1969 PCA patent application for the production of Jetset cement, which 

developed high very early strengths by containing some 0.5 % F and some 15 % C 11 A 7 CaF 2 . 

In laboratory trials at Holcim Group Support, Imlach (1974) showed that a lower burning 

temperature of 1350 °C was possible, but that a slow cooling of the liquid phase was 

necessary if the required C 11 A 7 CaF 2 was to be obtained instead of the normal C 3 A. 

Due to its lower hydraulic activity than C 3 A, it was considered that the setting and early 

strength development of Jetset cement would be controllable. This was found not to be the 

case and was very temperature sensitive. Set controllers containing K 2 SO 4 and citric acid 

were used at Holnam’s former Okay plant. Because of such problems the production of 

Jetset cement never became established. 

2.4.4.2 COMPENSATION FOR B 2 O 3 , P 2 O 5 AND SRO 

As previously reported both B 2 O 3 and P 2 O 5 can result in reduced early strength development. 

Both Moir (1992) and Gutt (1986) report on the use of F to compensate for the loss of 

strength incurred, this being achieved by destabilisation of the belite solid solution. However, 

this is a method that is not normally practised and will not be discussed further. The only 

practical application of fluoride to stabilise alite thus appears to be at Italcementi’s Vibo 

Valente plant to offset the effects of SrO as already indicated. 

2.4.4.3 RETARDING ACTION 

One of the certain drawbacks of producing clinker with fluoride is the increase in setting time 

that it causes. This is said to be due (Moir 1992) to the formation of an insoluble barrier layer 

of CaF2 on the surface of the hydrating clinker minerals. Whilst the alite structure can contain 

up to at least 2 % F (Paul and Glasser 1999), adding such levels to clinker would be both 

uneconomic and would result in an excessive setting time. According to Moir (1992) 

increasing the F content to 1.75 % results in setting times of around 10 hrs. During 

production trials at Torredonjimeno, Bachmann (1996) found that at 0.5 % % F in clinker, 

setting times of > 8 hrs were determined under laboratory test temperature of 20 °C. 

At lower temperatures the influence of F becomes even more troublesome. According to Moir 

(1992) the setting time at 5°C can be given by the equation: 

Setting time (min) = 360 + 500x F – 30xCaOf – 0.3 surface area. 

It is known that at one Blue Circle plant (Hope), which has F naturally present in the raw 

materials, the F content of the raw mix must be changed according to the time of year. 

According to Heinemeyer the presence of only 0.17 % F in clinker was sufficient to produce 


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Concrete 

concrete which had excessive de-moulding times cements when ambient air temperatures 

dropped to the region of °C. 

2.5 Trace Heavy Toxic Elements. 

Even when produced from only natural raw components, Portland cement clinkers always 

contain trace amounts of heavy toxic elements in quantities roughly proportional to their 

concentration in the Earth’s crust. Several of the toxic elements are of importance in that 

their emission from the exhaust gas stack is limited by strict regulations. These elements are 

split into classes and their emission levels are for example limited by the German TA Luft 

regulations as follows: 

♦ Class 1 (Cd, Hg, Tl) 0.2 mg/Nm 3 

♦ Class 2 ( As, Co, Ni, Se, Te) 1.0 mg/N/m 3 

♦ Class 3 (Cr, Cu, Pb, Pd, Pt, Rh, Sb, Sn, V) 5.0 mg/Nm 3 

♦ Unclassified (Zn) no limit 

The levels of these elements in clinker normally range from < 0.01 ppm to round about 100 

ppm (Imlach 1997). On the basis of cements investigated in the mid 1960’s, Blaine (1968) 

concluded that the heavy toxic elements in the concentration levels naturally present had no 

assured influence on strength development, especially at early ages. 

With the use of magnesia chrome bricks, petcoke, tyres etc, the level of Cr can be as high as 

320 ppm, the level of Ni 400 ppm and the level of V 135 ppm and the level of Zn 530 ppm. 

Heavy toxic elements at these concentrations are not considered to influence strength 

development potential (Stephan 1999), either positively or negatively. 

In the early 1970’s Onoda did patent a “doped-alite” cement which was reported to have a 

superior early strength development. The basis of this was the addition of chromite ore which 

resulted in the clinker having a Cr 2 O 3 content of > 1.0 %. This clinker was never produced on 

a routine basis due to the increased costs by using chromite ore and due to the higher 

content of soluble Cr6 + . The latter is associated with a mason’s skin disease (chrome 

eczema) and in Scandinavian countries the quantity of soluble Cr6 + in clinker is limited to < 2 

mg/ l, i.e. < 2 ppm. 

In laboratory based trials various authors from academic circles have investigated the 

influence of heavy metals on setting time and strength development. Here levels of up to 2.5 

% and above have been considered. Stephan et al. (1999) found that that Cr, Ni and Zn only 

had an influence on clinker properties when present in quantities > 5000 ppm, and therefore 

much higher than is normally the case. Schmidt (1980) showed that ZnO and PbO had no 

influence on strength development properties up to 7 days at a dosage rate of 1.0 % when 

incorporated into the lattice of the main clinker minerals. This is in contrast to the presence of 

soluble Pb and Zn salts in the gauging water. 

Today, even if a heavy toxic element were shown to vastly improve strength development 

characteristics, its routine implementation would definitely be opposed by environmental 

Groups. This would be on the grounds of increased stack emissions and on the leaching of 

such metals as Al, Cr etc. from concrete drinking water pipes. 


Cement 

Concrete 

3. Clinker Production Aspects 

3.1 Kiln Type 

According to Gebauer et al. (1980) the type of the kiln does not have a direct influence on 

cement properties 

3.2 Raw Meal Preparation 

Moir (1997) reports that in Blue Circle Industries models have been developed which 

satisfactorily predict the day to day variations in compressive strength development, 

especially at 28 days. However, significant differences exist between the predicted strength 

levels at different cement plants if a common expression is used, this being attributed to 

differences in microstructure. 

Moir’s study, performed on materials from 15 cement plants with 6 different kiln types, 

attempted to find out the influence of kiln feed heterogeneity and estimated burning 

temperature on clinker strength potential. No clear relationship was found between 

combination temperature and the main chemical parameters LSF and SR. A better 

correlation (r = 0.923) was found for the following expression: 

Temp (°C) for 1 % free CaO = 

414 + 21x acid soluble 90 µm residue+10 x LSF +3 x 150 µm residue + 32 x AR. 

Expressions were also derived for the strength of Type 1 (pure Portland) cements from the 

same 15 plants. Here the 2 day strengths according to EN 196-1 ranged from 24.8 to 31.9 

N/mm 2 and the 28 day values from 56.3 to 66.3 N/mm 2 . Some cements were “strength over 

achievers” i.e. had higher values than predicted, whilst others were “strength under 

achievers”. 

The “over achievers” were always those cements in which the 90 µm-residue of the raw mix 

had a higher LSF value than that of the bulk raw mix itself. The lower strength potential of 

clinkers with a lower LSF residue on 90 µm may be associated with the presence of belite 

clusters. No significant correlation was found between strength difference and estimated 

burning temperature. 

3.3 Alite Size 

Gebauer et al. (1980) consider that the clinker microstructure is of secondary importance 

regarding compressive strength development. Increasing the size of the alite usually leads to 

slower stiffening and setting times. For one extremely alite rich clinker (Höver), increasing the 

natural alite size by tempering the clinker in the laboratory had, with the same chemical 

composition, the following results: 

Original clinker 

Tempered clinker 

% alite < 20µm 80.9 63.6 

Penetration begin (hr) 1.37 1.88 

Setting begin (hr) 2.17 2.50 

2-day CS ISO (N/mm 2 ) 23.7 22.5 


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Concrete 

28-day CS ISO (N/mm 2 ) 48.2 51.3 

Munoz et al. (1995), on the basis of a statistical investigation of 29 hourly average clinker 

samples from a single plant, considered that the crystallite size and strains of alite, as 

determined by x-ray diffraction by applying the variance procedure on the (021) peak, 

influenced compressive strength development. They reported that the crystallite size of has a 

positive influence on strength development that substantially decreases with age of testing. 

They also claim that strains in the alite crystals have an adverse effect on compressive 

strength development at all ages, even when increasing lattice defects and surface fineness 

result in faster rates of hydration. The latter was explained as being due to a “memory effect” 

of the defect content of the original alite. 

In his cement industry based PhD thesis, Platzer (1998) reports on factors influencing clinker 

reactivity. Starting point of his study was the undesirable situation that the introduction of 

tyres as secondary fuel (20 % of heat) had definitely resulted in a deterioration of cement 

properties, especially in the colder part of the year. In the short term the symptoms of the 

problem were relieved with a changed clinker composition and finer cement. This, however, 

brought higher costs and incurred logistic (storage) problems. 

On the basis of the ensuing study Platzer showed the influence of the following factors, at the 

same basic clinker chemistry, on compressive strength development: 

♦ 

the Zn introduced by the tyres was not the reason, as the quantity was less than the 

demonstrated 0.5 % influence threshold 

♦ the mean alite size was increased from 31.5 µm to 39.7 µm by the use of tyres and 

showed a different size distribution 

♦ the increase in size was due to the much longer (too long) sinter zone 

♦ 

the increased quantities of MgO, TiO 2 and Zn assist by acting as mineralisers. 

The temperature profile of the kiln, especially with the use of secondary fuel, therefore has to 

be matched with the alite size and the clinker quality desired. Here the use of microscopy is 

unavoidable. 

3.4 Alite Polymorphism 

Ono et al. (1968) considered that the high strength development associated with slow cooling 

down to 1200 °C could be explained as follows. “The crystalinity of the R-form of alite rising 

at the lower part of its temperature stability range, and the inversion of modifications may be 

disturbed, and alite is in an active state”. 

On the basis of laboratory produced alite and alite + C 3 A mixtures, Aldous (1983) found 

evidence to indicate that pure, synthetic alite doped with MgO, Al 2 O 3 , Fe 2 O 3 , TiO 2 and F - 

exhibited differing compressive strengths according to their polymorphic modification. Higher 

strengths were observed at 2 days and longer for the rhombohedral modification over the 

triclinic form, the latter displaying strengths similar to a commercial OPC. With slightly lower 

levels of dopants, triclinic modifications were formed with lower reactivities as determined by 

compressive strength, heat development and by X-ray diffraction determination of the degree 

of hydration. On comparing strength development after the same degree of hydration, Aldous 

found that rhombohedral alite still exhibited a higher value. 

3.5 C 3 A Polymorphic Modification 

The aluminate (C 3 A) phase can exist in either a cubic or an orthorhombic modification, 

depending on its content of the alkalis Na 2 O and K 2 O. In the earlier literature the alkali 


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Concrete 

containing aluminate was given the formula NC 8 A 3 and KC 8 A 3 . According to Spierings 

(1976), the inclusion of Na 2 O into the C 3 A lattice results in a reduction of hydraulic activity as 

determined by heat evolution experiments. 

3.6 Clinker Microstructure 

Svinning et al. (1996, 1998) statistically investigated the influence of material and process 

parameters on the microstructure, and later compressive strength of clinkers from two 

Norwegian plants. Here the microstructure was partially investigated indirectly by X-ray 

diffraction using the peaks in the following 2 theta regions: 

♦ 

♦ 

32.4 °– 32.8 ° (overlap of alite and belite peaks) 

32.9 ° - 34.1 ° (principal aluminate and ferrite peaks) 

In addition the distribution of the size of the alite crystals (> 60 µm, 30 – 60 µm, 10 – 30 µm 

and < 10 µm) was determined by Scanning Electron Microscopy (SEM) . 

The materials and process parameters included in the evaluation were as follows: 

Materials Parameters: 

♦ raw meal fineness 

♦ 

♦ 

♦ 

♦ 

degree of raw meal pre-calcination 

coal parameters(x4) 

organic liquid waste burnt 

chemical composition parameters (x4) 

Process Parameters: 

♦ 

♦ 

♦ 

♦ 

♦ 

temperatures (x6) 

pressures (x8) 

environmental parameters (x6) 

feed of hot meal, liquid waste, oil, tyres, etc (x7) 

“others” (x6) 

To complete the evaluation Svinning (1996, 1998) determined both setting time and 

compressive strength development from 1 up to 28 days. 

Svinning’s studies were therefore very comprehensive in nature and a model was drawn up 

to predict cement properties at the Norwegian plants involved. The model involves X-ray 

diffraction profile at 32.9 and 34.1 ° 2-theta, mineralogy / microstructure of clinker and 

gypsum. A sufficiently good prediction of the clinker mineralogy / microstructure was possible 

by including only free CaO and XRD the profile. The explained variance of compressive 

strength at 1-day was 86 %. To obtain the full benefit of Svinning’s work, reference must be 

made to the original papers. 

Ghosh et al. (1998), studying two plant clinkers A and B, report higher early strengths at 3 

and 7 days for plant B material which is characterised by: 

♦ 

♦ 

♦ 

better developed alite and belite crystals 

no twinning of belite 

no decomposition rims around alite 


Cement 

Concrete 

♦ 

better micro-homogeneity, 

when compared to clinker from plant A. 

3.7 Rate of Clinker Cooling 

Ono et al. (1968) investigated the influence of 4 different cooling regimes on various clinker 

types corresponding to the ASTM Types 1, 2 and 3. These were burnt at 1450 °C (Type 3 at 

1500 °C) for 30 min. and cooled at rates varying between fast cooling from 1450 °C to very 

slow cooling down to 800 °C. It was found that the best strength development for the Type 3 

clinker was obtained by cooling from the burning temperature down to 1200 ° in 15 min. 

Sylla (1975), aware of conflicting findings of previous authors, reported on trials in a cyclone 

and in a grate pre-heater kiln in which the effect of changing the clinker cooling rate, both 

within the kiln and after discharge from the kiln, was studied. The former was varied by 

changing the shape of the flame and position of the burner and the clinker temperature at the 

kiln outlet used as a measure of the rate of kiln-internal cooling. Clinker outlet temperatures 

of between 1410 and 1450 °C (alkali rich clinker in grate pre-heater kiln) and between 1320 

and 1450 °C (low alkali clinker in cyclone pre-heater kiln) were obtained. From this work 

Sylla found that: 

♦ 

♦ 

♦ 

♦ 

♦ 

the rate of cooling at high temperatures in the kiln (> 1310 °C) had much more 

influence than the rate of external cooling 

for both clinkers (and kilns) the higher the clinker temperature at the kiln outlet the 

lower the strength development at 1 day 

this loss in strength with temperature was more pronounced for the alkali-rich clinker 

for the low alkali clinker a 6 N/mm 2 increase in 1-day strength was observed when the 

clinker outlet temperature was reduced from 1440°C to 1320°C 

the slower the cooling after the kiln also resulted in higher 1 day strengths for the alkalirich 

clinker but not for the low alkali clinker: Differences in the order of 6 N/mm 2 were also 

observed 

♦ the 28 day strength development increased for both clinkers with lowering kiln outlet 

clinker temperature. Again the alkali rich clinker showed the greatest change with 

temperature 

♦ the 28-day strength did not correlate with the rate of cooling outside of the kiln. 

Jepson (1976) on the basis of an evaluation of 14 industrial kilns fitted with grate and 

planetary coolers, showed that the type of cooler and hence rate of the cooling after the 

clinker leaves the kiln has no real influence on strength development. He also was of the 

opinion that the cooling rate within the kiln was the more critical factor. 

Chatterjee et al. (1980) reviewed the literature on the influence of cooling rate on cement 

properties. With respect to strength development he reported that in general rapid cooling 

produces lower earlier strengths and higher 28-day strengths. 

Ichikawa et al. (1995) considered that the cooling rate from 1300 °C can be estimated by x- 

ray diffraction. This is deduced from the angle (2-theta) and the width at half peak height of 

the ferrite 020 peak at around 12 °. The slower the rate of cooling the higher the 2 theta 

angle and the narrower the peak width at half height. For commercial clinkers the cooling 

rate, as is to be expected depends on the clinker nodule size. 


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Concrete 

Misteli (1999) considers that the degree of crystallisation of the liquid phase, and thus the 

temperature at which the clinker leaves the kiln is a critical factor. In clinker quenched from 

the maximum burning temperature, the aluminate and ferrite are finely dispersed and so the 

aluminate grains are “protected” by ferrite to the largest possible extent against hydration. 

For slowly cooled clinker, removed from the kiln after the crystallisation of the liquid phase, 

and so achieving complete separation of the aluminate and ferrite, this shielding of the 

aluminate in reduced to a minimum. 

3.8 Reducing Conditions 

According to Sylla (1981) on the basis of laboratory produced clinkers, reducing conditions - 

whether local or caused by the kiln atmosphere - changes the composition of the ferrite, and 

increases the content of C 3 A and its reactivity. They also decrease the stability of C 3 S and 

cause a lighter coloured clinker to be formed. To achieve the best cement quality the clinker 

should leave the kiln at a temperature above 1250 °C. 

Long (1985) reports that reducing conditions promote the replacement of Ca 2+ by Fe 2+ and 

results in decreased hydraulic activity. 

4. Implementation of findings 

4.1 Introduction 

The preparation and communication of the present literature review is not to be considered 

as an end in itself. Here the final aim is the successful industrial implementation of the 

present findings to produce clinkers with the highest possible early strength development. 

As was indicated in Chap. 1, the factors influencing strength development can be classified 

as being “material” or “process” in nature. In general the literature cited up to about 1975 / 

1980 was more concerned with the influence of “material” factors, the work performed since 

then being focussed more on “process” aspects. This is most probably due to the fact that 

easy to use laboratory instrumentation was first widely available for chemical analysis (e.g. 

XRD), whereas equipment for X-ray diffraction, reflected light microscopy, scanning electron 

microscopy is less widely available and requires specialists to interpret the findings. Whereas 

all cement plants (old or modern) possess an XRF, only a few posses the other instruments 

mentioned, which are mostly to be found at research institutes. The fine tuning with respect 

to maximum strength development of the chemical composition will therefore be easier to 

accomplish than fine tuning of the process. 

4.2 Barriers to Implementation 

Most of the findings presently reported have been known for many decades and the question 

thus arises as to why they have not been generally implemented. The reason for this is that 

various factors have been (and still are) operative which resist the formation of any change 

whatsoever. These can be classified as being influenced by the following aspects. 

♦ 

increased clinker production costs 

• use of external materials (e.g. fluorspar, high grade limestone, high alkali 

clay, etc.) 

• selective use of quarry (e.g. high grade limestone) 

• higher burning temperatures and higher fuel and refractory costs 

• higher quality control costs, etc. 


Cement 

Concrete 

♦ 

♦ 

♦ 

Changes in Cement Properties 

• longer setting times 

• higher alkali content 

• higher C 3 A content and hence lower sulphate resistance 

• different colour 

• changed workability, etc. 

Clinker production aspects 

• reduction of kiln output 

• more difficult to burn mix 

• increased pre-heater blockages 

• insufficient raw meal homogeneity, etc 

Personnel Aspects 

• change to established routine 

• increased demand on production personnel , etc. 

4.3 Fine Tuning of Material Aspects 

On the basis of the literature reviewed in Chap. 2.1 and 2.3, it can be seen that many authors 

have reported on the influence of chemical composition, especially the main elements (SiO 2 , 

Al 2 O 3 , Fe 2 O 3 and CaO) and the soluble volatile elements (K 2 O, Na 2 O, SO3 and Cl). Authors 

cited include Blaine, Alexander, Gebauer, Stürmer, Munoz and Ghosh. 

Basically these authors findings can be summarised by the following type of equation for 

which that of Gebauer will be chosen as representative for the group: 

CS 2-day (ISO) = -2.3 + 0.22 C 3 S + 0.40 C 3 A + 3.8 KNS (r = 0.839) 

CS 2-day (ISO) = -1.42 + 0.19 C 3 S 0.35 C 3 A + 8.5 K sol (r = 0.876) 

(KNS represents K 2 O + Na 2 O + SO 3 and K sol soluble K 2 O) 

As presented it is considered that the chemical composition is the major factor influencing 

compressive strength development. 

4.3.1 Principal Clinker Oxides 

This is essentially the easiest, most effective and proven way of improving clinker strength 

development characteristics and is possible using easy to control changes in chemical 

composition. 

On the basis of the just given model, reaching the highest early strength possible should be 

attempted by maximising the LSF and hence C 3 S content. (From recent experience this is 

possible up to a maximum of about 103). decreases the belite down to zero in the final 

instance. At present such extreme LSF clinkers are produced using fluorspar only at plants of 

the Apasco Group (since 1995) and at Cerro Blanco (since 1998). 

Various comments have been made on the influence of C 3 A, ranging from it being the most 

important factor (Alexander 1968) to it being of no influence on early strengths (Stürmer 

1990) to it having a negative influence (Munoz 1995). The influence of C 3 A will therefore 


Cement 

Concrete 

have to be decided on a plant to plant basis, and is probably influenced by the rate of clinker 

cooling (Chap 3.7). 

If it is required to increase strengths by increasing C 3 A the addition of bauxite to the raw mix 

is an already established method, although the increase will necessitate a better control of 

setting times. 

4.3.2 Soluble, Volatile Elements 

Referring to the results of Gebauer (1980) and Osbaek (1979) as basis, early strengths could 

be improved by increasing the content of the alkalis and SO 3 in clinker, with the soluble 

alkalis present as alkali sulphate being more important than alkalis and SO 3 incorporated into 

the clinker minerals’ lattices. 

Increasing the SO 3 content of the clinker is quite easy in that lower cost, high-S fuel can be 

used, e.g. petcoke.) Increasing the quantity of the alkalis is very difficult and is mostly 

impossible, as no cheap, easily available “alkali corrective” has been shown to exist. Suitable 

materials such as K 2 SO 4 are both too expensive and normally unavailable. 

4.4 Fine Tuning of Process Aspects 

If the findings of Gebauer (1980) are correct, only modest, secondary increases in early 

strength are to be expected by optimising process parameters. These will also require a 

higher, more sophisticated input in quality control in comparison to the easy measurement of 

chemical composition. Microscopy and x-ray diffraction become almost essential. 

Fortunately (Gebauer 1980), the type of kiln does not exert a direct influence on strength 

development characteristics. 

4.4.1 Raw Meal Preparation 

Moir (1997) considered that plants with a raw mix having a higher 90 µm residue LSF than in 

the bulk mix, resulted in cements with very high strength levels, so called “over achievers”. 

This was considered to be due to raw mixes having a lower LSF in the 90 µm residue being 

higher in SiO 2 and forming belite nests and less than expected alite. This raw mix property 

might be able by avoiding the use of quartz sand as a corrective and could be easily checked 

by sieving followed by chemical analysis. 

4.4.2 Control of Alite Size 

Controlling the size of the alite crystals almost certainly requires the use of clinker 

microscopy, or more complicated still x-ray diffraction. 

Gebauer (1980), however, was able to show that by tempering samples of an industrially 

produced clinker in a laboratory kiln to increase the size of the alite, the 2-day strengths 

dropped by 1.2 N/mm 2 whilst the 28-day strength increased by 3.1 N/mm 2 . Platzer (1997) 

demonstrated on an industrial scale that the alite size has to be matched with the quality of 

clinker desired. 

On the basis of the above it would definitely seem to be possible to increase compressive 

strength development by ensuring that the average size of the alite crystals are as small as 

possible. Achieving this would necessitate optimising the temperature profile of the kiln to 

achieve a shorter effective burning zone. 


Cement 

Concrete 

4.4.3 Control of Polymorphic Form of Alite 

According to Ono (1968) and Aldous (1983) higher strength development is achieved when 

alite is present in the rhombohedral form. That this form is present would require the use of 

x-ray diffraction as a quality control tool. 

It is known the that addition of small quantities of F can lead to the stabilisation of the 

rhombohedral modification, although this alone did not lead to improved strength 

development at the Cerro Blanco plant in Ecuador. 

4.4.4 Clinker Cooling 

On the basis of the work of Ono (1968), Sylla, and Jepson (1976), it would appear that 

clinker cooling at temperatures down to 1200 °C within the kiln, are much more important 

than cooling outside the kiln. An optimum cooling may increase compressive strengths by up 

to 6 N/mm 2 . 

The optimum cooling regime, which appears to involve a slow cooling within the kiln, can be 

obtained by inserting the burner pipe as far into the kiln as possible so as to obtain 

separation of the ferrite and aluminate phases. Methods for determining the rate of cooling 

would necessitate clinker microscopy, or alternatively x-ray diffraction to determine the width 

of the ferrite peak at around 12 ° 2 theta. 

4.4.5 Reducing Conditions 

Prevention of reducing conditions will ensure that no lowering in compressive strengths takes 

place due to this factor. Inspection of the colour of the inner core of large clinker grains or the 

use of the Magottaux test will demonstrate freedom from reducing conditions. 


Cement 

Concrete 

5. Literature Cited 

Aldous. R.T.H., “ The Hydraulic Behaviour of Rhombohedral Alite”, Cement and Concrete 

Research, Vol. 13, pp 89 – 96, 1983. 

Alexander, K.M., Taplin, J.H, and Wardlaw, J., “ Correlation of Strength and Hydration with 

Composition of Cement”, Proceedings of the 5 th International Congress on the Chemistry of 

Cement, Tokyo, 1968, Supplementary Paper III-72, Volume 3, pp 152 – 166. 

Bhatty, J.I., “Role of minor elements in cement manufacture and use”, PCA Research and 

Development Bulletin RD 109T, 1995. 

Blaine, R.L., Arni, H.T., Foster, B.E., et al., “Interrelations between cement and concrete 

properties, Part 1 – “Materials, techniques, water, requirements and trace elements”, United 

States Department of Commerce, National Bureau of Standards, Building Science Series 2, 

August 20, 1965, pp 1 – 35. 

Blaine, R.L., Arni, H.T., DeFore, M.R., “Interrelations between cement and concrete 

properties, Part 3 -”Compressive strengths of Portland cement test mortars and steam-cured 

mortars”, United States Department of Commerce, National Bureau of Standards, Building 

Science Series 8, April, 1968, pp 1 – 98. 

Bürki, P., Private communication, 1993. 

Chatterjee, T.K. and Ghosh, S. N., “ The effect of cooling rate on cement properties- a 

review”, World Cement Technology, June 1980, pp 252 – 257. 

Fletcher, J.G. and Glasser, F.P., “Phase Relations in the System CaO - B 2 O 3 - SiO 2 ”, J. 

Materials Science,, vol. 28, 1993, pp 2677 – 2686. 

Gebauer, J. et al., “Influence of Clinker Quality upon the Properties of Cement and Concrete, 

HMC Report MA 80/2712/E, 1980. 

Ghosh, S.P. and Mohan, K., “Interrelationship among Lime Content of Clinker, its 

Microstructure, Fineness of OPC Grinding and Strength Development of Hydrated Cement at 

Different Ages”, Proceedings of the 10 th International Congress on the Chemistry of Cement, 

Gothenburg, 1998, Volume 2, ii018, 4 pp. 

Gutt, W., “Manufacture of Portland cement from phosphatic raw materials”, Proceedings of 

the 5 th International Congress on the Chemistry of Cement, Tokyo, 1968, Volume 1, pp 93 - 

105. 

Heinemeyer, H. (private communication referring to Hardegsen plant) 

Ichikawa, M., and Komukai, Y., “ Estimation of clinker cooling rate by XRD pattern 

ddecomposition of ferrite phase and its correlation with strength development”, JCA 

Proceedings of Cement and Concrete, No 49, 1995, pp 8 – 13. 

Imlach, J.A., “The influence of heating conditions on the production of Fluuorine-containing 

Portland cement clinker”, Cement Technology, Vol. 5, No. 4,July/August 1974, pp 403 – 406. 

Imlach, J.A., “ Evaluation of the suitability of boron as a mineraliser in the production of 

Portland cement clinker”, HMC Report MA 94/3320/E. 

Imlach, J. A. “Sources and reductions of heavy metal emissions”, HMC Report MA 

97/13205/E, 1997. 


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Concrete 

Jepsen, O.L., “Zementfestigkeit und ihre Bezeihung zur Kühlgeschwindigkeit und Kühlertyp”, 

Zement –Kalk-Gips, Nr. 2, 1976, pp 62 - 64 

Knöfel, D., “Beeinflussung einiger Eigenschaften des Portlandzementklinkers und des 

Portlandzementes durch TiO 2 ”, Zement-kalk-Gips, vol. 4, 1977, pp 191 – 196. 

Knöfel, D., “Effect of manganese on the properties of Portland cement clinker and Portland 

cement”, Zement-kalk-Gips, vol. 7, 1983, pp 402 – 408. 

Long, G. R., Phil. Transactions. Royal Society London, 1985, A310, p 43. 

Misteli, B., CTS/MT, private communication. 

Moir, G. and Glasser, F.P, “Mineralisers, Modifiers and Activators in the Clinkering Processl”, 

Proceedings of the 9 th International Congress on the Chemistry of Cement, New Dehli, 1992, 

Volume 1, pp 125 - 153. 

Moir, G., “Influence of Raw Mix Heterogeneity on Ease of Combination and Clinker Strength 

Potential”, Proceedings of the 10 th International Congress on the Chemistry of Cement, 

Gothenburg, 1997, Volume 1, 1i041, 8 pp. 

Munoz,M., et al., “ Influence of the mineralogical composition, specific surface area and 

strains crystallite size of alite on the compressive mechanical strength of portland mortars. II. 

Clinkers of high tricalcium aluminate content”, Cement and Concrete Research, 1995, Vol. 

25,No 5, pp 1103 – 1110. 

Ono, Y., Kawamura, S., and Soda, Y., “Microscopic observations of alite and belite and the 

hydraulic strength of cement”, Proceedings of the 5 th International Congress on the 

Chemistry of Cement, Tokyo, 1997, Vol. 1, supplementary paper 1-79. 

Osbaeck, B., “Der Einfluss von Alkalien auf die Festigkeitseigenschsften von 

Portlandzement”, Zement-Kalk-Gips, Nr. 2, 1979, pp 72 – 77. 

Paul, M. and Glasser, F.P., “Mineralised Clinkers”, Unpublished HMC study. 

Platzer, E., “Untersuchungen zur Klinkerreaktivität im Werk Retznei der Lafarge Perlmooser 

AG, Gesteinshüttenkolloquium 1998, 23 Oktober 1998, Institut für Gesteinshüttenkunde, 

Montanuniversität, Leoben. 

Schmidt, O., “Einfluss von ZnO und PbO auf die Eigenschaften von Portlandklinker und 

Portlandzement”, Dissertation, Fakultät für Bergbau, Technische Universität Clausthal, 

Januar 1980. 

Spierings, G.A.C.M. and Stein, H.N., “The influence of Na 2 O on the hydration of C 3 A”, 

Cement and Concrete Research, Vol. 6, 1976, pp 265 – 272. 

Stephan,D., Maleki, H., Knöfek, D., Eber, B. and Härdtl, R., “ Influence of Cr, Ni and Zn on 

the properties of pure clinker phases, Part 1 – C3S, Cement and Concrete Research, vol. 29, 

1999, pp 545 – 552. 

Strung, J., Knöfel, D. and Dreizler, I., “Einfluss der Alkalien und des Schwefels aud die 

Zementeigenschaften”, Zement-Kalk-Gips, Nr. 3, 1985, pp 150 – 158. 

Stürmer S.et al., “ Einfluss des Trikalziumaluminat (C 3 A-) – Gehaltes im Portlandzement auf 

Brennverhalten und Phasenbestandder Klinker sowie Festigkeitsentwicklung der Zemente 

Svinning, K.and Bremseth, S.K., “ The Influence of Microstructure in Clinker and Cement on 

Setting Time and Strength Development until 28 Days”, Proceedings of the 18 th International 

Conference on Cement Microscopy, Houston, 1996, pp 514 – 533. 


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Svinning, K.and Bremseth, S.K., “X-ray Diffraction Studies on variations in Microstructure in 

Portland Cement ClinkerCorrelated to Variations in Production Conditions in the Kiln”, 

Proceedings of the 18 th International Conference on Cement Microscopy, Houston, 1996, pp 

382 – 403. 

Svinning, K.and Justnes, S., “ Application of Partial Squares Regression Analysis in 

Examination of Correlations between Production Conditions, Microstructures in Clinker and 

Cement and Cement Properties”, Proceedings of the 10 th International Congress on the 

Chemistry of Cement, Gothenburg, 1998, Volume 1, 1i038, 8 pp. 

Sylla, H.M., “Einfluss der Klinkerkühlung auf Erstarren und Festigkeit von Zement”, Zement- 

Kalk-Gips, H 9, Sept. 1975, pp 357 – 362. 

Sylla, H.M., “Einfluss reduzierenden Brennens auf die Eigenschaften des Zementklinkers, 

Zement-Kalk-Gips, H 12, December 1981, pp 618 – 630. 


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Mineral Components 

1. INTRODUCTION TO MINERAL COMPONENTS............................................................... 68 

1.1 Definition of Mineral Components ............................................................................ 68 

1.2 Types of Mineral Components ................................................................................. 68 

1.3 Industrial MIC - Production Worldwide.................................................................... 69 

1.4 Opportunities of MIC ................................................................................................ 72 

1.5 Threats of MIC ......................................................................................................... 72 

1.6 Mineral Components - A Core Business of Holcim ................................................. 73 

2. MINERAL COMPONENTS STRATEGY........................................................................... 74 

2.1 Introduction .............................................................................................................. 74 

2.2 Concept of a MIC Strategy....................................................................................... 74 

3. MINERAL COMPONENTS - OVERVIEW......................................................................... 76 

3.1 Mineral Components in Cementitious Applications.................................................. 76 

3.2 Chemical Composition of Mineral Components ....................................................... 77 

3.3 Performance of Mineral Components ...................................................................... 78 

3.4 Standards for Mineral Components ......................................................................... 82 

3.5 Testing Methods....................................................................................................... 83 

4. MAIN MINERAL COMPONENTS FOR PRODUCTION OF BLENDED 

CEMENTS.........................................................................................................................83 

4.1 Blast-Furnace Slag and other Slag Types ............................................................... 83 

4.2 Fly Ash ..................................................................................................................... 99 

4.3 Pozzolans............................................................................................................... 110 

5. REFERENCES.................................................................................................................. 120 


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1. Introduction to Mineral Components 

1.1 Definition of Mineral Components 

Mineral Components are materials with binding properties, which are not derived from the 

clinker manufacturing process. 

Mineral Components can be used 

- as alternative material for clinker (clinker substitute) or 

- for the manufacturing of concrete (cement substitute). 

Other terms used for Mineral Components are mineral additions, mineral additives, mineral 

admixtures, cement extenders, or for chemically inert material, fillers. 

1.2 Types of Mineral Components 

According to their reactivity, Mineral Components are subdivided in three groups: 

♦ latent hydraulic material (e.g. granulated blast-furnace slag) 

♦ pozzolanic component (e.g. natural pozzolana, fly ash, silica fume, burnt clay) 

♦ filler (usually limestone). 

Latent hydraulic materials have a natural hydraulic potential (i.e. they develop silicate 

hydrates by hydration reactions). To accelerate the reaction with water they require an 

activator such as: 

♦ Lime 

♦ Portland cement clinker 

♦ Gypsum 

♦ Chemical activator 

Blast-furnace slag is the most typical latent hydraulic material. 

Pozzolanic Materials can give rise to the formation of silicate hydrates only in presence of 

lime (calcium hydroxide, Ca(OH)2), as a consequence of its reaction with the amorphous 

(glassy) silica contained in the pozzolana. The hydration reaction of Portland cement clinker 

with water will provide the necessary lime to make the pozzolanic reaction happen. 

Natural pozzolanas, generally of volcanic origin, and low-calcium fly ashes are the most 

commonly used materials belonging to this group. 

Inert additions (fillers) possess no hydraulic or pozzolanic activity, but contribute to cement 

properties other than strength development. 

Limestone filler is the most commonly used, particularly in the production of fillerized 

cements, with up to 35% clinker replacement, and in the manufacture of masonry cements 

(up to 75% limestone). 


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Mineral Components can also be grouped according to their origin into natural and artificial 

materials. Artificial Mineral Components are either derived from industrial production as byproducts, 

or can be obtained by thermal activation of natural materials or by-products. 

Table 1 shows an overview of the classification of Mineral Components. 

Table 1 Classification of Mineral Components according to reaction mechanism 

Example: SLAGS 

Example: NATURAL POZZOLANS, FLY ASH 

artificial natural artificial 

* granulated blast-furnace 

slag (gbfs) 

* volcanic ashes * activated natural materials 

(burnt clays, shales, and volcanic 

rocks, metakaolin, Kalsin, etc.) 

* all other rapidly cooled slags * tuffs * industrial by-products (fly ash, 

silica fume, rice husk ash, etc.) 

* opaline cherts and 

shales 

* diatomaceous earth 

* activated industrial by-products 

(calcined red mud, waste, pulverized 

clay bricks or tiles, etc.) 

* rhyolites, etc. 

The properties of the two different groups of Mineral Components are described in detail in 

chapter 4. Owing to their wide application and strategic importance fly ashes are discussed 

separately from pozzolans in section 4.2. 

1.3 Industrial MIC - Production Worldwide 

The global volume of industrial MIC produced each year amounts to approximately 830 

million metric tons, compared to a total cement output of 1’500 million metric tons. 

Figure 1 shows the annually produced volumes of the main industrial MIC. Fly ash makes up 

for more than half of the total quantity, followed by blast-furnace slag. Almost two thirds of 

this slag is granulated and is hence suitable for cement addition. A yearly volume of 6 million 

metric tons of granulated blast-furnace slag is traded by ship and can potentially travel to any 

destination port around the globe. 


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Granulated 

Blast Furnace Slag 

Gbfs 

124 

Seaborne Slag Trading (6) 

60 

Steel Slag 

65 

Fly Ash 

490 

120 

Bottom Ash 

Global volumes: MIC cement = 614 mio t/y 

MIC aggregates = 245 mio t/y 

Cement production = 1.500 mio t/y 

Holcim = 142 mio t/y 

Figure 1 Global production of slag and fly ash (2002) 

Figures 2 and 3 give an overview on the geographic distribution of the produced blastfurnace 

slag and fly ash volumes. 

Rest of Eastern 

Europe / CIS 

Bfs 

volume 

Gbfs 

(mio t/y) 

9 China 

17 

Western Europe 

USA/Canada 

Ukraine 

16 

5 

Japan 

5 

6 4 6 7 

36 

19 

6 

5 

Rest of Latin 0.3 

7 

17 

America 

2 

Turkey, Middle East 

0.5 

Africa 

and Indian 

5 

Subcontinent 

8 

1.5 

0.7 

6 

Rest of Asia, 

Brazil 

Australia 

Air cooled bfs 

(mio t/y) 

Total bfs: 184 

Total gbfs: 124 


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Figure 2 Global production of gbfs and ungranulated bfs (2002, mio t/y) 

Fly ash 

production 

Used 

Directly usable 

Beneficiable 

Non-usable 

Global prod. : 490 

Utilization : 167 

Directly usable : 173 

Beneficiable : 90 

Non usable : 60 

USA/Canada 

73 / 33% 

10 3225 

6 

CIS 

Eastern Europe/Tk 

56 / 37% 

62 / 16% 

8 

12 

21 China 

Western Europe 14 10 

15 

100 / 60% 

39 / 33% 

16 

NE-Asia 

22 

6 4 

23 / 67% 

17 

18 

11 

30 60 

13 

5 16 

India 

80 / 10% 

Africa 

10 

8 

1 / 10% 

SE Asia 

20 

42 

7 / 47% 

Latin America 

6 / 16% 

3 3 

2 

1 

South Africa 

Australia 

3 

30 / 6% 

6 

12 / 16% 

2 

2 

6 

3 

8 

14 

1 

Total fly ash 

Current utilization 

production 

rate % 

Figure 3 Global production of fly ash (2000, mio t/y) 

Today, industrial MIC have become valued commodity products. The following trends 

contribute to this development: 

• Changes in environmental legislation / constraints 

Dumping of industrial by-products is being restricted or not allowed any more. At the 

same time, disposal costs increase. 

• Reduced margins on core products 

Increased competition in the steel sector and deregulation of power industry put the 

margins under pressure. Steelworks and power plants find new value potential in the 

commercialisation of their by-products. 

• High technical competence, sophisticated processes 

The improvements in their core processes also result in a more consistent quality of the 

by-products. Consequently, larger volumes of good quality slags and fly ashes can be 

expected. 

• Lower trading barriers 

• Lower transportation costs 


Cement 

Concrete 

1.4 Opportunities of MIC 

The integration of MIC offers considerable opportunities, ranging from environmental benefits 

to product performance, marketing aspects and financial profits. 

The main opportunities with MIC are: 

• Reduction of CO 2 : As a clinker substitute, MIC is the most important means to 

considerably reduce the output of CO 2 

• Reduction of operational costs 

• Reduction of net operating assets (NOA) 

• Extension of lifetimes (e.g. quarries, machines) and/or delay in investments 

• Differentiation of products 

• opportunity to produce tailored products 

• improvement of cement properties for selected applications 

• Entrance into new geographic markets 

Although the opportunities mentioned above rarely appear simultaneously, in most 

companies the significance of even one single opportunity justifies the integration of MIC. 

With CO 2 taxes soon to be imposed in many countries, the use of MIC as most effective 

means to reduce CO 2 emissions will gain further importance. 

1.5 Threats of MIC 

Figure 4 visualizes the integration of MIC in the cement process. The MIC deriving from 

pozzolan quarries, coal power stations or integrated steel mills can be introduced at different 

stages of the value chain: 

• As raw meal component for clinker production 

• As cement constituent in the cement mill (‘clinker substitute’) 

• Pure as concrete addition (‘cement substitute’) 

From a cement manufacturer’s point of view the MIC flows should be restricted to the first 

two channels, shown with green arrows in figure 4. The red arrows indicate the direct supply 

of MIC to the concrete producers. In this case the MIC bypass the cement process and 

partially substitute cement in the concrete mix. 


Cement 

Concrete 

Figure 4: Integrated Cement and MIC Business Structure 

This can have the following impacts: 

• Partial replacement of cement in concrete lowers our cement sales 

• MIC as traded commodities lower the entrance barriers for new competitors in the 

cement markets 

• New non-cement competitors try to control the MIC sources and the direct MIC 

channels to concrete producers and 

• will substantially reduce the cement price level by introducing low priced MIC in order to 

gain important market shares 

• Lower priced MIC blended cements compete against OPC (in spite of the same or better 

performance) 

• MIC enables competitors to react much faster in the markets 

1.6 Mineral Components - A Core Business of Holcim 

In 1997, MIC was declared part of Holcim’s core business. Thus, it must be integrated in the 

business plan of a Group company. 

Since then, a number of projects related to MIC strategies have been realized by the Group 

companies, ranging from sourcing strategies (e.g. Holdercim Brasil) to blast-furnace slag 

granulators (e.g. Alsen and Holnam) and grinding stations dedicated to composite cements 

(e.g. Juan Minetti). 

The HMC-Corporate Product Development division assists Group companies in developing 

their strategies, co-ordinates and acts as information turntable. 


Cement 

Concrete 

2. Mineral Components Strategy 


The development of an appropriate MIC strategy is an important part of any cement business 

plan. It should aim at revealing and preventing potential threats at an early stage and making 

best use of the opportunities offered by MIC. 

2.2 Concept of a MIC Strategy 

A comprehensive MIC strategy covers aspects along the entire value chain of cement 

business and comprises all MIC materials (blast-furnace slag, fly ashes, and other 

pozzolans). 

Following the value chain, the focus lies on five major topics: 

1. Sourcing 

The MIC sources are usually not owned by the cement industry, but are inter-linked with 

other production processes. Analysing and understanding the MIC supply market, 

keeping track of the developments of upstream industries and knowing the relevant 

sources are crucial factors in order to evaluate the accessible MIC volumes in the market. 

Furthermore, the quality of MIC material and its consistency over time need to be 

analysed carefully to decide on its suitability for cement production. 

2. Logistics 

An extensive use of MIC is linked with an increase in logistic flows. The optimization of 

these flows by using synergies becomes most important in order to reduce expenses. 

The MIC strategy process should comprise inbound, interplant and outbound logistics. 

3. Manufacturing 

The impact of MIC integration on cement production can achieve various dimensions: 

extension of quarry lifetime, modification of clinker properties, increase of cement 

capacity, elevation of production complexity. Therefore the MIC strategy process should 

take into account all activities from raw material exploitation to clinker and cement 

production and estimate the required investments. Environmental questions, like the CO 2 

issue, should also be addressed. 

4. Product 

Mineral Components are an adequate tool for product differentiation. Understanding the 

application segments and the resulting concrete property requirements within the market 

is essential for the development of customer-focussed products and services. 

5. Market 

Analysing and understanding the composite cement market, scrutinising the product mix 

and identifying competitors and their strategies are prerequisites for the assessment of 

the MIC potential in a market and the basis for the development of an accurate product 

mix and a suitable marketing concept. 


Cement 

Concrete 

HMC-CPD has developed a tool that visualizes the process of strategy shaping: the MIC 

Pyramid. 

Figure 5: The MIC Pyramid 

The functional structure of the MIC Pyramid follows the value chain from sourcing to 

marketing. The base of the pyramid is composed of 24 boxes containing the key topics for a 

thorough analysis of the MIC situation in a company. 

In the vertical dimension the pyramid is organized according to the concept of MIC strategy 

development. The analysis is followed by a synthesis, where opportunities, threats and key 

issues of the functional sections are recognized. In a next step MIC options are developed, 

which are interrelated to sourcing and marketing scenarios. The evaluation of the options 

regarding impacts and risks results in the definition of the most appropriate MIC strategy for 

the Group company. 

Going from top down, the MIC Pyramid visualizes the implementation process of the MIC 

strategy from the approved strategy to the individual action plan at operational level. 

MIC strategies can have different objectives, ranging from reduction of clinker factor to 

expansion of production capacities, product differentiation or prevention of market entrance 

by a competitor. In any case, the MIC strategy is part of the cement business plan and as 

such impacts on all issues covered by the latter, such as procurement, logistical set-up, 

investments, product-mix, financial projections etc. 


Cement 

Concrete 

3. Mineral Components - Overview 

3.1 Mineral Components in Cementitious Applications 

Slags have been known since ancient civilizations. It has been illustrated that ancient 

Egyptians produced glass slags, rich in vesicles (air bubbles) and containing crystals of the 

minerals melilite and tridimite, by burning wheat straw. This contains opal, an amorphous 

form of silica, that combines during burning with alkali to form glassy slag. 

More than 2000 years ago, the Romans discovered the activity of the volcanic ash from 

Pozzuoli when it was mixed with lime. This was used in many structures that lasted through 

the centuries and are still existing today, such as aquaducts, bridges, historical buildings like 

the Pantheon Figure 6. 

Vitruve, architect and engineer in the 1st century AC was the first who tried to explain the 

reactions that transform some rocks into cementitious materials. 

Figure 6 

Pantheon, Rome (2 nd century). 

More recently, the production of blended cements has been practiced for many decades in 

many countries. The latent hydraulic reactivity of vitreous blast-furnace slag was discovered 

by Emil Langen in 1862. The first use of slag in cement dates back to 1865, when in 

Germany a slag-limecement was commercially produced. In 1883 slag was used as raw 

material for Portland cement manufacture. The first production of a Portland blast-furnace 

type of cement by grinding together Portland cement and granulated slag occurred in 

Germany in 1892. 

Fly ash cements has been used since the 1930ies in cementitious applications. Cements 

containing natural pozzolanas have been firmly installed in the Italian and Greek markets for 

decades, and are used in practically all applications involving concrete construction. 


Cement 

Concrete 

Table 2 gives a rough overview on the present use of composite cements worldwide: 

Table 2 

Production of Composite Cements worldwide. 

Addition 

Situation 

 

Slag Ash Pozzolan Limestone 

established EC countries Europe Italy Europe 

Latin America Oceania Turkey Morocco 

East. Europe South Africa Latin America 

Japan 

Greece 

South Africa 

increasing Australia Canada Middle East East. Europe 

Brazil Far East Far East New Zealand 

Canada 

India 

3.2 Chemical Composition of Mineral Components 

Mineral Components exhibit in many respects very different properties. However, they have 

one thing in common: They consist essentially of the same major chemical elements as PC 

clinker: SiO2 - Al2O3 - CaO. 

The respective proportions regarding the CaO - SiO2 - Al2O3 diagram are shown in Table 3 

and represented in Figure 7. 

Table 3 Ranges of the chemical composition of Mineral 

Components (on the basis of dried and calcined materials) 

Elements 

Blast-furnace 

Slag 

Natural and/or 

Artificial Pozzolan 

Class F Fly Ash 

SiO 2 30 - 40 50 - 75 40 – 65 

Al 2 O 3 (TiO 2 ) 8 - 25 15 - 25 15 - 40 

Fe 2 O 3 0.5 - 1.5 3 - 10 3 - 17 

CaO 35 - 45 1 - 15 1 - 10 

MgO 1 - 18 < 5 - 3 

SO 3 1.5 - 6 0.1 - 1.5 0.3 - 3 

K 2 O 0 - 0.5 0.5 - 4 2 - 3 

Na 2 O 0 - 0.5 0.5 - 4 0.4 - 2 

MnO 0.2 - 2 - < 0.3 


Cement 

Concrete 

Figure 7 

CaO-SiO-AlO-System 

3.3 Performance of Mineral Components 

Mineral Components have to be activated for adequate hardening. 

Slag has a high silica and calcium oxide content. If activated by OH - or SO 4 -- ions, it displays 

hydraulic activity (cementitious properties). In practice, the activation is realized by addition 

of lime, Portland cement clinker (OH - ) or gypsum (SO 4 -- ). 

Silica, and alumina at a lower degree, are the main components of pozzolan, whereas the 

calcium oxide is low. Pozzolan supplies the silica (or alumina) that reacts with added lime or 

with the lime (Portlandite) produced by hydration of Portland cement clinker. 

When analyzing the calcium hydroxide content in mortar as a function of time, it can be 

observed that the quantity of CH decreases significantly for a a blended cement compared 

to pure Portland cement Figure 8. 


Cement 

Concrete 

Figure 8 

Calcium Hydroxide Content of Pozzolanic Cement and Portland Cement 

Mortar 

The main hydration products of Mineral Components when mixed with OPC and water are 

essentially the same as those formed during the hydration of Portland cement, namely nearly 

amorphous calcium-silicate hydrates (CSH) of different stoichiometric composition, the socalled 

AFt and AFm-phases (Aluminate-Ferrite-tri-sulphate, hydroxide etc.; C 3 (A,F) . 3(CaSO 4 , 

Ca(OH) 2 ) . aq and Aluminate-Ferrite-mono-sulphate, hydroxide, chloride, carbonate, etc.; 

C 3 (A,F) . (CaSO 4 , Ca(OH) 2 , CaCO 3 , CaCl 2 ) . aq, and Ca(OH) 2 . 

The amount of CSH gel of cements containing slag, fly ash or natural pozzolans is 

substantially higher than that of Portland cement, because less calcium hydroxide is 

generated due to the lower free lime content of blended cements compared with OPC. 

That leads to 

- a shift in pore size to smaller pores Figure 9 and 10 and 

- the blocking of corresponding pores ("pore blocking effect", Figure 10) 

In concrete the porous interfacial zone around the aggregates is considerably smaller when 

Mineral Components are used. 


Cement 

Concrete 

Figure 9 

Pore size distribution in hydrated binder vs. content of ground 

granulated blast-furnace slag. 

Figure 10 

Pore size reduction and pore blocking. 


Cement 

Concrete 

The denser microstructure of concrete containing Mineral Components significantly 

- decreases the permeability of the concrete and thus 

- increases the resistance to chemically aggressive environments 

- increases the strength at long-term (because of the lower hydration rate of Mineral 

Components) 

The CSH-phases of blended cements are able to incorporate alkalis. The "trapped" alkalis 

are no more available to form alkali silicates, which owing to volume expansion can damage 

the concrete. Concretes containing Mineral Components are less sensitive to alkali silicate 

reaction. 

Mineral Components also improve the properties of fresh concrete. They 

- improve workability 

- decrease the water demand. 

The rate of hydration of Mineral Components is lower compared with Portland cement. 

Therefore MIC additions result in lower early strength. When the concrete contains MIC 

proper curing is very important. 

The lower rate of hydration of the MIC is coupled with a lower heat development, which 

makes Mineral Components additions beneficial in mass concrete construction. 


Cement 

Concrete 

3.4 Standards for Mineral Components 

The increased use of Mineral Components in cement and concrete brought to the 

development of specifications describing the characteristics of the different materials and the 

testing methods applied to evaluate suitability of use in cementitious blends. 

These features are usually enclosed in the main cement standards (e.g. EN 197, ASTM C- 

595 and 1157). When the mineral component can be directly used in the mix design of 

concrete, specific standards are usually drafted. 

A comprehensive description of national and international specifications for blended cements 

and their mineral constituents is given in the chapter on cement standards. 

As an example, some of them are listed below. 

♦ ASTM C 618 “Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral 

Admixture in Portland-Cement Concrete” 

♦ EN 450 “Fly Ash for Concrete” 

♦ ASTM C 989 “Specification for Ground Granulated Blast-furnace Slag for Use in 

Concrete and Mortar” 

♦ ASTM C 1240 “Specification for Silica Fume for Use in Hydraulic Cement Concrete and 

Mortar” 

♦ EN 13263 "Silica Fume for Concrete". 

Often the question is raised whether it is more advisable to use Mineral Components in the 

manufacture of blended cements rather than in the preparation of concrete mixes. Basically, 

a concrete prepared with a blended cement and another prepared by addition of the mineral 

component directly into the concrete mixer, prove to be equivalent in performance. However, 

the use of blended cements offer the folowing advantages: a well established quality control 

on materials, the availability of large storage facilities that smoothen quality fluctuations, and 

the possibility to adjust the cement composition and production parameters to the desired 

final binder performance. 


Cement 

Concrete 

3.5 Testing Methods 

The most currently used testing methods for the determination of the quality of an addition 

are: 

♦ Chemical analysis including heavy metals and insoluble residue 

♦ Mineralogical analysis by means of XRD and microscopy 

♦ Calorimetric methods such as DTA, DSC or TGA 

♦ Particle shape (microscopy) 

♦ Density 

♦ Fineness and particle size distribution (Blaine, sieve analysis, laser granulometry) 

♦ Grindability (Holcim grindability test) 

♦ Activity index and pozzolanic activity determination: 

• Keil Index (hydraulic) 

• Strength Activity Index (SAI) according to ASTM C 311 

• CEN pozzolanic activity test 

♦ Test on standard laboratory cement 

♦ Specific accelerated mortar test, etc. 

A combination of 2 or 3 of the above methods is generally necessary for the current quality 

control of acceptance of an addition. 

4. Main Mineral Components for Production of Blended 

Cements 

4.1 Blast-Furnace Slag and other Slag Types 

4.1.1 General 

Slags are by-products of different metallurgical industries such as the ferrous industry or nonferrous 

industries like copper, lead, or nickel production. 

When metal is extracted from the ore or refined by a further process, slag of various qualities 

are obtained. The slags basically form by fusion of silica, alumina and alkali earth 

compounds from ore and flux and combustion residues of the fuel. These reactions take 

place at temperatures between 1300 and 1600°C. 

The chemical and mineralogical composition of the slag varies considerably according to the 

raw materials and the refining process Table 4. 


Cement 

Concrete 

Table 4 

Chemical Composition of Metallurgical Slags - Examples. 

Lead 

Zinc 

U.K. 

Nickel 

Canada 

Non-ferrous Slags 

Copper 

S. Africa 

Phosphorus 

Furnace 

USA 

Ferrous Slags 

Steel BOF 

Slag 

Germany 

Iron Blast 

Furnace 

Europe 

SiO 2 18 29 34 41 13 34 

CaO 20 4 9 44 47 41 

MgO 1 2 4 1 1 7 

Al 2 O 3 6 1 6 9 1 13 

FeO x + MnO x 38 53 41 1 31 1 

CaO/SiO 2 1.1 0.1 0.3 1.1 3.6 1.2 

Owing to the favourable chemical composition (no heavy metals, no unstable mineral 

phases), blast-furnace slag is the major slag type used in cementitious binders. 

Therefore the following chapters are related to blast-furnace slags. 

The amount of other slag types than blast-furnace slag for the production of Portland blended 

cements is limited. EN standards, for example, define a maximum content of 5%. 

Steel furnace slags are widely used as aggregates in road construction as pavement material 

(fill, subbase, base) and in asphalt and thin bituminous surfacings. 

4.1.2 Definition of Blast-Furnace Slag 

Blast-furnace slag is the non-metallic product, consisting essentially of silicates and 

alumosilicates of calcium and other bases that is developed in a molten condition 

simultaneously with iron in a blast furnace. 

4.1.3 Production of Blast-Furnace Slag 

4.1.3.1 ORIGIN AND CLASSIFICATION 

Blast-furnace slag (bfs) is a by-product in the manufacture of pig iron in the blastfurnace 

Figure 11. The raw materials (iron ore, flux, steel slag) and coke introduced at the top of the 

furnace move down and become heated from below. Due to air injection near the bottom of 

the furnace, the oxidation of the coke supplies enough energy to melt the burden. The oxidic 

iron ore is reduced to pig-iron. 

The blast-furnace slag forms by fusion of the gangue material of the iron ore (mainly silica 

and alumina compounds) with the remaining calcium and magnesium oxides of the thermally 

decomposed carbonatic flux (limestone, dolomite) and combustion residues of the coke. 

These reactions take place at temperatures between 1300 and 1600°C. 

The slag floats on the top of the liquid iron and is drawn off at regular intervals. In 

dependence of the ore composition and efficiency and size of the blastfurnace, the amount of 

slag per ton of pig iron varies. For an economic iron production the ratio of slag to pig iron 

weight should be as low as possible. In modern blast-furnaces processing high quality ore 

the slag/pig iron ratio is ~250-300 kg/t. 


Cement 

Concrete 

Figure 11 

Schematic Section of a Blast Furnace. 

The main constituents of bfs are lime-silica-alumina and magnesia compounds. The 

chemical composition of blastfurnace slags depends on the burden and the fuel used in the 

blastfurnace. Thus, the composition of slags from different sources varies within certain 

limits. Slags originating from the same blastfurnace exhibit a relatively constant composition, 

because to ensure a constant quality of the iron, significant changes of the feed have to be 

avoided. 

Other properties of the slag such as mineralogical composition, density and porosity are 

mainly influenced by the cooling procedure. With decreasing cooling rate the crystalline 

proportion of the slag rises. Basically two types of slag can be distinguished – air-cooled and 

quenched slag (Table 5). 


Cement 

Concrete 

Air-cooled slag (Figure 12) is obtained by slow cooling of the molten slag in open pits. It is 

mainly crystalline and hardly exhibits any cementitious properties. Crushed and sieved, the 

material is used as aggregate and filler in road construction as pavement material (fill, base, 

subbase) and also in concrete manufacture. 

The specific gravity of crystalline slag lies between 2.38 and 2.76, the bulk density between 

1150 and 1440 kg/m 3 . 

In the past 50 years the percentage of air-cooled slag has gradually decreased in favour of 

quenched slag, which owing to its reactivity is widely used in cementitious applications. 

Quenched slag, a predominantly vitreous product, is obtained by rapid cooling (quenching) 

of bfs. Depending on the quenching procedure, slag wool, expanded, pelletised, and 

granulated bfs can be distinguished. Due to their glass content, quenched slags exhibit 

latent hydraulic properties, i.e. upon activation, they show cementitious behaviour. Unground 

quenched slags can be used as aggregate or even lightweight aggregate. In ground form 

quenched slags are used in the production of blended cements as clinker substitute and in 

concrete manufacture as cement substitute. Granulated slag (Figure 12) is the most 

important slag type for cementitious applications. Therefore in the following, emphasis is laid 

on production and properties of granulated bfs. The production of pelletized slag (Figure 

12) is mentioned shortly as well. 

Table 5 gives an overview on the different types of blast-furnace slag. 

Figure 12 

Different Types of Blast-furnace Slag. 


Cement 

Concrete 

Table 5 Different Types of blast-furnace slag. 

Blast-Furnace Slag 

quenched 

air-cooled 

granulated pelletized foamed/ expanded 

mainly vitreous partially crystalline partially crystalline crystalline 

dense or porous porous porous dense 

mainly ground in 

cement or concrete 

lightweight aggregate 

or ground in 

cement/concrete 

lightweight aggregate 

road or concrete 

construction 

4.1.3.2 QUENCHING TECHNIQUES 

4.1.3.2.1 Granulation 

Wet granulation (with water) is the most common and well-established quenching method. 

Granulated blast-furnace slag (gbfs) is produced by breaking-up and quenching the stream 

of molten slag by water jets to particles with a maximum size around 5 mm. Figure 13 shows 

as an example a schematic illustration of the Salzgitter granulator, Germany, which is 

operated by Alsen. 

The formation of gbfs with a glass content >95% requires rapid quenching of the slag melt to 

temperatures below the crystallisation temperature of approx. 840°C. Therefore ~5-10 tons 

of water are necessary, depending on the granulation equipment. 

The bulk density of the granulate usually is between 0.9 and 1.1 kg/l. 


Cement 

Concrete 

Figure 13 

Schematic illustration of a granulator (Source: Alsen). 

From the granulation tank the mixture of granulate and water is transported to the dewatering 

system, which differs depending on the equipment supplier. The basic dewatering systems 

are 

- Pit method (granulate settles under gravity in a pond and is clammed out with a crane 

or excavator) 

- De-watering silos (granulate settles and water flows off the top through a steel mesh 

in the sides and discharge cone of the silo) 

- Gravel bed filters (similar to silos, only with a bed of gravel at the 

base of the cells acting as a filter. After drainage, the granulate is removed by an 

overhead crane) 

- INBA drum (Paul Wurth) (most widely used unit ; slurry flows under gravity to a 

distributor box located along the axis of a horizontal cylindrical mesh filter. The drum 

contains lifters that elevate the dewatering slag until it falls on a conveyor belt for 

drum exit) 

- Dewatering wheel (AJO) (Single or double wheels rotate slowly in a secondary slurry 

reservoir, wheels reclaim the gbfs via pockets with steel mesh to allow the water to 

flow back into the reservoir as the pocket rises above water level, gbfs falls out of the 

pocket onto a belt conveyor) 

- Screw conveyors (RASA) (screw conveyor rotates inclined at an angle in the reservoir 

elevating the granulate, while the water runs back into the reservoir under gravity, 

gbfs falls off the screw on a belt conveyor) 


Cement 

Concrete 

After dewatering the granulate is stored in silos or stockpiles, where it continues to drain. The 

residual moisture content is normally around 10 wt.-%. Depending on the grinding technique 

(compound or separate grinding) and equipment (mill type) drying of the gbfs before grinding 

can be necessary. 

4.1.3.2.2 Pelletizing 

The slag pelletiser was patented by National Slag Ltd., Hamilton, Canada in the late 1960’s. 

At present only few units are still working due to environmental and availability problems. 

Pelletised slag is formed by the expansion of molten bfs under water sprays. The pyroplastic 

material passes a spinning drum with fins, which break the slag and flinge it in the air, where 

due to surface tension, the pellets form (Figure 14). 

Figure 14 

Schematic illustration of a slag pelletizer 

Advantages are the lower water consumption compared with granulation (about 0.5 tons of 

water per ton of slag), and the low residual moisture of the pellets of ~5.5 wt.-%. Also gas 

emissions are lower owing to the entrapment of sulfide gases in the pores of the pellets. 

However, the emissions occur at ground level and cause more occupational health problems. 

Additionally, pelletisers create noise levels in excess of most industrial standards. Also the 

formation of considerable amounts of slag wool may create problems. 


Cement 

Concrete 

The glass content of pelletised bfs can be controlled by fractionation, because it increases 

with decreasing grain size. For the use as light weight aggregate, the demand for low water 

sorption and good thermal conductivity requires a quite crystalline structure. For this 

application bigger grains are used. The smaller fraction is used for cementitious applications, 

where higher glass contents are favourable. 

The grindability and also the hydraulic activity of slag pellets do not differ significantly from 

that of granulated slag. 

4.1.4 Processing of Blast-Furnace Slag 

4.1.4.1 GRANULATED SLAG 

The granulate is mostly stockpiled. During the storage dewatering continues. The granulate 

can be used in the unground form as sand substitute, e.g. in road construction. 

For the production of binders, the granulate has to be ground. This can be done either 

- separately or 

- together with the clinker. 

When gbfs and clinker are interground it is normally difficult to achieve the necessary slag 

fineness for optimum strangth development without overgrinding the clinker, which is easier 

to grind. Therefore separate grinding is recommended. Separate grinding offers 

furthermore a higher flexibility regarding the design of different cements with defined clinker 

and slag fineness according to the market demand. 

Depending on the grinding system and the moisture of the granulate drying of the slag prior 

to grinding can be necessary. 

Major factors influencing the grinding energy consumption of a gbfs are 

- bulk density 

- chemical composition, especially TiO 2 content 

- glass content 

- Degree of hydration / loss on ignition 

- Grinding system (see Chapter 12). 

Grinding aids, e.g. diethylenglycol, offer the possibility to decrease the grinding energy 

consumption in the range of 5-10%. 

Basically, the grinding energy consumption of gbfs increases exponetially with 

fineness (Figure 15). Therefore it is beneficial to process slags of high quality, which do not 

require too high finenesses for a satisfactory performance in cement or concrete. 


Cement 

Concrete 

Figure 15 

Grinding energy consumption of different slags (HMC Laboratory trials 

with ball mill). 

The ground slag is stored in silos. It can be added directly into the concrete or mixed with 

a cement to produce a blended cement. This is done in multiple chamber silos with batch or 

continuous mixing units. 

4.1.4.2 AIR-COOLED SLAG 

After cooling of the surface of the slag in the open pits it is sprayed with water to accelerate 

cooling and enhance crack formation by thermal shock. After entire cooling the slag can be 

digged out more easily. It is then transported to a crushing and sieving plant. The different 

grain size fractions are used a s aggregates in road construction and concrete. 

4.1.5 Properties of Granulated Blast-Furnace Slag and Influence on Processing 

and Performance 

4.1.5.1 CHEMICAL COMPOSITION 

The main constituents of bfs are lime-silica-alumina and magnesia compounds. In 

dependence on the composition of the burden and the fuel used, the chemical composition of 

slags from different sources varies within certain limits. Typical chemical compositions of bfs 

are listed in Table 6. 


Cement 

Concrete 

Table 6 Chemical composition of bfs worldwide (Locher, 2000). 

Western 

Europe 

Russia / 

Ukraine 

USA, 

Canada 

Rep. South 

Africa India Japan Australia 

SiO 2 30 … 39 30 … 40 33 … 42 30. … 36 27 … 39 31 … 40 33 … 38 

Al 2 O 3 9 … 18 5 … 17 6 … 16 9 … 16 17 … 33 13 … 17 15 … 19 

CaO 33 … 48 30 … 50 36 … 47 30 … 40 30 … 40 38 … 45 39 … 44 

MgO 2 … 13 2 … 14 1 … 16 8 … 21 0 … 17 2 … 8 1 … 4 

FeO 0,1 … 1 0,2 … 0,9 1,3 … 4,5 - < 0,5 < 0.7 - 

MnO 0,2 … 3 0,2 … 1,4 - - < 1 0,3 … 1,5 - 

Na 2 O 0,2 … 1,2 - - 0,2 … 0,9 - - < 0,2 

K 2 O 0,4 … 1,3 - - 0,5 … 1,4 - - < 0,5 

SO 3 0 … 0,2 - - - - - - 

S 2- 0,5 … 1,8 - - 1,0 … 1,6 < 1 - 0,6 … 0,8 

The chemical composition has a very strong influence on the reactivity of a slag, because it 

controls the solubility and hence the reactivity of the slag during hydration. In general, the 

hydraulic activity of a slag increases with increasing contents of CaO, (MgO), Na 2 O, and 

Al 2 O 3 and with decreasing contents of SiO 2 , FeO, TiO 2 , MnO, and MnS. 

For the prediction of slag reactivity, numerous compositional moduli were developed, for 

example 

♦ I - Basicity Index 1.0 ≤ CaO/SiO 2 ≤ 1.4 

♦ II - according to DIN 1164 

♦ III - EN Standard 

♦ III - Keil ("F-value") 

CaO + MgO + Al O 

SiO 

CaO + MgO 

≥ 1 

SiO 

2 

2 

2 3 

≥ 1 

(CaO+ 

0.5MgO+ 

Al2O3 

+ 2.25S 

F = 

(SiO + 1.29Mn) 

15 . ≤F ≤ 2. 

0 good hydraulic properties 10 . ≤ F ≤ 15 . poor hydralic properties 

2 

2− 

) 

♦ IV - Langavant Index i = 20 + CaO + Al 2 O 3 + ½MgO - SiO 2 

i ≤ 12 

poor hydraulic properties 12 ≤ i ≤ 16 good hydralic properties 

i>16 Very good hydraulic properties (but difficult to granulate) 

SiO 

♦ VI - Silica-alumina Ratio 18 . ≤ 

2 ≤19 

. 

Al O 

2 3 


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These moduli are convenient tools for rapid quality control of slag originating from the same 

furnace, but their applicability for a general prediction of strength development of blended 

cements is questionable. 

Strength testing remains the most reliable method to access slag reactivity. 

As a guideline, for optimum reactivity in cementitious applications the gbfs should meet the 

following chemical criteria (composition of granulate, without impurities): 

Desirable 

Optimum 

CaO/SiO 2 >1.0 1.3 

Al 2 O 3 >10% 13% 

MgO 5-10% 

TiO 2 

as low as possible ≤0.5% 

The CaO/SiO 2 ratio influences the solubility of the slag glass and therefore is a decisive 

parameter for slag reactivity. To a limited degree low CaO/SiO 2 ratios can be compensated 

by elevated Al 2 O 3 or MgO contents. 

Elevated Al 2 O 3 contents in the slag increase the strength development of composite 

cements, especially at early age owing to enhanced ettringite formation. 

TiO 2 in bfs is very undesired, because it strongly reduces reactivity and increases grinding 

energy consumption of the granulate. TiO 2 is added to the blast furnace in order to increase 

the service life of the refractory. 

The composition of the slag is adjusted by the iron producer in order to optimise the quality of 

the iron and to maximize the efficiency of the blast furnace. Subsequent changes in slag 

composition mostly are not advantageous for the cement producer. An adjustment of the slag 

composition according to the demands for cementitious applications is possible only to a 

limited degree. 

Because the composition of the bfs can change over longer time periods the cement 

producer must ensure to obtain granulate of a constant quality by specification of relevant 

slag properties in the supply contract he signs with the steel mill. 

4.1.5.2 MINERALOGICAL COMPOSITION AND GLASS CONTENT 

The reactivity of a gbfs cannot be evaluated based on the chemical composition only. Also 

the mineralogical composition, especially the glass content, influence reactivity. 

According to EN standard gbfs for cement should exhibit a glass content of at least 2/3 by 

mass standard. With state-of-the-art granulation equipment in most cases glass contents > 

90% are obtained, which from a reactivity point of view are satisfactory. 

Perfect vitrification is no criterion for optimum reactivity. Often an increase of the 

compressive strength of slag cements is observed when the slag contained small amounts of 

finely distributed crystals, which may act as hydration nuclei. 

The presence of crystal phases in gbfs reduces grinding energy consumption, however at 

higher amounts (>10-15%) at cost of reactivity. 

The main crystalline constituents in gbfs are calcium silicates and silico-aluminates (Table 

7). Melilite (solid solutions in the composition range from Gehlenite (C 2 AS) to Akermanite 


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(C 2 MS 2 )) and Merwinite are the most common mineral phases in gbfs. Slag granulate can 

also contain some metallic iron. The iron should be removed (magnetic separator) prior to 

grinding and within the grinding circuit to avoid a concentration of iron in the mill, which can 

damage the mill or cause higher grinding time. 

Table 7 Some crystalline constituents of blast-furnace slag. 

Mineral name mineralogical formula simplified formula 

Silicates 

Melilite 

Gehlenite 2 CaO . Al 2 O . 3 SiO 2 C 2 AS 

Akermanite 2CaO . MgO . 2SiO 2 C 2 MS 2 

Dicalcium Silicate* 2 CaO . SiO 2 C 2 S 

Rankinite 3 CaO . 2 SiO 2 C 3 S 2 

Wollastonite CaO . SiO 2 CS 

Forsterite 2 MgO . SiO 2 M 2 S 

Enstatite** MgO . SiO 2 MS 

Merwinite* 3 CaO . MgO . 2 SiO 2 C 3 MS 2 

Monticellite* CaO . MgO . SiO 2 CMS 

Anorthite** CaO . Al 2 O . 3 2 SiO 2 CAS 2 

Diopside** CaO . MgO . 2 SiO 2 CMS 2 

Oxides 

Spinels MgO . Al 2 O 3 MA 

Sulfurous compounds CaS, MnS, FeS 

Others Carbonaceous, sulphurous, nitrogenous compounds, alkali thiosulphates etc 

* only in basic slags; ** only in acidic slags 

In slags with high lime contents dicalcium silicate (C 2 S) can form. It occurs in three different 

crystalline forms. Below 675°C β-C 2 S is stable, which at atmospheric temperatures 

transforms into γ -C 2 S, accompanied by a volume increase of ~10%. This can lead to a 

spontaneous disintegration of the slag matrix. Therefore, in some standard specifications the 

CaO/SiO 2 ratio is limited (e.g. BS 6699 and 1047 CaO/SiO 2 max = 1.4). 

The mineralogical composition and glass content can be measured by X-ray diffraction 

(XRD) or by microscopy, the latter being often coupled with an image analysis system. 

By differential thermal analysis, vitreous slag shows irreversible exothermic peaks at about 

860°C, when heated between 800 and 900°C. These peaks are mainly due to the heat of 

devitrification of the glassy part of the slag. Some authors tried to find a correlation between 

the areas under the peaks and the slag content. 

4.1.5.3 AGE / LOSS ON IGNITION (LOI) 

As gbfs is latent hydraulic, it hydrates also in absence of an activator, for instance during 

being stockpiled. The loss on ignition is a measure for the degree of hydration of a slag 

glass. 


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The grinding energy required to grind a gbfs with high LOI (e.g. in the range of 2 wt.%) to the 

same fineness like a fresh gbfs (LOI normally below 0.5%) is considerably lower. The reason 

are the soft hydrates at the surface of the granules, which are very easy to grind and 

excessively contribute to the fineness measurement ("false Blaine"). The comparably lower 

fineness of the reactive slag glass causes a lower strength development compared with fresh 

ggbfs of same fineness. The lower reactivity can be compensated by higher fineness of the 

hydrated granulate. 

4.1.5.4 BULK DENSITY 

The bulk density of granulated slag influences 

- its moisture content 

- grinding energy consumption. 

A slag with low bulk density is easier to grind, but exhibits elevated moisture contents, which 

can create transportation problems, can reduce the stockpile life of the granulate and may 

require drying of the granulate prior to grinding. Granulate of high bulk density has low 

moisture contents, but requires a higher grinding energy and in some cases may also be less 

reactive. An optimum bulk density range would be 0.9 - 1.1 kg/l. 

Factors influencing bulk density are slag temperature, slag composition, temperature of the 

granulation water, and the granulation process. 

4.1.5.5 FINENESS AND GRAIN SIZE DISTRIBUTION 

As for most cementitious materials, the hydraulic activity of ggbfs increases with its surface 

area and thus, with the fineness. The effect is especially strong for the late strength 

development. 

The influence of the fineness on strength development can increase with the CaO/SiO 2 ratio 

of the slag. 

Finer grinding of gbfs is a common countermeasure for compensation of poor slag reactivity. 

The limiting factors for slag fineness are performance indicators such as shrinking and 

economical considerations (grinding costs). 

The experiences regarding the influence of the grain size distribution of the ggbfs on strength 

development are conflicting. A shallow grain size distribution can reduce water demand and 

thus favour strength development. But also opposite experiences were described. 

4.1.6 Application of Ground Granulated Blast-Furnace Slag 

Concrete containing ggbfs offer numerous advantages compared with concrete with pure 

OPC such as higher long-term strength, durability, and resistance to chemical attack, 

sea water, sulphates, lower heat of hydration, low sensitivity towards alkali silicate 

reaction, bright color. Also the properties of the fresh concrete are improved (lower w/c, 

improved workability). The hydration rate and early strength development is lower. 

Therefore curing is of paramount importance. 

Ggbfs is widely used in concrete construction, especially where strength and durability 

aspects are important: 

- Industrial construction (waste gas desulphurization plants, coking plants, silos, sewage 

treatment plants, towers, chimneys etc.) 

- Transportation (bridges, tunnels, parking houses and areas, air ports, etc.) 


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Concrete 

- Hydraulic / marine construction 

- Mining, etc. 

In mass concrete construction the low heat of hydration is beneficial for rapid construction 

progress. 

Ggbfs is used in precast products, in prestressed concrete, shotcrete, ultra-high 

performance concrete, and self compacting concrete. 

Granulated and ground granulated bfs is also used in road construction (e.g. in road 

binders). 

The following figures illustrate some applications of ggbfs. 

Figure 16 

TV Tower and administrative building, Duesseldorf, Germany. 

TV-Tower/Admin. Building: 350/300 kg/m3 slag cement, w/c 0.50/0.57, aggregate 1860 

kg/m3, Fly ash 0/50 kg/m3 (Source: Weber et al., 1998). 


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Figure 17 

Flood gates in the Philips-Dam, Netherlands. 

Prestressed concrete, impermeable, 300 kg/m3 slag cement, w/c ~0.5, aggregate 1895 

kg/m3, superplasticizer, air entraining agent (Source: Weber et al., 1998). 

Figure 18 

Coking plant in Duisburg-Huckingen, Germany. 

Heat and chemical resistant concrete with air cooled bfs as aggregate (no strength losses at 

elevated temperature (400°C), 350-440 kg/m3 slag cement, w/c ~0.5, aggregate 1660-1829 

kg/m3, partially superplasticizer (Source: Weber et al., 1998). 


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Figure 19 Concrete sculpture Beethoven in Bonn, Germany (Weber et al., 1998). 

Low heat of hydration, satisfactory strength, bright color, 380 kg/m3 slag cement, w/c 0.45, 

aggregate max. size 8 mm, retarder (Source: Weber et al., 1998). 

Figure 20 

Mixing of road binder with soil. 

Example for composition of a road binder for subbase and base layers: 76% slag, 10% 

clinker, 5% CKD, 9% gypsum, fineness ~3500 cm2/g. 

More details on slag processing and reactivity are given in the HMC report MIC 00/5005/E 

"Properties, Grindability, and Reactivity of Granulated blast-furnace slag: A Literature 

Review". 


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4.2 Fly Ash 

4.2.1 Definition of Fly Ash 

Fly ash is a fine powder of mainly spherical glassy particles derived from burning of 

pulverized coal, with pozzolanic properties consisting mainly of SiO2 and Al2O3. Fly ash is 

formed mainly by the unburnable part of the coal, which derives from inorganic material in 

the coal and bedrock material mined with the coal. 

4.2.2 Production of Fly Ash 

Fly ashes are obtained by electrostatic or mechanical precipitation of dust-like particles from 

the flue gases from furnaces fired with pulverized coal. 

The pulverized coal is injected into the furnace, ignites in the burner and burns while moving 

upwards through the boiler. Retention time of the coal particles in the boiler is around 10 

seconds, while the coal and ash particles see different temperature ranges as well as 

partially oxidizing and reducing atmospheres. Larger particles fall at the bottom of the boiler 

and are discharged wet or dry forming so called bottom ash. 

The non-burnable particles and partially unburned carbon is carried with the exhaust gases 

to the dust filters (electrostatic or baghouse filters), where they are separated from the flue 

gas and collected (Figures 21, 22). The electrostatic filters consist of a number of filter 

stages, usualy 3, where different fractions of the fly ashes are separated. The coarser 

particles are separated at the first stage, finer partcles at the following stages 2 and 3 

(Figure 23). 

The ratio between bottom ash and fly ash of the total ash content is around 20:80. Volume 

ratio of the fly ash at the filter stages is 80:16:4 from filter stage 1 to 3. 

Depending on the coal fired resp. the ash composition of the coal fly ashes are mainly 

characterized as siliceous or calcereous. The former have pozzolanic properties, and the 

latter have, in addition, hydraulic properties. There are no strict limits between these 

properties, as the types of coal are manifold. 

Fly ash is a mixture of mineral matters which have undergone thermal transformations and 

which contain still unburnt materials. The main components of the fly ash are complex glass 

phases consisting of Si, Al, Fe and Ca in various compositions. Quartz is the main cristaline 

phase. 


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Technically fly ashes can be categorized according to the burning temperature in the boiler. 

Three types of fly ash may be distinguished: 

♦ Type I: Fluidized Bed combustion 

• Burning temperature 850 to 1000°C 

• crystal structure remains 

• no melted material 

• pozzolanic properties due to sintered clays (high water demand) 

♦ Type II: Dry bottom furnace 


• most minerals are melted (about 50-80%) 

• slow reaction with Ca(OH), only medium pozzolanic activity 

• grain size distribution similar to cement 

♦ Type III: Wet bottom or slag tap furnace 


• all minerals are melted 

• grain size distribution similar to cement 

• rapid cooling of the fly ash induces the production of 60-80% of glassy particles 

• development of good pozzolanic properties 

It is generally known that the volume of fly ash produced in most countries exceeds largely 

the volume that can be utilized, but specific statistics are not available. 

Worldwide utilization rate of fly ash in all kinds of applications is estimated at 30%. Leaders 

in utilization rate and level of sophistication are Germany and France (100%), Japan (70%) 

and the US (30%). Free fly ash volumes are estimated at about 300 mio t not indicating 

suitable volumes regarding quality and geographical availability. 


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Figure 21 

Coal Fired Power Station - schematic. 

Figure 22 

Coal Fired Power Station. 


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4.2.3 Properties of Fly Ash and Influence on Processing and Performance 

The ash quality depends greatly on the type of coal and its bedrock material, type of boiler 

and its operation. The operating conditions as well as the coal quality strongly influence the 

variability of the ash with respect to residual carbon content, fineness, chemical composition 

and pozzolanic activity. Environmental measures to reduce SO2- and NOx-emissions can 

influence the fly ash properties negatively (increased carbon and SO3, ammonia smell). 

Key parameters influencing fly ash quality and quantity are: 

Coal 

- Coal type 

- Ash-content 

- Bed rock material 

Boiler 

- Boiler Type, Temperature 

Dedusting equipment 

- Electrostatic precipitator 

- Baghouse 

Environmental installation 

- High dust equipment for DeSOx and DeNOx 

4.2.3.1 CHEMICAL AND PHYSICAL PROPERTIES 

The main chemical components of ashes are SiO2, Al2O3, Fe2O3 and CaO. Substantial 

amounts of alkalis and sulfate may also be present. In the case of lignite or brown coal, the 

observed amount of free lime as well as of anhydrite is generally high (Table 8). Significant 

amounts of periclase can also be noticed in lignitic fly ash. The typical aspect of fly ash 

observed by microscopy is given in Phototable 1. The photos demonstrate the different 

morphology of the fly ash depending on the type of boiler. Figure 24 shows the grain size of 

the fly ashes from the different filter stages of the electrostatic precipitator obtained by laser 

granulometry. 


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Figure 23 

Granulometry of fly ash from different filter stages of the electrostatic 

precipitator (ESP) 

Figure 24 

Morphology of fly ashes from different boiler types (Scanning Electron 

Micrography) 


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Concrete 

4.2.3.2 MINERALOGICAL PROPERTIES 

The mineralogical composition of fly ashes depends on the amount of glassy material. The 

following minerals can be observed (Table 9), depending on the operating conditions and 

type of coal. Moreover, calcareous fly ash possesses hydraulic properties, due to a more or 

less greater amount of dicalcium silicate CS. 

Table 8 

Chemical and Physical Composition of Fly Ash 

Table 9 

Mineralogical Composition of Fly Ash 

Minerals 

Quantity % in weight 

Glass 70 – 98 

Quartz 1 – 15 

Mullite 1 – 10 

Magnetite 1 – 8 

Hematite 1 – 5 

Calcite < 2 

Plagioclase < 2 

Merwinite < 2 

Melilite < 2 

Anhydrite 1 – 8 

Free lime 1 – 8 

Periclase 1 – 6 

Wollastonite 1 – 5 

Dicalcium silicate 1 – 15 

4.2.3.3 


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4.2.3.4 CARBON CONTENT 

The carbon content is an important criterion to assess quality of fly ash. Residual carbon is 

due to the non-burnt organic matter and lies generally in the range of: 

♦ 5 to 12% in anthracitic fly ash 

♦ 2 to 8% in bituminous fly ash 

♦ 1 to 5% in sub bituminous fly ash 

♦ 1 to 4% in lignite fly ash 

The different C-contents are due to differences in burnability and grindability of the coal 

types. The variations in C-content of each coal are mainly due to instabilities of the burning 

and grinding system, to variations in burning intensity or to changes in coal supply. The 

installation of Low-NOx burners to reduce NOx emissions can lead to an increase of the 

carbon content. 

Types of unburnt carbon are either not burnt coal or coke. The latter is very porous and has a 

very high specific surface. 

A high carbon content (> 5%) is considered detrimental for the quality of concrete since it 

might 

• impair the air-entrainment in freeze/thaw resistant concrete 

• have a negative effect on workability and strength development of concrete 

From the manufacturing point of view, it is worth while mentioning that most of the unburnt 

material is agglomerated and concentrated in the coarse fraction of fly ashes. Recent 

developments in the technology of fly ash benefication allow to improve quality by 

mechanical or electrical separation of the organic matter, making it possible to use highcarbon 

fly ashes (separated unburnt coal can be used as additional fuel for clinker burning). 

The main beneficiaiton technologies are air classifiers, triboelectric separation and burn-out 

systems. 

4.2.3.5 CLASSIFICATION 

Fly ash can be classified according to its chemical and physical properties as well as to its 

performance. The main standards used world-wide are EN 197, EN 450 and ASTM C 618. 

Fly ashesa re in the following classes of Table 10. 

Table 10 

Classification of Ashes 

Characteristics ASTM EN 

Fly ash from anthracite or bituminous coal Class F 

Siliceous fly ash 

Class V 

Fly ash from lignite or subbituminous coal Class C 

Calcareous fly ash 

Class W 


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4.2.4 Standard Specifications 

The requirements do not significantly differ between ASTM and EN standards. Tables 11 

and 12 summarizes the ASTM 618 and EN 450 requirements for fly ash used in concrete, 

whereas those for EN 197 for cement additions are given in Table 13. 

Table 11 

EN 450 and ASTM 618 Chemical Requirements 

Table 12 

EN 450 and ASTM 618 Physical Requirements 


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Table 13 

EN 197-1 Requirements 

4.2.5 Optimum Fly Ash Properties 

The key quality parameters of fly ashes are fineness and unburnt carbon and additionally 

free lime content for lignite fly ashes. The following parameters give an indication what a 

good quality fly ash would look like: 

♦ Hard coal fly ash in Europe (EN 450, EN 197-1 Type V) 

♦ Sub bituminous fly ash in US (ASTM 618 Class C) 

♦ High glass content (> 80 %) 

♦ Spherical particles (> 50 %) 

♦ High total CaO content (> 20%) 

♦ Low CaO free content (< 1 % or highly reactive) 

♦ Low LOI (Europe: < 5%, US: < 2%) 

♦ High fineness (> 2500 cm 2 /g Blaine/ residue on 45µm < 10 %) 

Fly ash properties can be improved either by upgrading (carbon reduction, classification), 

activation (e.g. alkali activators) or grinding. 

4.2.6 Applications 

Fly ashes can be used in most building materials and construction applications. It is used as 

binder replacement as well as aggregate or conditioning material in soils. In countries where 


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fly ash is used it is a standard constituent of most of the concretes used and a part of the 

specifications. 

The following list gives an indication of the variety of applications and can also be seen an a 

value ranking of the fly ash by application: 

♦ Composite Cements 

♦ Concrete addition in all types of concrete 

♦ Autoclaved Aerated Concrete 

♦ Non-aerated concrete blocks 

♦ Sand lime brick 

♦ Bricks + ceramics 

♦ Lightweight aggregate 

♦ Cement raw material 

♦ Asphalt filler 

♦ Road construction 

♦ Grouting 

Actual developments are the use of fly ash in Self Compacting Concrete as well as in high 

performance concrete without silica fume. 

First applications date back in the 40ties, where fly ash was used to reduce hydration heat in 

mass concrete in dams (Figure 25). Over the last 60 years today sophistication of fly ash 

applications has increased considerably. Fly ash is used due to improved workability and 

durability in high performace concrete with up to 105 Mpa (Figure 26). 


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Figure 25 

First large scale application of fly ash in concrete 

Figure 26 

High performance application of fly ash in concrete 


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4.3 Pozzolans 

Pozzolans are classified according to their genesis into the two types ‘natural’ (Table 14) and 

‘artificial’ (Table 15). 

Table 14 

Natural Pozzolans 

Genetic process 

Examples 

1 Explosive volcanic activity Italian Pozzolan earth (‘Pozzolana’), 

Greek Santorin earth, volcanic ashes and 

pumicites 

2 Explosive volcanic activity + zeolitic 

diagenesis 

Italian Neapolitan Yellow Tuff, German 

Rhenish Trass 

3 Meteorite impact German Bavarian Trass 

4 Building of skeletons of siliceous Diatomaceous earth, Moler earth 

organisms 

5 Ultrafine weathering of siliceous rocks Gaize, Tripel, opaline cherts 

Table 15 

Artificial Pozzolans 

Genetic process 

Examples 

6 Fast cooling of silicate melts in Non-ferrous slags, HSR-granulate 

metallurgical processes 

7 Flue gas cleaning of power stations Coal fly ash (class F) 

8 Oxidation and condensation of SiO-gas Silica fume 

in metallurgical Si- and Ti-processes 

9 Thermal activation of clay minerals and 

rocks 

10 Controlled burning of agricultural, SiO 2 - 

rich wastes 

Metakaolin, oil schist, crushed bricks, 

shale, phonolite 

Rice husk ash, crop ash 

All examples have in common that they consist of fine glassy particles with a CaO : SiO 2 ratio 

below 0.5. Obviously this is prerequisite to develop a pozzolanic reaction. 

In the following sections focus will be on pozzolans 1, 2, 8 and 9 of Tables 14 and 15. More 

detailed information about pozzolans is given in HMC report “Pozzolan Survey 2001” by P. 

Kruspan/CPD. Due to their importance Fly Ashes class F (pozzolan 7 in Table 15) are 

discussed separately in the preceding chapter 4.2. 


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4.3.1 Definition of Pozzolans 

Pozzolans are siliceous or siliceous and aluminous materials which in themselves possess 

little or no cementitious properties. When finely ground, they react in the presence of water 

at ambient temperatures with dissolved calcium hydroxide (Portlandite Ca(OH) 2 ) from 

lime or Portland cement clinker to form strength developing calcium silicate and calcium 

aluminate compounds. 

Brought into a simplified chemical notation the pozzolanic reaction can be written as follows: 

x Ca(OH) 2 + y SiO 2 (amorphous) + z H 2 O → x CaO ⋅ y SiO 2 ⋅ (x+z) H 2 O 

Portlandite + Pozzolan + Water → Calcium Silicate (Hydrate) 

It becomes obvious that only with a constant supply of dissolved Portlandite the pozzolanic 

reaction can occur. Furthermore a fast pozzolanic reaction is directly controlled by the 

dissolution rate of the pozzolan. Therefore a ‘good’ pozzolan has the following 

characteristics: 

• small particle size 

• high specific surface/porosity 

• glass with high amount of (earth)alkalies 

• zeolites 

4.3.2 Natural Pozzolans 

The vast majority of natural pozzolans used today are of volcanic origin (pozzolans 1 and 2 

in Table 14). Therefore the discussion in this section is restricted to this type. 

The pozzolans were named after the Italian town Pozzuoli near Naples (Italy) where deposits 

were formed by the explosive eruption of Campi Flegrei caldera 12’000 years ago. The 

Roman used these pozzolans together with burnt lime as building materials, hardening either 

in air or even under water. Many remainders from that time prove the good quality of these 

materials. When Portland cement was invented in the 19 th century, pozzolans fell into 

oblivion, but today regained their importance. 

4.3.2.1 GENESIS AND ITS INFLUENCE ON PROPERTIES AND 

PERFORMANCE OF NATURAL POZZOLANS 

The genesis of pozzolans of volcanic origin follows three steps (processes): 

1) melting in the magma chamber 

2) fragmentation and cooling of the melt during the volcanic eruption 

3) alteration, weathering and diagenesis of the deposited volcanic material 

For every single process a certain amount of parameters can be defined which control the 

course of the process. Furthermore every process is influenced strongly by the preceding 

one. And to make it more complicated, even a single volcanic event does not produce 

materials with constant quality. Pozzolan deposits are therefore heterogeneous by their very 

nature. For this reason the main challenge is to find high-quality pozzolans by means of 

specific geologic prospecting. 


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Helpful for successful prospecting in a volcanic area or in a single deposit is the distinction 

between volcanic materials with different geologic histories (geneses). In Table 16 and 

Figure 27 two opposing histories are listed, one leading to high-quality pozzolans (‘Plinian’ 

genesis), the other one leading to low-quality pozzolans (‘Hawaiian’ genesis). 

The most important parameter for the melting, fragmentation and indirectly even the 

diagenesis process is the viscosity of the magma. In other words the whole genesis of 

pozzolans is mainly controlled by the viscosity. The viscosity on its part depends on 

temperature, chemical composition (SiO 2 , Fe 2 O 3 , FeO, CaO, Na 2 O, K 2 O), amount of volatiles 

(H 2 O, CO 2 , SO 2 ) and amount of crystallized phases. 

Table 16 

Pozzolans with different qualities depending on their genesis 

High quality pozzolans 

Low quality pozzolans 

Type of eruption Explosive (‘Plinian’) Non-explosive - effusive 

(‘Hawaiian’) 

Viscosity of magma High Low 

Degree of magma 

fragmentation 

High 

Low 

Cooling rate of magma High Low 

Eruption phenomena Pyroclastic flow, ash fall Fire fountain, lava flow 

Deposited material 

Examples 

Ash, tuff, pumice. 

Fine-grained, high glass 

content, high to medium 

porosity 

Mt. St. Helens, Vesuvius, Mt. 

Pinatubo 

Scoria, spatter, lava. 

Coarse-grained, low glass 

content or even fully 

crystallized, medium to low 

porosity 

Hawaii, Stromboli, Etna 


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Figure 27 

Two opposing types of volcanic eruptions: Plinian (left) and Hawaiian 

(right); (Table 16). Not to scale. 

In Figure 28 the pozzolanicity of samples with different geologic histories was tested 

according to EN 196-5. This test determines the calcium binding capacity of the pozzolan in 

an OPC-pozzolan paste (cf. chapter 4.3.1). The lower the CaO-concentration in the solution 

(y-axis), the higher the pozzolanicity of the sample. It can be seen that high pozzolanicities 

are favoured by pyroclastic flows generated exclusively in explosive Plinian eruptions. If such 

deposits of pyroclastic flows are additionally solidified by zeolitisation during diagenesis the 

pozzolanicity is risen significantly. 


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Figure 28 

Pozzolanicity (EN 196-5) of samples generated by volcanoes with Plinian 

and Hawaiian type of eruption, respectively. 

From Figure 27 it becomes clear that an evaluation of natural pozzolans starts in the field 

with an assignment of specifically collected samples to their correct geologic history. This 

knowledge will provide the quarry manager with the ability to separate high-quality pozzolans 

from low-quality material in order to premix different qualities as early as possible in the 

production chain. 

Ignoring the geologic context (genesis) and considering only certain properties of an 

unspecified pozzolan sample (e.g. chemical composition) will give results hardly useable for 

an evaluation. 

Therefore self-standing prescriptions of some pozzolan characteristics like specification 

ASTM C 618 (Table 17) should be used only as a very rough guideline. It is impossible 

to predict the performance of a pozzolan in cement or concrete on the basis of such a 

prescriptive specification. 


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Table 17 

Specification ASTM C 618 (chemical requirements for natural pozzolans) 

Specifications 

Class N 

- Silicon dioxide (SiO 2 ) + aluminium oxide (Al 2 O 3 ) + iron oxide (Fe 2 O 3 ), min % 70.0 

- Sulfur trioxide (SO 3 ), max. % 4.0 

- Moisture content, max. % 3.0 

- Loss on ignition, max. % 10.0 

Supplementary optional chemical requirements. These optional requirements apply only 

when specifically requested. 

- Magnesium oxide (MgO), max. % 5.0 

- Available alkalies, as Na 2 O equiv., max. % 1.5 

For the time being the cement producer should control the quality of a natural pozzolan by 

applying a combination of following methods: 

• chemical composition 

• mineralogical composition 

• physical properties 

• strength development of a blended cement (ASTM C 1157) or of a concrete mix 

4.3.3 Artificial Pozzolans 

4.3.3.1 SILICA FUME 

Silica fume is a by-product of the manufacture of silicon metal (Figure 29). Silicon metal is 

used for the production of ferrosilicon, which is required by the steel industry for the 

improvement of its products. 

SiO-gas produced in an electric arc furnace is oxidized, condensed to ultra fine SiO 2 -particles 

and subsequently separated from the flue gases in a baghouse filter where it is collected as 

silica fume. 

Figure 29 

Production of Silica Fume 

CO + O ⎯⎯→ CO 2 

SiO + O ⎯⎯→ SiO 2 (silica fume) 

↑ 

QUARTZ + COAL 

(SiO 2 + 2C) 

ELECTRIC ARC FURNACE 

(2000°C) 

⎯⎯→ Si (silicon metal) 

(98% purity) 

Condensed silica fume consists of very fine spherical particles with a high content of 

amorphous silica. It is an extremely fine powder, very much finer than Portland cement or fly 

ash, its fineness being roughly comparable with the finest particles in tobacco smoke (Table 

18). 


Cement 

Concrete 

Table 18 

Fineness of Different Materials 

Type of Material 

Fineness (cm 2 /g) 

Silica fume approx. 200’000 

Tobacco smoke approx. 100’000 

Fly ash 2’000 to 5’000 

Normal Portland cement approx. 3’000 

The grain size distribution is shown in Figure 30. The extreme fineness gives rise to a 

number of problems in handling and transporting this material. Its bulk weight is not higher 

than 300 kg/m 3 . Exposed piles are stirred by the least breath of wind. Silica fume is either 

packed in bags as such, or densified and packed in bags, as well as in the form of a 50% 

water slurry. Transport and transshipment facilities clearly necessitate efficient dedusting 

systems. 

The chemical composition (Table 19) may vary somehow depending on the impurities of 

quartz, the features of the manufacturing process, the dust precipitation facilities and the coal 

used. The effect of different compositions can become quite significant depending on the 

particular type of application. 

Table 19 

Chemical Composition of Silica Fume 

Elements 

Range 

Min. 

Max. 

Loss on Ignition 0.7 2.5 

SiO2 90.0 96.0 

Al2O3 0.3 3.0 

Fe2O3 0.2 0.8 

CaO 0.1 0.5 

MgO 0.5 1.5 

NaO 0.2 0.7 

HO 0.4 1.0 

C 0.5 1.5 

S 0.1 0.4 

Only silica fume that meets the following requirements shall be used: 

- amorphous silica SiO2 ≥ 85% by mass 

- loss on ignition ≤ 4% by mass 

- specific surface (untreated) ≥ 15 m 2 /g (BET) 

Owing to the great fineness, its completely amorphous state and its high content of SiO2, 

silica fume exhibits properties closely resembling those of pozzolan. However, the usual 

methods for characterizing the pozzolanic activity are not suitable and they had to be first 

adapted to suit its unusual properties. 

The high pozzolanic activity made it seem obvious to add the silica fume directly to cement 

or concrete. Tests performed in a great number of laboratories proved that there are a 

number of problems connected with the handling properties of the silica dust, however, they 

can be overcome when suitable modifications to the process technology are made. 


Cement 

Concrete 

The level of replacement cement by silica fume is limited and lies generally in the range of 8 

2%. The following hardening characteristics (Table 20) have been observed for an ISO 

standard mortar with a pure Portland cement compared to a 5% silica fume substitution. 

Table 20 

Characteristics of an ISO Standard Mortar 

Strength after ... Days Pure Portland Cement 95% PC 

+ 5% Silica Fume 

2 20.3 N/mm 2 21.4 N/mm 2 

28 42.8 54.1 

90 53.3 61.2 

The amount of water required by the binder is higher and the setting time is generally 

somewhat shorter compared to pure PC. The increase of strength is remarkable and conduct 

naturally to the use of silica fume for the production of high performance concrete. In order to 

reduce the higher water requirement, it is recommended to add superplasticizer in the 

concrete mix. In spite of its remarkably high price, this material is chosen in most cases 

where production of a high performance concrete is required. 

Figure 30 

Grain Size Distribution 


Cement 

Concrete 

4.3.3.2 THERMALLY ACTIVATED MINERALS AND ROCKS 

Artificial Pozzolans of this type are produced by means of thermal treatment from nonpozzolanic 

materials (e.g. marl, shale) or from materials with very low pozzolanic properties 

(e.g. phonolite). They are activated by a rise of temperature which lies between 150°C and 

about 1500°C depending on the nature of the raw material. The materials develop pozzolanic 

properties by a transformation of their crystalline structure into a glass. 

Clays, shales and rocks with very low pozzolanic properties need a calcination at 

temperatures between 500 and 1000°C in order to be activated. 

Burnt clays 

After calcination at a relatively low temperature (usually below 800 °C), some clays can 

be converted to pozzolanic materials, after production of reactive phases by alteration of 

the original crystalline structure of the clay. The required heat treatment is generally 

variable, since it depends on the nature and fineness of clays. Both the calcination 

temperature and time have to be adjusted to get best enhancement of pozzolanic 

activity. 

Burnt Shale, Calcined Marls and ‘KALSIN’ 

Burnt shale, in special cases burnt oil shale, calcined marls and Kalsin (a patented product of 

the ‘Holderbank’ Group) are produced in conventional rotary kilns as well as fluidized beds at 

a temperature of approximately 800°C. Owing to the composition of the natural materials and 

the manufacturing process, these products contain hydraulic mineral phases identical to 

those produced during the clinkering operation. These phases are mainly dicalcium silicate 

and monoaluminate as well as reactive gehlenite and calco-spurrite. Due to the specific 

burning process (generally under reducing atmosphere) only small amounts of free lime is 

produced whereas calcium sulfate proportion depends essentially on the sulfur present in the 

raw material. Beside these hydraulic minerals, large proportions of pozzolanic reacting 

oxides, especially silica and alumina are present. 

In a very finely ground state burnt shale, calcined marls and Kalsin show like Portland 

cement pronounced hydraulic and in addition pozzolanic properties. 

According to EN 196-1 these burnt products must develop a compressive strength of at least 

25.0 N/mm 2 after 28 days. If not they are classified in the category of artificial pozzolan. 

The expansion shall be less than 10 mm (Le Châtelier test) in accordance with EN 196-3 

using a mixture of 30% by mass burnt material plus 70% by mass reference cement. 

4.3.4 Applications 

As discussed in chapter 3.3 natural and artificial pozzolans are preferably used wherever a 

high durability, high long-term strength or a low heat development is needed. This is 

especially the case in structures severely exposed to water of different chemical quality and 

in mass concrete applications such as: 

• Spillways 

• Stilling basins 

• Water canals 

• Water and waste-water treatment facilities 


Cement 

Concrete 

• Landfill construction purposes 

• Underwater constructions and repairs 

• Dams 

• Bridges (Figure 31) 

• Offshore platform construction 

• Bank vault construction 

• High-pressure concrete pipes 

• Concrete in high-rise structures 

• Shotcrete operations 

Figure 31 

Construction of Golden Gate Bridge (San Francisco, USA) in 1932 using 

a Portland pozzolan cement with 25% interground calcined siliceous 

shales 


Cement 

Concrete 

5. References 

Locher, W. (2000) Zement, Grundlagen der Herstellung und Verwendung, Verlag Bau + 

Technik, 522 p. 

Matthes, W. (2000) Properties, Grindability, and Reactivity of Granulated blast-furnace slag: 

A Literature Review, HMC report MIC 00/5005/E, 91 p. 

Weber, R., Bilgeri, P., Kollo, H, Vissmann, H.-W (1998) Hochofenzement - 

Eigenschaften und Anwendung im Beton, Verlag Bau und Technik, 2nd edition, 56 p. 


Cement 

Concrete 

Cement Admixtures 

1. CEMENT ADMIXTURES / PROCESSING ADDITIONS................................................. 122 

2. GRINDING AIDS AND PERFORMANCE ENHANCERS ............................................... 122 

2.1 Functions and effects of cement admixtures.......................................................... 122 

3. ADDITIVES FOR THE MANUFACTURE OF MASONRY CEMENT .............................. 123 

4. FUNCTIONAL ADDITIONS FOR USE IN HYDRAULIC CEMENTS .............................. 124 

5. THE MOST FREQUENT SUPPLIERS OF CEMENT ADMIXTURES ARE: ................... 124 

6. SERVICES OF CEMENT ADMIXTURE SUPPLIERS: ................................................... 124 


Cement 

Concrete 

1. Cement Admixtures / Processing Additions 

Definition: Cement Admixtures are added to the cement raw mix during or before the 

grinding process in amounts of less than 1% of cement weight. Typical 

dosages are 200 - 500 g admixture per ton of cement. Cement Admixtures 

are based on organic and inorganic compounds. 

An inquiry on application of cement admixtures within the "Holcim"-group was answered by 

80 plants in 1998. We received the following results: 

• with 57% Cost saving is the most-used argument for 

admixture application. 

• Some 41% of the "Holcim" plants answered that 

admixture application is a must for receiving the desired cement quality (pack-set, 

early strength). 

• On the other hand special characteristics are with 2% of 

applications real minor in quantity. But with cement admixtures some niche 

products are produced as well, with good additional customer values (and 

interesting margins). 

Cement admixtures can be divided into the following groups, depending on their purpose 

of use: 

1. Grinding Aids and Performance Enhancer. 

2. Additives for the Manufacture of Masonry Cement. 

3. Functional Additions for Use in Hydraulic Cements. 

2. Grinding Aids and Performance Enhancers 

Grinding Aids and Performance Enhancers are traditionally most widespread additions in 

cement manufacture. In 1998, 77% of the "Holcim" plants used such cement admixtures. In 

Europe 100%, in North America 96%, and in Latin America 83% of the cements with a 

fineness above 400 m 2 /kg were produced with admixtures. One or several of the following 

effects are achieved. 

2.1 Functions and effects of cement admixtures 

Grinding aides - typically organic compounds based on alcohol and amines - do not really 

change the engineering properties of cement. The action of the grinding aids is based on the 

reduction of the adhesive forces between the cement particles. They may, however, facilitate 

the handling of the cement due to the resulting improvement in flowability. 

Grinding aids acts on: 

• Coating reduction of grinding bodies 

(Reduction of specific energy consumption / improvement of specific mill output) 

• Improvement of flow properties / "pack-set" reduction 


Cement 

Concrete 

Performance modifiers influencing significantly the cement quality, in particular water 

requirement and strength development.The performance modifiers are of similar nature as 

the products used in the concrete mix. Such admixtures are generally based on accelerators 

and water reducers and thus improve the workability and strength development of the 

cement. The performance enhancer allows: 

• Optimized particle size distribution (lower average diameter at same Blaine) → 

higher strength 

• Activation of clinker hydration 

• Activation of mineral components (GBFS, Puzzolan) 

• Water reduction in case ASTM - testing (constant flow) 

Cement admixtures are placed in the first compartment of the mill or on the clinker on the 

conveyer belt at mill feed. Cement admixture has shown positive effects on all mill types. 

The dosage of cement admixtures is a function of the cement fineness and the desired 

effect. Admixtures used as processing additions are added within a dosage range of 100 - 

200g/t of active materials. As performance enhancer a minimum content of 200g/t is required 

and the dosage may be as high as 3kg /t. Limits by EN197/1 are 0.5% for active organic 

material and 1% in general (except for pigments). 

As a quality target, periodically the flow properties of the cements should be measured with 

an adequate test. We recommend the "HGRS-cement flow test". This measurement is 

specially recommended during new application tests with processing admixtures. 

To produce ASTM standard cements with cement admixtures testing of these products is 

required. Cement admixtures have to fulfill requirements according to ASTM C 465 

(Standard Specification for Processing Additions for Use in the Manufacture of Hydraulic 

Cements). 

As a quality target it is recommended to use ASTM 465 requirements for all cement 

admixtures used by "Holcim" plants. 

3. Additives for the manufacture of masonry cement 

Most of the masonry cements are produced in America and in Europe. There are three 

mortar types recognized under ASTM C270 "Standard Specification for Mortar for Unit 

Masonry". They are type N (750 psi min.), type S (1800 psi min.) and type S (2500 psi min.). 

Masonry cements are produced with limestone addition and an integrated air entrainer to get 

an air content of up to 18% in the fresh mortar. In the masonry cement production, various 

types of admixtures are used: 

• Air Entrainers (e.g. resin soaps, surfactants) 

• Retarding Admixtures (e.g. phosphates, saccharids) 

• Water Retaining Agents (e.g. modified cellulose) 

• Hydrophobing Agents (e.g. salts of fatty acids) 


Cement 

Concrete 

4. Functional additions for use in Hydraulic Cements 

Functional additions for use in hydraulic cements are described in ASTM C 688. On 

purchasers request, hydraulic cements may be modified by functional additions out of the 

following classes: 

• Accelerating Additions 

• Retarding Additions 

• Set-Control Additions 

• Water-Reducing and Accelerating Additions 

• Water-Reducing and Retarding Additions 

Cements produced according to this standard are always speciality products for special 

markets. In certain regions special "low water binders" for high performance concrete 

production were developed. Cements with addition of water-reducing admixtures are one 

solution. 

Addition of accelerator to cement can be used to produce speciality cements for spayed 

concrete applications (dry shotcrete). 

5. The most frequent suppliers of Cement Admixtures are: 

‣ Grace 

‣ Holderchem Building Chemicals, Lebanon (Société Ciments Libanais) 

‣ Westvaco 

‣ CP-Cervices 

‣ Roan Industries 

‣ Tecnochem 

‣ Chryso (Lafarge.Group) 

‣ Addiment (Heidelberger-group) 

‣ Chemical companies (Hoechst, BASF, Shell, Union Carbid, … ) for base materials 

like Diethylene glycol, Dipropylene glycol and Triethanolamine 

6. Services of Cement admixture suppliers: 

‣ Consulting in optimum cement mix design 

‣ Support in process optimization 

‣ Providing of equipment (Dosage pumps, storage tanks) 

‣ Performing of pre-test with local components to evaluate optimum admixtures. 


Cement 

Concrete 

Cement Grinding 

1. GENERAL....................................................................................................................... 126 

1.1 Grinding of Composite Cement.............................................................................. 126 

1.2 Particle size distribution in the different grinding systems...................................... 127 

2. CONCEPTS FOR THE PRODUCTION OF COMPOSITE CEMENTS .......................... 128 

2.2 Temperature and moisture conditions.................................................................... 133 

3. GRINDING TECHNOLOGY FOR CLINKER AND MIC'S............................................... 136 

3.1 The Ball Mill option................................................................................................. 137 

3.2 The Vertical Roller Mill option ................................................................................ 137 

3.3 The Roller Press option.......................................................................................... 138 

3.4 The Horizontal Roller Mill option ............................................................................ 139 

3.5 System Design and equipment Selection .............................................................. 140 

4. FINAL COMMENTS........................................................................................................ 145 

5. MESSAGES .................................................................................................................... 145 

6. LITERATURE.................................................................................................................. 146 


Cement 

Concrete 

1. General 

The cement components have to be ground to fine particles, in order to attain the required 

cementitious properties. The fineness after grinding is usually characterized by the specific 

surface area or by the particle size distribution (PSD). The type of cement mill used can have 

a considerable effect on the PSD. 

During the grinding process with the traditional systems (ball mills), only a small portion of 

the introduced energy is consumed for the comminution of the cement particles. A large 

quantity of heat is set free and the temperature of ground cement increases appreciably. In 

the modern grinding systems, less heat is produced, resulting in lower cement temperature 

during grinding. 

Both, the fineness and the temperature of grinding are principal factors in determining the 

cement properties. 

1.1 Grinding of Composite Cement 

The properties of composite cements are decisively influenced by the fineness of the cement 

and its components respectively. Composite cements must generally be ground to a higher 

overall fineness than Portland cements to maintain a similar strength development. 

The grinding behaviour of the different components in composite cements may vary quite 

significantly as illustrated in Figure 1. At constant fineness, the softer materials like limestone 

and natural pozzolan yield a wider PSD than the clinker and blast furnace slag. Despite its 

worse grindability, the grain size distribution of blast furnace slag does, however, not differ 

too much from the one of clinker. The mentioned differences in grindability are of great 

significance in the grinding of composite cements. 

1 

Steepness of Rosin-Rammler distribution 

0.8 

0.6 

0.4 

Characteristic diameter 

of Rosin-Rammler-distribution 

d' = 16 µm 

0.2 

0 20 40 60 80 100 120 

Grindability index in cm²/(g·s) 

Blast furnace slag Clinker Pozzolan Limestone 


Cement 

Concrete 

Figure 1: Steepness of the RRS-distribution of ground blast furnace slag, clinker, pozzolan 

and limestone at same characteristic diameter d' in function of the grindability index 

1.2 Particle size distribution in the different grinding systems 

The grinding in the modern cement mills goes together with a narrower PSD of the produced 

cements. Due to the more efficient grinding process, less under- and over-size particles are 

produced, which obviously leads to a shorter particle range and to higher steepness of the 

PSD. 

The steepness n as expressed by the RRS-distribution ranges from 0.8 for an open circuit 

ball mill up to 1.2 for the newest grinding systems like vertical mill. Typical n values of 

cements ground in various industrial mill systems are indicated in Table 1. 

The characteristic diameter d' of commercial cements produced in the different grinding 

systems varies typically between 10 and 30 µm. For identical specific surface, the d' values 

are lower in the systems which give a narrower PSD, that means that the overall fineness of 

the cement at same Blaine will be higher. At same d', the Blaine will be lower when the PSD 

gets narrower. 

Table 1: Typical n values for PSD of cements ground in various industrial mill systems 

Mill type Steepness n of RRS-distribution 

Ball mill (open circuit) 0.8 - 0.9 

Ball mill (closed circuit) 0.9 - 1.0 

Ball mill (high efficiency separator) 1.0 - 1.1 

Vertical mill, roller press, Horomill 1.1 - 1.2 

As mentioned before, the different PSD of the various grinding systems are also reflected in 

the relationship between Blaine and sieve residues (e.g. on 45 µm), which are the usual 

fineness measures applied in practice. The corresponding trends observed in the modern 

grinding systems compared to the traditional ball mills are as follows: 

♦ lower Blaine at same sieve residue or 

♦ lower sieve residue at same Blaine 

It is important to mention that, in view of certain quality problems experienced with a too 

narrow PSD, the actual tendency for the new grinding systems is to adjust the PSD to a 

somewhat wider distribution. 


Cement 

Concrete 

2. Concepts for the production of composite cements 

Composite cements are produced according to one of three basically different grinding 

concepts: 

 

 

 

by compound grinding of the constituent cement components, 

by separate grinding oft the cement components, or 

by semi-compound grinding of the components. 

Each of these solutions has its merits and disadvantages. 

2.1.1 Compound grinding 

The compound grinding of clinker, gypsum and mineral component(s) is still the most 

common practice for the production of composite cements. 

The combined grinding with mineral components softer than the clinker like limestone will 

widen the grain size distribution of the resulting composite cement, whereas the mixture of 

clinker with a harder material like blast furnace slag will give a somewhat steeper PSD than 

the ground clinker alone. The different PSD can be explained by the fact that for compound 

grinding, the harder material is enriched in the coarser fraction and the softer material in the 

finer fractions of the cement. 

In compound grinding, the different cement components can accordingly not be ground 

individually or independently from each other. For a given grinding system, the fineness of 

the components is pre-determined by their respective grindabilities; it is thus not possible to 

adjust freely their fineness. The inevitable enrichments of certain components in the fine or 

coarse fraction of the composite cement are, however, reduced with the modern grinding 

technologies. 

This lack of flexibility in compound grinding may limit the optimisation of the properties of 

composite cements. With soft mineral components, the clinker will always remain rather 

coarse, in particular at higher replacement levels, so that its hydraulic potential cannot be 

fully exploited. On the other hand, there might be an overgrinding of the mineral component 

like in the case of the natural pozzolans leading to an increase in water demand. This is not 

optimum solution also with regard to the energy efficiency of the grinding process. 

In case of slag cement, the clinker will get indeed finer and contribute as desired to the 

strength development. The slag may, however, not be adequately refined and activated. 

Compound grinding of the cement components is a strong solution in cases 

 

 

 

that sufficient grinding capacity is available anyway, 

that the portion of mineral components added to the cement is less than 30%, thus 

rather low, and 

that the envisaged annual production rates are low. 


Cement 

Concrete 

2.1.2 Semi-compound Grinding 

Semi-compound grinding is a solution that has been selected sporadically only for production 

of composite cements (e.g. for the Tecoman and the Nobsa works). The concept allows for 

separate pre-grinding of the harder component, preventing by doing so that the soft 

component is overground. It is evident that energy efficiency of the grinding process is better 

compared to compound grinding. Disadvantage is the additional grinding unit required, above 

all in the case of low capacity installations. Despite this disadvantage semi-compound 

grinding is an option to be considered in case that a works grinding capacity needs to be 

increased as a prerequisite for the production of composite cements. 

2.1.3 Separate grinding 

Separate grinding of composite cements gives more flexibility in the design and optimisation 

of the cement quality than compound grinding, since it permits free choice of the fineness of 

the cement components. Nevertheless, the opinions on the real benefits of separate griding 

are still controversial: It is evident that energy efficiency of such a concept is high. 

Disadvantage again is the additional grinding unit required. 

Separate grinding of the cement components is an option to be considered in cases: 

 

that introduction of composite cement ask for the installation of additional grinding 

capacity, 

that the portion of mineral components added to the cement is high (i.e. exceeding 40%), 

 

 

that production of client specific products, thus a high product variety is required, and 

that high annual production rates of composite cements are required. 

In the following, the experience with separate grinding for the most relevant composite 

cements containing blast furnace slag, fly ash, natural pozzolan and limestone is discussed. 


Cement 

Concrete 

2.1.3.1 SLAG CEMENTS 

The studies on separate grinding of slag cement revealed that the fineness of the clinker and 

slag influence the cement quality in the following way: 

♦ the clinker fineness is mainly related to early strength. In cements with low slag content 

(

Cement 

Concrete 

2.1.3.2 FLY ASH CEMENTS 

The separate grinding of fly ash cement as such has hardly been investigated. It appears 

that at constant grinding energy separate grinding gives certain possibilities to fine tune the 

final strength development of the fly ash cement. 

Presently the most appropriate solution to produce fly ash cements is to add the fly ash to 

the separator of the grinding system. The example in Figure 3 of a cement containing 16% fly 

ash demonstrates that in terms of quality and consumption of grinding energy, this seems to 

be the best solution, also compared to intergrinding. 

60 

50 

OPC 30 

OPC 40 

28 d 

MPa (Rilem) 

40 

30 

20 

addition to separator 

intergrinding 

mixing 

OPC 40 

10 

OPC 30 

2 d 

0 

0 10 20 30 40 50 

kWh/t cem 

Figure 3: Influence of treatment undergone by the fly ash on the strength of cement with 16% 

fly ash 

2.1.3.3 POZZOLANIC CEMENTS 

Separate grinding of cements with natural pozzolan gives a somewhat higher early strength 

and lower final strength than intergrinding at constant energy input. This relationship seems 

quite logical as in intergrinding the clinker responsible for the early strength remains rather 

coarse and the pozzolan contributing to the final strength is refined. 

The studies on separate grinding of pozzolanic cements carried out at Holcim showed a 

certain potential to increase the clinker factor at same cement quality, though at the expense 

of a higher grinding energy. A typical increase might be in the order of 5% as it is illustrated 

by the comparison of intergrinding and separate grinding for a pozzolanic cement from 

Mexico in Table 2. 


Cement 

Concrete 

Table 2: Comparison of intergrinding and separate grinding for pozzolanic cement from 

Mexico 

Physical and mechanical 

properties 

Compound grinding (ball mill) 

Separate grinding 

(ball mill and vertical mill) 

Cement 

Pozzolan (%) 20 25 

Blaine (cm 2 /g) 4170 4120 

n (-) 1.0 x) 

R 45 µm (%) 3.3 7.5 

Paste ASTM 

Water demand (%) 28.3 27.0 

Setting time (min.) 

- initial 160 145 

- final 225 175 

Mortar ASTM 

w/c-ratio 0.52 0.53 

Compressive strength (MPa) 

- at 1 day 11.0 11.6 

- at 3 days 20.9 20.7 

- at 7 days 27.8 26.0 

- at 28 days 35.0 34.8 

x) Pozzolan: n = 0.95 R 45 µm = 20.9% Blaine = 2170 cm 2 /g 

Clinker/gypsum: n = 0.95 R 45 µm = 3.1% Blaine = 4300 cm 2 /g 

2.1.3.4 LIMESTONE CEMENTS 

Studies on separately ground limestone showed that the limestone fineness as such has 

virtually no influence on the strength development. The PSD of the limestone powder can, 

however, play a role with regard to the workability characteristics of the limestone cement: a 

wide distribution is in this respect more favourable than a narrow one. 

In combined grinding with clinker, the limestone is automatically ground to the favourable 

wide PSD. This quite advantageous behaviour in intergrinding, at least at lower limestone 

dosages (up to 20%) may also explain the fact that separate grinding of limestone cement to 

improve cement quality has usually not been applied in practice. 


Cement 

Concrete 

2.2 Temperature and moisture conditions 

The grinding of cement influences the properties of cement not only through an increase in 

fineness, but also through the reactions taking place in the cement mill. Depending on the 

temperature and moisture conditions prevailing in the mill, dehydration and hydration occur 

which influence the grinding process, flowability, lump formation in silos, setting and 

hardening of cement. 

Due to the heat liberated during the grinding process, the temperature in the traditional ball 

mills rises to temperatures above 100°C. In the modern grinding systems, the grinding 

temperatures are significantly lower (down to 50°C - 60°C). In a particular mill, the exit 

temperature of cement can vary in a wide range, in function of the inlet temperature of 

clinker, cooling conditions and fineness of grinding. 

The effect of the grinding temperature on the cement properties is mainly related to the 

dehydration of gypsum. With increasing temperature, gypsum (CaSO 4 2H 2 O) gets unstable 

and transforms to hemihydrate and anyhdrite III under the release of water. The dehydration 

of the gypsum will not only depend on the temperature, but also on the time the gypsum is 

exposed to this temperature (Figure 4). Another factor of less importance for gypsum 

dehydration is the humidity in the mill atmosphere (Figure 5). 

Figure 4: Influence of temperature on the dehydration of gypsum 


Cement 

Concrete 

Figure 5: Influence of humidity on the gypsum dehydration 

According to the degree of dehydration, the gypsum will exert a different influence on the 

cement properties (see also paper on cement hydration). If great part of the gypsum is 

converted to the more easily soluble hemihydrate and anhydrite III, there may be some 

problems with false setting in case a clinker of low reactivity is used. On the other hand, a too 

low degree of dehydration may lead to flash setting tendency with reactive clinkers. 

The dehydration of the gypsum may also have an impact on the storage stability of the 

cement. If the cement enters the silo with a high temperature (80 - 90°C), further water can 

be released form the still not dehydrated gypsum and lead to the hydration of the cement. 

These hydration reactions can cause lump formation and affect the strength of the cement 

(Figures 6 and 7). Clinkers with high C 3 A and alkali content are particularly subject to 

hydration reactions during storage. 


Cement 

Concrete 

Figure 6: Lump formation in a storage sensitive cement after one-week storage at various 

temperatures 

Figure 7: Compressive strength of a storage sensitive cement after one week Storage at 

various temperatures 

Some measures to ensure the storage stability of the cement are: 

♦ low cement temperature in the silo 

♦ short storage time 

♦ reduction of gypsum content in the cement 

♦ substitution of gypsum by natural anhydrite 

The storage stability is usually less problematic with the new grinding technologies, where 

the temperatures of the cement coming from the miss are generally low. The cement 


Cement 

Concrete 

temperatures in ball mills can be lowered by cooling the cement during the grinding process 

(e.g. water injection) or by installing a cement cooler after the mill. For the cooling by means 

of water injection, the temperature in the mill should always be kept above 100°C. Otherwise, 

prehydration of the cement and strength losses may occur. 

3. Grinding technology For clinker and mic's 

As seen before, the response of the different cement constituents to grinding can be quite 

different: 

 

 

 

Grindability is good for limestone but gets worse for clinker and blast furnace slag. 

Clinker is at about two times harder to grind compared to limestone and granulated blast 

furnace slag even up to three times. 

The slope of product particle size distribution too varies in a wide range. It is flat for fly 

ashes but steeper for clinker and ground granulated blast furnace slag. Particle size 

distribution of the composite cement affects sensitive characteristics as rheological 

properties and strength performance. 

The effect on (hydraulic) activity is different for the different mineral components. 

Limestone in contrast to slag do not contribute to the (hydraulic) activity and by this the 

strength performance of a concrete based on composite cement. 

It is evident that the nature of the mineral component that is selected for a project affects 

system design of as well as equipment selection for the grinding installation. 

The question to which fineness the components of composite cements shall be ground to 

obtain optimum cement properties is often debated. The general concept of Holcim Group 

Support is that the hydraulic potential of the clinker should be used as much as possible by 

grinding it to a sufficiently high fineness. The mineral components may be ground coarser, 

but latent hydraulic and pozzolanic materials must still have a sufficient fineness to be 

suitably activated to provide good final strength. 

Selection of the appropriate grinding technology is out of a variety of options. Prerequisite for 

finding the optimum solution for a given project is the knowledge of all process technological 

possibilities. 

Conceptual system design follows two lines: 

single stage grinding, and 

two stage grinding. 

Speaking of single stage grinding, equipment selection is basically out of four options 

(Figures 8a to 8d): 

 

 

 

 

the ball mill system, 

the vertical roller mill system, 

the roller press system and 

the horizontal roller mill system. 


Cement 

Concrete 

Figure 8b: Vertical roller mill 

Figure 8a: Ball mill 

Figure 8c: Roller press system 

Figure 8d: Horizontal roller mill 

3.1 The Ball Mill option 

The ball mill is typically operated in a closed circuit with a dynamic separator. This concept 

represents the conventional solution in cement and mineral component grinding. Operation 

of ball mill systems is easy, not asking for highly skilled staff, although optimisation for 

efficient performance requires quite some effort. Common product fineness levels, which 

may be as high as 5700 cm 2 /g (e.g. for ground granulated blast furnace slag of the Grade 

120 class) are not a limiting factor for the use of a ball mills. Product drying can take place 

within the mill, but the mill can handle pre-dried components without any problems as well. 

Product handling within the system is not problematic. 

But energy efficiency of the ball mill is poor. This limits the system's production rate despite 

the permitted high drive power of up to 6500 kW, in rare cases of up to 8000 kW. 

3.2 The Vertical Roller Mill option 

In vertical roller mill systems (Fig. 9) product collection is by means of a bag type dust 

collector. The concept represents the standard solution in raw and coal grinding. 

Although the application for grinding clinker and mineral components is proven since many 

years, the market was sceptic regarding product quality. Major concern was the steeper 

slope of the product grain size distribution that affects the cements rheological properties as 

well as its strength performance. Recent analysis of cements and fine slag produced on 

vertical mill systems in the Far East proved that the vertical roller mill products are 


Cement 

Concrete 

comparable with ball mill products with regard to particle size distribution, rheological 

properties and strength performance. 

The vertical roller mill is the optimum concept regarding product drying. It is fit for both, 

compound and separate grinding applications. Mill energy efficiency is significantly higher 

compared to a ball mill (about 2.5 times for slag grinding; about 2 times for clinker grinding). 

The largest mill sizes available allow for a drive power rating of about 4000 kW and as a 

consequence for high production rates. 

But the application of the vertical mill concept is limited by the maximum product fineness 

levels that safely can be achieved in a single stage, namely 5000 cm 2 /g for granulated blast 

furnace slag and 4500 cm 2 /g for ordinary Portland cement. 

Product 

FIGURE 9: Vertical mill 

3.3 The Roller Press option 

The roller press (Fig. 10) as a single stage grinding system is typically operated in a closed 

circuit with a disagglomerator and a dynamic separator. The product is collected in a bag 

type dust collector. The market was sceptic with regard to product quality for the same 

reasons as mentioned for the vertical roller mill concept. 

Energy efficiency of the roller press is slightly better than for the vertical roller mill, thus 

significantly better compared to a ball mill (about 2.5 times for slag grinding; up to 2 times for 

clinker grinding). The largest press sizes available allow for a drive power rating of up to 2 x 

2200 kW and as a consequence for high production rates. Product fineness levels that safely 

can be achieved in a single stage installation, namely 5500 cm 2 /g for granulated blast 

furnace slag and 4500 cm 2 /g for ordinary Portland cement hardly limit the system's 

application. 


Cement 

Concrete 

As drying is possible in the separator only feeding roller presses is critical in that respect that 

hot and dry recycle material is mixed with moist fresh feed. This may result in local 

condensation of the generated vapours and by this in material build-up, e.g. in the shaft of 

the recycle bucket elevator and auxiliaries dust collectors. As a consequence heating and 

insulation of the auxiliary equipment is indispensable as to prevent that system temperature 

fall locally below dew point. 

Furthermore roller presses are sensitive to damages of the roller surfaces by pieces of 

tramp-metal and excessive feed granulometry of the fresh feed (the maximum size of the 

feed grains should as a rule of thumb not exceed two times the operational gap width). 

Product 

FIGURE 10: Roller press mill 

3.4 The Horizontal Roller Mill option 

The horizontal roller mill (Fig. 11) represents the most recently developed grinding 

technology. In a single stage configuration it is operated, similar as the roller press, in closed 

circuit with a dynamic separator but does not require the installation of a disagglomerator. 

The product is collected in a bag type dust collector. 

Energy efficiency is comparable to that of a vertical roller mill, thus significantly better 

compared to a ball mill (about 2.5 times for slag grinding; about 2 times for clinker grinding). 

The limits of the concept regarding production rate, achievable product fineness levels, ease 

of operation, etc. are not established yet. The concept is fit for compound as well as for 

separate grinding applications. 

But horizontal roller mill systems are limited in drying, as drying is possible in the separator 

only. Similar as for the roller press systems a complex dedusting system is required including 

heating and insulation of the auxiliary equipment as to prevent local condensation due to 

high dew points. The first horizontal roller mill installations suffered from mechanical reliability 

and operational problems, which seem to be solved in the meantime according to the 

information received from the supplier and some of the users. 


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Concrete 

The further development of the horizontal roller mill technology needs to be followed 

carefully. For the time being an industrial application would ask for careful analysis and 

system design. 

FIGURE 11: Horizontal mill 

3.5 System Design and equipment Selection 

A decision for a ball mill system is a low risk, but conservative selection. 

Energy efficiency of the available modern grinding technology based either on a vertical roller 

mill, a roller press or a horizontal roller mill is significantly better compared to that of the ball 

mill technology. This, as comminution is achieved by compression in a bed of material and 

no longer by friction. 

The vertical roller mill as well as the roller press can not only be used in a single-stage 

grinding arrangement but also as a pregrinder in a two-stage configuration with a ball mill 

(Figures 12a and b) for separate, semi-compound and compound grinding applications. 


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Concrete 

FIGURE 12a: Vertical roll mill + ball mill 

FIGURE 12b: Roller press mill+ ball mill 

The vertical roller mill system as a pregrinder to a ball mill may be considered in cases that 

high production rates and/or high fineness requirements must be met. Drying will exclusively 

take place in the vertical roller mill. 

The roller press will be considered above all for the modifications of ball mill systems with 

regard to a capacity increase or the introduction of composite cement production. Addition of 

a closed circuit roller press system for pre-grinding purposes results in a complex, difficult to 

operate system. Addition of an open circuit roller press system with slab recirculation as a 


Cement 

Concrete 

pregrinding system is worth to be considered above all for semi-compound grinding 

applications. 

To facilitate selection of the appropriate grinding technology based on process technological 

criteria decision-trees have been developed 

 

 

for the production of composite cements based on compound grinding of the constituent 

components (Figure 13), 

for separate grinding of granulated blast furnace slag (Figure 14) and 

for the production of ordinary Portland cement (Figure 15). 

1) BASED ON ENERGY CONSUMPTION 

VRM, RP OR HM 

Fineness 

≤4500 

No, >4500cm 2 /g 

2) BASED ON ENERGY CONSUMPTION 

BM 

3) BASED ON TOTAL MILL FEED 

1) 

Yes 

Abs. Power Mill (FI) 

t/h x kWh/t 

No, ≤4000kW 

>4000kW 

Yes 

3) 

Feed moisture 

Yes 

Feed moisture 

2) 

Abs. Power Mill (BM) 

t/h x kWh/t 

≤2% 

Yes 

No, ≤X% 

No 

(Comparable BM) 

Particle Size Distr. 

Steep 

Yes 

≤2% Yes 


No, ≤X% 

No 

(Comparable BM) 

Steep 

Yes 

>8000kW 

Yes 

Feed moisture 

No, ≤8000kW 

% Min. Component 

% Min. Component 

≤2% 

Yes 

high/ 

low 

high 

low 

high/ 

low 

high 

low 

No, ≤X% 

VRM 

HM 

RP 

2 VRM 

2 HM 2 RP VRM+BM RP+BM BM 

FI , ONE GRINDING UNIT FI , TWO GRINDING UNITS SF BM 

FIGURE 13: Decision-tree for the production of composite cements based on compound 

grinding of the constituents. 


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Concrete 

Fineness 

5300cm 2 /g 

1) BASED ON ENERGY 

CONSUMPTION 

VRM, RP OR HM 

1) 

Yes 

Abs. Power Mill (FI) 

t/h x kWh/t 

2) BASED ON ENERGY 

CONSUMPTION BM 

No, ≤4000kW 

>4000kW 

Yes 

Complexity of System 

Yes 


2) 


t/h x kWh/t 

simple / 

complex 

complex 

simple / 

complex 

complex 

>8000kW 

No, ≤8000kW 

simple 


simple 


Yes 

medium 

Steep 

steep 

Yes 

No 

experience 

medium 

steep 

No 

experience 

Steep 

Yes 

VRM 

HM 

RP 2 VRM 2 HM 2 RP 

VRM+BM RP+BM BM 

FI , ONE GRINDING UNIT FI , TWO GRINDING UNITS SF BM 

FIGURE 14: Decision-tree for separate grinding of granulated blast furnace slag 

Fineness 

4000kW 

Yes 


Yes 


2) 


t/h x kWh/t 

simple / 

complex 

complex 

simple / 

complex 

complex 

>8000kW 

No, ≤8000kW 

simple 


simple 


Yes 

medium 

steep 

Steep 

Yes 

medium 

steep 

Steep 

Yes 

VRM 

HRM 

RP 2 VRM 2 HRM 2 RP 

VRM+BM 

RP+BM 

2 BM 

BM 

SINGLE STAGE GRINDING 

ONE UNIT 


TWO UNITS 

TWO STAGE 

GRINDING 

SINGLE STAGE 

GRINDING 

FIGURE 15: Decision-tree for the production of ordinary Portland cement 


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Concrete 

From these decision-trees the process technological superiority of the modern grinding 

technologies, above all the vertical roller mills becomes evident. This applies above all for 

granulated blast furnace applications with its high energy substitution factor (Figure 16). 

[cm2/g] 


ONE UNIT 


TWO UNITS 

TWO STAGE 

GRINDING 

SINGLE STAGE 

GRINDING 

VRM HM RP 2 VRM 2 HM 2 RP VRM+BM RP+BM 2 BM BM 

50% 47% 47% 50% 47% 47% 

79% 

82% 

100 

% 

100 

% 

≤ 4000 [kW] > 4000 [kW] > 4000 [kW] 

48% 46% 47% 

48% 46% 47% 

75% 

84% 

100 

% 

100 

% 

≤ 4000 [kW] 

> 4000 [kW] > 4000 [kW] 

72% 

87% 

100 

% 

100 

% 

FIGURE 16: Comparison between energy consumption for blast furnace slag grinding 

Factors that have influence on the selection of the grinding technology for composite cement 

applications are, besides process technological criteria: 

 

 

 

 

 

 

the geographical location, 

requirements and conditions of the local market, 

investment versus operation cost, 

flexibility in system operation, 

flexibility in product quality, 

etc. 

As to keep the decision trees simple these factors could not be considered. 


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Concrete 

4. Final comments 

‣ For "Holcim" group CTS/PT observes a trend towards compound grinding 

solutions for the production of pozzolana, limestone and fly ash based 

composite cements. Exceptions: Morning Star Cement, Vietnam; LIMED 

(CIOR), Morocco. 

‣ For composite cements based on granulated blast furnace slag separate 

grinding is the preferred concept. 

‣ With regard to fly ash addition to the cements CTS/PT observes that the 

concepts are followed in Europe and the US are quite different. In Europe fly 

ash is typically added to the separator feed preventing by this over-grinding 

of the already sufficiently fine portion while in the US fly ash is typically feed 

to the mill. 

‣ Regarding equipment selection still more weight is given to the criteria 

investment cost and technological risk, outweighing the advantage of energy 

savings and by this the selection of modern solutions. This despite industrial 

experience has confirmed the lower energy requirement, the reliability of 

modern grinding technologies. Reservations regarding product quality based 

on a too steep product particle size distribution can hardly be maintained any 

longer. 

5. Messages 

‣ The modern grinding systems have proven superior energy efficiency as well 

as operational reliability in grinding of clinker and mineral components. 

‣ For the selection of the appropriate technology system for new composite 

cement production facilities efficiency characteristics should be considered 

as well and not by principal lowest investment exclusively. Reservations 

regarding product quality based on product particle size distribution can 

hardly be maintained any longer. 

‣ Give modern, energy efficient grinding technology a chance. It should have a 

predominant place in the "Holcim" group. 


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Concrete 

6. Literature 

Grinding and cement properties 

Bapat, J.D., Higher qualities from modern finish grinding processes, International Cement 

Review, January 1998, pp. 54 - 56 

Montani, S., Influence of grinding on the properties of composite cements, 34th Technical 

Meeting, Davos, 1996, PT 96/14'096/E 

Albeck, J., Kirchner, G., Influence of process technology on the production of marketorientated 

cements, Cement-Lime-Gypsum, No. 10, 1993, pp. 615 - 626 

Gebauer, J:, Cement grinding and quality problems, 32nd Technical Meeting, Montreux, 

1992, VA 92/5972/E 

Schiller, B., Ellerbrock, H.-G., The grinding and the properties of cements with several main 

constituents, Cement-Lime-Gypsum, No. 7, 1992, pp. 325 - 334 

Ellerbrock, H.-G., Deckers, R., Mill temperature and cement properties, dto., No. 1, 1988, pp. 

1 - 12 

Sprung, S., Kuhlmann, K., Ellerbrock, H.-G., Particle size distribution and properties of 

cement, dto., Part I: No. 4, 1985, pp. 169 - 178, Part II: No. 9, 1985, pp. 528 - 534 

Sprung, S., Influence of process technology on cement properties, dto., No. 10, 1985, pp. 

577 - 585. 


Cement 

Concrete 

Properties and Application of Composite Cements 

1. COMPOSITE (BLENDED) CEMENTS.............................................................................. 149 

1.1 Definition................................................................................................................. 149 

1.1.1 Abbreviations ........................................................................................... 149 

1.2 A brief history of composite cements...................................................................... 150 

2. GENERAL PROPERTIES OF COMPOSITE CEMENTS.................................................. 151 

2.1 Bleeding.................................................................................................................. 151 

2.2 Workability .............................................................................................................. 152 

2.3 Setting time............................................................................................................. 154 

2.4 Strength .................................................................................................................. 155 

2.5 Shrinkage................................................................................................................ 157 

2.6 Creep...................................................................................................................... 159 

2.7 Heat of hydration .................................................................................................... 160 

2.8 Porosity................................................................................................................... 162 

2.9 Durability................................................................................................................. 163 

2.10 Lime leaching.......................................................................................................... 164 

2.11 Carbonation ............................................................................................................ 165 

2.12 Sulphate attack....................................................................................................... 165 

2.13 Chloride attack........................................................................................................ 166 

2.14 Sea water attack..................................................................................................... 167 

2.15 Alkali Silica Reaction .............................................................................................. 168 

2.16 Frost resistance ...................................................................................................... 169 

3. ASPECTS OF MANUFACTURE OF COMPOSITE CEMENTS ....................................... 171 

3.1 Pretreatment of additions........................................................................................ 171 

3.2 Properties of the addition and type of grinding ....................................................... 171 

3.2.1 Grindability ............................................................................................... 171 

3.2.2 Strength activity........................................................................................ 172 

3.2.3 Type of grinding ....................................................................................... 172 

3.2.4 Use of chemical admixtures ..................................................................... 173 

3.3 Proportioning .......................................................................................................... 174 

4. TRENDS OF PRODUCTION AND MARKETING OF COMPOSITE 

CEMENTS....................................................................................................................... 175 


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Concrete 

5. CONCLUSIONS ................................................................................................................ 176 

6. LITERATURE REFERENCES .......................................................................................... 176 


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Concrete 

1. Composite (blended) cements 

1.1 Definition 

A Composite or Blended Cement is a binder that contains 

Portland clinker 

gypsum or other set regulators 

and one of, or a combination of, the following materials in relevant amount (normally 

>5%) 

a latent hydraulic component 

a pozzolanic component 

an inert component (filler) 

and is produced by grinding (separate or compound) or blending of the constituents. 

Typical materials for the production of composite cements are therefore 

Latent hydraulic 

Having natural hydraulic potential (they harden when mixed with water). A suitable activator 

is needed to accelerate the reaction with water (examples: blast furnace slag, class C fly 

ash) 

Pozzolanic 

Having no hydraulic properties. They react in presence of water and Ca(OH) 2 from clinker 

hydration, to form compounds contributing to strength (examples: natural pozzolana, class F 

fly ash) 

Inert 

Having no real participation in the chemical hydration process (examples: limestone, sand). 

Important to mention is that clinker hydration, slag hydration and reaction of pozzolana with 

lime cause the formation of the same type of compounds, i.e. calcium-silicate-hydrates 

possessing binding properties. 

For specific aspects regarding composition and properties of mineral components, please 

refer to the related chapter. 

1.1.1 Abbreviations 

In the following text and in relevant literature, acronyms and abbreviations may be used to 

indicate specific materials. These are the most important. 

mic 

mineral component 

(g)(g)bfs (ground)(granulated) blast-furnace slag 

(p)fa 

(c)sf 

(pulverised) fuel ash or fly ash 

(condensed) silica fume 


Cement 

Concrete 

1.2 A brief history of composite cements 

The hydraulic properties of blends of pozzolana and lime are known from thousands of 

years, from the times of the ancient Greeks and Romans, whose constructions (“opus 

cementitium”) survived the centuries and can be still seen nowadays. At those times, natural 

pozzolana or crushed bricks were used as cement constituents together with lime, but the 

association of pozzolana with Portland cement only started at the beginning of the 1900. 

The practice of replacing a hydraulic material for Portland cement dates back to the end of 

the 19 th and the beginning of 20 th century. 

The discovery of the hydraulic properties of blast furnace slag was made in 1862 and the first 

use in Germany dates back to 1882. 

During the two World Wars the clinker shortage suggested the addition of finely ground 

limestone to Portland cement to increase the availability of cement. At that time, the 

replacement was considered not legal or at least questionable; however, the use of this 

cement did not give rise to any claims from the users owing to the good results obtained in 

terms of both strength and durability. In the sixties, at the end of long and accurate studies, 

limestone cement was definitively accepted among standard cements. 

An example of the many different composite cements is given in the following table, where 

the cement types according the European standard EN 197/1 are listed. 


Cement 

Concrete 

2. General properties of Composite cements 

Blended cements have properties very similar to those of Portland cements for two main 

reasons: 

all of them contain Portland cement clinker 

their products of hydration are identical to those occurring in Portland cement pastes both 

in terms of composition and microstructure. 

Increasing amounts of blending components gradually change any original property of the 

plain Portland cement. This replacement may either improve or worsen the properties of the 

parent Portland cement (clinker) as a consequence of the effect of mineral components and 

additions on chemical, physical and mechanical properties of cement, mortar and concrete. 

Typically, addition of most mineral components in relevant quantities reduces the strength, 

but increases the chemical resistance and the related durability of the cementitious products. 

Proper cement design may contribute to limit the undesired effects to the minimum and 

enhance the advantages of mineral components. 

In the following chapters, the impact of mineral components on the most important properties 

of blended cements is considered. 

2.1 Bleeding 

Bleeding occurs when the various constituents of a mix start to separate so letting the water 

rise to the surface of the fresh concrete. Whereas a certain amount of bleeding is favourable 

for adequate curing of concrete, an excess of bleeding water can cause undesired surface 

effects like efflorescence (crystallisation of calcium carbonate and alkali salts) and weaker 

surface strength. 

Bleeding depends on the grain size distribution and the specific surface of the cement and of 

the individual cement components. Therefore, natural pozzolanas, burnt clay, silica fume and 

limestone reduce bleeding, while fly ash and ground granulated blastfurnace slag tend to 

increase it. 

On the other hand, an increase of water demand in concrete due to the presence of highspecific 

surface materials, may have the contrary effect of increasing the porosity in the 

hardened dry structure, reducing the strength and increasing the permeability. 


Cement 

Concrete 

2.2 Workability 

As a general rule, workability of concrete decreases with the increase in water demand of the 

cement and therefore with the specific surface area of the components. 

As a consequence, workability of cements containing slag, fly ashes and limestone on 

average is higher than that of the parent Portland cement, whereas that of cements 

containing natural pozzolanas and silica fume is lower. 

However, within each cement type and cement class, the values of workability (slump test) 

are widely scattered owing to the large variability of both chemical and mineral composition 

and fineness of cements. 

Example: slump frequency distribution 


Cement 

Concrete 

The different performance of fly ash and slag cements can also be explained by the following 

reasons 

little water absorption of the gbfs/fly ash particles 

smooth surface of the gbfs and fly ash particles. 

Problems may arise with very soft and porous pozzolanas, which tend to reduce workability. 

Example: compaction time for OPC/BFS cements 


Cement 

Concrete 

2.3 Setting time 

The degree to which the setting time is affected depends on: 

the grinding fineness 

the type of clinker and mic used 

the mic content of the composite cement 

the initial curing temperature of the concrete 

the water/cement ratio of concrete 

Typically, the initial set is extended by half-an-hour to one hour at temperatures of 23° C / 

73° F. Above 29° C / 85° F no change in setting time occurs compared to OPC. 

Example: data from Products Handbook 


Cement 

Concrete 

2.4 Strength 

On replacing a Portland cement with other fine materials, the strength development curve 

changes depending on the type and the amount of the addition. 

Clinker is the main responsible for early and medium term strength development, and 

therefore its substitution with less active constituents may lead to reduced strength. The 

difference from the plain Portland cement tends to disappear after about 28 days of curing, 

owing to the reaction of the mic’s and depending on their activity. In the case of silica fume, a 

very reactive material, strength recovery takes place earlier. 

However, when clinker replacement does not exceed 10%, early strength of cement may 

increase since fine additions tend to accelerate hydration. 

The ultimate strength can be higher than that of OPC when the 

cement contains other hydraulic components. In this case, after 28 

days, the strength development curve can intersect and surpass the 

curve of the parent Portland cement. 


Cement 

Concrete 

Strength and strength gain of concrete with blended cement depend on following factors: 

Fineness of the cement 

Mic and clinker reactivity 

Curing temperature 

Content of mic in the blended cement 

The drop in early strength should not always be considered as a negative effect since it is 

often associated with the improvement in other properties. 

In any case, the cement factories can remedy the strength loss by taking appropriate action. 

Such corrective actions may increase production costs, so the advantage of any solution 

must be assessed on a case-by-case basis. 

As a consequence, blended cements predominate in the cement classes having lower 

strength. 

This prevalence does not mean that it is impossible to produce rapid hardening and highearly 

strength composite cements, but that they are not often produced, at least in large 

quantities, since they are more expensive than Portland cement. 

Concrete strength depends on a number of factors, the most significant of which are: 

♦ cement strength, 

♦ 

♦ 

♦ 

cement content, 

water/cement ratio, 

curing degree. 

The type of cement is not a primary factor provided that cements with the same 

strength and the same w/c ratio are compared. 

On the contrary, if concrete is compared on the basis of equal workability, some 

differences could occur depending on the different water demand. 


Cement 

Concrete 

2.5 Shrinkage 

Shrinkage of cementitious products depends on the initial water content of the mix. 

For this reason, shrinkage of standard mortars made with the same w/c ratio is not 

influenced by the cement type. 

In the practice, differences in shrinkage occur if comparison of different cement types is 

made on mortars or concrete having the same workability but different w/c ratio. 

Differences among cements, if any, decrease passing from paste to mortar and concrete, the 

shrinkage of concrete being about 25% of that of a mortar with the same w/c ratio. 


Cement 

Concrete 

In any case, the influence of the type and strength class of cement on shrinkage is noticeably 

less than that of the water/cement ratio of concrete and of the type of aggregate used 

therein. 

Beneficial effects from the use of fly ash and blast furnace slag have been noticed, in 

combination with adequate curing of the structure. 


Cement 

Concrete 

2.6 Creep 

Creep of concrete represents the deformation of concrete under load. It.depends on the 

water content of the mix and the modulus of elasticity of the aggregate. 

The creep value is linked to the strength of the concrete at the time of loading and so, all 

other conditions being equal, it depends on: 

♦ 

♦ 

♦ 

the strength class of the cement, 

the water/cement ratio, 

the curing degree. 

Thus, if the same load is applied on concrete having the same strength, the cement type is 

not significant. 

Creep in blended cement concrete is higher than in Portland cement only when concrete is 

loaded too early. 


Cement 

Concrete 

High early creep may have a positive effect since, as an example, it allows massive 

structures to settle before the concrete becomes dangerously rigid. 

2.7 Heat of hydration 

Blending Portland cement with natural and artificial pozzolana, ground slag and calcareous 

filler of similar fineness lowers strength and heat of hydration. 


Cement 

Concrete 

However, if the composite cement attains the same strength as the plain Portland cement, 

thanks to finer grinding or because it contains particularly active components such as silica 

fume, its heat of hydration is the same as that of the plain Portland cement. 

In fact, there is a significant correlation specially between the early compressive strength of 

mortars and the heat of hydration of cement pastes after 24 and 48 hours of curing. 

An increasing interest for crack prevention in voluminous concrete elements leads to an 

increasing demand of blended cements in many countries. Applying these cements for mass 

concrete leads to economical benefits for the concrete producers as well as for the 

construction companies (no cooling system or chemical admixtures are needed). 


Cement 

Concrete 

2.8 Porosity 

Porosity is an intrinsic property of concrete, which may be limited but not completely 

eliminated. 

Porosity mostly results from the porosity in the cement paste and the paste/aggregate 

interface. It is responsible for many properties of concrete, from its mechanical features to its 

durability and directly affects strength, since pores reduce the cross sectional area of the 

structure. 

Several experimental works have assessed that hardened plain cement without pores would 

attain compressive strength higher than 700 MPa. 

Hardened Portland cement paste has a lower porosity than pozzolanic and blastfurnace slag 

cements and thus it should have higher strength. However, differences are little and they 

become negligible in concrete where the interfacial porosity is definitely higher than that of a 

bulk paste. 

Moreover, the interfacial zone of concrete made with blended cements is generally less 

porous, less permeable and poor in portlandite crystals. For this reason the interfacial bond 

is stronger, as is shown by the higher flexural strength. 

Porosity is also related to the following transport properties of concrete: 

permeability (entry of fluids under pressure), 

sorptivity (entry of fluids by capillary suction), 

diffusion (entry of gas and ions dissolved in the water). 


Cement 

Concrete 

These properties are not synonymous with porosity since they depend on the structure of the 

pores rather than on the total porosity of cementitious products 

As a matter of fact, hardened cement pastes containing ground blastfurnace slag or 

pozzolana have greater porosity but lower permeability and sorptivity than Portland cement 

pastes, due to the difference in pore diameters. 

2.9 Durability 

The improvement achieved with the use of active mineral components is direct consequence 

of: 

♦ 

♦ 

♦ 

lower permeability of cement stone 

lower content of calcium hydroxide 

reduced leaching of calcium hydroxide 

Permeability of hardened concrete with blended cement is decreased due to the reduction of: 

♦ 

♦ 

the pore size in the hydrated cement gel 

the filling of capillaries by further hydration products 

The decreased permeability prevents the penetration and migration of damaging chemicals 

such as chloride and sulfates and leads to high durability of the concrete 

Actually, pores of pozzolanic cement pastes - which are larger than Portland cement ones - 

are connected by more segmented or finer pores. 

The differences in porosity and permeability of cement pastes as a result of the type of 

cement have, in any case, very little impact on the actual concrete where the porosity of the 

aggregate/cement paste interface is much higher than that of the bulk paste. 

When concrete is dense, i.e. strong, any difference in permeability becomes statistically very 

little and only low strength concrete shows a wide variability in permeability 

In the practice, when 28-day strength exceeds about 35 N/mm2, permeability does no longer 

significantly decrease. 


Cement 

Concrete 

2.10 Lime leaching 

Portlandite makes up some 20-22% of hardened Portland cement paste and is quite soluble 

in water. So, concrete that is permanently kept in contact with water will lose lime. 

Leaching of Ca(OH)2 makes porosity and permeability increase and strength and durability 

decrease. 

Cement pastes containing pozzolanic materials, as well as granulated blast furnace slag, 

release less lime than Portland cement. This is because they have a smaller Ca(OH) 2 

content and a greater C-S-H gel content that make paste generally less permeable. 

The effectiveness of hydraulic additions increases as their % content increases. 


Cement 

Concrete 

Leaching rate increases when waters contain aggressive carbon dioxide but blended 

cements resist better than Portland cement. 

Reduced hydrated lime availability decreases susceptibility to acids. 

2.11 Carbonation 

For some time, it had been generally held that pozzolanic cements and cements with a high 

slag content were less resistant to carbonation than Portland cements due to the lower 

Portlandite content in their pastes. 

However, a number of studies have established that there is no connection between the 

depth of carbonation and the type of cement, but that the depth of carbonation decreases 

with increasing strength, i.e. with decreasing porosity and permeability. 

2.12 Sulphate attack 

Waters and soils containing sulphate ions attack concrete through the formation of ettringite 

and, occasionally, gypsum. 

Preventing or reducing the consequences of the attack requires the following factors to be 

minimized: 

♦ 

♦ 

♦ 

tricalcium aluminate (C3A) content in the clinker, 

Ca(OH) 2 content in the paste, 

permeability of concrete. 

Cements rich in ground granulated blastfurnace slag and pozzolanic cements satisfy the 

three criteria and thus resist well to sulphate attack. 


Cement 

Concrete 

Blended cements decrease the permeability of concrete but their high resistance to the 

sulphate attack is due also to other factors. 

In fact, by comparing Portland cement and fly ash cement pastes, both stored in a 0.7M 

Na 2 SO 4 solution for 12 weeks, it was found that, while their permeability was roughly the 

same, the moment corresponding to the onset of the first crack differed by one order of 

magnitude. 

Replacement of part of the sand in concrete with ground limestone reduces sulphate 

expansion in mortars. However, this result cannot be attributed to chemical reasons. It is due 

to the decrease in permeability caused by an increase in the fine particles of the mix 

2.13 Chloride attack 

Waters containing chlorides are detrimental to the concrete structure because they may 

cause or facilitate: 

♦ 

♦ 

♦ 

leaching of free lime, 

break-up of concrete, 

corrosion of the reinforcement. 

Blended cements containing high percentages of natural pozzolanas, fly ash, silica fume and 

slag significantly reduce these risks since the resulting concrete shows: 

♦ 

♦ 

a lower portlandite content and 

a lower diffusion coefficient of the dissolved ions 


Cement 

Concrete 

The compressive strength of pozzolanic cement or blastfurnace cement pastes is little 

affected by prolonged immersion in concentrated CaCl 2 solution, whereas the strength of the 

parent Portland cement already begins to drop after 7 days’ immersion. 

2.14 Sea water attack 

Seawater attacks concrete as a result of the penetration of chloride and sulphate. No 

concrete is strictly impermeable, thus any structure exposed to seawater for many years 

shows: 

♦ 

♦ 

decrease in CaO content, 

increase in MgO and SO 3 content. 


Cement 

Concrete 

The chemical attack is associated with: 

♦ 

♦ 

mass loss and 

expansion. 

Apart from the general requirement of high compactness, concrete attack can be reduced by 

using pozzolanic and blastfurnace cement since the resulting pastes have: 

♦ 

♦ 

a lower content of soluble CaO, 

a higher C-S-H content 

and this helps reduce: 

♦ 

♦ 

the water permeability and 

the diffusion coefficient of the aggressive ions. 

Marine structure built by the Romans with pozzolana concrete have kept a large part of 

original strength after about two thousand years. 

2.15 Alkali Silica Reaction 

Certain constituents of the aggregates can react with the alkali ions present in the pore 

solution of the cement paste giving rise to expansion and cracking of concrete and 

consequent loss of strength and durability of the structure. 

The majority of research studies have concerned the “alkali-silica reaction” resulting from 

certain forms of reactive silica in the aggregate. 

Harmful expansion can be prevented by using Portland cements with an equivalent Na 2 O 

content of less than 0.6%. However, modern cement technology and pollution-preventive 

regulations make this target too expensive. 

Blended cements containing considerable amounts of natural pozzolana, fly ashes, silica 

fume or blastfurnace slag give the same result. Alkalis react quickly with the amorphous 

silica of the fine ground mineral component and are no longer available for further reactions 

with the aggregates. 


Cement 

Concrete 

Limestone decreases expansion not because particular reactions occur but only because it 

makes the total alkali content in cement diminish. 

2.16 Frost resistance 

In many countries frost is a serious cause of damage of concrete. Freezing of free water 

present in the hardened cement paste results in an increase of volume, which causes the 

formation of stresses inside the concrete. If these exceed the flexural strength of concrete, 

cracks occur. 

High strength concrete resists better than low strength concrete, but the sole system that has 

proved to be effective in preventing the effects of frost is the entrainment of microscopic air 

bubbles inside concrete. 


Cement 

Concrete 


Cement 

Concrete 

3. Aspects of Manufacture of Blended Cements 

For optimum production of blended cements, some important aspects related to the grinding 

process should be carefully evaluated 

♦ 

♦ 

♦ 

♦ 

pretreatment of additions 

 

 

drying 

preblending 

properties of the addition 

 

 

grindability 

strength activity 

type of grinding 

 

 

compound 

separate 

dosing of components. 

3.1 Pretreatment of additions 

The additive may have a considerable moisture content, and drying has to be done prior to or 

during the grinding process. The dosing facilities should be adequate to allow precise and 

trouble free operation even in case of very moist and sticky materials. 

Depending on the nature and the number of the additions used, pre-blending of the materials 

would be necessary to achieve sufficient homogeneity of the component and of the cement 

itself. Some mic’s are industrial by-products and therefore subject to changes in composition 

and physical state. 

3.2 Properties of the addition and type of grinding 

3.2.1 Grindability 

The grindability of the components is generally different, even in materials of the same type. 

Big differences might therefore be justified between different plants, and generally a specific 

solution has to be found for each plant. 

The following table summarizes some data, taken out of the annual report, giving information 

on physical properties and the grinding energy needed for the production of blended cements 

containing slag, pozzolan or fly ash compared to Portland cement. 


Cement 

Concrete 

Average Physical Properties and Grinding Energy for Blended Cements 

Material Density 

[g/cm 3 ] 

Blaine 

[cm 2 /g] 

Grinding 

Energy 

[kWh/t] 

Clinker 3.18 3135 32.43 

Slag 2.90 2980 34.17 

Nat. Pozzolan 2.55 6150 20.92 

Fly ash 2.45 4405 11.92 

This table shows that slag is usually harder to grind than Portland cement clinker, while 

pozzolanic materials are mostly softer. The advantage of fly ash is that it can be added 

directly to the separator feed, since most of it is already of the required cement fineness. 

This also implies that during grinding of a slag cement, clinker will be ground finer, thus 

contributing to early stregth development, while the slag remains coarser and will react lately. 

Thanks to its glassy nature, slag does not greatly affect the water demand and the 

workability characteristics and can be used at very high addition rates. 

In the case of pozzolanic cements, the very soft pozzolana will concentrate in the fine 

fraction of cement, thus affecting water demand, workability and early strength development. 

Proper selection of the grinding equipment (central discharge mills, vertical roller mills, 

separate grinding) will prevent overgrinding of pozzolanas and improve cement properties. 

High fineness of silica fume and/or important variability of the fineness of fly ash may be 

responsible for severe problems of handling, transporting and proportioning. This type of 

material is generally introduced after the mill, in the output bucklett or directly in the 

separator, in order to provide a good mixing, avoid quality fluctuations and improve mill 

operation. 

When designing a new grinding plant for blended cement manufacturing, the process can be 

optimized to the requirements. Unfortunately, in most plants blended cements have to be 

produced in old grinding equipment designed for Portland cement production. 

3.2.2 Strength activity 

A mineral component is clearly expected to contribute to strength development of cement. Its 

strength activity will reflect on cement design and on the proportioning system. Typical 

dosage of a mineral component ranges between 25 and 40%; other contents can be chosen 

depending on standards and target performance. 

3.2.3 Type of grinding 

As already mentioned, grindability of the various components can influence the choice of the 

grinding system, especially in new plants. 

Intergrinding of cement is easier from the point of view of plant design and operation, but 

requires accurate dosing and might be considerably disturbed by quality fluctuations of the 

different constituents, also in terms of grindability. 

The advantage of separate grinding is that each component can be ground at the optimum 

fineness, thus enhancing its peculiarities and reducing drawbacks usually associated with 

unproper grinding. 


Cement 

Concrete 

3.2.4 Use of chemical admixtures 

Some of the drawbacks of blended cements can be compensated by the use of selected 

chemical admixtures. 

Besides the simple addition of grinding aids especially in the case of high replacement rates 

with hard to grind materials, more sophisticated quality improvers can be applied 

♦ 

♦ 

♦ 

water reducers/plasticizers 

early strength improvers 

multipurpose admixtures. 


Cement 

Concrete 

3.3 Proportioning 

The most important quality requirement of blended cements are usually related to their 

performance in the different applications. 

Some of these properties can be summarized as follows: 

♦ 

♦ 

♦ 

♦ 

♦ 

♦ 

♦ 

Satisfactory rheological properties for good workability in concrete and mortar 

Acceptable setting behavior 

Adequate strength development and sufficiently high early and 28-day strength 

Satisfactory expectations for durability of the resulting concrete, as regards 

residual porosity and permeability 

resistance to carbonation 

freeze-thaw resistance 

resistance to chemical attack (sulfates, pure water, sea water, weak acids) 

Acceptance of resulting concrete color 

Reduction of Alkali Aggregate Reaction (AAR) risks 

Lower heat of hydration 

and all specific properties providing better service or higher performances compared to 

ordinary Portland cement. 

The design of composite cements requires first of all the establishment of clear objectives 

with respect to product characteristics and performances. Both characteristics and 

performances must comply to cement standard specifications and test methods as well as for 

concrete production. 

The optimum proportion of mineral additions in blended cements is then to be found as a 

consequence of the available materials and the related cement standards. 


Cement 

Concrete 

In general terms, slags are usually characterised by a good hydraulic potential and a low 

water requirement in cement, derived from their glassy nature; these features allow for the 

production of slag cements with high contents of BFS (up to 95%!). 

On the other hand, the amount of pozzolana is a compromise between the minimum amount 

necessary to combine the hydration lime and produce additional silicate hydrates and the 

maximum acceptable content due to the softness and high porosity of pozzolanas that yield 

particles with high water demand, thus affecting cement workability. In this case, a normal 

range for natural pozzolanas or activated clays in cement is 20-45%. 

As a rule of thumb, one shall consider that pure replacement of OPC with a mineral 

component will cause a loss in early strength of 1.5 times the amount of the addition. That is 

to say that 20% replacement will drop early strength by approximately 30%. This strength 

loss can be compensated to a great extent by finer grinding, either the cement as such in 

case of intergrinding, or the clinker fraction in case of separate grinding and following 

blending. 

Increase of grinding fineness will anyway reflect in higher energy consumption of the mill and 

could impair some of the cement characteristics, especially water demand. In this respect, 

the technology of chemical admixtures is capable to provide a selection of suitable products 

for the various needs. Through the proper use of additions, one can improve mill 

performance, increase early strength, reduce water demand, improve workability. 

4. Trends of production and marketing of composite cements 

The present and future challenges for the cement industry relate to its positioning with 

respect to the various environmental matters. 

On one side, it can help solve the problems related to an optimum reuse of industrial byproducts, 

as alternatives for raw meal, fuel and cement materials. On the other hand it will be 

pushed to reduce CO 2 emissions mostly deriving from the production of clinker. 

The consequences of these trends are 

• the limited ability to comply with specific requirements by pure OPC type cements, 

requiring clinkers of specific composition, which are not suitable in the production of other 

types of binders (example – low-alkali, low C 3 A, low-heat clinkers and cements) 

• the increased versatility in providing different performing cements, produced with the 

same clinker, but with different type and content of additions. 

The production of composite cements is therefore going to gain increasing importance in the 

next years, as well as the drafting of new standards where blended cement properties are 

adequately considered and specified. 

Rather than talking about cements, it will be necessary in the next years to consider binding 

agents and concrete mixes, in which Portland cement clinker will still be the principal active 

ingredient. Already today, concretes are being produced in which the clinker represents only 

the minor part of the binding agent, the rest of the constituents such as fly ash, silica fume, 

ground slag, limestone filler, etc. being added directly at the concrete batching plant. 

If we want to maintain the same quality of concrete and assure the future of our industry, we 

must increase drastically the proportion of additions in cement and master the production of 

binders with a maximised content of clinker substitutes. The possibilities for substitution are 

numerous and the optimum cement design will derive from the optimisation of 

♦ clinker composition and production 


Cement 

Concrete 

♦ 

♦ 

♦ 

♦ 

optimum gypsum content 

mic type and content 

grinding process 

use of chemical admixtures. 

5. Conclusions 

The production of composite cements is based on technical, economical and environmental 

reasons. 

The use of ground granulated blastfurnace slag cements as well as pozzolanic cements has 

long been confined to those applications where resistance to chemical attack and lower heat 

of hydration were considered more important than strength. 

Later on, their production has been seen as an advantageous way to find a use for waste 

materials from certain industrial processes or as a way to save on energy. 

Also the Portland limestone cement, largely used in the past only in specialised fields, has 

proved to have useful properties like other more known cements. 

All these historical reasons have, however, been swept away by years of laboratory and field 

research which have shown that blended cements are interchangeable with Portland 

cements in the overwhelming majority of building applications. 

Only in special cases some type and classes of cement are specifically recommended. 

Typically, Portland cement is preferred whenever a rapid hardening is required, whereas 

blended cements, with high content of complementary hydraulic constituents, perform best in 

aggressive environment conditions. 

The real degree of replacement for these types of substitute materials will vary as a function 

of their individual reactivity. They can be mixed with other types of possible additions (triple 

blends or multiple blends or ‘cocktail’ cements), the clinker (or the activator) proportion 

depending on the quantity of CaO needed for the activation of the additions. 

6. Literature References 

1) Lea’s Chemistry of Cement and Concrete, 4th Edition - edited by P.C. Hewlett - Arnold 

2) Mineral Admixtures ic Cement and Concrete, vol. 4 - Sarkar, Ghosh - abi New Delhi 

3) Fly Ash in Concrete, 2nd edition - Malhotra, Rameziananpour - Canmet Canada 

4) Proceedings of the 9th Int. Congress on the Chemistry of Cement, vol. 1 - New Delhi 


Cement 

Concrete 

Special Cements 

1. DEFINITION ...................................................................................................................... 178 

2. TYPES OF SPECIAL CEMENTS...................................................................................... 178 

2.1 ...Special Portland Cements for Durability ................................................................ 179 

2.1.1 Sulfate resisting cements ......................................................................... 179 

2.1.2 Low heat cements .................................................................................... 179 

2.1.3 Leaching resistant cements...................................................................... 180 

2.1.4 Low alkali cements................................................................................... 180 

2.1.5 Sea-water resisting cements.................................................................... 180 

2.1.6 Freeze-thaw resisting cements ................................................................ 180 

2.2 ...Composite Cements for Durability ......................................................................... 180 

2.3 ...High Early Strength Cement, Rapid Hardening Cement........................................ 181 

2.4 ...Fast Setting Cement (Vicat Cement) .................................................................... 181 

2.5 ...Sulfo-aluminate Cement......................................................................................... 182 

2.6 ...Regulated Set (Regset) Cement ............................................................................ 183 

2.7 ...Oil-well cements..................................................................................................... 183 

2.8 ...White cement ......................................................................................................... 186 

2.9 ...Hydrophobic cement .............................................................................................. 186 

2.10 Masonry Cements................................................................................................... 186 

2.11 Ultrafine Cements (Microcements) ......................................................................... 187 

2.12 High Alumina Cement............................................................................................. 188 

2.13 Phosphate cements ................................................................................................ 190 

2.14 Other non-Portland cements................................................................................... 191 

2.14.1 Alkali-activated cements........................................................................... 191 

2.14.2 Alkali-activated slags................................................................................ 191 

3. OVERVIEW OF PRODUCTION IMPLICATIONS IN SPECIAL CEMENTS ..................... 192 

4. LITERATURE.................................................................................................................... 193 


Cement 

Concrete 

1. Definition 

Special cements are cements with special properties that meet particular requirements which 

are not fulfilled by ordinary cements. 

These properties refer either to the performance of cement in fresh and hardened concrete 

as well as in other cementitious blends, or to a special field of application. They can be 

produced with appropriate selection of clinker raw materials and/or cement constituents, 

adoption of special measures in manufacturing, tailored cement compositions. 

As a consequence of these actions, special cements can still comply with existing standards 

on common cements, but very often they are better described in appropriate specifications, 

or otherwise they are produced on the basis of specific agreements between producer and 

user. 

In spite of the several types listed in the following, their application is still limited in quantity 

and the total amount of marketed special cements can be estimated in the order of 10 to 

15% of production. Nevertheless the additional possibilities given by the recently issued new 

cement standards and the increased severity of the environments where concrete is put into 

service are going to make this quantity increase in the near future. 

2. Types of Special Cements 

Special cements are usually developed and produced to meet performance and durability 

requirements, in particular 

♦ improved strength development 

♦ increased resistance to chemical attack 

♦ improved compatibility with reactive aggregates 

♦ suitability for use at elevated temperatures and pressures 

♦ suitability for use in special applications 

♦ applicability in architectural purposes 

As already discussed in the chapter on special clinkers, special cements may belong to three 

main categories 

• Portland cement or composite Portland cement 

• Modified Portland cement 

• non-Portland cement. 


Cement 

Concrete 

2.1 Special Portland Cements for Durability 

Their main hydraulic constituent is generally Portland cement clinker, very often tailored to 

obtain special characteristics that yield the desired properties to the cement. For this reason, 

particular measures need to be taken in the production of clinker, expecially from the point of 

view of the selected raw materials to employ. In some cases this could not be enough or the 

involved costs are much higher than the obtained benefit. 

So, the same or even better final properties can be achieved by blending clinker with 

appropriate mineral components and/or additions, as described in chapter , dealing with 

design and properties of composite cements. 

Main durability characteristics for Portland type special cements are 

• resistance to sulfate attack 

• low heat of hydration 

• resistance to pure water attack 

• low alkali content or low reactivity with amorphous silica 

• resistance to freeze-thaw cycles. 

Before dealing with the different durability aspects that can require use of special cements, a 

general remark must be done. The main factor influencing durability is the proper design, 

production, compaction and curing of concrete. Any special cement, designed for the 

enhancement of durability will fail when used in the production of a poor concrete. A well 

compacted, high strength, low porosity concrete will be by far less prone to be attacked by 

external agents, even when produced with ordinary cements. 

2.1.1 Sulfate resisting cements 

Sulfates can be found in natural and industrial waters, as well as in soils. Soluble sulfates 

can react with lime and aluminates present in the hardened concrete and form respectively 

gypsum and ettringite. Both reactions entail expansion and consequent concrete 

deterioration. Sulfate resisting cements are characterized by a low C3A content, to minimize 

the risk of ettringite formation. This type of binders set and harden normally and in fully 

compacted concrete are not attacked by sulfates in a wide range of concentration. At the 

same time they possess low-heat properties. 

2.1.2 Low heat cements 

Hydration reactions of cement develop heat. When cement is used in the production of mass 

concrete, temperature gradients generate between core and surface of the conglomerate 

cause strains and may eventually lead to cracking. Low heat cements have a reduced heat 

of hydration, obtained by altering the chemical composition (low C3S and C3A contents). The 

use of low-heat cement is recommended for mass concrete production or for large structural 

sections. They usually set and harden at a lower rate than for ordinary cements, especially 

in cold weather, but ultimate strengths may be higher. They possess also good sulfate 

resisting properties. 


Cement 

Concrete 

2.1.3 Leaching resistant cements 

Waters with low salinity or a high content of carbon dioxide (CO2) are capable to dissolve 

hydration lime present in hardened concrete structures and may subsequently also subtract 

lime from silicate hydrates, thus causing damage to the hardened cement paste. Cements 

resisting to leaching have a low development of calcium hydroxide (lime) after hydration of 

clinker silicates, as a consequence of their low C3S content. Their use is suggested in 

hydraulic works like basins, river barriers and sides. At the same time they possess rather 

low heat evolution characteristics. 

2.1.4 Low alkali cements 

Some aggregates may contain forms of reactive amorphous silica. In the presence of water 

this can react with the soluble alkali of cement and form locally an expansive gel that can 

deteriorate concrete. In such cases, when the use of reactive aggregates is absolutely 

unavoidable, the use of a cement proven to counteract alkali-silica reaction (ASR) is 

suggested. Such cements can either be low-alkali or composite cements, since the 

pozzolanic or slag material can immediately react with alkali and prevent subsequent 

reaction with aggregates in the hardened paste. 

2.1.5 Sea-water resisting cements 

Deterioration of concrete which is in contact to sea water takes place as a consequence of 

some of the already described phenomena. Concurring factors are chemical attack by 

MgSO4, mechanical stress caused by tydal waves, crystallisation pressure due to deposition 

of salts in the wind and water line. Cold climates add freeze-thaw effects, while in warm 

areas some reactions are accelerated. Sea-water resisting cements are standardised in 

some countries, being moderate C3A content or composite cements. 

2.1.6 Freeze-thaw resisting cements 

In harsh climates with high temperature differences and repeated freeze-thaw cycles, 

freezing of water contained in gel and aggregate pores will cause a volume increase of ab. 

10% and the consequent development of internal pressure; repeated actions of this type 

deteriorate the concrete. Entrainment of air in form of microbubbles will produce a closed 

artificial porosity acting as expansion chambers for the ice generated. Some standards such 

as ASTM provide for cement types with air entrainment. 

2.2 Composite Cements for Durability 

In the chapters 2.1.1.to 2.1.5 specifications set limits for clinker components, i.e. maximum 

C3A and C3S content, maximum Na20 equivalent, as reflected in the ASTM C150 

specification for Portland cement. 

In the case of Composite cements, it would be more correct to refer to these values 

expressed as total content in cement, as the clinker fraction may vary from case to case. As 

a matter of fact, using less clinker to produce a composite cement is a good starting point to 

reduce the amount of the harmful clinker components in that cement. 

Additionally, the use of a mineral component like slag, pozzolan or fly ash will improve the 

durability and the pore structure of hardened concrete by lowering its lime content and 

porosity as a consequence of the enhanced development of calcium silicate hydrates. 

Then, the ASTM C595 and C1157 deal with composite cements and set limits referred to the 

performance of cement with respect of sulfate resistance and heat of hydration, without any 

prescription on the basis of cement composition. 


Cement 

Concrete 

If we look at these durability aspects in the context of the European standard EN 197-1, we 

can immediately realize that most of the Portland composite cements of the II/B type, with 

addition of 21 up to 35% of non-clinker materials, as well as type III (slag), type IV (pozzolan) 

and type V (composite) cements can be considered as “special” with respect to many 

properties mainly related to durability. 

Nevertheless, a CEN working group is now drafting new ENV 197 parts specifically dealing 

with special cements, in particular low heat- and sulfate resisting cements. 

2.3 High Early Strength Cement, Rapid Hardening Cement 

High early strength cement (HES) and rapid hardening cement (RHC) may either be finer 

than ordinary cement or have a special clinker composition. 

Especially in the past, production of HES/RHC cements often required the production of a 

special clinker, with high C3S and C3A contents. 

In present times, the improvements gained in grinding technology and in the use of quality 

enhancers as grinding aids, combined with the need of rationalization for storage and 

transports in cement plants, allow for the production of high early strength cements based on 

the same clinker used for ordinary binders. The higher grinding fineness and the related 

enhanced reactivity usually require increased gypsum dosage. 

Physical properties of HES/RHC cements in comparison with ordinary Portland cements are 

shown in table 1. It should be noted that an increase in fineness would often also reflect in 

higher late strengths. 

Table 1 

Physical Properties of High Early Strength and Ordinary Portland 

Cement 

Type Blaine (cm²/g) Initial setting Compr. strength MPa 

time (minutes) 2 days 28 days 

OPC 3000 ÷ 3500 150 ÷ 240 10 ÷ 20 38 ÷ 43 

High early strength 3800 ÷ 4500 120 ÷ 180 20 ÷ 30 48 ÷ 55 

Rapid hardening 4800 ÷ 5500 90 ÷ 150 30 ÷ 40 58 ÷ 67 

(ISO) 

The use of HES/RHC cements is indicated when a rapid strength development is required, 

e.g. if formwork has to be removed or re-used after a short time (precast elements 

production) or when sufficient strength is required for further construction (slipforming). 

However, since rapid strength gain is usually associated to high rate of heat devlopment, 

HES/RHC cements should not be used in mass concrete or in large structural sections. On 

the other hand, concreting at low temperatures would profit from the use of a high heat 

cement as a safeguard against early frost damage. 

2.4 Fast Setting Cement (Vicat Cement) 

A particular type of fast setting cement is the so called Vicat cement from the name of its 

inventor and main producer. It is obtained by burning at low temperature (1200 to 1250 °C) 

selected natural marls with rather high alumina contents. The clinker produced is mainly 

composed of belite and aluminates; after grinding it is capable to set in a few minutes, 

developing sufficient strength to fulfil requirements for easy and fast repair or small 

construction jobs. 


Cement 

Concrete 

“Artificial” fast setting cement can be produced by blending OPC and High Alumina cement 

(see § 2.12) approximately at a 9:1 ratio. 

2.5 Sulfo-aluminate Cement 

Cements having calcium sulfo-aluminate (C4A3S*) as main component. Examples of this 

binder type are type K cement produced in USA and the so called third cement series (TCS) 

in India and China. Typical composition ranges are reported in Table 4. 

Characteristics of these cements are 

∗ reduced setting times 

∗ high workability, low water demand 

∗ rapid strength development 

∗ low shrinkage (even expansive) 

Hydration of C4A3S* leads to the formation of ettringite, which is mainly responsible for early 

strength development. Microstructure of ettringite depends on the presence of lime. When 

ettringite forms in presence of lime it provokes expansion and this property is used to 

produce no-shrinkage cements. In the absence of lime, ettringite is not expansive and mainly 

contributes to strength development. 

Binders of this type can then be used, according to mineralogy, to prevent shrinkage in 

concrete or to develop high early strength for special applications. 

The blend of TCS cements with OPC yields to flash setting. 

Table 4 

Chemical and mineralogical composition of Sulfo-aluminate Cements 

Sulfo-aluminate 

clinker (type K) 

TCS sulfo-aluminate 

cement (SAC) 

SiO2 2 - 4 3 - 10 6 - 12 

Al2O3 45 - 49 28 - 40 25 - 30 

Fe2O3 1 - 2 1 - 3 5 - 12 

CaO 37 - 39 36 - 43 43 - 46 

SO3 7 - 10 8 - 15 5 - 10 

CaO free 0 - 0.3 0 - 0.3 0 - 0.3 

mineralogical composition 

C4A3S* 55 - 70 55 - 75 35 - 55 

CA 15 - 20 - - 

C2AS 15 - 20 - - 

C4AF 0 - 5 3 - 6 15 - 30 

C2S - 15 - 30 15 - 35 

TCS ferro-aluminate 

cement (FAC) 


Cement 

Concrete 

2.6 Regulated Set (Regset) Cement 

Modified Portland cement type with rapid setting and hardening characteristics. The active 

component is a calcium fluoroaluminate (11 CaO. 7Al2O3. CaF2). 

The regset cement is characterized by a setting time of 15 to 60 minutes. The setting is 

controlled by the addition of retarders (citric acid). Additional characteristic property is its 

unusually high early strength. A comparison between strengths achieved with Regset and 

HES cement is reported in Table 2. 

Table 2 

Properties of Regset and High Early Strength Cement 

EN method Regset Cement H.E.S. Cement 

Compr. Strength MPa 

2 hours 6 0 

8 hours 8 2 

16 hours 9 15 

2 days 10 35 

7 days 18 47 

28 days 35 60 

Setting time minutes 

Initial 45 120 

Final 75 180 

The very early strength gain makes this cement useful for all applications where there is a 

vital need for short times between placing and hardening of concrete, i.e. shotcrete, repairs 

on airport runways or highways, pavements. 

Regset cements are batched, handled and mixed in pretty well the same way as Portland 

cements, making however the necessary provisions for rapid handling and placing of 

concrete. Although production is as cheap and easy as for Portland cement, the fast and 

often unpredictable setting behaviour puts serious limits to the use in constructions and the 

total world production is estimated in the order of 10000 tons/year. 

2.7 Oil-well cements 

Oil-well cements are developed for use in oil and gas wells and are designed to set and cure 

at high temperatures and pressures in well grouting. They can also be used for sealing water 

wells, waste disposal wells and geothermal wells. Cement plays an important part in the 

successful drilling of a well. It is used primarily to seal the annulus between the walls of the 

borehole and the steel casing, to isolate the pressured or weak zones encountered whilst 

drilling. 

The oil-well cement must possess the following properties: 

∗ low permeability 

∗ form a good bond between rock and casing 

∗ maintain these properties under downhole temperature and pressure conditions 


Cement 

Concrete 

∗ 

protect the casing against corrosion and collapse 

To achieve these aims, the cement slurries must stay pumpable for sufficient time to permit 

placement, give stable suspensions, harden rapidly once in place and retain high strength 

and low permeability during well lifetime. 

API specification 10 from American Petroleum Institute classifies eight different oil-well 

cements. Other national standards exist, e.g. in Russia, China, India, most Eastern European 

countries, but so far no EN standard has been drafted. In Table 3 an overview of API 10 

cements is compiled. 

Table 3 

Class 

A 

B 

C 

D 

E 

F 

G and H 

J 

Overview of oil-well cements 

Typical use 

from surface to 1830 m, special properties not required, ASTM type I 

from surface to 1830 m, moderate or high sulfate resistance 

from surface to 1830 m, high early strength 

between 1830 and 3050 m, moderately high T and p conditions, moderate 

or high sulfate resistance 

between 3050 and 4270 m, high T and p conditions, moderate or high 

sulfate resistance 

between 3050 and 4880 m, extremely high T and p conditions, moderate 

or high sulfate resistance 

from surface to 2440 m, for use with accelerators or retarders, moderate 

or high sulfate resistance, class H coarser than G 

between 3660 and 4880 m, pure OPC, extremely high T and p conditions 

Such cements need special test procedures for suitable characterisation and additional care 

during manufacture so as to ensure consistency of quality between batches of the same 

plant. 


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In use, they are frequently mixed with additives in various proportions to produce satisfactory 

slurry performance for given well conditions, so they should additionally be compatible and 

responding to these additives (Table 4). 

Table 4 

Common types of additives for Oil-well Cements 

Classification Function Example 

Accelerator Reduces thickening time of cement CaCl2, sea-water 

Retarder Lengthens thickening time Lignosulfonates, sugars 

Dispersant Improves flow properties of cement Superplasticizers 

Lightweight extender Improves stability of suspension Bentonite, various clays 

Weighing agent Improves density of slurry Haematite, barite, sand 

Lost 

controller 

circulation 

Prevents cement losses through strata 

Walnut shells, cellophane 

flakes, expanded clay 

Inhibitor of strength 

retrogression 

Prevents loss of strength and 

formation of low strength silicate hydr. 

Silica flour, silica sand 

Fluid loss controller Controls rate of water loss polymers, cellulose 

Defoamers Removes foaming during mixing Lauryl alcohol, glycols 


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2.8 White cement 

One of the most important special Portland cements. It is characterized by a white colour, 

obtained with suitable selection of raw materials, in which the colouring elements iron, 

chromium and manganese must be kept at the lowest possible level. Reduced formation of 

melt phase during burning is sometimes compensated by addition of fluoride as mineralizer. 

Mechanical properties of white cements are comparable to those of OPC. Lower strength 

binders are produced intergrinding (up to 35%) high purity limestone. To improve whiteness, 

use of “optical whiteners” such as methylene blue in cement grinding can be applied. 

White cement is used for architectural purposes in white or coloured concrete. To achieve 

best results, a properly coloured aggregate has to be used. 

2.9 Hydrophobic cement 

A small amount of a water-repellent agent (stearic acid, oleic acid, a.s.o.) is added to 

Portland cement during grinding. This forms a protective coating around each cement 

particle that retards hydration until cement is mixed with water and prevents deterioration 

during storage, especially in humid countries. 

2.10 Masonry Cements 

Masonry cements are successfully used in the production of mortars and plasters for most 

non-structural building purposes. 

Their main characteristics are: low early- and late strengths, low shrinkage, limited water 

permeability, high water retention, excellent plasticity and cohesiveness in the fresh state, 

frequently also air entrainment for better workability and freeze-thaw resistance. 

These properties are achieved by a low to medium clinker content, use of a suitable 

limestone and/or other mineral additions, use of air-entraining agents. 

MC’s are mostly produced by intergrinding Portland cement clinker, gypsum, precrushed 

limestone and/or other mineral additions. When the grindability of the constituent materials is 

much different, it might be opportune to grind them separately, especially if the following 

blending facilities are available. 

The main advantage from the production point of view is the limited clinker content (may be 

as low as 25%) and the availability of the limestone in the plant. Production 

25 Holcim Group plants produce masonry cements in an extremely wide range of 

compositions and properties, reported in the following table 5 (based on 1996 Annual 

Technical Report). 


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Table 5 

Characteristics of Masonry Cements in the Holcim Group 

Masonry Cement Characteristics avg. min. max. 

Clinker content, % 

1) 

54.2 24.0 81.5 

Specific surface acc. to Blaine, cm²/g 6470 3765 9420 

Residue on a 45-µm sieve, % 8.9 1.7 25.7 

Residue on a 90-µm sieve, % 5.5 1.1 9.5 

Air entraining agent, dosage g/t 1210 91 4000 

Sulfate content, % SO3 1.93 0.62 3.00 

Water demand, % 

2) 

26.3 21.5 30.2 

Initial setting time, minutes 2) 190 113 383 

Compressive strength 7 days, MPa 

Compressive strength 28 days, MPa 

2) 

2) 

12.8 3.7 25.6 

15.2 3.4 29.5 

Specific milling energy consumption, kWh/t 65.6 34.3 132 

1) 

main other constituent is limestone, but also fly ash and pozzolana are used 

2) 

figures related to both ASTM and EN test methods are considered 

2.11 Ultrafine Cements (Microcements) 

These binders are characterized by a narrow and steep particle size distribution (see figure 

1), specially designed for injection grouts used for sealing and improving mechanical 

properties of porous systems (rocks, damaged concretes, soils). 

Due to the reduced particle size, water-microcement suspensions are highly stable and 

penetrating than OPC grouts. Results obtained using microcement injections are comparable 

to those of chemical products such as resins and soluble silicates, with the advantage of 

being more environment friendly. 

Microcements are usually Portland or blast furnace slag cement based and are produced by 

ultrafine grinding or subsequent efficient separation of finer fractions from common cements. 

Particle size distribution may range between 0 and 10 -15 µm. Due to this, they also develop 

much higher early strength than the corresponding common cement , but usually require 

higher water demand. This is not a drawback in most applications, since for injection grouts a 

W/C ratio of 1.5 to 3 is quite in the normal range. 


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Figure 1 

Particle size distribution of various cement types 

100 

Particle size distribution of various cement types 

% 

pa 

ssi 

ns 

80 

60 

40 

Microcement 

HES 

OPC 

20 

0 

1 1.5 2 3 5 10 15 30 50 75 100 150 

sieve opening (µm) 

As mentioned, their main use is in fields where common cements cannot be used due to their 

limited fineness characteristics 

• agglomeration of loose soils 

• sealing of microcracked rocks 

• restoration of foundations, tunnels, leaching dams, historical buildings. 

2.12 High Alumina Cement 

Typical non-Portland cement, high-alumina cement (HAC) produces a concrete which has an 

exceptionally fast rate of hardening and is resistant to attacks by most sulfate solutions. It 

also has a higher resistance against acidic solutions than Portland cement based concretes, 

but it does not resist the attack of caustic alkali.The strength development of HAC is 

demonstrated in Figure 2. About 80% of its ultimate strength is achieved after only 24 hours. 

The high rate of strength gain of HAC is due to the rapid hydration of the anhydrous calcium 

aluminate (CA). 

Rapid hardening is not accompanied by fast setting. Initial setting takes place between two 

and six hours after mixing, becuase of the slow setting pattern of hydration of the main 

compound CA. 

Setting time can be shortened by addition of OPC. HAC/OPC blends are used in applications 

where rapid setting is compulsory, but lower ultimate strengths are then obtained. 

Inversely, the same effect on setting is achieved by replacement of 10 to 20% HAC to OPC. 

The high rate of heat evolution (Figure 3) of high-alumina cement (ab. 40 J/g.hour in the first 

24 hours) makes it necessary for HAC concrete to be placed in thin sections and never in 

large mass. The rise in temperature causes cracking and adversely affects strength. HAC 


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concrete needs also more water for hardening and better curing during the first two days 

than OPC concrete. 

The main drawback of high-alumina cement concrete is the loss of strength associated with 

expansion due to the conversion of the aluminate hydrates under moist conditions at 

elevated temperatures. The hexagonal hydrate CAH10 is converted into the cubic aluminate 

C3AH6 as from the reaction 

3 CAH10 → C3AH6 + 2 AH3 + 18 H 

This means that concrete which is properly placed and has developed a high strength will 

lose a considerable proportion of its strength upon exposure to temperatures over 30 °C and 

moisture. 

Figure 2 

Strength development of different cements 

Compressive strength [N/mm²] 

50 

40 

30 

20 

10 

HAC (High alumina cement) 

Type III 

Regset 

Type I 

0 

15 1 5 1 3 7 

28 

minutes 

hours 

Age 

days 


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Figure 3 

Heat evolution of different cements 

50 

Aluminous cement 

Rise in temperature [°C] 

40 

30 

20 

10 

Rapid hardening 

Portland cement 

Normal Portland cement 

0 

0 10 20 30 40 50 60 70 

Time [hours] 

2.13 Phosphate cements 

A mixture of tetracalcium phosphate and dicalcium phosphate, when mixed with a dilute 

phosphoric acid or other aqueous solutions will harden like a cement-producing 

hydroxyapatite, Ca10(PO4)6HOH, as the final product. The setting property, combined with 

biocompatibility, makes calcium phosphate cements useful in many applications in dentistry 

and medicine. 

Pastes prepared from diammonium orthophosphate, as well as NaH2PO4 or Napolyphosphate, 

and calcined MgO exhibit a fast setting and hardening at room temperature 

associated with NH3 liberation. MgO-phosphate binders may be used for high temperature 

applications, since strength remains preserved up to 1000 °C. 


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2.14 Other non-Portland cements 

2.14.1 Alkali-activated cements 

“Pyrament “ (developed in USA) belongs to this type of binders; they are mainly composed of 

pozzolans and possibly other active silica-based materials such as silica fume, fly-ash, slag 

or Portland cement, and alkali compounds (alkali silicate, hydroxide or carbonate); water 

reducers and retarders are also added to set regulation. They display excellent early strength 

properties as well as high density and strength at later age, but the complicated 

multicomponent formulation indicates a very sensitive system, difficult to control under field 

conditions. 

Development of “Geopolymers” is based on the work of Davidovits. The main reaction takes 

place between sodium hydroxide and kaolinite to form hydrosodalite at room temperatures or 

preferably between 150 and 180 °C. This reaction is the typical hydrothermal synthesis of 

zeolites. 

2.14.2 Alkali-activated slags 

The ability of activating blast furnace slags (BFS) by the addition of alkalis has been known 

for many decades. Hydration of slag requires the breaking of bonds and dissolution of the 

three-dimensional structure of glass and this is easily achieved in the high pH environments 

produced by alkali. Research on slag activation dates back to the early 50’s; interest in 

alkaline activation has grown markedly and in recent years alkali-activated cement and 

concrete have received greater attention worldwide. 

Compared with ordinary Portland cement and interground slag cement, alkali activated slag 

cement has some advantageous properties, including rapid and high strength development, 

good durability and high resistance to chemical attack. 

Finely ground, well granulated BFS can be utilized in the production of cements suitable for 

the precast industry, after addition of alkaline activators and superplasticizers, as for the “F” 

cement (Finland). When used with thermal curing, these cements can develop strengths 30% 

higher than normal Portland cements. 


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3. Overview of Production Implications in Special Cements 

In the following table 5, the implications related to the production of special cements are 

summarized. In particular, after highlighting the main properties and applications of each 

special cement type, a list of special measures that need to be taken at the plant to achieve 

the expected properties is compiled. 

Table 4 

Properties , application and measures for proper production of special 

cements 

Type Properties Application 

Raw 

mat 

Man 

ufact 

Addi 

tions 

App 

licat 

ion 

OPC normal workability 

and stength 

general application in 

building and construction 

- - - - 

ASTM II / 

SRC/LHC 

moderate sulfate res. 

low heat of hydration 

drainage, large piers and 

retaining walls, sea water 

x - (x) - 

ASTM III / 

HES-RHC 

high early strength, 

rapid hardening 

precast concrete, repairs, 

cold weather concreting 

- x 

finer 

- - 

ASTM IV / 

LHC 

low heat of hydration mass concrete, large dams x - x x 

ASTM V / 

SRC 

sulfate resistant 

severe sulfate action in 

(soils, ground water) 

x (x) x x 

Air entrain. frost resistance roads, freeze-thaw action - - x - 

Low alkali low reactivity with 

amorphous silica 

in concrete with reactive 

aggregates 

x x x - 

Leaching 

resisting 

low content of hydrat. 

lime 

in presence of pure waters 

or high CO2 solutions 

x - x - 

Oil well retarded setting, 

moderate sulfate res. 

in oil, gas and other types 

of wells 

x - (x) x 

Regset fast setting time road repairs, dry mortars x x - x 

White cem white colour architectural concrete x xx (x) x 

Sulfoalum. 

cement 

fast setting, high 

workab., (expansive) 

precast concrete, repairs, 

no-shrinkage concrete 

x x - x 

Ultrafine max size < 15 µm injection grouts - xx (x) xx 

High alum. 

cement 

high early strength, 

rapid strength devel. 

demand of very high early 

strength, refractories 

x xx - xx 


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4. Literature 

1) Special and New Cements - A K Chatterjee Proceedings of the 9th ICCC, New Delhi 

1992 

2) Development in non-Portland Cements - Nuzhen, Kurdowski, Sorrentino as above 

3) Mineral Admixtures in Cement and Concrete - Sarkar, Ghosh Progress in Cement and 

Concrete vol. 4 - Akademia Books International, New Delhi 1993 

4) Specialty Cements with Advanced Properties - Scheetz, Landers, Odler, Jennings 

Symposium Proceedings Materials Research Society 1989 

5) International Development Trends in Low-energy Cements - Stark, Müller ZKG 4/88 

6) J. Bensted - Oilwell cements World Cement 10/89 

7) Structure and Performance of Cements - ed.Barnes Applied Science Publishers 1983 

8) New Ultra-rapid Cements - Costa Proceedings of the FAST Congress, Milan 1997 

9) Special Inorganic Cements - I. Odler E&FN SPON, London 2000 


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Cement Standards 

1. INTRODUCTION ............................................................................................................... 195 

1.1 ...Importance of Standards........................................................................................ 195 

1.2 ...Development of Standards..................................................................................... 195 

2. CEMENT STANDARDS.................................................................................................... 196 

2.1 ...Product Standards ................................................................................................. 196 

2.2 ...Significance of Specifications................................................................................. 197 

2.3 ...Testing Methods..................................................................................................... 198 

3. INTERNATIONAL CEMENT STANDARDS ..................................................................... 199 

3.1 ...The ASTM Standards............................................................................................. 199 

3.2 ...THE EUROPEAN STANDARD ENV 197-1 ........................................................... 204 

3.3 ...THE AUSTRALIAN STANDARD AS 3972-1991.................................................... 209 

3.4 ...Conclusion ............................................................................................................. 211 

4. STANDARDS FOR MINERAL COMPONENTS ............................................................... 211 

5. CONCRETE STANDARDS............................................................................................... 212 

5.1 ...Purpose.................................................................................................................. 212 

5.2 ...Content of the Standards and Specifications ......................................................... 212 

5.2.1 Quality of the Concrete Components ....................................................... 212 

5.2.2 Quality of Fresh Concrete ........................................................................ 213 

5.2.3 Strength of Hardened Concrete ............................................................... 213 

5.2.4 Durability of Concrete............................................................................... 214 

5.3 ...The European Standard ENV 206 ......................................................................... 215 

5.3.1 Cement Content and Durability ................................................................ 215 

5.3.2 Chloride Content ...................................................................................... 219 

5.3.3 Alkali Aggregate Reaction........................................................................ 219 

5.3.4 Maintenance............................................................................................. 219 

5.4 ...Referenced documents .......................................................................................... 220 

5.4.1 Relevant ASTM Standards for Concrete Components............................. 220 

5.4.2 Relevant EN Standards for Concrete Components.................................. 220 


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1.1 Importance of Standards 

In many of our daily activities we are unconsciously confronted with standards. 

When we go to see a football game at 3.30 p.m. we seldom realize that if it really begins at 

the scheduled time it is simply because we have standardized our time according to fixed 

rules. Then, it is up to us to decide buying an expensive Swiss watch in case we look for a 

reliable product, proven to keep its conformity to the time standard long enough. 

Many other less trivial examples could be reported to witness to what extent our life is 

defined and conditioned by standards of any type (mainly moral...). 

We need standards because they are the way we have to fix generally valid and accepted 

rules to measure and compare things with one another and so define the relationship 

between “producer” and “consumer”. 

Producing according to an official standard means then putting on the market a product of 

well defined, measurable and recognizable characteristics. 

This will positively affect the producer’s position with respect to own customers in terms of 

reliability, confidence and commercial relationship and will protect him against unfair 

competition and undue complaints. 

The consumer is then assured that by using a standardized product he can rely on a marketconforming, 

well defined and reasonably constant quality product, that will reflect in a 

consistent and cost-effective production. 

The designer and contractor will be provided with confidence about the essential material 

characteristics they need to design and execute the desired structures. 

It is therefore of vital importance that cement and concrete producers be aware of the 

expected developments of own standards and, if needed, take the necessary actions to 

influence development in the desired direction, be it through either direct or own 

association’s involvement. 

1.2 Development of Standards 

Developing a standard is not an easy deal. From previous comments, it should be clear that 

a product standard involves both the producer’ and the consumer’s interests and this is not 

an ideal starting point to find rapidly an overall agreement on the standard objectives. 

On the other hand, standards can meet easy and widespread acceptance only when all parts 

involved participated in its development. 

Standards shall then be a common elaborate of 

• the producer 

• the seller 

• the consumer 

• the designer 

• the official testing institute 

• the universities or research laboratories 


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• the government. 

They should also be conceived (and periodically revised) taking into account 

• the present technical situation of the industry 

• the need of progress for the country 

• an effective environmental compatibility (energy saving and by-products recycling) 

• all technical improvements and economic changes that took place from the last 

edition 

• modified market exigences and demands 

• last but not least, the effort to pull down trade barriers in large State federations. 

2. Cement Standards 

2.1 Product Standards 

Product standards, which we are mostly interested in, are usually meant to define 

♦ the quality of a product, in terms of composition, performance and application (i.e. the 

European ENV 197-1 standard on common cements) 

♦ the common rules for uniformly testing and assessing the prescribed product quality (i.e. 

the associated EN 196 series of testing methods) 

♦ the conditions for the use of the product in particular applications (i.e. recommendations 

for durability of concrete structures, a.s.o.). 

They include classification, composition, specification and compliance criteria. As regards 

specification, that is a statement of one or a set of requirements the material shall comply 

with, they can be prescriptive- or performance oriented. 

The prescriptive specification defines a product according to its composition, the 

performance specification defines a product according to its function in application, thus 

products of different composition can comply. 

It is rather difficult to say which is better. On one hand a performance standard is supposed 

to be tightly related to the product’s field performance and should better represent its ability 

to fulfill the customer’s expectations and needs. On the other hand, assessing particular 

properties can involve use of complicated and time consuming testing methods; sometimes 

even the correlation between lab testing and field performance is still to be demonstrated. 

Then, in many cases, an easy prescriptive standard (i.e. maximum C 3 A for sulfate 

resistance) is preferred. 

We should not forget anyway, that some of the specifications for cement rely on performance 

testing, such as setting time and strength. 

In the case of cement, product specifications take into account 

♦ production aspects, as regards raw materials availability, plant design, environmental 

needs 

♦ application aspects, as regards experience of use, available technology, needs of 

differentiation, customer expectations 

♦ marketing aspects, as regards cost effectiveness of products, principles for fair 

competition, appropriate price/quality differentiation 


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♦ quality aspects, by setting minimum and/or maximum acceptable values for most of the 

standardized properties, as a protection against dangerous behaviour of non-conforming 

products. 

Some of the most recent international standards (e.g. ENV 197-1 on common cements) now 

include also a chapter on conformity evaluation. 

This is a very innovative and clever approach to product standardization, since it introduces 

statistical tools to evaluate quality, not simply in terms of fulfilling absolute limit values, that 

are still considered as threshold values for conformity, but mainly taking into account the 

characteristic values, that include calculation of mean value and standard deviation of the 

measured property. An example will be given in the following pages. 

After highlighting the merits of standards, we cannot help mentioning their main drawback. 

Product standards are capable to depict the present situation and technology only, without 

being able to forecast, and open paths for, technical development. This sometimes reflects in 

a serious hurdle to innovation, since a real new product will hardly find a corresponding 

standard to be referred to. 

This is a strong argument for those people who are in favour of performance standards, that 

hinder technical progress much less than prescriptive ones. 

Standardization bodies should therefore find the right balance and make their mind more 

progress-oriented, so to walk aside innovation and not run after it. 

2.2 Significance of Specifications 

We have seen that a specification is a requirement the product shall comply with. But why 

are these requirements specified? 

The main concern in a cement standard is that the binder has to be used in constructions 

where safety, comfort and durability must be safeguarded. Additionally, special applications 

need special cement properties that have to be adequately described in specifications. 

In the following, a series of examples indicate properties that are specified for cements and 

also the inconveniences they must prevent; as mentioned, requirements can be related 

either to cement composition or to performance. 

• minimum setting time - to prevent early or flash setting of cement, that would 

excessively shorten the life time of the fresh and workable blend; 

• soundness (Le Chatelier or autoclave test) - maximum expansion is specified to 

prevent the risk of cracking in hardened structures; 

• maximum SO3 content - same as above; 

• maximum C3A content - to limit reactivity to sulfate attack and heat development of 

cement; 

• maximum C3S content - to limit reactivity to pure water attack and heat development 

of cement; 

• maximum heat of hydration - to prevent excessive heat development; 

• compressive strength - to guarantee a minimum strength development in properly 

designed concretes and cementitious blends; 

and so on. 


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2.3 Testing Methods 

Product standards usually deal with the characteristics of a product, making reference to the 

proper testing methods to be used for the assessment of these characteristics. 

Standards about testing methods aim at defining uniform conditions under which the product 

is tested. 

They fix the product’s testing conditions, in the case of cement if the measurement of the 

property will be carried out on 

• powder 

• paste 

• mortar 

• concrete; 

they define 

• scope of testing 

• referenced documents 

• testing apparatus 

• reactants 

• calibration of apparatus 

• testing procedure 

• calculation of results 

• reporting 

• precision and bias of the method. 

As for product specifications, the purpose is to have a common tool to evaluate the product 

and reproduce the results obtained by different testers with reasonably narrow deviation. So, 

a product with a wide (even transnational) market distribution can be checked in different 

places with sufficient confidence on the accuracy and reliability of results. 

This is clearly assuming a growing importance in the view of free trade activities, but the 

most practical advantage for a plant technologist is to use the same language and the same 

criteria to identify products and properties. 

Drafting testing methods is usually easier than for product specifications, because it does not 

involve commercial and political issues, nevertheless some main principles should be 

observed. A testing method should be 

♦ reliable (repeatable and reproducible) and meaningful 

♦ able to allow easy correlations between results and product characteristics and/or 

properties 

♦ easy to be implemented in any official as well as plant laboratory 

♦ as far as possible not hazardous to workers or environment. 

Most of the main testing methods for cement are well established standards. If a new 

property needs to be measured, then a working group is usually formed and a draft test is 


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issued; the following round-robin testing will prove the effectiveness of the method to 

transform it into an official standard. 

3. International Cement Standards 

Standards are usually issued on a National basis by the local standardization institute. 

Such institutes are ASTM for USA, BSI for UK, DIN for Germany, AFNOR for France, and so 

on. 

Recent formation of large State federations (i.e. the European Community) have brought to a 

centralized management of standardization, to make it compatible with the free trade of 

products among countries. The European Committee for standards (CEN) has then rapidly 

become the main technical reference for all member and affiliated countries in Europe and 

also in some other areas of the world. 

In the context of international standardization of testing methods, even ISO, the International 

Standards Organization, has simply and directly adopted some of the new documents 

developed by CEN technical Committees. 

As a consequence, the trend all over the world is towards a reduction of the number of 

standards to a selected minimum, even maintaining some national peculiarities. Therefore 

we are going to mention here the cement standards that gained worldwide recognition and 

application, the ASTM and the EN specifications, as well as the Australian standard, an 

example of a very simple and effective way to draft a technical specification for cement. 

People that are interested in a complete compilation of the world cement standards can 

consult the publication “Cement Standards of the World”, issued by Cembureau, Brussels. 

3.1 The ASTM Standards 

ASTM standards are widely adopted not only in the United States of America, but also in 

many other countries of Latin America, as well as Asia and Africa. 

In the following pages, the specifications contained in the relevant ASTM cement standards 

are reported 

♦ C 150 - “Standard Specification for Portland Cement” 

♦ C 595M - “Standard Specification for Blended Hydraulic Cements” 

♦ C 1157M - “Standard Performance Specification for Blended Hydraulic Cements”. 

a) Cements defined by C 150 are divided in five different types. 

• Type I For use in general concrete construction 

• Type II For use when exposed to moderate sulfate action, or where 

moderate heat of hydration is required 

• Type III For use when high early strength is required 

• Type IV For use when low heat of hydration is required 

• Type V For use when high sulfate resistance is required 

(Types I to III can also be produced as air-entrained cements, when air entrainment is 

desired; in this case they bear the suffix “-A”). 


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Table 1 

ASTM C150 - Standard Specification for Portland Cement 

Cement type → I I A II II A III III A IV V 

SiO2, min % - 20.0 - - - 

Al2O3, max % - 6.0 - - - 

Fe2O3, max % - 6.0 - 6.5 - 

MgO, max % 6.0 6.0 6.0 6.0 6.0 

SO3, max % 

when C3A8% 3.5 not applicable 4.5 n.ap. n.ap. 

Loss on ignition 3.0 3.0 3.0 2.5 3.0 

Insoluble resid. 0.75 0.75 0.75 0.75 0.75 

C3S, max % - - - 35 - 

C2S, min % - - - 40 - 

C3A, max % - 8 - 7 5 

C4AF+C3A, - - - - 25 

max % 

% air in mortar 

min - 16 - 16 - 16 - - 

max 12 22 12 22 12 22 12 12 

Fineness, m²/g 

turbidimeter 160 160 160 160 - - 160 160 

air permeability 280 280 280 280 - - 280 280 

Autoclave exp. 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 

Compr. 

strength 

MPa 1 day - - - - 12.0 10.0 - - 

3 days 12.0 10.0 10.0 8.0 24.0 19.0 - 8.0 

7 days 19.0 16.0 17.0 14.0 - - 7.0 15.0 

28 days - - - - - - 17.0 21.0 

Gillmore setting 

minutes init.set 60 60 60 60 60 60 60 60 

final set 600 600 600 600 600 600 600 600 

Vicat setting 

minutes init.set 45 45 45 45 45 45 45 45 

final set 375 375 375 375 375 375 375 375 

For special applications, additional chemical and physical requirements are set, e.g. 

• Limits on C3A content for cement types III and III A for moderate (

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b) Provisions for blended cements in C 595 are as follows 

• Type IS - Portland Blast-Furnace Slag Cement (slag content 25÷70%) 

• Type IP - Portland-Pozzolan Cement (pozzolan content 15÷40%) 

• Type P - Portland-Pozzolan Cement with low early strength 

• Type S - Slag Cement (slag content > 70%) 

• Type I(PM) - Pozzolan-modified Portland Cement (pozzolan content < 15%) 

• Type I(SM) - Slag-modified Portland Cement (slag content < 25%) 

these types can be MS (moderate sulfate resistent), A (air entrained) or MH (moderate heat 

of hydration). 

Table 2a ASTM C595M - Specification for Blended Hydraulic Cement - 

Composition 

Cement type 

Clinker 

+ gypsum 

BF slag 

Pozzolan 

/ fly ash 

IS (ev. MS, A, MH) 30 - 75 25 - 70 

S (ev. A) < 30 > 70 

IP (ev. MS, A, MH) 60 - 85 * 15 - 40 

P (ev. MS, A, MH) 60 - 85 * 15 - 40 

I (PM) (ev. MS, A, MH) > 85 * < 15 

I (SM) (ev. MS, A, MH) > 75 < 25 

* These cements can be produced by blending pozzolan either with ordinary Portland cement 

or with an IS type cement. 

Table 2b 

ASTM C595M - Specification for Blended Hydraulic Cement - Chemical 

Requirements 

Cement type → 

I(SM), I(SM)-A, 

IS, IS-A 

S. S-A I(PM), I(PM)-A, 

P, PA, IP, IP-A 

MgO, max % - - 6.0 

SO3 , max % 3.0 4.0 4.0 

Sulfide sulfur, max % 2.0 2.0 - 

Insoluble resid., max % 1.0 1.0 - 

Loss on ignit., max % 3.0 4.0 5.0 

Water sol. alkali, max % - 0.03 - 


Cement 

Concrete 

Table 2c 

ASTM C595M - Specification for Blended Hydraulic Cement - Physical 

Requirements 

Cement type 

→ 

I(SM) 

I(PM) 

IS, IP 

same 

with 

air en. 

IS(MS) 

IP(MS) 

same 

with 

air en. 

S SA P PA 

Autoclave exp. 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 

A. contraction 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 

Vicat setting 

minutes initial 45 45 45 45 45 45 45 45 

hours final 7 7 7 7 7 7 7 7 

% air of mortar 12 19±3 12 19±3 12 19±3 12 19±3 

Compr.strengt 

h 

min. MPA 3 d 13.0 10.0 11.0 9.0 - - - - 

7 d 20.0 16.0 18.0 14.0 5.0 4.0 11.0 9.0 

28 d 25.0 20.0 25.0 20.0 11.0 9.0 21.0 18.0 

Heat of hydrat. 

kJ/kg max 7d 290 290 290 290 - - 250 250 

28 d 330 330 330 330 - - 290 290 

Water req. % - - - - - - 64 56 

Drying shrink. - - - - - - 0.15 0.15 

Mortar 

expans. 

max % 14 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 

d 

8 weeks 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 

Sulfate resist. 

max exp.180 d - - 0.10 0.10 - - - - 

c) An interesting example of a performance oriented standard is ASTM C 1157M. Here 

blended cement are classified according to their performance, with no restrictions on the 

composition of the cement or its constituents. 


Cement 

Concrete 

The specified cement types are based on specific requirements for general use (GU), high 

early strength (HE), resistance to sulfate attack (MS and HS), heat of hydration (MH and LH), 

low reactivity with alkali-reactive aggregates (R). 

Table 3 

ASTM C1157M - Performance Spec. for Blended Cement 

Cement type → GU HE MS HS MH LH 

Autoclave length change, max % 0.80 0.80 0.80 0.80 0.80 0.80 

Vicat setting time, minutes 

initial 45 45 45 45 45 45 

final 420 420 420 420 420 420 

% air of mortar to be specified on documents to customer 

Compressive strength, min MPa 

1 day - 10.0 - - - - 

3 days 10.0 17.0 10.0 5.0 5.0 - 

7 days 17.0 - 17.0 10.0 10.0 5.0 

28 days - - - 17.0 - 17.0 

Heat of hydration, max kJ/kg 

7 days - - - - 290 250 

28 days - - - - - 290 

Mortar bar exp. 14 days, max % 0.020 0.020 0.020 0.020 0.020 0.020 

Sulfate exp., max % 6 months - - 0.10 0.05 - - 

1 year - - - 0.10 - - 

Option R, low ASR reactivity 

expansion 14 days, max % 0.020 0.020 0.020 0.020 0.020 0.020 

expansion 56 days, max % 0.060 0.060 0.060 0.060 0.060 0.060 

Optional physical requirements 

Early stiffening, final penetration 

min % 50 50 50 50 50 50 

Compressive strength, min. MPa 

28 days 28.0 - 28.0 - 22.0 - 


Cement 

Concrete 

3.2 THE EUROPEAN STANDARD ENV 197-1 

This standard was issued in the early 90’s after some 25 years of drafting, with the aim at 

including in one and only specification all the cements produced all over Europe. It is clear 

that the extremely variable climatic, industrial and economic conditions of the continent were 

the main reason of the huge diversity of binders produced and consequently of the very 

tough job for the members of CEN to reach a reasonable compromise among member 

countries. 

The ENV 197-1 standard is divided in nine chapters, the most important are 

♦ chapter 4 “Constituents”, dealing with cement components; here some main 

characteristics of the materials to be used in cement production are set 

♦ chapter 5 “Cement types, composition and designation”, where the official names and 

abbreviations are described for every type of cement, according to its composition 

♦ chapter 6, 7, 8 “Mechanical-, Phisical-, Chemical requirements” setting limits for the main 

cement properties 

♦ chapter 9 “Conformity Criteria”, dealing with the procedures to apply for the autocontrol 

testing of cement and the subsequent evaluation of its conformity to the specifications. 

Description of cement components (constituents) in Chapter 4 is very accurate, complete 

and rigorous, including additional specifications (Table 5) that define the main component 

characteristics in order to assure their performance in cement. 

The ENV 197-1 standard recognizes and legitimates the use of some constituents that have 

a long tradition of use in many countries, but at the same time are not available in other 

areas (i.e. natural pozzolan, fly ash, burnt shale). There is absolute freedom, with the 

exception of Portland cement clinker as the only obligatory constituent, in the choice of 

materials to produce cements according to ENV 197-1, provided they comply with the 

requirements of Chapter 4. 

This freedom is reflected in Chapter 5 (Table 4), where cement compositions are reported. 

As many as 25 different types of cements can be produced, using one or more of the 

indicated constituents. 

It is worthwile noting that the relative amounts are in mass-% on the cement nucleus, that is 

without considering gypsum (since its amount in cement can vary according to purity and 

optimum gypsum content). Then, for each type of cement the industrial composition shall be 

calculated with the actual gypsum content. 

Mechanical, physical and chemical requirements are listed in Table 6 and 7. A significant 

difference in the strength classification is the subdivision of every main strength class into 

two subclasses, to differentiate rapid hardening cement from those with normal strength 

development. This makes the theoretical number of producible cements as high as 150 (25 

types x 6 classes)! 

Additionally, the upper limit for 28 day strength is also set. This is somewhat a marketing 

besides technical requirement, it has the advantage to force all producers to keep cement 

strengths (and quality) within a certain interval and at the same time protects against unfair 

competition. The drawback is, for some blended cements (high slag content, mainly), the 

serious difficulty to comply with both the minimum 2-day and the maximum 28-day strength 

limit, that is often exceeded. 


Cement 

Concrete 

The last chapter introduces a new criterion to evaluate conformity of cement, based on a 

continuous statistical control (autocontrol). 

Cements must fulfill 

• conformity criteria on single absolute values 

• statistical conformity criteria (according to variables or attributes) on characteristic 

limits. 

This means that for the main parameters, cement must conform to a minimum (or maximum) 

limit value, as it was previously provided by the standards, and also to a characteristic limit. 

All results over a six- or twelve month period are evaluated according to the mean value and 

standard deviation and calculated to yield a consumer’s risk lower than 5% (that is the risk 

that a defective lot is accepted as conforming the standard) for lower strength limits and 10% 

for the upper one. 

To make it simple, let’s consider the conformity for 28 day strength. According to ENV 197-1, 

the following equation shall apply 

x - k A s ≥ L (lower limit) as well as x + k A s ≥ U (upper limit) 

where L is the lower (resp. upper) strength limit at 28 days, s is the calculated standard 

deviation, k A is the acceptability constant (depending on the number of tested samples). 

Now if a cement of mean 28 day strength = 38.0 MPa is produced with s = 2.0 and tested 

over 110 samples/year (k A = 1.93 for L and 1.53 for U), the conformity equation for a 32.5 

MPa characteristic value will yield a result of 

x - k A s = 38.0 - 2.0 x 1.93 = 34.1 MPa, which is higher than 32.5 as well as 

x + k A s = 41.1 MPa which is lower than 52.5 then the cement is conforming the standard. 

But a value of s = 3.2 will yield 

x - k A s = 38.0 - 3.2 x 1.93 = 31.8 which is lower than 32.5; in this case the cement does not 

fulfill the standard specification set for minimum late strength. 

The following graphs will help to visualize the situation. The first one shows that a “good” 

cement, with low strength variability (s = 2) fulfill the requirements with an average 28-day 

strength of 36.4 MPa, while the other refers to a “bad” cement (s = 4) and the necessary 

average strength to fulfill specs is 40.2 MPa (3.8 MPa higher!). 

This approach is quite interesting and innovative, because it comes clear from the proposed 

example, that a consistent production, with low deviation, can allow for the production of a 

complying cement with lower mean strength values, that cannot be sufficient if the deviation 

is higher, thus forcing to raise the average strength to higher and more costly levels. 


Cement 

Concrete 

Figure 1 Conformity of a “good” cement (s = 2) 

60 

Compr. strength (MPa) 

55 

50 

45 

40 

35 

30 

25 

52.5 

32.5 

x - k . s > L 

a 

x + k . s < U 

a 

20 

0 1 2 3 4 5 6 7 

Standard deviation (s) 

Figure 2 Conformity of a “bad” cement (s = 4) 

60 

Compr. strength (MPa) 

55 

50 

45 

40 

35 

30 

25 

52.5 

32.5 

x - k . s > L 

a 

x + k . s < U 

a 

20 

0 1 2 3 4 5 6 7 

Standard deviation (s) 


Cement 

Concrete 

Table 4 

The ENV 197-1 specification on common cements - Cement types and 

composition 

Cement 

type 

I 

Designation Abbrev. Clinker GGBF slag Micro 

silica 

Portland 

Cement 

Natural 

pozzol. 

Industr. 

pozzol. 

Silic. 

fly ash 

Calcar. 

fly ash 

Burnt 

shale 

I 95-100 - - - - - - - 

Portland Slag II/A-S 80-94 6-20 - - - - - - 

Cement II/B-S 65-79 21-35 - - - - - - 

Portland MS 

Cem 

Portland 

Pozzol. 

II/A-D 90-94 - 6-10 - - - - - 

II/A-P 80-94 - - 6-20 - - - - 

II/B-P 65-79 - - 21-35 - - - - 

Cement II/A-Q 80-94 - - - 6-20 - - - 

II/B-Q 65-79 - - - 21-35 - - - 

II II/A-V 80-94 - - - - 6-20 - - 

Portland 

Ash 

Fly 

II/B-V 65-79 - - - - 21-35 - - 

Cement II/A-W 80-94 - - - - - 6-20 - 

Portland 

Burnt 

Shale 

Cement 

Portland 

Limest. 

II/B-W 65-79 - - - - - 21-35 - 

II/A-T 80-94 - - - - - - 6-20 

II/B-T 65-79 - - - - - - 21-35 

II/A-L 80-94 - - - - - - - 

Cement II/B-L 65-79 - - - - - - - 

Portland 

Compos 

Limest. Other 

constit 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

- 0-5 

6-20 0-5 

21-35 0-5 

II/A-M 80-94 

Cement II/B-M 65-79 

III/A 35-64 36-65 - - - - - - 

III Slag Cement III/B 20-34 66-80 - - - - - - 

III/C 5-19 81-95 - - - - - - 

- 0-5 

- 0-5 

- 0-5 

IV Pozzolanic IV/A 65-89 - - - - 0-5 

Cement IV/B 45-64 - - - - 0-5 

V Composite V/A 40-64 18-30 - - - - 0-5 

Cement V/B 20-39 31-50 - - - - 0-5 


Cement 

Concrete 

Table 5 

ENV 197-1 - Requirements for cement constituents 

Type of constituent Property Conformity Limit 

Clinker sum of silicates C3S + C2S > 2/3 of total 

ratio CaO / SiO2 > 2.0 % 

MgO content < 5.0 % 

Blast Furnace Slag glass content > 2/3 of total 

CaO + MgO + SiO2 

> 2/3 of total 

CaO + MgO / SiO2 > 1.0 

Fly ash loss on ignition < 5.0 % 

Siliceous fly ash reactive CaO < 5.0 % 

reactive SiO2 > 25 % 

Calcareous fly ash reactive SiO2 > 5 % 

28 d strength of ground material > 10 MPa 

expansion on a 30% blend < 10 mm 

Pozzolans reactive SiO2 > 25 % 

Burnt shale 28 d strength of ground material > 25 MPa 

expansion on a 30% blend < 10 mm 

Limestone CaCO3 content > 75 % 

clay content (methilene blue test) < 1.2 % 

total organic carbon (TOC) < 0.2 % 

Table 6 

ENV 197-1 - Mechanical and Physical Requirements 

Strength Compressive strength (N/mm² - MPa) Initial Expans. 

class Early strength Standard strength setting (mm) 

2 days 7 days 28 days time(min) 

32,5 - > 16 > 32,5 < 52,5 

32,5 R > 10 - > 60 

42,5 > 10 - > 42,5 < 62,5 < 10 

42,5 R > 20 - 

52,5 > 20 - > 52,5 - > 45 

52,5 R > 30 - 


Cement 

Concrete 

Table 7 

ENV 197-1 - Chemical Requirements 

Property Test refer. Cement type Strength class Requirement 

Loss on ignit. EN 196-2 CEM I All < 5.0 % 

CEM III 

Insol. residue EN 196-2 CEM I 

CEM III 

CEM I 

CEM II 

Sulfates SO3 EN 196-2 CEM IV 

CEM V 

CEM III 

All < 5.0 % 

32,5 - 32,5 R 

42,5 

< 3.5 % 

42,5 R 

52,5 - 52,5 R < 4.0 % 

All 

Chlorides EN 196-21 All All < 0.10 % 

Pozzolanicity EN 196-5 CEM IV All positive test 

After drafting for common cements, CEN is also preparing new specifications for “special 

cements”, such as sulfate resisting and low heat cements. The drafts are in an advanced 

stage and are likely to be distributed for approval by member States in 1998. 

3.3 THE AUSTRALIAN STANDARD AS 3972-1991 

This is a good example of how a standard can be drafted in a simple, clear and effective 

way. 

It consists of two pages only, where reference documents, materials and cements are listed 

and defined, as well as requirements, properties and dispatching conditions. 

All one need to know is contained in this astonishingly essential document. 

Cement types are defined as follows 

• type GP - general purpose Portland cement 

• type GB - general purpose blended cement 

while special purpose cements are 

• type HE - high early strength cement 

• type LH - low heat cement 

• type SR - sulfate resisting cement. 


Cement 

Concrete 

A blended cement should contain more than 5 % of mineral addition (fly ash, BF slag, or 

both). 

Specified properties are compiled in Table 8. 

Table 8 

AS 3972-1991 - Portland and blended cements 

Property 

Type Setting time Exp. SO3 Compr. strength Heat hydrat. C3A 

min. max. max max minimum MPa max. J/g max 

min h mm % 3 d 7 d 28 d 7 d 28 d % 

GP 45 10 5 3.5 - 25 40 - - - 

GB 45 10 5 3.5 - 15 30 - - - 

HE 45 10 5 3.5 20 30 - - - - 

LH 45 10 5 3.5 - 10 30 280 320 - 

SR 45 10 5 3.5 - 20 30 - - 5.0 

Additional properties such as 

• loss on ignition 

• fineness or fineness index 

• nature and proportion of materials in the cement 

• major oxide composition of the cement 

• chloride content, if exceeding 0.05 % 

can be provided by the manufacturer upon specific request from the purchaser. 


Cement 

Concrete 

3.4 Conclusion 

The importance of standards in our technical life and the present situation for cement have 

been highlighted. The expected trend for cement standards is represented in table 9. 

Table 9 

World trends in cement standards 

Object Past/present situation Trend 

Number of standardized 

cements 

Mineral components or 

additions in cement 

Few Increasing number of 

common and special 

cements 

Not allowed in OPC, limited 

use of blended cements 

Allowed in OPC, increased 

number of blended cements 

Strength Compressive and flexural Only compressive str. 

Compr. strength limit Minimum strength requir. Min. and max. stength 

Age of tests 1, 2, 3, 7, 28 days 2 and 28 days 

Standard mortar constant consistency, constant W/C ratio 

constant W/C ratio 

W/C ratio different in each country 0.5 

Setting time initial and final settiong t. initial setting time 

4. Standards for Mineral Components 

Mineral components or additions have always been used in the production of building 

materials. 

In ancient Greece and Rome blends of burnt lime and pozzolan were used for brickworking 

and building purposes. 

Nowadays the use of mineral additions has improved in quantity and quality. 

On one hand the available mineral components are quite extensively evaluated and utilized 

in cement manufacture, for production, cost-effectiveness and environmental purposes, on 

the other hand the advancement in technology of high performance concrete, in terms of 

ultra-high early strengths but also high durability, have benefited by the availability of these 

materials. 

Then the more sophisticated uses of mineral components require adequate standards to 

describe their properties and performance in cement and concrete. 

As a matter of fact, mineral components (and other mineral additions) can be mainly used as 

♦ cement constituents, in the production of blended or Portland modified cements 

♦ raw materials in concrete production, as value added products which impart additional 

characteristics to the cementitious conglomerate. 

Recent standardization has covered both of these aspects, and more is expected in the 

future. 


Cement 

Concrete 

Requirements set forth by standards dealing with cement production (see as an example 

Table 7 in previous chapter) are usually enclosed in the standard itself; they consider 

aspects of the chemical composition of mineral components and put sometimes also limits 

with respect to the hydraulic activity, the main responsibility on the effectiveness of the 

addition being left on the cement producer’s shoulders since he has to comply with the final 

product requirements. 

Standards on materials to be used as main concrete constituents are separate documents. 

They deal about the same parameters as for cement production, but they are mainly 

focussed on the impact that these characteristics will have on concrete. 

Some examples related to mineral components are reported 

♦ ASTM C 311 “Sampling and Testing Fly Ash or Natural Pozzolans for Use as a Mineral 

Admixture in Portland-Cement Concrete” 

♦ EN 450 “Fly Ash for Concrete” 

♦ ASTM C 989 “Specification for Ground Granulated Blast Furnace Slag for Use in 

Concrete and Mortar 

♦ ASTM C 1240 “Specification for Silica Fume for Use in Hydraulic Cement Concrete and 

Mortar. 

5. Concrete Standards 

5.1 Purpose 

The purpose of the concrete standards and specifications is to regulate the relations between 

the different parties involved in the activity of concrete construction. 

Besides the interest to regulate the interaction between the different parties, there is a 

supreme interest of the society to ensure that the constructions are stable, aesthetic and 

durable. A typical example are the antiseismic codes, which, although they lead to more 

costly structures, prevent enormous losses of human lives and goods in case of earthquakes 

compared to structures built in a normal way. 

Similarly to cement standards, the responsibility for the emission of the concrete standards 

varies a lot from country to country. For instance in Germany and Great Britain, this is the 

responsibility of the national standard entity (DIN and British Standards respectively), 

whereas in the United States and Switzerland, it is the task of a professional organisation 

(ACI (American Concrete Institute) and SIA (Society of Engineers and Architects) 

respectively). In other countries like Italy, it can also be the responsibility of the government 

through the Ministry of public works. 

5.2 Content of the Standards and Specifications 

It will be referred here exclusively to the aspects of concrete technology within the wider field 

of codes, standards and specifications, with a special emphasis on the corresponding 

prescriptions in use in the United States (ASTM, ACI) and in Europe (ENV 206). 

5.2.1 Quality of the Concrete Components 

In general, the concrete standards make reference to the respective standards for each of 

the ingredients (cement, aggregates, water, mineral and chemical admixtures). That is to say 

it is simply indicated that the components must satisfy the quality requirements established in 


Cement 

Concrete 

the mentioned standards. The relevant ASTM and EN standards for the concrete 

components cement, admixtures and aggregates are listed in the annex. 

5.2.2 Quality of Fresh Concrete 

The following properties of the fresh concrete are specified: 

• consistency/workability (always) 

• air content (when air is intentionally entrained) 

• temperature (in extreme climates) 

• density (for light weight or heavy concrete) 

• stiffening rate (in extreme climates or for slip forming) 

In general, the constructor specifies the consistency of the concrete adequate for the 

structural element to be concreted and for the available means of placing and compacting. 

The concrete producer has to deliver a material which complies with this consistency within a 

certain tolerance. For instance the ASTM standard C 94 for ready-mix concrete prescribes: 

Specified Slump 

Tolerance 

< 50 mm ± 15 mm 

50-100 mm ± 25 mm 

> 100 mm ± 40 mm 

With respect to the content of intentionally entrained air, the ACI recommends percentages 

which depend on the severity of exposure of the concrete and the maximum aggregate size. 

A higher severity and a lower maximum aggregate size correspond to higher percentages of 

air. The ASTM standard C 94 establishes a tolerance of ± 1.5% for the specified air content. 

5.2.3 Strength of Hardened Concrete 

The strength is the most important characteristic to be specified for the hardened concrete. In 

the past, it was common to specify the mean strength of the concrete, so that, if the average 

of the results of the specimens was equal or greater than the specified values, the strength 

requirement was considered as fulfilled. Based on this criterion, the following two series were 

equivalent, since both presented the same average (30 MPa): 

Series "A": 32, 28, 34, 29, 28, 30, 32, 28, 29, 30 

Series "B": 40, 27, 48, 30, 15, 30, 36, 20, 28, 26 

At simple view, it results that the series "A" is better than "B", because its values are more 

uniform (s = 2 MPa against s = 9 of the series "B"). That is to say, although both comply with 

the specified mean strength, a structure built with concrete "A" will be safer from the 

structural point of view than if it is built with concrete "B", as the latter presents a strength 

result which is only the half of the specified value. 


Cement 

Concrete 

As already mentioned for cement, standards and specifications take into account the 

variability of concrete and apply the criterion of fractiles to specify the concrete strength. The 

specified strength corresponds to a fractile related to a certain probability, which means that 

the designer of the structure accepts that a certain percentage of the produced concrete is 

"defective". The allowed percentage of "defectives" varies according to the country (it has to 

be mentioned that the percentage has not necessarily to be related to the safety of the 

structures): 

Percentage p 

Country 

2 % Switzerland 

5 % Europe 

10 % United States 

20 % United States (massive concrete) 

Assuming that the distribution of strength values follows the law of Gauss, the fractile x P is 

calculated as 

x P = x M - z P . s 

where z P is a function of the percentage of "defectives" p. We can see that the mean x M as 

well as the standard deviation s participate in this criterion, which explains its universal 

acceptation. 

This principle has now to be applied for the design of the concrete mixes. If we have 

specified a certain strength that we will denote f' C (which corresponds to the fractile x P for a 

certain percentage of "defectives"), we have to design our mix with a certain margin taking 

into account the expected variability s E in the production process. That is to say we have to 

design the mix for a certain mean design strength f' D which will be equal to: 

f' D = f' C + margin = f' C + z P 

. sE 

It is evident that the producer which elaborates the concrete in a more uniform manner (lower 

s E ) will be able to design his mix for a lower strength and therefore more economically. 

5.2.4 Durability of Concrete 

The traditional criterion to guarantee the durability of the structures against attack of the 

environment has been the establishment of limits with respect to concrete composition. For 

instance ENV 206 and ACI code 318 for reinforced concrete establish limits regarding the 

w/c-ratio of the concrete in function of the exposure condition to which the structure will be 

submitted, trying to control concrete permeability to improve its durability against aggressive 

agents. 

The fundamental problem of such type of specification is that it is often omitted at the 

moment of ordering the concrete and anyway its interpretation is unclear (are they mean 

values, absolute maximums, fractiles?). Moreover, its compliance is very difficult to verify in 

practice (how is the w/c-ratio of a concrete determined?). The same criticism can be made 

with respect to the project of the European Standards, where, apart from the maximum w/cratio, 

also a minimum cement content is specified. 

A more practical criteria is the one established in the Australian Standards, where, instead of 

fixing limits for the concrete composition, a minimum strength is specified according to the 


Cement 

Concrete 

type of exposure to which the structure will be submitted. The advantage of this criterion is 

that it is more easy to interpret and to verify its compliance in practice. 

5.3 The European Standard ENV 206 

Most discussions on concrete standards are concentrated on the issue of concrete durability, 

and in this context the specifications on cement content, water cement ratio, chloride content 

and alkali aggregate reaction. 

The durability aspects are here discussed in connection with the new ENV 206 draft 

„Concrete. Performance, production, placing and compliance criteria“, which was issued as a 

prestandard in 1989. The development of this standard has a similar history to the EN 

cement standard; the CEN Committee TC 94 started work in 1981, and the present draft is 

far from being the final version. Nevertheless, it is a good review of the present state of 

knowledge on the topic, comprising a consensus of expert opinions in Europe. 

ENV 206 should cover concrete in general; for all types of concrete - site, precast and ready 

mixed concrete, plain, reinforced and prestressed concrete. For special purposes, however, 

additional specifications may be needed, and for these reference is made to the individual 

national standards. The standard also makes reference to other European standards as 

regards types of cements, aggregates, mineral and chemical admixtures. 

5.3.1 Cement Content and Durability 

The minimum cement content in steel reinforced concrete is specified according to 

environmental conditions and type of concrete structure; it varies between 260 to 300 kg/m 3 , 

as shown in tables 10 and 11. 


Cement 

Concrete 

Table 10 

Exposure Classes related to Environmental Conditions 

Exposure Class Examples of Environmental 

Conditions 

1 Dry environment interior of dwellings or offices 1) 

2 Humid 

environment 

a 

without frost 

b 

with frost 

3 Humid environment with frost 

and de-icing agents 

4 Seawater 

environment 

a 

without frost 

b 

with frost 

- interior of buildings where humidity is 

high (e.g. laundries) 

- exterior components 

- components in non-aggressive soil 

and/or water 

- exterior components exposed to frost 

- components in non-aggressive soil 

and/or water and exposed to frost 

- interior components where the 

humidity is high and exposed to frost 

interior and exterior components 

exposed to frost and de-icing agents 

- components completely or partially 

submerged in seawater or in the 

splash zone 

- components in saturated salt air 

(coastal area) 

- components partially submerged in 

seawater or in the splash zone and 

exposed to frost 

- components in saturated salt air and 

exposed to frost 

The following classes may occur alone or in combination with the above 

classes: 

5 Aggressive a - slightly aggressive chemical 

environment 2) - aggressive industrial atmosphere 

chemical 

environment (gas, liquid or solid) 

b moderately aggressive chemical 

environment (gas liquid or solid) 

c 

highly aggressive chemical environment 

(gas, liquid or solid) 

1) This exposure class is valid only as long as during construction the structure or some of 

its components is not exposed to more severe conditions over a prolonged period of time 

2) Chemically aggressive environments are classified in ISO 9690. The following equivalent 

exposure conditions may be used: 

∗ 

∗ 

∗ 

Exposure class 5a: ISO classification A1G, A1L, A1S 

Exposure class 5b: ISO classification A2G, A2L, A2S 

Exposure class 5c: ISO classification A3G, A3L, A3S 


Cement 

Concrete 

Table 11 

Durability Requirements related to Environmental Exposure 

Requirements Exposure Class according to Table 2 

Max. w/c ratio for 2) 

- plain concrete - 0.70 

1 2a 2b 3 4a 4b 5a 5b 5c 1) 

- reinforced concrete 0.65 0.60 0.55 0.50 0.55 0.50 0.55 0.50 0.45 

- prestressed concrete 0.60 0.60 

Min. cement content 2) 

in kg/m 3 for 

- plain concrete 150 200 200 200 

- reinforced concrete 260 280 280 300 300 300 280 300 300 

4) 4) 4) 

- - yes yes - yes - - - 

- prestressed concrete 300 300 300 300 

Min. air content of 

aggregate size of 3) 

fresh concrete in % for 

nominal max 

- 32 mm - - 4 4 - 4 - - - 

- 16 mm - - 5 5 - 5 - - - 

- 8 mm - - 6 6 - 6 - - - 

Frost resistant 

aggregates 6) 

Impermeable concrete 

according to clause 

7.3.1.5 

Types of cement for 

plain and reinforced 

concrete according to 

EN 197 

- - yes yes yes yes yes yes yes 

sulfate resisting 

cement 5) for sulfate 

contents 

> 500 mg/kg in water 

> 3000 mg/kg in soil 

These values of w/c ratio and cement content are based on cement 

where there is long experience in many countries. However at the 

time of drafting this pre-standard experience with some conditions in 

some countries. Therefore during the life of this pre-standard, 

particularly for exposure classes 2b, 3, 4b the choice of the type of 

cement and its composition should follow the national standard or 

regulations valid in the place of use of the concrete. Alternatively the 

suitability for use of the cements may be proved by testing the 

concrete under the intended conditions of use. 

Additionally cement CEI may be used generally for prestressed 

concrete. Other types of cement may be used if experience with 

these types is available and the application is allowed by the national 

standards or regulations valid in the place of use of the concrete. 


Cement 

Concrete 

1) In addition, the concrete shall be protected against direct contact with the aggressive 

media by coatings unless for particular cases such protection is considered unnecessary. 

2) For minimum cement content and maximum water/cement ratio laid down in this standard 

only cement listed in clause 4.1 shall be taken into account. When pozzolanic or latent 

hydraulic additions are added to the mix, national standards or regulations, valid in the 

place of use of the concrete, may state if and how the minimum or maximum values 

respectively are allowed to be modified. 

3) With a spacing factor of the entrained air void system < 0.20 mm measured on the 

hardened concrete. 

4) In cases where the degree of saturation is high for prolonged periods of time. Other 

values or measures may apply if the concrete is tested and documented to have 

adequate frost resistance according to the national standards or regulations valid in the 

place of use of the concrete. 

5) The sulphate resistance of the cement shall be judged on the basis of national standards 

or regulations valid in the place of use of the concrete. 

6) Assessed against the national standards or regulations valid in the place of use of the 

concrete. 

These requirements reflect the generally accepted opinion that the durability of steel 

reinforced concrete is governed mainly by its porosity and thus strongly affected by the w/c 

ratio and cement content. 

An important feature of the standard is the differentiation of the cement content according to 

the severity of its exposure. This allows the concrete producer to use their skills and 

knowledge in order to design concrete mixes more economically. A prerequisite of this 

differentiation is, of course, that information on the different conditions to which the specific 

concrete job is subjected is available. 

The prescription of cement content and w/c ratio has some problems: It is difficult to 

determine both of them in fresh and hardened concrete for control purposes. Furthermore, 

concrete durability depends not only on cement content as a w/c ratio, it is affected as well 

by the care taken in its transport, placing, compacting and curing. Therefore, it is 

indispensable that the quality of concrete in the construction after placing and curing is 

tested. We know that the porosity of a concrete governs nearly all aspects of durability. 

Therefore, investigations are under way to introduce a test method enabling the 

measurement of the porosity of the concrete from specimens taken from the hardened 

concrete structure. It consists of measuring the amount of gas which flows through the pore 

system of the concrete specimen in a unity of time. By so measuring the porosity, not only is 

care taken by the concrete producer, but also that of the contractor placing, compacting and 

curing the concrete is checked. 

An alternative way of testing the porosity and additional aspects of the concrete microstructure 

is the microscopical examination of very small specimens. It is very useful for a 

qualitative inspection of concrete quality, however, it seems difficult to apply this method for a 

quantitative assessment in the framework of a standard. 


Cement 

Concrete 

5.3.2 Chloride Content 

The maximum chloride content in concrete permitted in plain, reinforced and prestressed 

concrete is shown in table 12. 

Table 12 

Maximum Chloride Content of Concrete 

Concrete 

C1- by Mass of Cement 

Plain concrete 1% 

Reinforced concrete 0.4% 

Prestressed concrete 0.2% 

The relatively high content of chloride permitted in steel reinforced concrete, reflects the 

results of recent investigation, which show that no corrosion of steel is expected at a chloride 

content of 0.4% by mass of cement. Similar soft limits are prescribed in the ACI standards as 

shown in table 13. 

Table 13 Chloride Content in Concrete, ACI 318-83 

Maximum water-soluble chloride ion concentrations in hardened 

concrete at an age of 28 days contributed from the ingredients 

including water, aggregates, cementitious materials and admixtures 

Type of Member 

Limit 

(by mass 

of concrete) 

Prestressed concrete 0.06 

Reinforced concrete exposed to chloride in service 0.15 

Reinforced concrete that will be dry or protected from moisture 1.00 

in service 

Other reinforced concrete construction 0.30 

5.3.3 Alkali Aggregate Reaction 

To prevent deterioration of concrete due to alkali aggregate reaction, it is recommended to 

apply one or more of the following measures: 

♦ Limit the total alkali content of the concrete mix 

♦ Use a cement with a low effective alkali content 

♦ Change the aggregates 

♦ Limit the degree of saturation of the concrete e.g. by impermeable membranes 

Unfortunately no mention is made of the effective measures of using blended cements or 

mineral admixtures. 

5.3.4 Maintenance 

Finally, the author would like to point out one serious deficiency of concrete standards; it is 

the lack of specifications on maintenance of concrete. This is becoming recognized as a gap 

and attempts are being made to bridge it. Of course this means turning away from the 

opinion the cement producers have frequently promoted in the past, that concrete need no 

maintenance whatsoever. 


Cement 

Concrete 

5.4 Referenced documents 

5.4.1 Relevant ASTM Standards for Concrete Components 

5.4.1.1 CEMENT 

C 150 

C 595 

Specification for Portland Cement 

Specification for Blended Hydraulic Cements 

C 1157 Performance Specifications for blended Hydraulic Cements 

5.4.1.2 ADMIXTURES 

C 260 

C 494 

Specification for Air-Entraining Admixtures for Concrete 

Specification for Chemical Admixtures for Concrete 

C 618 Specification for Fly Ash and raw or Calcined Natural Pozzolan for Use as Mineral 

Admixture in Portland Cement Concrete 

5.4.1.3 AGGREGATE 

C 33 Specification for Concrete Aggregates 

C 330 

C 331 

C 332 

C 637 

Specification for Lightweight Aggregates for Structural Concrete 

Specification for Lightweight Aggregates for Concrete Masonry Units 

Specification for Lightweight Aggregates for Insulating Concrete 

Specification for Aggregates for Radiation-Shielding Concrete 

5.4.2 Relevant EN Standards for Concrete Components 

5.4.2.1 CEMENT 

ENV 197-1 Common Cement 

ENV 197-X Low-heat Cement 

ENV 197-Y Sulfate resisting Cement 

5.4.2.2 ADMIXTURES 

EN 480 Admixtures for Concrete, Mortar and Grout. Test Methods 

EN 934 Admixtures for Concrete, Mortar and Grout 

5.4.2.3 AGGREGATES 

EN 932 Tests for General Properties of Aggregates 

EN 933 Tests for Geometrical Properties of Aggregates 

EN 1097 Tests for Mechanical and Physical Properties of Aggregates 

EN 1367 Tests for Thermal and Weathering Properties of Aggregates 

EN 1744 Tests for Chemical Properties of Aggregates 


Cement 

Concrete 

Concrete - Contents 

Chapter No. 

1. CONCRETE MAIN COMPONENTS................................................................................. 2 

2. FRESH AND HARDENED CONCRETE ........................................................................ 33 

3. CONCRETE MIX DESIGN ............................................................................................. 68 

4. REDUCTION IN MATERIALS COSTS........................................................................... 85 

5. CONCRETE ADMIXTURES........................................................................................... 99 

6. CONCRETE PRODUCTION PRACTICES................................................................... 114 

7. CONCRETE SHRINKAGE ........................................................................................... 135 

8. CONCRETE DURABILITY........................................................................................... 157 

9. ALKALI-AGGREGATE REACTIONS IN CONCRETE ................................................ 168 

10. SELF-COMPACTING CONCRETE.............................................................................. 180 

Additional Papers 

CONCRETE TECHNOLOGY ............................................................................................. 180 

DURABLE HIGH-PERFORMANCE CONCRETE.............................................................. 216 

Course for Cement Applications - 2005 Concrete Section - Page 1 of 235

Cement 

Concrete 

Concrete Main Components 

1. MAIN COMPONENTS OF CONCRETE ............................................................................... 3 

1.1 Definition of concrete.................................................................................................. 3 

1.2 Cement ....................................................................................................................... 3 

1.3 Aggregates ................................................................................................................. 4 

1.3.1 Aggregates from natural sources ................................................................. 4 

1.3.2 Classification ................................................................................................ 6 

1.3.3 Chemical properties ..................................................................................... 9 

1.3.4 Physical properties....................................................................................... 9 

1.3.5 The grading ................................................................................................ 12 

1.3.6 Alternative aggregates ............................................................................... 16 

1.4 Admixtures................................................................................................................ 18 

1.4.1 Workability agents...................................................................................... 19 

1.4.2 Air-entraining agents .................................................................................. 23 

1.4.3 Agents affecting setting and hardening...................................................... 25 

1.4.4 Other admixtures........................................................................................ 27 

1.5 Mixing and curing water for concrete........................................................................ 28 

1.5.1 Introduction ................................................................................................ 28 

1.5.2 Effect of impurities...................................................................................... 29 

1.5.3 Effects of algae on air content and strength............................................... 30 

1.5.4 Curing water............................................................................................... 30 

2. LITERATURE FOR ADMIXTURES AND MIXING WATER................................................ 31 

3. APPENDICES ..................................................................................................................... 31 

3.1 REFERENCES ......................................................................................................... 31 

3.2 Relevant ASTM Standards ....................................................................................... 32 

3.2.1 Aggregate................................................................................................... 32 


Cement 

Concrete 

1 Main Components of Concrete 

1.1 Definition of concrete 

Concrete is a composite material 

that consists of aggregate (gravel + sand), 

cement and water 

and frequently admixtures and/ or additives. 

The aggregate consists of a conglomerate of generally different large grains, mostly natural 

rocks. In particular cases also of waste wood, polystyrene or metals (waste steel or other). 

As binders hydraulic materials are used, generally ordinary Portland cement. In special 

cases asphaltic materials or artificial resin will be applied. 

Aggregates are generally designated as either fine (sand: 0.025 to app. 5 mm) or coarse 

(gravel: from app. 5 to 32 mm or larger). A 'concrete' with sand only is named mortar. 

The cement paste coats the particles of aggregate and fills the spaces between them. While 

fresh, the cement paste also provides the lubrication that reduces the friction between the 

aggregate particles and imparts workability to the fresh mix. When hardened, the paste (now 

called cement stone) binds together the particles of aggregate. 

The following figure shows the 

SYSTEM: Binder + Water + Aggregate = Concrete 

General Case 

Special Case 

Concrete = Filler + Binder 

OPC concrete = (Gravel + Sand) 

aggregate 

+ OPC paste 

Mortar = Sand + OPC paste 

OPC paste = OPC + Water 

1.2 Cement 

The most important component of concrete, the cement, has been treated in detail in a 

separate chapter. 


Cement 

Concrete 

1.3 Aggregates 

1.3.1 Aggregates from natural sources 

Definition 

Natural aggregates are a mixture of uncrushed and/or crushed rocks and minerals. It 

consists of particles of different (or sometimes approx. equal) sizes and are used with a 

binder (cement) and water to produce concrete or mortar [1]. 

General 

The mineralogical, physical and chemical characteristics of rocks are determined mainly by 

the events of their geological history. A knowledge of the ways in which rocks are formed, 

and of the various natural processes (whereby their original characteristics are altered) may 

therefore lead to a better understanding of those intrinsic properties which determine the 

suitability of a rock as a source of concrete aggregate. 

Rock classification according to their formation: 

♦ Igneous rocks 

♦ Sedimentary rocks 

♦ Metamorphic rocks 

Igneous rocks 

Igneous rocks are those which are formed by the solidification of molten masses, and many 

of their characteristics are determined by the rate and condition of cooling. Extruded volcanic 

rocks, i.e. those which have been ejected on the earth's surface, are cooled very rapidly, so 

that crystallisation of the component minerals is generally only partly effected, and the 

resulting rock consists of a mixture of crystalline ingredients and glassy matter. 

On the other hand rocks of the intruded igneous type, i.e. those which are formed from 

molten rock which has been intruded into overlying rock masses to form sills (a tabular 

intrusion of the surrounding rock), laccoliths (a concordant intrusion that has domed the 

overlying rocks) and dikes (rock solidification as a tabular body in a vertical fissure) etc. have 

been allowed to cool slowly, so that all the several compounds of the rock mass have had 

time to become thoroughly crystallised [8, 9]. 

The igneous rocks are the primary rocks and from these all the other rocks are ultimately 

derived. The mineral constituents of igneous rocks have been classified as follows: 


Cement 

Concrete 

Table 1: 

Minerals of igneous rocks 

Feldapatic silicates 

Orthoclase 

Plagioclase 

Leucite 

Ferromagnesian silicates 

Pyroxene 

Amphibole 

Biotite 

Olivine 

Free silica 

Quartz 

Tridymite 

Opal 

Accessory minerals 

Magnetite 

Ilmenite 

Haematite 

Apatite 

Sedimentary rocks 

Sedimentary rocks are derived from the chemical or mechanical breakdown of older rocks. 

The fragments resulting from such disintegration accumulate in deposits, for the most part 

under water, and the particles may be cemented together by the deposition of other 

siliceous, calcareous, argillaceous or ferruginous materials to form a dense mass. 

Chemical precipitates are crystalline, but by far the greater proportion of sedimentary rocks 

are made up of fragments of all sizes of earlier rocks. As in the case of sand or gravel beds, 

the fragments may lie loosely together, or may be firmly cemented as a compact material. 

The fragments of the older rocks may be sharply angular, but as they are often transported 

by wind or by water or by glacier for considerable distances, attrition may cause them to 

become smoothly rounded in their passage to the final deposit. 

As a result of their mode of deposition, the structure of sedimentary rocks is almost invariably 

stratified, and is essentially different from that of igneous rocks. Glacial deposits or coral 

reefs are not stratified and in this respect differs from other rocks of this class. 

Due to the geological and climatological changes, sudden radical changes often occur in the 

nature of the material being deposited. For this reason limestone are frequently interbedded 

with shale, sandstone with siltstones and quartzite with dolomite [3]. 

Metamorphic rocks 

Metamorphic rocks are those resulting from the alteration in place of pre-existing 

sedimentary or igneous rocks. Such alteration is brought about by the application of high 

temperatures and/ or pressures to the rock mass. 

A large group of rocks in this class is characterised by foliated structure, which is not to be 

confused with the stratification of sedimentary rocks nor with the flow banding of some lava, 

but which is the result of the segregation of one or more of the constituents minerals and 

their reorientation in form of parallel plates. 

Metamorphic rocks vary greatly both in structure (the attitude and relative position of the rock 

masses of an area) and in texture (the general appearance of a rock, e.g. the size, shape, 

and arrangement of the constituent elements). Where the rock has been formed under high 

temperature and pressure, an equigranular texture and a massive internal structure results 

and lend great strength and toughness to the rock. Such rocks include many hornfelses and 

quartzites. 


Cement 

Concrete 

1.3.2 Classification 

From the petrologic view of point the aggregates, whether crushed or naturally reduced in 

size, can be divided into several groups of rocks having common characteristics. The group 

classification does not imply suitability of any aggregate for concrete-making: unsuitable 

material can be found in any group, although some groups tend to have a better record than 

others. 

Table 2: Classification of natural aggregates according to rock type [4]. 

Basalt Group Flint Group Gabbro Group 

Andesite Chert Basic Diorite 

Basalt Flint Basic Gneiss 

Basic Porphyrites Hornstone Gabbro 

Dolerites 

Hornblende-rock 

Spilite 

Norite 

Serpentine 

Granite group Gritstone group Hornfels group 

Gneiss Arkose Contact-altered rocks 

Granite Greywacke (all kinds except marble) 

Granulite 

Grit 

Pegmatite 

Sandstone 

Syenite 

Tuff 

Pophyry Group Limestone group Quartzite group 

Aplite Dolomite Ganister 

Felsite Limestone Quartzitic sandstone 

Granophyre Marble Re-crystallized quartzite 

Porphyry 

Rhyolite 

Trachyte 

Schist group 

Phyllite 

Schist 

Slate 

All severely shared rocks 


Cement 

Concrete 

Figure 1: 

Classification according other parameters: 

According to type of particle 

Naturally granular 

Crushed 

According to the origin of the 

Igneous rock 

Sedimentary rock 

Metamorphic rock 


Cement 

Concrete 

According to particle size 

Fine Sand Gravel Coarse 

The particle dispersion limits are 

indicated in national standards 

According to particle characteristics 

Surface texture 

General characteristics 

Smooth 

Moderately 

rough 

Rough 

Weathered 

Flaky 

Healthy 

Shape 

Compact 

Flat 

Long 

Rounded or angular 


Cement 

Concrete 

1.3.3 Chemical properties 

While it is desirable that the aggregate should as far as possible be chemically inert, many 

natural aggregates contain substances which are deleterious in concrete. Substances 

considered chemically deleterious may be broadly classified into five groups: 

Group 1: 

Substances soluble in water, which may be leached out of the aggregate thereby 

weakening it or promoting efflorescence in the concrete, e.g. common salt. 

Group 2: 

Soluble substances, or substances which become soluble in the cement matrix, which may 

interfere with the normal hydration of the cement, e.g. humid acid. 

Group 3: 

Substances which react with the cement destroying its properties, e.g. sodium sulphate. 

Group 4: 

Substances which may react with the alkali constituents of the cement, e.g. opal (AAR, 

Alkali-Aggregate Reaction). 

Group 5: 

Substances which may cause corrosion of reinforcing steel, e.g. common salt. 

1.3.4 Physical properties 

Perhaps the most important concept developed from research is that the aggregate must be 

studied not only in its relation to the hardened cement paste, i.e. as a component of 

concrete, but in relation to the environment of the concrete during its service life. With this 

concept in mind, the physical properties of natural stone aggregates may be considered in 

terms of following factors: 

Table 3: 

Properties of rocks 

Rock Type 

Relative 

density 

[kg/m 3 ] 

Various properties 

Water 

Absorption 

[Vol. %] 

Compres 

-sion str. 

[MPa] 

10%- 

Crushing 

value [kN] 

Strength Properties 

Modulus 

of rupture 

[MPa] 

Modulus of 

elasticity 

[GPa] 

Shear 

strength 

[MPa] 

Andesite 2,7 - 2,9 0,4 - 0,5 500 - 540 450 -- 80 - 110 -- 

Basalt 2,8 - 3,0 0,1 - 0,3 190 - 470 340 14 - 24 49 - 98 -- 

Dolerite 2,8 - 3,1 0,1 - 0,7 160 - 375 180 - 340 14 -24 60 - 105 -- 

Dolomite 2,7 - 2,9 0,1 - 0,3 200 - 380 130 - 180 -- 100 - 130 -- 

Felsite -- 0,2 - 1,5 360 - 450 230 - 380 -- 70 - 90 -- 

Granite 2,6 - 2,8 0,2 - ,5 70 - 325 120 - 220 0 - 20 14 - 70 14 - 30 

Hornfels 2,6 - 2,8 -- -- 140 - 260 -- -- -- 

Limestone 2,6 - 2,9 0,2 - 0,6 20 - 240 180 4 - 15 21 - 71 8 - 21 

Marble 2,6 - 2,9 0,2 - 0,6 20 - 240 -- 4 - 24 48 - 96 9 - 45 

Quartzite 2,6 - 2,8 0,2 - 0,6 105 - 480 160 - 280 12 - 24 64 - 86 -- 

Rhyolite 2,6 - 2,8 -- 180 - 530 210 - 290 -- -- -- 

Sandstone 2,5 - 2,7 0,2 - 0,9 10 - 255 50 - 280 3 - 14 14 - 55 2 - 21 

Syenite 2,6 - 2,7 0,4 - 1.5 95 - 445 -- -- 55 - 72 -- 


Cement 

Concrete 

Strength 

The compressive strength of cubical specimens of natural stone from which acceptable 

aggregate is derived, normally varies from about 70 to 400 MPa, while individual results as 

high as 540 MPa have been recorded [5]. 

With a wide range there appears to be only a poor correlation between the compressive 

strength of the aggregate and the flexural or compressive strength of the concrete. 

As an index of overall quality the "10 % fines aggregate crushing value" or 10 % FACT value 

of coarse aggregates is useful (BS 812). However, it must be repeated that the usefulness of 

these tests is confined to a general assessment of quality and to the establishment of 

acceptance limits. New researches by Davis and Alexander have, however, shown a 

relationship between the aggregate type and the properties of concrete [6]. 

Elasticity 

The modulus of Elasticity of concrete depends to a considerable degree on that of the 

aggregate from which it is made. The flexural strength of concrete is also depending on this 

property of the aggregate, and the use of an aggregate having a high elastic modulus will 

usually result in a concrete of high flexural strength, other factors being equal [7]. 

The drying shrinkage of concrete is reduced by the use of aggregate having a high elastic 

modulus. Low shrinkage, induced by the use of rigid aggregates may be undesirable as the 

restraint provided by the aggregate increases the cracking tendency of the paste, thereby 

reducing the durability of the concrete. 

It would appear on balance that the reduction in durability resulting from the use of aggregate 

of high elastic modulus would in most cases more than offset any advantages which may be 

gained thereby. 

Porosity 

Many authorities consider that the size, abundance and continuity of pores in a rock particle 

are its most important physical properties. It is considered that the size and nature of the 

pores affect the physical strength of the aggregate, and control water absorption and 

permeability, thereby determining the durability of the aggregate in regard to freezing and 

thawing, and its resistance to chemical attack. 

It has been previously pointed out that the strength of the aggregate over a wide range 

cannot be considered as an important factor. Furthermore, in tropic countries a high 

resistance of freezing and thawing is not often an important quality of concrete. This property 

should, however, be considered where impermeability or high resistance of chemical attack 

are important features of the construction. Sandstone and shale show an average porosity of 

18 to 19 %, some limestone types 8 % and quality rocks 1 to 3 %. Individual results may be 

much higher [3]. 

Thermal expansion 

In recent years it has come to be appreciated that the deterioration of concrete structures 

may be significantly affected by differences between the coefficients of thermal expansion of 

aggregate and the cement matrix in which it is embedded. In particular, the use of an 

aggregate of very low coefficient of expansion may lead to disintegration of the concrete. As 

the temperature of concrete, made with such an aggregate is lowered, the cement paste 

tends to contract more than the aggregate, with the result that tensile stresses are set up in 

the former, which may result in cracking. 


Cement 

Concrete 

Bond characteristics 

Perhaps one of the most important attributes of a concrete aggregate is its capacity for 

bonding strongly with cement paste. This factor has a significant influence on the flexural 

strength [7]. 

In a wider field the word "surface texture" should be replaced by "bond characteristics". The 

latter term embraces not only surface texture, but the extent to which cement paste can 

penetrate into pores are surface depressions, the angularity of planes of fracture, the friable 

of the surface, and the presence or absence of loosely bonded or friable coatings. 

The effect of bond characteristics, while sufficiently significant in the medium strength range 

of mixes, becomes much more pronounced in the case of high-strength concretes. 

Particle shape and surface texture 

The shape of aggregate particles in both sand and stone, is one of the most significant 

factors affecting the behaviour of a concrete mix. Concrete water demand and water 

requirement on the design of concrete mixes, are strongly influenced by the shape of 

aggregate. Spherical, cubical or chunky shapes produce concrete having lower water 

demand than particles that are elongated or flaky. 

Surface texture of the grains also affects water demand, although to a lesser extent than 

shape. Rough textures increase water demand due to greater surface area and to increase 

friction and mechanical interlock of the particles. 

It seems that the shape and surface texture of aggregate influence considerably the strength 

of concrete. The flexural strength is more affected than the compressive strength Some data 

of Kaplan's research [7] are reproduced in the following table, but this gives more than an 

indication of the type of influence. 

Table 4: 

Effect of aggregate properties 

Relative effect of aggregate properties 

Property of concrete Shape Surface Texture Modulus of 

Elasticity 

Flexural strength 31 % 26 % 43 % 

Compressive strength 22 % 44 % 34 % 

Thermal properties 

Thermal properties which may be of significance are: 

• specific heat (or heat capacity) 

• thermal conductivity 

• thermal diffusivity 

All these properties are significant in the design of radiation shielding for nuclear power 

plants and in estimating loads on air-conditioning plant for buildings. 

Resistance to abrasion 

This is of significance in the choice of aggregate for pavements, industrial floors, channels, 

conveying abrasive materials and for certain type of silos. 


Cement 

Concrete 

Soundness 

The sulphate soundness test (ASTM, C 88 and SABS 1083) is not highly significant but 

provides a rough indication of the durability of an aggregate when subjected to expected 

environmental conditions. There is no evidence available to suggest that the mechanism of 

disruption of the test can be directly correlated with performance of an aggregate when 

subjected to these conditions. For this reason it is important that when an aggregate is to be 

evaluated on the basis of this test, it should be done by comparison with an aggregate of 

similar mineralogical composition and geological history and which has proved to be 

satisfactory in practice. 

1.3.5 The grading 

The grading of an aggregate refers to the distribution of particles of various sizes, and is 

determined by passing a representative sample through a series of standard sieves. 

Concrete aggregates are divided into two categories of fine aggregate or sand and coarse 

aggregate or stone. The boundary between these two is the 4 mm sieve but a fine aggregate 

may contain a small proportion of oversized particles and coarse aggregates may have some 

undersized material and still comply with the definition. 

The German standard DIN 1045 sieves for fine and coarse aggregates are: 

0.25 - 0.50 - 1.0 - 2.0 - 4.0 

8.0 - 16.0 - 31.5 - 63.0 - mm 

The sizes of the openings in the consecutive sieves are related by a constant ratio, the clear 

opening of each sieve size being twice or nearly twice that of the next smaller size. 

Fineness modulus 

The grading analysis provides data from which the fineness or coarseness of aggregate can 

be judged. The measure of fineness or coarseness is expressed in terms of an index known 

as the fineness modulus or FM. This is defined as an empirical factor obtained by adding the 

total percentages of material retained on each of the standard sieve sizes, except this 

amount smaller than 0,25 mm, and dividing the sum by 100. An example is given in the 

following table: 

Table 5: 

Determination of fineness modulus 

Sieve size 

[mm] 

Mass retained on 

sieve [g] 

Mass retained on 

sieve [wt-%] 

Total retained on 

sieve [wt-%]* 

Total passing on 

sieve [wt-%] 

31,5

Cement 

Concrete 

The FM is an index of the material, that is, a measure of the average particle size based on 

purely empirical classification. But the index in itself does not describe the grading. The FM 

indicates whether a material is fine, medium or coarse. A very fine aggregate grading with a 

maximum grain size of 31,5 mm is one having a modulus of 3,30 or less but in general run 

up to about 4.0. Medium aggregates are those with FM from 4.0 to 5.0 while coarse 

aggregates have higher fineness modulus (> 5.5). 

Grading of sand 

While the grading of a sand has a relatively minor effect on water demand, it has a major 

influence on the workability, cohesiveness and bleeding properties of concrete in its plastic 

state. Experience gained over many years has shown that the proportions of sand passing 

the 0.090, 0.125 and 0.25-mm sieves have the greatest effect on the properties of the mix 

while the contribution on the remaining fractions is less significant. Real values are shown in 

the following table: 

Table 6: 

A guide to sand grading 

Sieve Size [mm] 

Percentage passing 

Suggested outer limits Preferred limits *) 

4,0 80 - 100 90 - 100 

2,8 68 - 100 80 - 100 

2,0 55 - 100 75 - 95 

1,4 43 - 92 70 - 85 

1,0 32 - 85 55 - 70 

0,5 16 - 65 40 - 60 

0,25 5 - 43 20 - 40 

0,125 2 - 22 10 - 20 

0,09 0 - 11 3 - 6 

*) limits are suggested for pump concrete and for concrete used in sliding formwork 

The dramatic increase in surface area as the particle size decrease is illustrated by a few 

examples. The effect of grading on concrete behaviour is not constant but depends on the 

cement content and workability of the mix. Generally it may be accepted that a lower cement 

content calls for a finer grading of the aggregates: in other words, the leaner the mix, the 

higher should be the proportion of fineness (the total sum of sand < 0,1 mm plus cement 

should be approx. 350 kg per m 3 concrete). 

Table 7: 

Specific surface of various materials 

MATERIAL 

Specific Surface [m 2 /kg] 

32-mm concrete aggregate 0,07 

Average grading (B32) of aggregates 2,7 

Average concrete sand 3,5 

Silt 35 

Ordinary Portland cement 300 

Kaolinite 5'000 


Cement 

Concrete 

Blending of sands 

The grading of sand has a more pronounced effect on workability than has that of the coarse 

aggregate. While sand from a single source may not meet the grading requirements, it is 

often possible to overcome this difficulty by using a combination of sands. 

In the following table the grading is tabulated for the mixture of aggregates of 67 % of the 

crusher sand and 33 % of the pit sand: 

Table 8: 

Grading of mixture of two sands 

Sieve size [mm] 

Crusher Sand 

A 

Percent passing 

Pit Sand 

B 

Mixture 

67 % A + 33 % B 

4,0 82 100 88 

2,0 56 100 71 

1,0 45 100 63 

0,5 33 97 54 

0,25 19 58 32 

0,125 7 31 15 

0,090 3 18 8 

FM 3.58 1.14 2.77 

A comparison of concrete with crushed aggregates and concrete with rounded aggregates is 

shown in the following table: 

Table 9: 

Properties of fresh concrete with crushed aggregates 

Fresh concrete 

Crushed aggregate has in comparison with rounded aggregate: 

• Better stability of stiff concrete after immediate demoulding 

• Comparing flowing properties during vibration 

• Comparable properties of pumped concrete 

• Less bleeding 

• Comparable or better concrete surface 

• Consistency (on DIN A flow table) less favourable 

Table 10: 

Properties of hardened concrete with crushed aggregates 

Hardened concrete 

Crushed aggregate has in comparison with rounded aggregate: 

• Better flexural strength 

• Higher grip resistance 

• Less depth of water penetration 


Cement 

Concrete 

Grading of stone 

The grading of coarse material has a smaller influence on the workability of a mix than that of 

the sand but haphazard grading cannot be permitted where the quality of the concrete is of 

importance. For this reason the material is screened into its various size fractions and 

recombined to conform with specified or suitable grading requirements. The following figure 

shows the grading limits according to DIN 1045. 

Figure 2: 

Examples of particle size distribution for different gradings 

Pa 

ss 

in 

g 

[% 

100 

80 

60 

40 

20 

A - B favorable 

B - C usable 

U gap 

Grading acc. DIN 1045 

C 

B 

A 

U 

0 

0 0.125 0.25 0.5 1.0 2.0 4.0 8.0 16.0 31.5 

Sieve size 

Gap-graded and continuously-graded concrete 

The relative merits of concrete made with gap-graded and continuously-graded stone have 

been much debated [10, 11,12]. The technical advantages of each are listed below but, in 

comparing merits, it must be stated that economic considerations may outweigh the 

technical. 

Table 11: 

Properties of gap-graded concrete 

Gap-graded concrete [2,12] 

compared with continuous-graded concrete 

• Less danger of particle interference. 

• Grater sensivity of consistence to change in water content. 

This makes for more accurate control mixing of water which in 

turn ensures more consistent strength results. 

• Stiffer mixes are more responsive to vibration. 


Cement 

Concrete 

Table 12: 

Properties of continuously-graded concrete 

Continuously-graded concrete 

compared with gap-graded concrete 

• Wetter mixes are less prone to segregation. 

• Less sensitive to slight changes in water content. This is an advantage 

where uniform workability is important. 

• Improve pumpability especially at higher pressure. 

• Improve flexural strength due to the increased surface area of graded stone. 

1.3.6 Alternative aggregates 

Aggregates from natural sources make up the bulk of the aggregates used in concrete. 

However, there are a number of alternative materials which can be used as aggregate and 

concrete technologists should be encouraged to explore their potential performance and 

economy for use in concrete. 

Materials used for a greater or lesser extent of natural aggregate are: 

♦ Metallurgical slag 

Metallurgical slags that have been found suitable for use in concrete include blastfurnace, 

ferromanganese, ferro-silicon-manganite, phosphate, chrome, copper and platinum slag 

[14]. 

♦ Clinker 

Well-burnt furnace residues from furnaces fired with pulverised fuel (BS 1165). 

♦ Expanded Clays (shale and slate) 

When certain clays or shale are rapidly heated to the point of incipient in fusion, the 

material softens, becomes plastic and tends to entrap gases which are generated within 

its mass. Trade names are: Haydite, Cel Seal, Aglite, Gravelite. Leca and Güllät. 

♦ Sintered fly ash 

In one of the manufacturing processes of low-density aggregate from fly ash, the ash is 

first palletised and then formed noodles are sintered at 1'000 to 1'200 °C. 

♦ Burnt-clay bricks 

Burnt-clay aggregate made by crushing broken bricks is being used more and more to 

some extent in cast-in-situ concrete, but mainly for making precast concrete panels and 

concrete masonry units. 

♦ Colliery Spoil 

In the UK in 1972, two plants were operating on colliery waste and producing an 

aggregate known as Aglite. It is an expanded low-density aggregate. 

♦ Exfoliated Vermiculite 

Vermiculite is the geological name given for a group of micaceous minerals. It has the 

unique property that when heated to ground 1'200 °C, the flakes expanded (exfoliated) 

up to 15 times their original volume. 

♦ Perlite 

Perlite and certain other volcanic glasses expand when heated to the point of incipient 

fusion. Expanded perlite is usually produced only in sand size. It has a maximum bulk 

density of 240 kg/m 3 . 


Cement 

Concrete 

♦ Glass 

Waste glass is a potential aggregate for concrete and has been used in precast concrete 

elements. Waste glass is susceptible to alkali-aggregate-reaction and may produce 

concrete with a high expansion if used in combination with a high alkali content. 

♦ Recycled concrete as aggregate 

Depletion of normal aggregate sources and waste disposal problems have made 

concrete reclaimed from the demolition of concrete structures an attractive proposition as 

aggregate. Useful data have been published by Buck [13]. 

♦ Sawdust and Wood Wool 

Concrete made from mixtures of Portland cement and sawdust is generally a rather 

unreliable material and its properties cannot be easily predicted. 

♦ Expanded polystyrene 

Expanded polystyrene beads have a closed cellular structure and can easily be used to 

produce cellular concrete. Expanded polystyrene beads are extremely light (density 12 to 

16 kg/m 3 ) so that they can segregate from the mix and are hydrophobic. 

♦ Remarks 

Some of the alternative aggregates, such as air-cooled metallurgical slag are used 

merely because they are more economical than natural aggregates and can be used 

without detriment. In other cases, certain technical properties are required (e.g. low 

density, superior thermal insulation) and for these purposes aggregates are often 

"purpose-made" for example low-density aggregates such as bloated clay and shale, 

sintered fly ash and exfoliated vermiculite. Many of these materials are only used to make 

precast concrete products such as concrete masonry units. 


Cement 

Concrete 

1.4 Admixtures 

Admixtures are chemicals which are added in relatively small quantities to the basic 

constituents of concrete. The quantity of an admixture is usually measured against the 

quantity of cement, expressed as its percentage by mass. 

It is convenient to make a distinction between admixtures and additives. Admixtures are used 

in quantities of maximum 5 wt-% (usually 0.5 to 2.0%). Additives such as fly ash, or other 

pozzolanas and blast furnace slag, are applied in quantities of more than 5% by mass of 

cement (usually 15 to 35%). Additives should therefore be considered as additional 

constituents of the concrete mix. 

Admixtures are usually categorised according to their principal uses or according to their 

primary effects as follows: 

• Improvement of workability of fresh concrete 

• Control of setting time and early hardening 

• Air-entrainment 

• Other effects (stability, high cohesion, colouring, etc.) 

The official definition of an admixture according to ASTM C125: 

♦ An admixture is a material other than water, aggregates, hydraulic cement, and fibre 

reinforcement used as an ingredient of concrete or mortar and added to the batch 

immediately before or during its mixing. 

This definition encompasses a wide range of materials that are utilised in modern 

concrete technology. Subsections of admixtures are: 

• Accelerating admixtures 

Admixtures that accelerates the setting and early strength development of concrete. 

• Air-entraining admixtures 

Admixtures that causes the development of a system of microscopic air bubbles in 

concrete or mortar during mixing. 

• Retarding admixtures 

Admixtures that retards the setting of concrete. 

• Water-reducing admixtures 

Admixtures that either increases the slump of freshly mixed mortar or concrete 

without, increasing the water content, or that maintains the slump with a reduced 

amount of water due to factors other than air entrainment. 


Cement 

Concrete 

1.4.1 Workability agents 

Admixtures in this category are either called 

• plasticizers 

• superplasticizers 

• water-reducing agents 

• high range water-reducing agents. 

The primary effect of the admixtures is an improvement of workability. 

The following diagram shows the different purposes of using plasticizers in a typical concrete 

mix: 

Figure 3: 

1 constant workability (flow); reduced w/c ratio and increased strength 

2 constant w/c ratio and strength; increased workability (flow) 

3 mix of both cases 

70 

65 

60 

with SP 

without SP 

Flow acc. DIN [cm] 

55 

50 

45 

40 

1 

3 2 

35 

30 

0.45 0.5 0.55 0.6 0.65 0.7 0.75 

w/c ratio 

Admixtures in this group are all based on chemical compounds which affect the forces 

between solid particles suspended in water and reduces the surface tension of water. The 

admixtures contain surfactants which is being absorb on the surface of the particles. The 

strength of the adsorption depends on the type of particle. In case of Portland cement the 

C 3 A compound appears to provide the strongest attraction. The dispersing action is also 


Cement 

Concrete 

enhanced by the development of a layer of adsorbed molecules of the plasticizers which 

separate the particles of cement; see following figure: 

Figure 4: 

Cement particle 

floc 

Particle repulsion 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

_ 

Flocculated particles of cement 

before the addition of a superplasticizer 

The negative charges of the 'tails' of 

the molecules of the admixture 

adsorbed on to the cement particles 

generate repulsive forces and 

disperse the particles 

The superplasticizers are broadly classified into four groups, namely: 

• SMF: 

• SNF: 

• MLS: 

• Others: 

Sulphonated Melamine-Formaldehyde condensate 

Sulphonated Naphthalene-Formaldehyde condensate 

Modified Ligno Sulphonates 

Polyacrylates, sulphonic-acid-esters, carbohydrate esters etc. A very new 

invention is based on derivatives of maleic acid and vinyl monomers. 

Variations exist in each of these classes and some formulations may content a second 

ingredient. 

Ordinary plasticizers 

Ordinary plasticizers are mainly based on lignosulphonate salts - a minority use salts of 

hydroxy-carboxylic acid. Calcium lignosulphonate and the better water soluble sodium 


Cement 

Concrete 

lignosulphonate normally used as admixtures for concrete. The lignosulphonate molecules 

are in the form of polymers with molecular weights varying from approx. 20 to 30'000. 

Dosage of lignosulphonate type plasticizers varies between 0.2 to 0.6% of the cement in the 

mix. The effectiveness of the lignosulphonate plasticizers depends on the composition of the 

particular Portland cement used. Cements with high content of C 3 A are likely to require 

increase dosage of admixtures. The lignosulphonate admixtures appear to be less effective 

for cements with moderate high cement content than for mixes with low cement contents, 

below approx. 270 kg/m 3 . 

Lignosulphonate based plasticizers have the tendency to produce significant side effects, 

namely: 

(1) Air-entrainment 

The additional percentage of entrained air which can be generated by normal doses 

varies between 0.5 to 2.5 vol-% (slump approx. 6 cm, cement content approx. 300 

kg/m 3 ). 

(2) Retardation 

The lignosulphonates themselves interfere with the hydration of cement and cause 

some retardation. This effect is more pronounced when the calcium lignosulphonate 

admixture is used. High dosages of such admixtures can lead to unacceptable 

retardation. 

The hydroxy-carbolic plasticizers (mostly sodium salts of citric, tatratic, gluconic, and maleic 

acid) are not very common, and hydroxylated polymers are rarely found in concrete 

construction practice. 

Overdosing the concrete with an ordinary plasticizer increases workability. The increase in 

non-linear and the effect varies with the cement content and the initial workability (slump) of 

the mix. The following graphic shows the increase of slump as a function of the dosage of an 

ordinary Portland cement: 

Figure 5: 

20 

18 

16 

14 

Slump [cm] 

12 

10 

8 

6 

4 

2 

0 

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 

Dosage rate of lignosulphonate [wt-%] 

Influence of the dosage rate of an ordinary lignosulphonate plasticizer on slump 


Cement 

Concrete 

Superplasticizers 

Superplasticizers are based mainly on two types of polymers, namely the salts of 

formaldehyde naphthalene sulphonate and formaldehyde melamine sulphonate. The term 

superplasticizer indicates the much greater potential for increasing workability of concrete 

without undesirable side effects when compared to ordinary plasticizers. 

The chemical composition of the superplasticizers differ from that of the ordinary plasticizers 

in that they do not delay the setting times and hardening of fresh concrete. On the contrary, 

some acceleration of the setting and hardening is usually observed. It is not entirely clear if 

the acceleration is due simply to a better dispersion of the cement particles or if other 

processes are also involved. 

The accelerating effect of the superplasticizers appears to be primarily responsible for the 

relatively short periods of effectiveness of the admixture. Small additions of purified 

lignosulphonates are sometimes added to the admixture to moderate the rapid early loss of 

workability. 

The periods of effectiveness of the superplasticizers have been quoted to vary between 15 

minutes to 40 minutes. The period of effectiveness of the superplasticizer is usually 

measured as the time it takes for the workability of the mix to decrease to the level of the 

initial slump before the admixtures had been added. 

It has been common practice in the ready-mixed concrete industry to delay the first dose of 

the superplasticizing admixture until the time the concrete reaches the delivery point. It is 

then possible to re-mix the concrete more than once, each time adding another dose of the 

superplasticizer and thus maintaining or even increasing workability without detrimental 

effect on the properties of hardened concrete. 

The chemical nature of the superplasticizer determines its effectiveness in increasing the 

workability (slump, flow table spread, etc.). For e.g. to obtain a slump of about 25 cm from an 

initial value of 5 cm, it may be necessary to add 0.6% SMF or MLS-based superplasticizer 

whereas this could be accomplished with only 0.4% SNF-based admixture. In the following 

diagram the loss of workability is shown in a control concrete (containing no admixtures) 

compared with that containing MLS (Modified Ligno Sulphonate), SMF (Sulphonated 

Melamine-Formaldehyde) and SNF (Sulphonated Naphthalene-Formaldehyde): 


Cement 

Concrete 

Figure 6: 

Flow table spread [cm] 

70 

65 

60 

55 

50 

45 

40 

35 

30 

25 

0 0.25 0.5 0.75 1 1.25 1.5 

Time [hours] 

MLS 

SMF 

SNF 

Ref 

1.4.2 Air-entraining agents 

Effect of MLS, SMF and SNF on loss of flow table spread 

The air-entraining admixtures are invariably organic substances which helps to generate 

microscopic bubbles of air in the fresh concrete. The majority of the commercially available 

ones are based on neutralised wood resins (vinsol) in which salts of abietic and pimeric 

acids are usual active chemical ingredients. A few air-entrained admixtures are based on the 

salts of fatty acids or other organic chemical compounds. It is also possible to use some 

types of the lignosulphonate based admixtures in higher dosages to produce simultaneous 

improvement of workability and generation of air-entrainment. 

The technique of air-entrainment was originally developed in the USA primarily to increase 

the resistance of concrete to freezing and thawing and to the scaling effects produced by deicing 

salts (mostly sodium or calcium chloride). The entrainment of air in concrete has been 

defined as the introduction into fresh concrete of air in controlled amounts and in the form of 

properly-sized bubbles (preferably within the size range 0.05 to 0.3 mm diameter). 


Cement 

Concrete 

The entrained air in concrete should be clearly distinguished from accidentally entrapped air. 

The two differ in magnitude, amount, and properties of the air bubbles: 

♦ Entrained air 

This air is intentionally incorporated by means of chemical admixtures, usually between 3 

to 7% by volume and a maximum size of about 0.5 mm; entrained air produces discrete 

cavities in the cement paste so that no channels for the passage of water are formed and 

the permeability of the concrete is not increased. The voids never become filled with the 

products of hydration of cement as gel can form only in water. 

♦ Entrapped air 

Accidentally incorporated air is called entrapped air. This air usually forms very much 

larger bubbles, some as large as the familiar pockmarks on the surface of the concrete. 

The amount is in general between 0.5 to 1.5% by volume. 

The air-entrained admixtures contain surfactants which are adsorbed on to the surfaces of 

the cement grains. As the microscopic bubbles form during mixing of the concrete, they 

stabilise in their small sizes and are attracted to the layers of surfactant on the cement 

particles. A simplified diagram of the cement-water-air structure is shown in the following: 

Figure 7: 

- 

- - + - - 

water 

a 

- 

- c + - - 

- - + - 

- - - - 

+ 

+ + 

- 

- - 

+ 

a 

- - c 

- - 

aggregate + 

- 

a + 

-- 

- 

- + + 

+ 

+ 

- 

-- 

- 

entrapped 

- 

+ - 

- - 

a 

air 

a 

- - 

- - 

- + 

- 

+ 

+ 

- - 

- - 

+ + 

- + + 

-- 

+ - + 

c 

- - - 

+ - - + 

- + - 

- + + 

+ c 

+ + - 

- + 

- 

- + - a 

- 

- 

- 

- a - - - 

- 

- 

- - 

- - - 

- - 

- - - 

a 

a 

- + 

- 

- + 

- - 

- 

entrapped 

+ + 

- 

aggregate 

c 

- 

air - - + 

-+ 

- 

+ 

- 

- - - 

- a - 

+ + + 

a 

- 

- + 

- - - - 

c 

- 

a 

bubbles of entrained air 

c 

particles of cement 

Wo-concprop.pre-95 

A simplified structure of the cement - water - aggregate - entrained air system 

in an air-entrained concrete mix 

Air entraining agents should be added as solution, dissolved in the mixing of the concrete. If 

other admixtures are also used, the air entraining agent should be added separately rather 

than mixed with the other admixtures, because sometimes there are reactions between 

materials that result in a decrease in the effectiveness of the air entraining agents. 


Cement 

Concrete 

The usual dosage rate of these materials is between 0.3 to 1.0 ml (density ≤ 1.1 g/cm 3 ) per 

kg of cement. This rate is roughly equivalent to 0.01%, solid admixtures substance to 

cement. The dosage rate can vary according to the composition of the mix. 

Air entraining agents can be used with cements other than Portland. When used with 

blended cements, a larger amount of agent may be required to obtain the desired air content 

of the concrete. 

1.4.3 Agents affecting setting and hardening 

Accelerators 

Accelerators have their primary application in cold weather concreting where they may be 

used to permit earlier starting of finishing operations. They reduce the time required for 

curing, and permit earlier removal of forms or loading of the concrete. Accelerators cannot be 

used as antifreeze agents since, at the allowable dosages, the freezing point will be lowered 

less than 2 °C. 

Accelerating admixtures can be divided in three groups: 

(1) Soluble inorganic salts 

Most soluble inorganic salts will accelerate the setting and hardening of concrete to 

some degree; calcium salts generally being the most effective. Calcium chloride is 

the most popular choice because it gives more acceleration at a particular rate of 

addition than other accelerators and is also reasonably inexpensive. Admittedly it is 

very corrosive (as all water soluble chlorides) against the reinforcement of the 

concrete and therefore in many countries forbidden or limited at a particular level. 

Soluble carbonates, aluminates, fluorides, and ferric salts have quick-setting properties. 

Sodium carbonate and sodium aluminate are the most common ingredients of 

shotcreting admixture formulations used to promote quick setting. Calcium fluoroaluminate 

can be used as admixtures to obtain rapid-hardening characteristics. 

(2) Soluble organic compounds 

A variety of organic compound have accelerating properties (although many more act 

as retarders), but triethanolamine, calcium formiate, and calcium acetate account for 

most commercial uses. They are commonly used in formulations of water-reducing 

admixtures to offset their retarding action. 

Although triethanolamine is listed as an accelerator, recent research shows that its 

reaction with Portland cement is rather complex. It can cause retarding or flash setting, 

depending on the amount used. 

(3) Miscellaneous solid materials 

Retarders 

Solid materials are not often used for accelerating. Addition of calcium aluminate cements 

cause Portland cements to set rapidly, but strength development is poor. Concrete 

can be "seeded" by adding fully hydrated cement that has been finely ground 

during mixing to cause more rapid hydration. Finely divided carbonates (calcium or 

magnesium), silicate minerals, and silicas are reported to decrease setting time. 

Retarders can be used whenever it is desirable to set off the effects of high temperatures 

which decrease setting times. Prolonging the plasticity of fresh concrete can be used to 

advantage in placing mass concrete. Successive lifts can be blended together by vibration, 


Cement 

Concrete 

with the elimination of cold joints that would occur if the first lift were to harden before the 

next were placed. 

Retarders can also be used to resist cracking due to form deflection that can occur when 

horizontal slabs are placed in sections. Concrete that has set but has acquired little strength 

is liable to microcrack when subsequent pouring alters the amount of form deflection. If the 

plastic period is prolonged, the concrete can adjust to form deflection without cracking. 

The composition of retarders can be divided into several categories, based on their chemical 

composition: 

Lignosulphonic acids and their salts (1) 

Hydroxycarboxylic acids and their salts (2) 

Sugar and their derivatives (3) 

Inorganic salts (4) 

It will be noted that categories (1) and (2) also possess water-reducing properties, and these 

admixtures can be classified under both groups. Lignosulphonate-based admixtures are 

prepared from pulp and paper industrial wastes, and studies have indicated that most of the 

retarding properties of these admixtures may be due to compounds that belong to category 

(2) or (3). Some inorganic salts (borates, phosphates, and zinc and lead salts) can act as 

retarders but are not used commercially. 

The influence of an admixture on air entrainment should be considered, particularly if the 

admixture also has water-reducing properties. Retarders may also increase the rate of loss 

of workability in fresh concrete (slump loss), even when abnormal setting behaviour does not 

occur. 

Whenever a retarding admixture is used, some reduction in the 1-day strength of the 

concrete should be anticipated. Within 7 days, the strength should approach that of an 

unretarded concrete unless an overdose has been used (see following diagram): 


Cement 

Concrete 

Figure 8: 

Compressive strength [MPa] 

55 

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

Accelerated No admixture (Over-)retarded 

2 4 6 8 10 12 14 16 18 20 22 24 26 28 

Time [days] 

Effect of retarders and accelerators on strength development of concrete 

Retarding admixtures have been reported to increase ultimate compressive strength and, to 

a lesser extent, flexural strength. Although set-controlling admixtures are reported to 

increase drying shrinkage and creep, the effects depend on changes in mix design, time of 

hydration, and time of drying or loading. 

1.4.4 Other admixtures 

There are many other types of admixtures that are commercially available. The consumption 

of these various materials added together is less than the amount used of any single type so 

far mentioned. Some brief discussion of the more important kinds is warranted, however. 

Bonding (or polymer) admixtures 

Polymer latex emulsions are used to improve the bonding properties of concrete. This can be 

bonding between old and new concrete in repair work, or bonding between concrete and 

other materials, such as steel. 

The brittle nature of concrete is an inherent property of the material and one that is overcome 

by the use of reinforcing materials. The very high porosity of concrete is also a disadvantage. 

Several approaches have been taken to improve concrete properties, resulting in quite 

different materials. Three different kinds of materials are often used: 

PIC: Polymer-impregnated concrete 

PIC involves filling the capillary pores of hardened concrete 

with a polymer 

LMC: Latex-modified concrete 

LMC is made by incorporating a polymer latex with fresh 

concrete, which im-proves the tensile properties of concrete. 


Cement 

Concrete 

Corrosion inhibitors 

The incorporation of compounds that will prevent or reduce corrosion has been suggested for 

concretes in which corrosion of reinforcement can be a problem. Generally, these will be 

salts that contain an oxidizable ion, such as nitrites, thiosulphates, benzoates, stannous 

salts, and ferrous salts. 

It is however, doubtful whether the use of inhibitors is really warranted, since they are not 

considered to provide protection in the presence of chloride ion, which is precisely the 

situation in which protection is desired. 

Dampproofing admixtures 

The term 'dampproofing' implies prevention of water penetration into dry concrete or the 

transmission of water through concrete. No admixture can actually prevent such movement 

of water, although it may reduce the rate at which it occurs. 

Certain formulations based on salts of fatty acids (soaps) or petroleum products (mineral 

oils and asphalt emulsion) may give the concrete a water-repellent effect. Such materials 

have been used to prevent the penetration of rain into porous concrete blocks but are not 

likely to affect the performance of dense, well-cured concrete. 

Expansive Cements 

One of the major disadvantages of Portland cement concrete is its high drying shrinkage and 

its susceptibility to tensile strength when volume contraction is wholly or partially restrained. 

The development of expansive cements dates back about 60 years. Commercial production 

began in the US in the late 1960s, although total production remains quite small, about 

500'000 tons annually. A standard specification, ASTM C845-90, covers expansive cements. 

All three variants of present-day expansive cements (Type K, M, and S) are based on the 

formation of ettringite (hydrated calcium sulphoaluminate) in considerable quantities during 

the first few days of hydration. The material from which ettringite is formed differ substantially 

in each cement, but all require a source of calcium aluminate and sulphate ions. Expansion 

has also been achieved by using clinker with high content of free lime as admixture to cause 

expansion of a superplasticized concrete mix. 

Successful use of expansive cements depends upon proper control of the expansion of the 

cement during hydration and is sensitive to a number of variables, for example: 

Reinforcement -- Mix design -- Handling and curing 

Grouting admixtures 

Cement-based grout used for speciality applications such as cementing oil well contain 

different admixtures. Flocculating admixtures, thickeners, and mineral admixtures are used to 

prevent bleeding and segregation and to increase cohesion and retention of water during 

pumping. Retarders are commonly used to extend pumping times. 

1.5 Mixing and curing water for concrete 

1.5.1 Introduction 

The quality of water is important because poor-quality water may affect the time of setting, 

strength development, or cause staining. Almost all natural water, fresh water, and water 

treated for municipal use are satisfactory as mixing water for concrete if they have no 

pronounced odour or taste. 


Cement 

Concrete 

Because of this, very little attention is usually given to the water used in concrete, a practice 

that is in contrast to the frequent checking of admixture, cement, and aggregate components 

of the concrete mixture. 

1.5.2 Effect of impurities 

A popular criterion as to the suitability of water for mixing concrete is the classical 

expression: 

If water is fit to drink 

it is all right for making concrete 

This does not appear to be the best basis for evaluation, since water containing small 

amounts of sugar or citrate flavouring would be suitable for drinking but not mixing concrete, 

and, conversely water suitable for making concrete may not necessarily be fit for drinking. 

The most extensive series of tests on the subject "Impurities in mixing water" was conducted 

by Abrams (ACI Proceedings, Vol 20, 1924, 442-486). Approximately 6000 mortar and 

concrete specimens representing 68 different water samples were tested in this investigation. 

Among the water tested were sea and alkali water, bog water, mine and mineral water, and 

water containing sewage and solutions of salt. Tests with fresh and distilled water were 

included for comparative purposes. Some of the more significant conclusions based on these 

data are as follows: 

The time of setting of Portland cement mixtures containing impure mixing water was about 

the same as those observed with clean fresh water with only few exceptions. In most 

instances, the water giving low relative compressive strength of concrete caused slow 

setting. 

♦ Non of the waters caused unsoundness of the neat Portland cement paste when tested 

over boiling water. 

♦ In spite of the wide variation in the origin and type of water used, most of the samples 

gave good results in concrete due to the fact that the quantities of injurious impurities 

present were quite small. 

♦ The quality of mixing water is best measured by the ratio of the 28-day concrete or mortar 

strength to that of similar mixtures made with pure water. Water giving strength ratios that 

are below 85% should be considered unsatisfactory. 

♦ Neither odour nor colour is an indication of quality of water for mixing concrete. Water 

that was most unpromising in appearance gave good results. Distilled waters gave 

concrete strength essentially the same as other fresh waters. 

♦ Based on a minimum strength-ratio of 85% as compared to that observed with pure 

water, following samples were found to be unsuitable for mixing concrete: 

• acid water 

• lime soak water from tannery waste 

• carbonated mineral water discharged from galvanising plants 

• water containing over 3% sodium chloride or sulphate 

• water containing sugar or similar compounds 

The concentration of total dissolved solids in these waters was over 6'000 ppm 

except for the highly carbonated water that contained 2'100 ppm total solids. Very few 

natural waters other than sea water, contain more than 5'000 ppm of dissolved solids. 


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Concrete 

♦ Based on the minimum strength-ratio of 85%, the following waters were found to be 

suitable for mixing concrete: 

• bog and marsh water 

• waters with a maximum concentration of 1% sulphate 

• sea water (but nor for reinforced concrete) 

• alkali water with a maximum of 0.15% Na 2 SO 4 or NaCl 

• water from coal and gypsum mines 

• waste water from slaughterhouses, breweries, gas plants, 

and paint and soap factories. 

1.5.3 Effects of algae on air content and strength 

A rather extensive series of laboratory tests showed that the use of water containing algae 

had the unusual effect of entraining considerable quantities of air in concrete mixtures with 

an accompanying decrease in strength. The data in the following table were based on tests 

with 19-mm maximum-size aggregate concrete having a w/c ratio of 0.5 and a slump of 4.0 

to 7.5 cm, with a constant ratio of coarse to fine aggregate: 

Table 13: 

Algae in mixing water [%] Air in concrete [%] Compr. strength at 28 days [MPa] 

none (control mix) 2.2 33.3 

0.03 2.6 33.4 

0.09 6.0 27.9 

0.15 7.9 22.8 

0.23 10.6 17.8 

In addition to the detrimental effect of strength, one of the important aspects of these data is 

that considerable quantities of air can be entrained in concrete by the use of mixing water 

containing algae. 

1.5.4 Curing water 

There are two primary considerations with regard to the suitability of water for curing 

concrete: 

♦ One is the possibility that it might contain impurities that would cause staining, and the 

other 

♦ that it might contain aggressive impurities that would be capable of attacking or causing 

deterioration of concrete. The latter possibility is unlikely, especially if water satisfactory 

for use in mixing concrete is employed. 

In some instances the staining or discoloration of the surface of concrete from curing water 

would not be objectionable. 

The most common cause of staining is usually a relatively high concentration of iron or 

organic matter in the water; however, relatively low concentrations of these impurities may 

cause staining, especially if the concrete is subjected to prolonged wetting by run off of 

curing water from portions of the structure. 

Test data show that there is no consistent relationship between dissolved iron content and 

degree of staining. In some cases, 0.08 ppm of iron resulted in only a slight discoloration and 


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Concrete 

in other cases, waters with 0.06 ppm of iron gave a moderate rust-coloured stain, while 0.04 

ppm produced considerable brownish-black stain. 

2 Literature for admixtures and mixing water 

♦ P. Klinger, J. Lamond: Concrete and Concrete-Making Materials; ASTM, STP 169C, Aug. 

1994 

♦ P. Bartos: Fresh Concrete, Properties and Tests; Elsevier, Amsterdam, 1992 

♦ K. Wesche: Baustoffe für tragende Bauteile, Teil 2: Beton, Mauerwerk; Bauverlag, 

Wiesbaden, 1992 

♦ A. Neville: Properties of Concrete; Longman Scientific & Technical, New York, 1991 

♦ B. Addis: Fulton's Concrete Technology: Portland Cement Institute, Midland, South 

Africa, 1986 

♦ S. Mindess: Concrete; Prentice-Hall, Englewood Cliffs, New Jersey, 1981 

3 Appendices 

3.1 References 

[1] DIN 4226 (1983): Zuschlagstoff für Beton: Deutsches lnstitut für Normung e.v.; Beuth 

Verlag GmbH, Berlin 

[2] B. Addis et al.: Fulton's Concrete Technology, chapter 3, PCI, Midland, South Africa, 

1986; (All extracts mainly from this paper) 

[3] R. Rhoades et al.: Petrographic and mineralogic characteristics of aggregates; ASTM 

symp. on Mineral Aggregates, Philadelphia, 1948, p. 20 - 48 

[4] British Standard 812 (1967): Mineral, Aggregates, Sand & Fillers, Brit. Stand. House, 

2 Park Street, London, W1Y 4AA 

[5] J. Phemister et al.: Roadstone, geol. aspects and phys. tests; London, Dept. of Sc. 

and And. Res. Road Spec. Report No. 3,1946 

[6] D. Davis, M. Alexander Properties of aggregate in concrete; Hippor Quarries Techn. 

Publ. (1992), 94 Rivonia Road, Sandton 2199, South Africa 

[7] M. Kaplan: The flexural and compressive strength of concrete as affected by the 

properties of coarse aggregates; Proc. America Concrete Institute v. 55, May 1959, 

p. 1193 ff 

[8] L. Roberts et al.: Dictionary of Geological Terms; American Geological institute, 

Anchor Books, New York (1983) 

[9] Webster's New World Dictionary of Amedcan English, Third College Edition, 

Cleveland, USA (1988) 

[10] L. Mercer et al.: The law of grading for concrete aggregates; Melbourne, Techn. Coll. 

Press, 1951, Research Bull. no. 1 

[11] V. Barnher Gap-graded concrete; London Cement & Concrete Association, 1952, C 

& CA Library Translation no. 42 

[12] H. Schäffer Beton mit Ausfallkörnungen; Betonwerk + Fertigteil-Technik, Heft 6/1979 


Cement 

Concrete 

[13] A. D. Buck: Recycled concrete as source of aggregate; Proc. American Concrete 

Institute, v. 74, 1977, p. 212-219 

[14] F. Rossouw: Report on the suitability of some metallurgical slags as aggregate for 

concrete; Pretoria, NBRI, 1981, NBRI Special Report Bou 56, p. 1 - 25 

3.2 Relevant ASTM Standards 

3.2.1 Aggregate 

C 33-90 

C 40-84 

C 70-79 

C 88-90 

C 123-90 

C 131-89 

Specification for Concrete Aggregates 

Test for Organic Impurities in Sands for Concrete 

Test for Surface Moisture in Fine Aggregate 

Test for Soundness of Aggregates by Use of Sodium Sulphate or Magnesium 

Sulphate 

Test for Lightweight Pieces in Aggregates 

Test for Resistance to Degradation of Small-Size Coarse Aggregate by 

Abrasion and impact the Los Angeles Machine 

C 227-87 Test method for Potential Alkali Reactivity of Cement-Aggregate 

Combinations (Mortar-Bar Method) 

C 289-87 

C 294-86 

C 330-89 

Test method for Potential Reactivity of Aggregates (Chemical Method) 

Descriptive Nomenclature of Constituents of Natural Mineral Aggregates 

Specification for Lightweight Aggregates for Structural Concrete 

C331-89 Specification for Lightweight Aggregates for Concrete Masonry Units 

C 332-87 

C 586-86 

C 637-84 

C 638-84 

E 11-87 

Specification for Lightweight Aggregates for Insulating Concrete 

Test method for Potential Alkali Reactivity of Carbonate Rocks for Concrete 

Aggregates (Rock Cylinder Method) 

Specification for Aggregates for Radiation-Shielding Concrete 

Descriptive Nomenclature of Constituents of Aggregates for Radiation 

Shielding Concrete 

Specification for Wire Cloth Sieves for Testing Purposes 


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Concrete 

Fresh and Hardened Concrete 

1. GENERAL.........................................................................................................................35 

2. DEFINITION ......................................................................................................................35 

2.1 Defintion of concrete ................................................................................................ 35 

2.2 Composition of concrete .......................................................................................... 36 

2.3 Green and young concrete, workability and resistance to loading of 

concrete ................................................................................................................... 37 

2.4 Strength of concrete................................................................................................. 37 

3. FRESH CONCRETE ......................................................................................................... 38 

3.1 Workability................................................................................................................ 38 

3.2 Influence on the Workability ..................................................................................... 40 

3.2.1 Effect of water ............................................................................................ 40 

3.2.2 Effect of solid constituents ......................................................................... 40 

3.2.3 Effects of admixtures.................................................................................. 41 

3.2.4 Effect of temperature.................................................................................. 41 

3.3 Other properties of fresh concrete ........................................................................... 41 

3.3.1 Bulk density (unit weight) ........................................................................... 41 

3.3.2 Air content .................................................................................................. 42 

3.4 From fresh to hardened concrete - Stages of development of concrete .................. 42 

3.5 Properties of ‘Green’ and ‘Young’ Concrete............................................................. 43 

4. HARDENED CONCRETE............................................................................................... 181 

4.1 General .................................................................................................................. 181 

4.2 Strength.................................................................................................................. 183 

4.3 Deformation under load: modulus of elasticity and creep ...................................... 184 

4.4 Density (weight of volume unit) .............................................................................. 184 

4.5 The durability of concrete....................................................................................... 184 

4.5.1 Volume changes ...................................................................................... 185 

4.5.2 Volume changes due to physical stress................................................... 187 

4.5.3 Volume changes due to alterations of the substance............................... 187 

5. FACTORS INFLUENCING THE STRENGTH OF CONCRETE ..................................... 190 

5.1 Influence of the constituents .................................................................................. 191 

5.1.1 Aggregates............................................................................................... 191 


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Concrete 

5.1.2 Water........................................................................................................ 192 

5.1.3 Cement..................................................................................................... 115 

5.2 Influence of mix proportions ................................................................................... 115 

5.2.1 Water / Cement ratio ................................................................................ 116 

5.2.2 Cement content........................................................................................ 116 

5.2.3 Aggregate/Cement ratio ........................................................................... 117 

5.3 Influence of handling .............................................................................................. 117 

5.4 Influences of curing ................................................................................................ 117 

5.4.1 Moisture ................................................................................................... 118 

5.4.2 Temperature............................................................................................. 119 

5.5 Influences of testing methods ................................................................................ 119 

6. CONCLUSIONS.............................................................................................................. 120 

7. SUPPLEMENTARY LITERATURE (BOOKS):............................................................... 120 


Cement 

Concrete 

1 General 

The properties of a building material are of great importance with respect to the function for 

which the building was intended. Besides the required load capacity and durability, which are 

the main conditions, a building must protect against cold, heat, rain, wind, etc. A comfortable 

and pleasant living atmosphere should be created, which cannot be achieved simply by the 

design of the building or the application of the specific material, but by the favorable 

combination of several materials. The correct choice of material, however, can only be made 

if everybody involved with the construction has good knowledge of the material properties. 

The properties of building materials such as bricks and steel will remain unchanged 

throughout the building process, while the final properties of concrete will only become 

established after placing. Cement is only an intermediate product of a building material. 

New developments in concrete technology and building technique, based on many years of 

research, have made it possible to build such constructions as the 550 m tall TV tower in 

Toronto, prestressed concrete bridges with a span of up to 240 m and drilling platforms in the 

ocean. Flowing concrete has changed the method of placing. So far, concrete has been able, 

in most cases, to compete with other building materials. 

All of these constructions and techniques have been made possible by the improvement of 

cement quality and on the methods of its application. Should further material requirements 

arise, would it be possible to adapt the concrete properties? Can the cement manufacturer 

contribute? He should at least make an attempt to meet any new requirements, because 

each successful concrete construction will favorably affect the cement production. 

On the other hand, the cement manufacturer must be able to defend himself if defects in 

concrete are unjustly attributed to the cement. He can only be persuasive if he has thorough 

knowledge of concrete properties and concrete technology. 

2 Definition 

2.1 Defintion of concrete 

ACI has defined concrete as follows: 

Concrete is a composite material 

consisting essentially of a binding medium, 

within which particles or fragments of aggregate are 

embedded. 

In Portland cement concrete, the binder is a mixture of 

Portland cement and water. 


Cement 

Concrete 

2.2 Composition of concrete 

Fig. 1: Range of Proportions of materials used in concrete (by weight) 

Stages of concrete 

Coarse aggregate 

Fine aggregate 

Cement 

Water 

Air 

Admixture 

0 5 10 15 20 25 30 35 40 45 50 55 60 

Minima/maxima proportions (wt-%) 

The properties of concrete depend very much on its age. Roughly three stages can be 

distinguished. 

Fresh 

(a workable mass) 

 

concrete 

Transition 

through intermediate stages 

(sometimes called ‘green’ or ‘young’ concrete) 

 

Hardened 

concrete 

(an artificial stone which has reached the required 

properties for a specific structure) 


Cement 

Concrete 

The transition from fresh to hardened concrete is a continuous process during which it 

changes from a workable mass to an artificial stone. The performance of the concrete at 

certain ages has a great influence on its applicability, and, therefore, it is of interest to know 

the concrete properties not only when placed (fresh) or used (hardened), but sometimes also 

during the entire development. 

2.3 Green and young concrete, workability and resistance to loading 

of concrete 

The concrete is called ‘green’ as soon as it is compacted in the framework until its 

solidification by setting. When the concrete turns solid, it is called ‘young’ until it reaches a 

certain degree of strength permitting the removal of the form. 

For the practical behaviour of concrete in service, its mechanical properties are decisive. Its 

resistance to loading is essential in the hardened stage. It is, however, insignificant in fresh 

concrete where the workability is of main concern. 

Workability is not well defined and, therefore, not directly measurable, because it includes a 

certain number of fresh properties. As an example, two definitions of workability from the 

same country (USA) follow: 

♦ WORKABILITY is that property of freshly mixed concrete or mortar which determines the 

ease and homogeneity with which it can be mixed, placed and compacted and finished. 

(ACI definition) 

♦ WORKABILITY is that property of concrete which determines the effort required to 

manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity. 

(ASTM definition) 

Resistance to loading is the ability of the hardened concrete to bear the service load (dead 

and live load); (dead load = constant load in structures due to the mass of the members, the 

supported structure and permanent attachments or accessories; live load = any load that is 

not permanently applied to the structure). 

Resistance to loading can be specified and measured exactly for different types of loads. 

Usually, it is expressed as strength. 

2.4 Strength of concrete 

Strength is defined as maximum resistance to load that a member or structure is capable to 

develop before failure occurs. It is measured with reference to the cross section of the 

structure member. 

F ⎡ N ⎤ 

Strength : σ = ⎢ orMPa 

2 

A 

⎥ 

⎣mm 

⎦ 

where: F = applied load 

A = cross section on which the load is applied 

We distinguish different types of strength according to the type of load exerted: 

Compressive, tensile, flexural splitting, 

shear, torsion adhesive, and impact 

strength. 


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Concrete 

The loading resistance of various structural members results from the combination of 

different types of strength, according to the actual stresses, and from concrete quality. 

3 Fresh concrete 

Fresh Concrete is the product that is obtained immediately after mixing the components. 


The homogenized concrete mix, after it is taken from the mixer, must be suited to be 

transported to the destination point and to be placed into the moulds or formwork. The fresh 

concrete must completely fill the mould, even if the shape of the elements is very 

complicated and the interstices between the reinforcement are very small. A good 

compaction must be achieved and through all these steps the mix must remain 

homogeneous without segregation. 

The ability of fresh concrete to meet all these requirements is called workability which 

includes a number of more or less defined properties (see following figure). 

Fig. 2: Properties of fresh concrete related to workability 

Workability 

ease of the mixing 

transportability 

compactibility 

consistency (flow) 

stability 

mobility 

compactibility 

finishability 

viscosity of paste 

no segregation 

bleeding 

water retention 

no honeycombing 

friction of aggregate 

air content 

The workability influences not only all operations of placing and consolidating fresh concrete 

but also to a large extent, the quality of the hardened concrete. A dense concrete must 

contain a high amount of solid matter and very few voids filled with water, vapor or air. Very 

important concrete properties depend on the density. 


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Concrete 

Fig. 3: Effect of the workability on fresh and hardened concrete properties 

WORKABILITY 

FRESH CONCRETE 

Easy mixing 

Easy transportation 

(no segregation) 

Easy placing 

(no segregation) 

Easy compaction 

(minimum of voids) 

HARDENED CONCRETE 

Density 

Mechanical properties 

Durability 

Impermeability 

Appearance 

The workability requirements vary from one country to another. They depend on the level of 

the building industry, on the quality requirements and on the quality of the available 

materials. Furthermore, tradition, economical and subjective factors influence the technical 

demands. 

To characterize the workability of concrete mixes, the following terms are usually used in 

Central Europe: 

Terms for workability: 

very stiff 

stiff 

plastic 

soft (wet) 

flowing (liquid) 

However, those terms are not clearly defined. In England for instance, completely different 

terms are used: 

♦ Low, medium, and high consistency. 


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Concrete 

3.2 Influence on the Workability 

The workability of concrete is influenced in various ways by its solid and liquid components 

and environmental conditions. 

3.2.1 Effect of water 

The workability is related to the water content that is available for the lubrication of a mix. By 

increasing the water content in the mix up to a certain limit, the workability of the mix can be 

improved, i.e. the mix will be more wet. If the water content exceeds a certain amount, there 

is the danger of segregation. 

The water content of the mix is expressed in liters or kilograms of water per cubic meter of 

concrete (pound per cubic yard). 

3.2.2 Effect of solid constituents 

Solid matter (aggregate + cement) shows a double effect on the workability: 

♦ The shape of the solid grains influences the mobility of concrete in the following manner: 

• Coarse particles impede the mobility by their angularity and friction; 

• The fine grains, on the other hand, improve it because they act almost like ballbearings 

between the coarse grains. This action is distinctly noticeable when lime or 

fly ash are added to concrete: their spherical particles improve concrete consistency. 

♦ By absorption of the surface, eventually also by chemical bond, part of the mixing water 

is fixed. Only the remaining ‘mobile’ part influences concrete consistency. 

The effect of aggregate properties on workability is considerable. 

Note: 

Grain size distribution, angularity and surface texture of the 

aggregates significantly affect concrete consistency. 

The effect of cement properties on workability is very small 

The effect must be attributed to the water requirement of cement which can be determined 

with standard methods on the cement paste. The chemical-mineralogical composition has a 

stronger influence on the water requirement than fineness and grain size distribution. Grain 

size distribution shows only little variation in industrial cements. 

If the amount of cement added to a concrete mix is increased at a constant water content, a 

stiffening action is the result because more water is absorbed. If, however, both cement and 

water are increased, so that the w/c ratio remains unchanged, the lubricating action of the 

additional cement paste increases the fluidity. 

Thus, the workability of a given aggregate mix can be improved in two ways: by increasing 

the water content only, or by increasing the dosage of both, water and cement. In the first 

case the quality of hardened concrete will be inferior; in the second case the quality is 

maintained but at higher costs. 


Cement 

Concrete 

3.2.3 Effects of admixtures 

Some admixtures such as plastifiers, water reducers and superplastifiers, can modify the 

concrete consistency even if added in small quantities (see chapter ‘Concrete Main 

Components’, paragraph 3.). 

3.2.4 Effect of temperature 

Increased temperature of the concrete and surrounding air contributes towards a stiffer 

consistency. 

Fig. 4: Effect of temperature on the consistency (slump) 

12 

11 

10 

Slump (cm) 

9 

8 

7 

6 

5 

4 

0 5 10 15 20 25 30 35 40 

Temperature (°C) 

The consistency in the above mentioned figure was tested immediately after the mixing of 

the concretes according to the same mix design. Only the temperature of the materials 

(cement + aggregate + water) and the ambient temperature were changed. 

3.3 Other properties of fresh concrete 

3.3.1 Bulk density (unit weight) 

The unit weight of fresh concrete gives some indication about the final void content which is 

responsible for final concrete properties. It is also a measure of the yield; i.e. it indicates the 

concrete volume produced with a specific amount of cement. The bulk density is determined 

by weighing a defined concrete volume. It depends very much on the water and less on the 

cement dosage. After compaction, the unit weight of ordinary concrete should be higher than 

2300 kg/m 3 . 


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Concrete 

3.3.2 Air content 

Ordinary concrete which is well compacted, has an air content of about 0.5 to 1.5%. The 

measuring of the air content is important if entrained air is used. Air-entrained concrete is 

produced by using either an air-entrained cement or an air-entraining admixture during the 

mixing of concrete. Air-entrained concrete contains 3 to 7 Vol. % pores. - Entrained air 

improves the workability of fresh concrete. 

3.4 From fresh to hardened concrete - Stages of development of 

concrete 

‘Green’ and ‘young’ concrete are the terms for specific intermediary stages during the 

transition of concrete from a workable, more or less plastic mass, to an artificial stone. 

With the development of modern concrete technology and building methods, the properties 

of concrete at these intermediate stages have become important as well. The continuous 

development of hardened concrete is a sequence of periods of: 

Concrete is a process: 

Stiffening → Setting → Hardening 

These periods are characterized by different growth rates of the various mechanical 

properties of the concrete (see following figure). 

Fig. 5: Stages of development of concrete 

Stiffening 

of concrete is a change in the workability (sometimes also called slump loss) and begins 

immediately after mixing, sometimes even during mixing. 


Cement 

Concrete 

This can have unfavourable consequences if fresh concrete is not placed properly after 

mixing, or, especially if ready mix concrete is used, in precast manufacturing, or on large 

building sites and placing has to be delayed. 

Concrete should be placed as soon as possible after mixing, but often there may be a time 

lapse of up to one hour or even more between mixing and placing. In these cases, too rapid 

stiffening can impede placing. 

The time during which concrete is still workable - at the right 

consistency - is very important for transporting and placing. 

This time depends on the purpose for which concrete is used and on 

the method of placing. 

Setting 

is the beginning of the hydration process and is indicated by the transition from the plastic to 

the solid state within a relatively short period of time. 

The resistance against deformation during setting increases rapidly, strength less rapidly. 

Note: 

The time of setting of concrete is not identical with that of cement 

measured on paste according to standards. 

The reason is that the setting of concrete is influenced not only by the setting behavior of the 

cement, but also by varying cement and water contents, by temperature and type of 

construction. 

Until setting, deformations of concrete are almost totally irreversible; the elastic part of 

deformations becomes predominant only after setting. 

Hardening 

is the subsequent improvement of mechanical properties of concrete after setting. Soon after 

setting, the strength begins to increase more rapidly than the elasticity (Young-modulus). The 

rate of increase reaches its maximum between 5 and 20 hours after the addition of water. 

Green concrete: 

3.5 Properties of ‘Green’ and ‘Young’ Concrete 

The mechanical properties of green concrete are important in practice, especially in the 

precast industry, where blocks, tubes and other concrete products are moulded by pressing. 

The moulded pieces have to be removed from the press as soon as possible in order to 

make room for the next series. However, this is only possible if the cohesion of the concrete 

is high enough, even before setting, to bear its own weight without deformation. Sometimes 

the moulded pieces (e.g. blocks) are stored in several layers. In this case, the strength after 

demoulding will have to be higher, so as to carry the whole load. 


Cement 

Concrete 

Young concrete: 

Since young concrete at early age very often has to support a mechanical stress, it must 

have a minimum strength. Thus, the strength at this stage (after some hours) is decisive in 

the precast industry, where it determines the intervals at which precast elements can be 

demoulded, transported and piled up. It is also important in other building processes, for 

instance with prestressed concrete. The strength requirements vary according to the size 

and shape of the concrete element and the building method. 

Early strength: 

The compressive strength during the first few hours after placing is 

called early strength. 

It must reach approx. 10 to 20 MPa for demoulding in reinforced 

concrete and 

35 MPa for the release of the prestressing wires in the pretensioned, 

prestressed concrete. 

4 Hardened concrete 

4.1 General 

Hardened concrete is the final building material as it is obtained after stiffening, setting and 

hardening of fresh concrete. Hardening, however, continues for many years, slowing down 

after a certain strength has been reached. Therefore, it is generally accepted to consider the 

properties of hardened concrete at the age of 28 days as characteristic. They are commonly 

used for the design of concrete structures. 

Hardened concrete must meet various requirements and maintain its properties during a very 

long time. Most important are the load-bearing properties and the durability of concrete. 

The resistance to loading of concrete depends on its strength. But a building can never be 

loaded to the strength limit. Structural members are designed in such a way that the 

calculated stresses in concrete do not exceed certain permissible working values. According 

to the function of the building, other special requirements may be of importance. 

A large variety of concrete properties can be obtained by the choice of the components and 

the mix design. However, the nature of concrete, the availability of the materials and 

economical considerations limit these possibilities. 

4.2 Strength 

According to the type and direction of load and stress, various types of strength react in 

concrete: 

♦ Compressive strength: 

Compressive strength is the most important characteristic of hardened concrete. High 

compressive strength is, in most cases, accompanied also by an improvement of the 

other properties. compressive strength determinations show the best reproducibility. 

Therefore, compressive strength is considered as a general measure of concrete quality. 

The compressive strength of commonly used concrete after 28 days is in the range of 10 

to 70 N/mm 2 . The low values (∼ 10 to 20 N/mm 2 ) are used for plain concrete, the medium 

values (∼ 20 to 45 N/mm 2 ) for reinforced concrete and the high values (∼ 50 to 70 N/mm 2 ) 

for prestressed concrete and precast elements. 


Cement 

Concrete 

♦ Tensile strength: 

Tensile strength is relatively low and amount to only approx. 1/10 of the compressive 

strength of hardened concrete. Because the tensile strength is low, it is practically not 

taken into consideration for structural design. Tensile stresses in the construction are 

carried by steel reinforcements. 

♦ Flexural strength: 

It is difficult to determine the tensile strength of concrete and therefore bending or flexural 

strength is measured. 

♦ Impact strength; 

Impact strength plays a significant role in special applications, e.g. for piles to be driven 

into the ground. 

4.3 Deformation under load: modulus of elasticity and creep 

Even momentary loads cause deformation of concrete. If they exceed certain limits, there is 

a risk of cracking. 

Note: 

Concrete is a plastic-elastic material 

Its deformation is always composed of the two components: elastic and plastic. 

The elastic deformation disappears when the load is removed, the plastic deformation 

remains. 

Deformation 

Elastic deformation 

REVERSIBLE 

Plastic deformation 

IRREVERSIBLE 

In hardened concrete, the main part of deformation is elastic. 

A quantitative measure of elasticity is the ratio between stress and corresponding strain. This 

ratio is termed modulus of elasticity E (Young modulus = initial tangent modulus). 

σ ∆L 

E= ε = 

ε 

[ GPa] [] 1 

L 0 

The modulus of elasticity may be measured in tension, compression or shear. The modulus 

in tension is usually equal to the modulus in compression and is frequently referred to as 

Young Modulus of elasticity (Table). 


Cement 

Concrete 

Table 1: Modulus of Elasticity of Different Building Materials 

Material 

Modulus of elasticity 

[GPa] 

Steel 200 to 230 

Aluminium 74 

Copper 130 

Natural stone 12 to 80 

Concrete 20 to 50 

Mortar 5 to 20 

Timber 6 to 15 

Due to the fact that concrete is neither ideally plastic nor ideally elastic material, the manner 

in which its modulus of elasticity is defined is somewhat arbitrary. Various forms of the 

modulus, which are used, are illustrated on the stress-strain curve in following diagram: 

Fig. 6: Typical stress-strain curve for concrete 

Initial tangent (= Young) 

modulus 

Stress (MPa) 

Secant modulus 

Unloading 

Tangent 

modulus 

Strain (%) 

It also has to be distinguished between the ‘dynamic E-modulus’ and the ‘static E-modulus’. 

The dynamic E-modulus is applied when concrete is exposed to oscillation. It can be 

calculated, for instance, from the rate of propagation of ultrasonic impulses and is a measure 

for the progression of deformation resistance. Using certain formulas, the compressive 

strength can be estimated from these results. 

Creep: 

Plastic deformation becomes more pronounced with longtime loading. The irreversible 

deformation by longtime loading is called creep. 


Cement 

Concrete 

Definition of plastic deformation: 

The modulus of deformation is the ratio between the applied load and 

the irreversible deformation, expressed as function of time. 

The creep is strongly influenced by the stress/strength ratio. With higher stress/strength ratio 

the creep increases. It also depends on other factors, such as temperature, humidity, etc. 

Creep attains approx. 1.5‰ per 1 MPa load during 1 year. Besides being a disadvantage, 

creep is also useful because it diminishes internal stresses. On the other hand, it reduces the 

effect of prestressing. 

The deformability of concrete has certain limits: 

♦ If the stress grows beyond these limits, the concrete cracks or breaks. 

♦ Strength and resistance against deformation dictate the limits: 

• The higher the strength and the lower the resistance against deformation, the higher 

the limits of deformation. 

σ 

lim 

Deformation limit: ε 

lim 

= ⋅1000(‰ 

) 

E 

Where: σ = strength, E = Young modulus 

Fig. 7: Time-dependent deformations in concrete subjected to a sustained load 

Deformation 

Creep 

Total deformation 

Shrinkage 

Elastic strain 

Time since application of load 

The deformability of hardened concrete is in the range of about 1‰. Another characteristic of 

the deformability is the ratio of the transverse strain to the longitudinal compression or of the 

transverse contraction to the longitudinal strain. 

Poisson’s ration = ε ε 

transverse 

longitudinal 


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Concrete 

While the modulus of elasticity indicates only the alteration of size in one direction, the 

Poisson’s ratio indicates to what extent the load modifies the shape and the volume of the 

concrete (compressibility). It decreases with time and is about 0.2 in hardened concrete. 

Poisson’s ratio and modulus of elasticity describe completely the deformation behavior of a 

material. 

4.4 Density (weight of volume unit) 

The dry density of the dry solid mass and the bulk density of the concrete have to be 

distinguished. 

Density: 

The density (specific gravity) - the weight per unit volume of a dry and pore-free substance 

(mass) - depends above all on the mix design as the density of cement (ρ = 3.0 to 3.15 

g/cm 3 ), aggregate (ρ = 2.6 to 2.7 g/cm 3 ) and water ((ρ = 1.0 g/cm 3 ) vary little. The specific 

gravity of concrete is in the order of 2.3 to 2.5 g/cm 3 . 

Bulk density: 

The bulk density (unit weight) - the weight of concrete per unit volume including voids - 

(about 2.2 to 2.4 t/m 3 for ordinary concrete) depends on the compaction of the concrete. 

The ratio 

Specificgravity−Bulkdensity 

Specificgravity 

indicates the amount of voids in the bulk volume which are filled with water or air. 

Voids weaken all mechanical properties of concrete and are, furthermore, decisive for the 

impermeability and thus the durability of concrete. Therefore, it is most important to compact 

the concrete as firmly as possible. Well compacted concrete contains not more than 1 to 2% 

voids of its volume. 


Cement 

Concrete 

4.5 The durability of concrete 

It is essential that concrete keeps its shape and size and does not suffer any deterioration of 

its substance which could also cause volume changes (soundness). 

As was shown in previous chapters, the mechanical properties of concrete generally 

continue to improve with time. Concrete resists moisture and putrefaction as well as high 

temperatures (between 200 and 300°C). It does not burn. These are very important 

advantages that concrete has over other building materials. 

In this paragraph, some factors influencing the durability are discussed. 

Fig. 8: Durability of concrete 

4.5.1 Volume changes 

Concrete is always subject to changes of volume which can be detrimental if they exceed 

certain limits. 

4.5.2 Volume changes due to physical stress 

There are several types of stress which may cause volume changes: 

♦ Temperature Changes 

Temperature changes cause expansion and contraction in concrete as in all other 

materials. These changes are in the same order of magnitude as in steel (approx. 10 -5 for 

1°C). If these volume changes are impeded, high stresses result, causing cracks. 

Changes due to the freezing - thawing cycle are very hazardous. At freezing 

temperatures, the water volume in concrete increases by about 9%. Due to this 

expansion and thermal stress, concrete can disrupt. The risk is heightened if de-icing 

agents (salts) are employed, because of additional complicated, detrimental effects. The 

best way to avoid this reaction is to created voids allowing the water to expand. This is 

done by enlarging pore volume by about 3 to 7 Vol.% with the aid of air-entraining agents 

(air-entrained concrete), (see chapter ‘Concrete Main Components’, paragraph 3.4). 


Cement 

Concrete 

♦ Moisture Changes: 

Moisture changes - desiccation or absorption of water in hardened concrete - cause 

shrinkage or swelling. These changes continue until an equilibrium of moisture with the 

surroundings is reached which usually takes several years. Maximum final shrinkage 

(determined as a change in length) of the hardened concrete is 0.2 to 0.65 mm/m, 

maximum swelling through storage in water at 20°C, 0.1 to 0.3 mm/m depending on 

atmospheric conditions. 

Fig. 9: Moisture movements in concrete - swelling and shrinkage 

Specimen A 

0.2 

Swelling (%) 

Shrinkage (%) 

0.15 

0.1 

0.05 

0 

-0.05 

-0.1 

-0.15 

-0.2 

-0.25 

-0.3 

0 

Specimen B 

Stored in water 

Stored in air 

Drying 

Specimen A 

Alternative 

wetting and drying 

Time (days) 

Much higher and also more dangerous is shrinkage before the setting of concrete - plastic 

shrinkage. At intensive desiccation it can reach several per mill (‰). If a lot of water is 

allowed to evaporate during the critical period, namely when concrete has only low strength 

and is not prevented from shrinking, e.g. through reinforcement, plastic shrinkage-cracks 

may result. 

To avoid the early shrinkage-cracks, concrete must be protected against desiccation. This 

can be achieved by covering the concrete with burlap or plastic sheets or by spraying it with 

water. 

4.5.3 Volume changes due to alterations of the substance 

Chemical alterations of a substance result in volume changes, causing stresses and possibly 

cracks. 

In concrete mainly the cement stone or the reinforcement (corrosion) are attacked while 

aggregates are generally more resistant. 


Cement 

Concrete 

The volume of cement stone decreases during hydration because the volume of the 

hydration product is about 3 to 11% smaller than the original volume of cement and water. 

This chemical shrinkage has to be distinguished from drying shrinkage. Chemical shrinkage 

enlarges the gel pores and generally does not cause cracks. 

A higher risk for concrete is the expansion of the cement stone caused by the reaction of free 

lime, periclase and sulfate. These compositions produce unsoundness. 

Subsequent reactions between cement and reactive aggregates in hardened concrete can 

have a deteriorating effect on concrete, especially if alkalis in the cement react with reactive 

silica in the aggregates. 

From the external chemical attacks the most important reactions are those with CO 2 in the 

air, with acids, sulfates and ammonium salts. 

5 Factors influencing the strength of concrete 

The concrete properties are the result of a combination of many factors. Some can be 

attributed to the material itself, but just as important are the external influences. As has been 

mentioned previously, the most important and most characteristic property of concrete is its 

compressive strength after 28 days which can also serve as an indication for other 

properties. Therefore, this paragraph will be mainly concerned with concrete strength. 

The main factors influencing the strength are (see also Fig. 10): 

Strength influencing factors: 

♦ Properties of the constituents 

♦ Mix proportions (mix design, formula) 

♦ Way of handling fresh concrete 

♦ Conditions under which the concrete hardens 


Cement 

Concrete 

Fig. 10: Factors influencing the strength of concrete 

Water 

Aggregates 

Mix Desgin 

Cement 

Admixtures 

Quality of Components 

Properties 

Testing 

of 

Concrete 

Curing 

Time 

Humidity 

Temperature 

Batching 

Homogenity 

Placing 

Mixing 

Degree of 

Compaction 

Air Content 

external influences influence of materials 


Cement 

Concrete 

One and the same concrete may show various values when tested with different methods. 

Thus, the method of testing can influence the test results but not the actual properties of 

concrete. 

The following figure gives an indication of the range in which strength values can vary; it 

shows the results of tests carried out on specimens of the most common cements produced 

in ready-mix plants which are affiliated with Holcim. 

Fig. 11: Compressive strength after 28 days of samples of 44 Ready-Mix Plants 

5.1 Influence of the constituents 

5.1.1 Aggregates 

Aggregates represent the largest part of concrete in volume (60 to 75%) as well as in weight. 

Compressive strength of natural aggregates in normal weight concrete exceeds 2 to 3 times 

the strength of cement stone. Thus, it is the strength of the cement stone or the bond that 

limits the concrete strength, the cement stone being the weaker constituent. 

Aggregates of various origin - if they are clean and free of deleterious substances - develop 

practically equal concrete strength if used with the same cement and mix formula (see 

following figure). 


Cement 

Concrete 

Fig. 12: Effect of aggregate on compressive strength concrete with 350 kg/m 3 cement 

and w/c ratio of 0.55 

Note: 

The strength of aggregates does not have a influence on 

the compressive strength of ordinary concrete if they meet 

basic quality requirements. 

The concrete made of various aggregates with equal strength show very different 

consistencies This is obviously due to the grading, angularity and surface roughness of the 

aggregates, requiring various amounts of water to obtain concretes of the same workability. 

The water requirement is mostly influenced by the amount and properties of sand (fine 

aggregates). Grading, the maximum size and shape of the aggregates determine the volume 

of voids in a compacted aggregate mix as well. The percentage of void volume (varying 

between 20 to 40%) indicates the volume of cement paste (cement plus water) required to 

obtain a good concrete mix. 

Note: 

Grading and shape of the aggregates determine the required 

amount of water and cement and thus strongly influence the 

strength of concretes of equal consistency. 

Other properties of aggregates such as: porosity, unsoundness or lack of chemical 

resistance affect the concrete durability. 


Cement 

Concrete 

5.1.2 Water 

Water represents the second largest portion of the volume of fresh concrete. The quality of 

water only exerts influence on concrete strength if it contains deleterious impurities. 

The required water content of a concrete mix depends on the other constituents (cement, 

aggregate, admixture). 

5.1.3 Cement 

Cement has a primary and direct effect on concrete strength by its material properties: 

Composition Water requirement 

= Cement properties Stiffening and hardening 

Fineness Final strength 

The water requirement of cement measured on paste of normal consistency has only little 

influence on the water requirement of concrete (Fig. 13), much less than the aggregate. 

Table 6: Water requirement of standard cement paste and concretes of different 

Consistency 

OPC Cement A OPC Cement B OPC Cement C 

Consistency 

Ref.: Standard 

cement paste 

Water 

Requirement 

(%) 

Vebe 

Consistency 

(sec) 

Water 

Requirement 

(%) 

Vebe 

Consistency 

(sec) 

Water 

Requirement 

(%) 

24 -- 29 -- 29.75 -- 

Vebe 

Consistency 

(sec) 

Concrete: stiff 52 14.8 53.5 15.0 

Stiff-plastic 53.5 10.0 55 10.5 

Plastic 55 5.0 57.5 4.5 58 5.6 

Concluding from the strength test results on standard cement mortar, only a rough estimate 

of the concrete strength can be made. 

With increasing standard mortar strength, concrete strength (with the same formula and 

aggregate mix) generally tends to increase slightly, especially after 28 days (see diagram 

below). The correlation between strength of concrete and mortar is poor; the ratio of both 

varies strongly with each individual cement. Cements with higher mortar strength can have 

even lower concrete strength. 


Cement 

Concrete 

Fig. 13: Relation between concrete and standard mortar strength 

(determined in Concrete Laboratory of the TC-MD on 37 OPC) 


Cement 

Concrete 

Note: 

It is not possible to deduce from the standard mortar 

strength of various cements the strength of concretes of 

equal composition. 

Important statement: 

The hardening rate of concrete is much faster than that of 

standard mortar, as can be seen in the following figure. 

This is of utmost practical importance because on the job 

site under normal conditions (t = 15 to 25°C) the concrete 

reaches a certain percentage of its final strength much 

sooner than standard mortar. 

Fig. 14: Maturity Percentage of Mortar and Concrete 

Due too different rates of hardening, the effect of cement properties on early 

strength is much stronger than on final strength. Finer grinding results in only slightly higher 

final strength but considerably higher early strength. With different cement compositions 

(above all blended cements) a concrete showing lower initial strength may have the same or 

even higher final strength than a concrete with higher initial strength. For more information 

regarding the influence of the cement properties, see paper ‘Cement’. 


Cement 

Concrete 

The influence of admixtures has already been described in paper ‘Concrete Main 

Components’. 

5.2 Influence of mix proportions 

5.2.1 Water / Cement ratio 

As already mentioned, the concrete strength depends essentially on the strength of the 

cement stone, and is only partially determined by the cement strength as measured on 

standard mortar. There must be other factors as well. The strength of mortar made with a 

given cement depends on its compaction, i.e. on the part of volume occupied by solid 

material and by voids (gel pores and capillaries). 

The water requirement of cement for complete hydration is about 25%; another 15% is 

contained in the gel pores. If concrete contains less than 40% water, cement does not 

hydrate completely. Furthermore, since an extremely dry concrete cannot be compacted 

adequately, a deficiency of water causes inferior strength. For reasons regarding the 

workability, however, the concrete usually contains more water than the cement requires. 

The following figure shows how the compaction of mortar depends on the ratio of the water 

content to the cement content: 


Cement 

Concrete 

Figure 15: Structure of fresh cement mortar 

This weight proportion is usually termed water/cement ratio (w/c ratio). While 

standard mortar has always the same prescribed w/c ratio, the water content of concrete 

varies according to the desired consistency and the water requirement of the aggregate and 

of the cement to obtain this consistency. The next two diagrams show the effect of the w/c 

ratio on the concrete strength. 


Cement 

Concrete 

Fig. 16: Relation between compressive strength and water/cement ratio of concrete 

Important statement: 

For the best concrete quality it is important to choose the 

lowest possible w/c ratio that still enables the concrete to 

be perfectly compacted. 

In the concrete standards of different countries the maximum permissible w/c ratio for 

different types of structure is fixed (see tables later: Requirements for concrete acc. to DIN). 


Cement 

Concrete 

One of the most common causes of poor quality of concrete is the addition of too much 

water. Following figure shows how an inaccurate measurement of the quantity of mixing 

water or an uneven moisture content of aggregates may impair the strength of concrete. The 

moisture content of the aggregates must be deduced from the amount of water to be added. 

Fig. 17: Influence of change in water content on compressive strength 

Fig. 18: Relation between calculated and observed concrete strength 


Cement 

Concrete 

The calculated concrete strength is only obtained, however, if the concrete is perfectly 

compacted (porosity < 1%). 

5.2.2 Cement content 

The content of cement or cement paste in concrete must be sufficient to envelop the 

aggregate grains in order to reduce their friction, to glue them, to fill the voids between them 

and also to protect the reinforcement against corrosion. Thus, an insufficient amount of 

cement impairs the workability and compaction of concrete and as a consequence, its 

strength and durability. 

After all voids are filled, a surplus of cement paste does not increase the concrete strength 

any further since cement stone has a lower strength than aggregate (Fig. 20a). By increasing 

the cement content above an optimum, the ratio between compressive strength and cement 

content decreases (see figure). If the cement content in concrete is sufficient for full 

compaction, the strength of fully compacted concrete is given by the strength of the cement 

stone. It depends only on its w/c ratio and on the standard cement strength. 

Fig. 19: Utilization of cement in concrete at constant workability 

5.2.3 Aggregate/Cement ratio 

The optimum ‘aggregate/cement’ ratio is not only considered from a technical but also from 

an economical point of view since aggregate is stronger and cheaper than cement. Thus, the 

grading of aggregate is most important, not only for workability but also for the minimum 

volume of voids. It makes it possible to obtain the required strength with less cement. 

5.3 Influence of handling 

It is most important that the consistency of concrete permits full compaction with the tools 

that are available on the job site. The need for compaction becomes apparent in the following 

figure: 


Cement 

Concrete 

Fig. 20: Relation between strength and compaction 

Another prerequisite for the optimum utilization of the material properties is the homogeneity 

of the mix. To maintain uniformity within one batch and between several batches, accurate 

weighing, thorough mixing and careful transporting and placing is necessary. These 

measures also prevent segregation. 

5.4 Influences of curing 

5.4.1 Moisture 

After placing, the subsequent conditions strongly influence the development of the concrete 

properties. As for the hydration of cement water is required, loss of moisture must be 

prevented or even additional moisture supplied. The next figure shows how concrete strength 

is impaired by the lack of moisture, especially during the first 3 days. 

Fig. 21: Strength of concrete increase as long as moisture is present forhydration of 

cement 

Concrete that hardens submerged in water has the highest strength. Once it is hardened, dry 

concrete has higher strength than moist concrete. 


Cement 

Concrete 

5.4.2 Temperature 

Higher temperatures accelerate setting and hardening of concrete, like other chemical 

processes(see following figures). Seasonal and even daily temperature fluctuations alter the 

hardening characteristics of concrete. 

Fig. 22: Effect of temperatures on the compressive strength of concrete at various 

ages (T ≥ 20 °C) 

Fig. 23: Effect of temperatures on the compressive strength of concrete at various 

ages (T ≤ 20 °C) 


Cement 

Concrete 

Note: 

♦ The temperature during the first 24 hours approximately strongly affects the initial 

strength development of concrete and it predetermines the later hardening and even the 

final strength. Thus, it is futile to maintain high curing temperatures after the first 24 

hours. 

♦ Concrete cured at low temperature achieves a slightly higher final strength than the 

concrete cured at 30 °C or more and vice-versa. 

Accelerated hardening obviously creates structures of hydration products that are less 

favorable for later hardening. 

The effects of temperature depend not only on external curing conditions, but also on the 

temperature within the concrete created by accumulation of hydration heat. 

The development of concrete temperature depends on cement properties, the composition of 

concrete and the size and shape of the concrete element. This fact is illustrated the following 

figure which compares the temperatures of mortar and concrete and of prisms and cubes. If 

concrete is protected against heat-losses and ‘autocuring’ takes place; some mass-concrete, 

the internal temperature of which may rise up to 90 °C, has to be cooled to prevent cracks 

caused by internal stress. 

Figure 24: Temperature of mortar and concrete specimen 

It is important to note that sooner or later the temperature or curing effects may activate the 

potential for hardening of various cements; the potential as such, however, cannot be 

increased by these measures. 

5.5 Influences of testing methods 

The influence of the testing method can sometimes be decisive for the final test result. 

Specimen size, moulding, curing and testing procedure are some of the influencing factors. 

The above mentioned figure demonstrates how test results of temperature evolution 

measurements depend on specimen size and concrete composition. The differences 

between results on test specimens and concrete in construction can be very significant. 

Thus, results of specimen tests are never identical to those obtained from tests on concrete 

in situ. They merely give some indications. (See separate paper: ‘Testing’.) 


Cement 

Concrete 

6 Conclusions 

There are many factors which influence the properties of hardened concrete. The next figure 

summarizes the effect of these various factors. 

Fig. 25 

Factors Influencing the Properties of Concrete 


Cement 

Concrete 

7 Supplementary Literature (Books): 

• P. Hewlett, LEA's Chemistry of Cement & Concrete, 1997 

• J. Skalny, S. Mindess, Materials Science of Concrete II, 1997 

• ACI Manual of Concrete Practice, 1996 

• A.M. Neville, Properties of Concrete, 1996 

• Behavior of Fresh Concrete During Vibration / Aci, 1993 

• P.K. Mehta, P.J.M. Monteiro, Concrete: Structure, Properties and Materials (Prentice 

Hall International Series in Civil Engineering and Engineering Mechanics), 1992 

• P. Bartos, Fresh Concrete. Properties and Tests, 1992 

♦ A.M. Neville, Hardened concrete: physical and mechanical aspects. 


Cement 

Concrete 

Concrete Mix Design 

1. GENERAL.........................................................................................................................69 

2. BASIC DESIGN CONSIDERATIONS............................................................................... 69 

2.1 Costs ........................................................................................................................ 69 

2.2 Workability................................................................................................................ 72 

2.3 Strength and durability ............................................................................................. 72 

3. SPECIFICATIONS FOR CONCRETE MIXES .................................................................. 73 

4. PROCESS OF MIX DESIGN FOR NORMAL-WEIGHT CONCRETE............................... 75 

5. EXAMPLE OF MIX DESIGN CALCULATION.................................................................. 79 

6. CONCLUDING REMARKS............................................................................................... 83 

7. LITERATURE.................................................................................................................... 84 


Cement 

Concrete 

1 General 

Mix design is a process that consists of two interrelated steps: 

(1) Selection of the suitable ingredients (cement, aggregate, water and admixture) of 

concrete and 

(2) Determination of their relative quantities to produce as economically as possible 

concrete of appropriate workability, strength and durability 

Although many concrete properties are important, most design procedures are aimed at 

achieving a specified compressive strength at a given workability; it is assumed that if this is 

done, the other properties will also be satisfactory. An exception represent the resistance to 

freeze-thaw and other durability problems (for instance sulphate resistance), which require 

special attention in the mix design. 

2 Basic Design considerations 

2.1 Costs 

The cost of concreting is made up of material costs, plant and labour expenses. Except for 

some special concretes, the costs of labour and equipment are, however, to a large extent 

independent of the type and quality of concrete produced. It is therefore the material costs 

that are most important in determining the relative costs of different mix designs. Since 

cement is much more expensive than aggregate (see Table 1), it is clear that minimising the 

cement content is the most important single factor in reducing concrete costs (see also 

Figure 1). 

Table 1: Prices of concrete constituents in Switzerland per ton (approx.) 

Concrete constituent 

Price (CHF) 

OPC cement silo 110.-- 

OPC cement bag 125.-- 

Sand fraction 0/4 mm 20.20 

Gravel fraction 4/8 mm 16.90 

Gravel fraction 8/16 mm 12.-- 

Gravel fraction 16/32 mm 9.40 

To economise on material costs, the proportioning should minimise the cement content 

without scarifying concrete quality. Since the quality depends primarily upon the w/c ratio, the 

water content should be reduced to lower the cement content. Some of the steps to minimise 

water and cement contents are to use: 

♦ the stiffest practicable mixture 

♦ the largest possible maximum size of aggregate 

♦ the optimum ratio of fine and coarse aggregates 

The cement reduction is, however, often restricted by specifications stating the minimum 

cement content (see Table 2). 


Cement 

Concrete 

Table 2: 

Minimum cement content in concrete for different national standards 

(kg/m 3 ) 

Type of concrete 

Germany 

DIN 1045 

Switzerland 

SIA 162 

France* 

NF P-18-305 

USA 

England 

Plain concrete ≥ 100 -- -- -- -- 

Reinforced/prestressed 

concrete 

280 (OPC 

25) 

240 (OPC 

35) 

300 

for class 250 

and higher: 

(250 + 

B)/D 1/5 none none 

* B = compr. strength in bar; D = max. aggregate size 


Cement 

Concrete 

Figure 1: 

Costs of concrete: material costs 

Cement 

17.4 

Rich mix 

Lean Mix 

Cement 

9.3 

W: 6.7 

Water 

7.8 

Cement 

60.2 

Fine 

aggreg. 

Cement 

46.5 

Fine 

Aggreg. 

28.0 

37.4 

Fine 

aggreg. 

Coarse 

Aggreg. 

37.4 

Fine 

aggreg. 

22.8 

Coarse 

aggreg. 

Coarse 

aggreg. 

56.0 

21.4 

Coarse 

aggreg. 

32.1 

17.0 

Mix proportions 

by weight % 

Costs 

% 


by weight % 

Costs 

% 

It should be noted here that in addition to cost, there are other benefits by using a low 

cement content; shrinkage will in general be reduced and there will be less heat of hydration. 


Cement 

Concrete 

However, if the cement contents are too low, they will diminish the early strength and 

durability of concrete and will make uniformity of the concrete a more critical consideration. 

Besides the cement reduction as such, there is also an interesting potential to reduce costs 

through the replacement of cement by mineral components (e.g. fly ash or ground blast 

furnace slag). Prerequisite is of course that mineral components of good quality are available 

at the concrete plant at convenient prices. 

To determine the most economical mix proportions, the relative costs of fine and coarse 

aggregates should also be taken into consideration. Since admixtures to reduce the water 

requirement will increase material costs, it should be assessed in each case whether their 

use is justified by the savings in labour costs and cement cost eventually. 

The economy of a particular mix design should also be related to the degree of quality 

control that can be expected on a job. At least on small jobs, it may be cheaper to overdesign 

the concrete than to provide extensive quality control that would be required with a more 

cost-efficient concrete. 


Clearly, a properly designed mix must be capable of being placed and compacted properly 

with the equipment available. Finishability must be adequate, and segregation and bleeding 

should be minimised. As a general rule, the concrete should be supplied at the minimum 

workability that will permit adequate placement. The water requirement for workability 

depends mostly on the characteristics of the aggregate rather than of those of the cement. 

Where necessary, workability should be improved by increasing the mortar content rather 

than by simply adding more water or more fine material. Thus, co-operation between the mix 

designer and the contractor is essential to ensure a good concrete mix. In some cases, a 

less economical mix may be the best solution. 

2.3 Strength and durability 

In general, concrete specifications will require a minimum compressive strength. They may 

also impose limitations on the permissible w/c-ratios and minimum cement contents. It is 

important to ensure that these requirements are not mutually incompatible. It is not 

necessarily the 28 day strength that is most important; strength at other ages may control the 

design. 

Specifications may also require that the concrete meet certain durability requirements, such 

as resistance to freezing and thawing, or chemical attack. These considerations may provide 

further limitations on the w/c-ratio or cement content and in addition may require the use of 

admixtures. 


Cement 

Concrete 

3 Specifications for Concrete Mixes 

There are three systems that can be applied to specify structural concrete. These differ with 

respect to the basis of specification, responsibility for the mix design and the parameter by 

which the concrete is judged for compliance, as indicated in Table 3. 

Table 3: 

Types of concrete mixes and their method of specification 

Type of mix Designed mix Codified mix Prescribed mix 

Design 

stage 

Production 

stage 

Compliance 

stage 

Basis of 

specification 

Strength 

classes 

Responsibility 

for mix design 

Permitted 

materials 

Strength testing 

for information 

Basic 

parameters of 

concrete for 

compliance 

testing 

Strength Mix Proportions Mix Proportions 

all ≤ 25 N/mm 2 all 

Producer 

Any materials 

complying with 

National 

Standards 

Basis of mix 

Strength 

National code 

or specification 

Restricted 

range of 

materials 

complying with 

Nat. Standards 

Not usually 

necessary 

Purchaser 

any 

Desirable 

especially for 

higher strength 

classes 

Mix proportions Mix proportions 


Cement 

Concrete 

Designed mixes 

The mix should be designed to have an adequate margin of strength between the specified 

characteristic strength or the designed mean strength based on the standard deviation 

obtained through experience. If there are no previous data, or if there are less than 30 results 

obtained under equal conditions (same plant, source of materials, and supervision), the 

proposed minimum value for standard deviation as per curve A (Figure 2) should be 

considered. 

Figure 2: 

Proposed minimum values for the standard deviation 

If there are between 30 and 100 results, the standard deviation should be the value obtained 

but not less than that given by curve B, i.e. for characteristic strength equal to or greater than 

20 N/mm 2 , the minimum standard deviation is 4 N/mm 2 . For more than 100 results curve C 

gives the minimum standard deviation. 

These values of standard deviation will be used for the calculation of characteristic strength. 

Designed mixes are the most common types of mixes used in concrete practice. 

Codified mixes 

Codified mixes are recommended in National Standards or Codes and are based on the 

characteristics of the cement and aggregates available in each country. The adequacy of the 

structure is generally assured since the cement content will usually be greater than that of 

the corresponding designed mixes. 

Codified mixes are restricted to the lower strength classes of concrete and may be made 

only with restricted types of materials. They are sometimes used as approximate guidelines 

for designed mixes. 


Cement 

Concrete 

Prescribed mixes 

Prescribed mixes are applied when the purchaser wishes to specify the mix proportions to be 

used. There are a number of circumstances which call for such mixes; for example, if the 

purchaser knows that with local materials certain mix proportions will produce concrete of the 

required proportions, or if he requests the use of specific mixes because he wants a concrete 

with special characteristics (high or low density, etc.). Since the purchaser designs the mix, it 

is also his responsibility to ensure that the strength and other requirements for the safety of 

the construction are met. 

4 Process of mix design for normal-weight concrete 

Before a concrete mix can be designed and proportioned, certain points of information 

should be known: 

1) Size and shape of structural members 

2) Spacing and diameter of reinforcement 

3) Required strength 

4) Exposure conditions (requirements for durability and chemical attack) 

5) Placing and compaction methods 

6) Basic material quality data on cement and aggregate 

It is up to the design engineer and the architect to provide the information for points 1), 2) 

and 3). The information for points 5) and 6) can be obtained from the contractor firm and 

material supplier. As to point 4), the requirements for exposure conditions are normally 

specified in the standards. 

The basic factors that have to be considered in determining the mix proportions are 

represented schematically in Figure 3. 


Cement 

Concrete 

Figure 3: 

Basic factors in the process of mix design 

Liability to chemical 

attack, or size of 

concrete mass 

Method 

of compaction 

Size of section and 

spacing of reinforcement 

Quality 

control 

Minimum 

strength 

Required 

workability 

Maximum size 

of aggregate 

Aggregate shape 

and texture 

Mean 

strength 

Type of cement 

Durability 

w/c Ratio 

Aggreg./Cement 

Ratio 

Grading of 

aggregate 

Proportion 

of each size 

fraction 


The American Concrete Institute ACI recommends a maximum permissible w/c ratio for 

different types of structures and degree of exposure. The European Norm EN 206 for 

concrete describes as well the maximum permissible w/c ratio, minimum cement content, the 

minimum air content and range of aggregate grading for the different exposure conditions. 

It should be explained that a design in the strict sense of the word is not possible: many of 

the material properties and effects in the concreting process cannot be truly assessed 

quantitatively, so that we are really making no more than an intelligent guess at the optimum 

combinations of the ingredients on the basis of the relationships established empirically. 

Therefore, we not only have to calculate or estimate the proportions of the available 

materials, but must also make trial mixes. Properties of trial mixes are checked and 

adjustments in the proportioning are made until a fully satisfactory mix is attained. 

Trial mixes are usually relatively small batches made with laboratory precision so that a 

certain security factor should be calculated when using laboratory results on large job-site 

batches. 


Cement 

Concrete 

The calculation of material quantities for mix design of ordinary normal-weight concrete is 

based on the absolute volume of the ingredients: 

Volumes in 1m 3 compacted fresh concrete: 

3 

[ ] 

C A W 

+ + + P= 

1000 dm 

δ δ δ 

c 

A 

w 

C = cement content in kg/m 3 

A = aggregate content in kg/m 3 

W = water content in kg/m 3 

P = air pores; 

in compacted non-air-entrained concrete:10 ÷ 20 dm 3 /m 3 ; 

in air-entrained concrete: 30 ÷ 70 dm 3 /m 3 

δ c = bulk density of cement kg/dm 3 

δ A = bulk density of aggregate kg/dm 3 

δ w = bulk density of water = 1.0 kg/dm 3 

Guide values for the above bulk densities are given in Table 4 

Table 4: Guide values for bulk densities δ in kg/dm 3 

Cements 

Aggregates 

Portland cement 3.05 - 3.15 kg/dm 3 Sand, gravel 2.6 - 2.65 kg/dm 3 

Blast furnace 

3.0 kg/dm 3 Limestone 2.7 kg/dm 3 

slag cement 

Pozzolanic 

2.9 kg/dm 3 Basalt 2.9 kg/dm 3 

cement 

Volcanic gravel + 2.1 - 2.4 kg/dm 3 

sand 

Lightweight 

aggregate 

for structural 

lightweight 

concrete 

0.4 ÷ 1.9 kg/dm 3 

There are various methods to calculate a concrete mix. The difference between those 

methods is not to be attributed to the basic factors but rather to the mode of calculation and 

adjustment applied. As example, three methods to calculate the mix design of normal weight 

concrete are compared in Table 5. 

Here, only the general principle of the mix design procedure shall be briefly presented (see 

also example of mix design in the next chapter): 

First of all, the maximum permissible w/c-ratio for the required concrete strength has to be 

fixed; this value can be taken from the relationship w/c-ratio - concrete strength in function of 

the strength class of the cement. 


Cement 

Concrete 

Then, the required water content w (mixing water plus surface humidity of aggregate) has to 

be defined. The water content w can be estimated based on the needed consistency and the 

aggregate grading and modulus respectively. 

Table 5: 

Example of methods to calculate a concrete mix 

Step 

No. 

United States 

ACI 

Country & Standard (Code) 

England 

Dep. of Environment 

1. workability = slump mean strength (w/cratio) 

2. max. size of aggregate water content 

(workability) 

3. mixing water + (air cement content 

content) 

W. Germany 

DIN 

cement quality 

consistency 

grading of 

aggregate 

4. w/c ratio aggregate content water content 

5. cement content fine/coarse aggregate concrete strength 

6. coarse aggregate content trial mixes w/c ratio 

7. fine aggregate content cement content 

8. adjustment for aggregate 

moisture 

weight of 

ingredients 

9. trial batch adjustments trial mix 

For 

details 

consult: 

ACI 211.1-91, ACI 

Manual of Concrete 

Practice, American 

Concrete Institute, USA 

A. Neville: Properties of 

concrete. Chapter 14. 

Mix Design., Longman, 

1995 

K. Walz: 

Herstellung von 

Beton nach DIN 

1045. Beton-Verlag 

GmbH, Düsseldorf, 

1971. 

The necessary cement content c in the concrete mix can accordingly be calculated with the 

w/c-ratio and the water content w by means of the following formula: 

c = w/(w/c) 

Knowing the cement and water content, we can calculate the required amount of aggregate 

using the equation on the absolute volume of the ingredients (assumption on air pores p). 

Thus, the weight of oven dry aggregate A for 1 m 3 of concrete is: 

A = δ A (1000 - c/δ c - w - p) 

If humid aggregate is used, then the amount of surface humidity during concrete preparation 

has to be determined and to be included for the proportioning of the mixing water and the 

aggregate. The mixing water is calculated by subtracting the content on surface humidity 

from the water content w. For the proportioning of the aggregate, the amount A calculated 

according to the above equation has to be increased by the content of surface humidity. 

If plasticising concrete admixtures (e.g. water reducers or air entrainer) are added to the 

concrete, the water content w for a given consistency is reduced. The fine air pores produced 

by the addition of air entrainer improve also indeed the workability, but they reduce at the 

same time the concrete strength; in case of air entrained concrete, the real water content has 


Cement 

Concrete 

therefore to be adjusted for both the plasticising and strength reducing effect of the air 

entrainer. 

5 Example of Mix Design Calculation 

For illustration, a mix design shall be calculated here with the aid of Table 6 and Figures 4 to 

6 from DIN standard 1045. 

In our example, the concrete requirements shall be as follows:: 

♦ consistency: compaction factor 1.20 

♦ strength class: B 35 

♦ exposure condition: interior of building (thus no further limitations on w/c-ratio and cement 

content) 

♦ max aggregate size: 32 mm 

♦ aggregate grading: between sieve curves A and B (see Figure 6) 

The available concrete components are: 

♦ cement class Z 35 (density 3.10 kg/dm 3 ) 

♦ aggregates: 

sand 0/2 mm (density 2.52 kg/dm 3 ) 

natural aggregate 2/8 mm (density 2.62 kg/dm 3 ) 

natural aggregate 8/32 mm (density 2.72 kg/dm 3 ) 

with the following grading: 

Passing sieves (%) 0.25mm 0.5 mm 1 mm 2 mm 4 mm 8 mm 16 mm 32 mm 

sand 6 50 80 97 100 100 100 100 

aggr. 2/8mm 3 8 10 10 55 95 100 100 

aggr. 8/32 mm 2 2 3 3 4 6 50 100 

The average compressive strength tested on three cubes in one trial batch for the concrete 

strength class B 35 should be at least 45 N/mm 2 (see Table 6). Accordingly, the 

water/cement-ratio can be estimated from Figure 4; it amounts to 0.47. 

Aiming at a grading of the aggregate mixture between A and B sieve curves, the estimated 

amount of aggregate fractions is: 

♦ sand: 

25 vol.% 

♦ 2/8 mm: 23 vol. % 

♦ 8/32 mm: 52 vol. % 

The resulting grading of the aggregate mixture is thus: 

Passing sieves (%) 0.25 mm 0.5 mm 1 mm 2 mm 4 mm 8 mm 16 mm 32 mm 

3 15 24 28 39 49 74 100 


Cement 

Concrete 

With the corresponding grading modulus 4.68 and the concrete compacting factor of 1.20, 

the water content w estimated from Figure 5 is 153 kg/m 3 . 

The calculated cement content c is therefore: 

153 : 0.47 = 325 kg/m 3 of concrete 

The volume proportion of the oven dry aggregate mixture in 1 m 3 of concrete can then be 

calculated by means of the absolute volume of the ingredients (assuming an air content P of 

15 dm 3 ): 

consisting of: 

A = 1000 - (c/3.10 - w - P) = 1000 - (325/3.10 - 153 - 15) = 727 dm 3 

727 x 0.25 x 2.62 = 476 kg of sand 

727 x 0.23 x 2.62 = 438 kg of fraction 2/8 mm 

727 x 0.52 x 2.72 = 1028 kg of fraction 8/32 mm 

That means 1942 kg of aggregate mix in 1 m 3 of concrete. 

The mix design is thus: 

aggregate 1942 kg/m 3 

cement 325 kg/m 3 

water 153 kg/m 3 

resulting in 2420 kg/m 3 of fresh compacted concrete. 

Table 6: Requirements for concrete in preliminary test 

Required Group of concrete Strength class Required compr. 

strength 

(N/mm 2 1), 2) 

) 

consistency 

values 2) 

B I B 5 

B 10 

B 15 

B 25 

≥ 11 

≥ 20 

≥ 25 

≥ 35 

K 1: v = 1.30...1.26 

K 2: v = 1.15...1.11 

a = 39...40 cm 

K3: v = 1.06...1.04 

a = 48...50 cm 

B II B 35 

B 45 

B 55 

40 + m 3) according to 

60 + m 3) site, incl. margin 

50 + m 3) requirements of the 

1) 

2) 

average compressive strength of three cubes of one batch 

site-mixed and ready-mixed concrete, not for concrete in concrete works 

3) choose margin m according to experience, otherwise m ≥ 5 MPa are to be used 


Cement 

Concrete 

Figure 4: 

Relationship strength versus w/c ratio 


Cement 

Concrete 

Figure 5: Relationship between consistency, grading modulus and water content of 

concrete 

Correction of water content: 

- by using crushed + 5 ÷ 10% 

aggregate 

- by using plasticisers - 5% 

- by using air-entraining 

agents 

- 1% per 1% of air 

content 


Cement 

Concrete 

Figure 6: 

Standard grading curves 

6 Concluding Remarks 

There are several well established methods to calculate concrete mixes. Given the variability 

of the properties of ingredients and the difficulty in describing them, the results of these 

calculations are, however, really only guesses. On the other hand, such methods are 

concerned basically with the technical aspects of mix design without proper consideration of 

the economical side of the problem. 

The establishment of a proper concrete mix design will always involve the preparation and 

testing of trial mixes and consecutive adjustments. The experience and knowledge on the 

influence of the various factors upon the properties of concrete can of course help to improve 

the first guess and limit the number of trial mixes to be tested. 

To facilitate the selection of the optimum concrete mix design (also from the economic point 

of view), more and more computer based tools are used nowadays in practice. Such tools do 

not replace experience, but allow to explore more quickly the different alternatives and to 

arrive faster at the optimum solution. 


Cement 

Concrete 

7 Literature 

ACI 211.1-91, Standard practice for selecting proportions for normal, heavyweight, and mass 

concrete, in: ACI Manual of Concrete Practice 1996, Part 1, American Concrete Institute, 

Farmington Hills, USA, 38 pp. 

Neville, A.M., Selection of concrete mix proportions (mix design), in: Properties of Concrete, 

Longman, England, 1995, pp. 724 - 772 

Day, K.W., Concrete mix design, quality control and specifications, E & F.N. Spon, London, 

1995, 350 pp. 

Kosmataka, S.H, and Panarese, W.C., Design and control of concrete mixtures, PCA, 

Skokie, 1994, 205 pp. 

Daly, D.D., Concrete mix design, in: Fulton's Concrete Technology, PCI, Midrand, 1994, pp. 

209 - 217 

Torrent, R., and Honerkamp, M., Computer aided optimised concrete mix-design, 33rd 

Technical Meeting/10th Aggregate and Ready-Mixed Concrete Conference, Basle, 1994, 

HMC Report MA 94/3157/E 

Bai, Y., and Amirkhanian, S.N., Knowledge-based expert system for concrete mix design, 

Journal of Construction Engineering and Management, Vol. 120, No. 2, 1994, pp. 357 - 373 

Foo, H.C., and Akhras, G., Expert systems and design of concrete mixtures, Concrete 

International, July 1993, pp. 42 – 46 


Cement 

Concrete 

Reduction in Materials Costs 

1. INTRODUCTION............................................................................................................... 86 

2. DESCRIPTION OF THE PROBLEM................................................................................. 86 

3. OPTIMISATION THROUGH PROPER SELECTION OF THE 

COMPONENTS................................................................................................................. 87 

3.1 Cement..................................................................................................................... 87 

3.2 Mineral Additions...................................................................................................... 89 

3.3 Aggregates............................................................................................................... 90 

3.4 Chemical Admixtures ............................................................................................... 93 

4. OPTIMISATION TROUGH REFINEMENT IN STRENGTH LEVEL.................................. 93 

5. CONCLUSIONS................................................................................................................ 98 

6. REFERENCES.................................................................................................................. 98 


Cement 

Concrete 

1 Introduction 

We are convinced that, even though most Ready-Mixed Concrete (RMC) companies within 

the "Holderbank" Group operate at high levels of rationalisation in terms of materials and 

processes, there is always room to achieve further reductions in materials costs . 

The objective of this contribution is to discuss the basic aspects of the selection of raw 

materials for concrete, as well as their proportioning, in view of possible cost reductions in 

the production of RMC. It is expected that the discussion of those aspects serves as a 

motivation and incentive to our companies in their search of optimising their costs (BCM 

Project). Although they will not be dealt with here, it must be mentioned that aspects of 

production process and quality control must always be considered in the optimisation, since 

they are very important as well. 

2 Description of the Problem 

The basic problem consists in minimising the cost of concrete ($h): 

where: 

$h = C.$c + A.$a + W.$w + M.$m + Q.$q (1) 

$h = materials cost of concrete ($/m3) 

C ; $c = content (kg/m3) and price of cement ($/kg) 

A ; $a = idem for aggregates 

W ; $w = idem for mixing water 

M ; $m = idem for mineral additions 

Q ; $q = idem for chemical admixtures 

Clearly, the solution of the problem does not consist in choosing the cheapest components, 

because the mix design will depend on their quality. Moreover, the terms in (1) are not 

independent, since the sum of the volumes of the components must always add to 1 m3: 

C A W M Q 

--- + --- + --- + --- + --- + P = 1 m3 (2) 

dc da dw dm dq 

where di means the density of component i en kg/m3 and P is the volume, in m3, occupied 

by entrapped or entrained air. 


Cement 

Concrete 

1 

0.9 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0 

Figure 1 

Switzerland 

Argentina 

Cement Gravel Sand Plasticizer 

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

Fig. 1 shows the relative unit prices of the main concrete components in Switzerland and 

Argentina (Cement =1). As is well known, cement price is several times higher than that of 

the aggregates and, hence, to a large extent cost reductions in concrete have to be achieved 

by reducing its cement content. Moreover, the relatively high unit price of plasticizers either 

increase the cost of the mix or has to be compensated by larger savings in cement costs to 

make their use economical. 

The following analyisis of cost optimisation will be made on the basis of mixes that are 

technically equivalent (competitive). That means that they must fulfil the characteristics that 

are normally specified by the customers, i.e. they must possess similar 

consistency/workability and compressive strength. 

3 Optimisation through proper Selection of the 

Components 

3.1 Cement 

The type and physical/chemical characteristics of the cement may have a considerable 

influence on their consumption in the concrete mixes. 


Cement 

Concrete 

Figure 2 

Binder Content (kg/m 3 ) 

for concrete with Slump= 70 mm and f’c cyl@28 

= 25 MPa 

400 

350 

300 

250 

200 

150 

100 

50 

0 

Blends with UNT2 

RO GA UNT5 UNT2 Fly Ash 

(20%) 

Slag 

(35%) 

Filler 

(15%) 

Binder Type 

Fig. 2 shows the cement content required to produce concretes of similar performance 

(consistency, air content and 28-day strength), for various Portland and blended cements [1]. 

It can be seen that there is a considerable difference in their consumption. The most efficient 

cement (GADOR, Type II, export-quality Spanish cement) requires some 225 kg/m3 whilst 

the lest efficient (ROCHE Special, Switzerland) requires 340 kg/m3 to produce equivalent 

concretes. It must be mentioned that the latter is not a commercial cement, because it was 

purposely ground rather coarse (Blaine 2470 g/cm²) and, besides, it possesses a low C3S 

content. In any case, GADOR cement demands some 50 kg/m3 less than the other 

commercial cements, produced at UNTERVAZ, Switzerland, that have average 

characteristics of the market. The consumption of blended cements is somewhat higher than 

that of their Portland component (UNTERVAZ M.2), especially of that containing limestone 

filler, which reflects the scarce hydraulic contribution of this addition. 

The convenience of selecting one of the different solutions varies from case to case. Clearly, 

it depends on the relative prices of each cement type (and of the mineral additions when they 

are added directly into the mixer). But even for a given plant it depends on the characteristics 

of the mix being designed. For instance, a more efficient, albeit more expensive cement, 

might be more convenient for concretes of relatively high strength, but not so for concretes of 

lower strengths or when a minimum amount of cement has to be added anyway due to 

particular specifications. 


Cement 

Concrete 

Cement Content in Concrete (kg/m³) 

Figure 3 

350 

RO 

GA 

U5 

U2 

300 

FAsh 

Slag 

Filler 

250 

200 

40 45 50 55 60 

28-day ISO Mortar Strength (MPa) 

Fig. 3 shows that the cement strength, measured on standard mortar, is not a very accurate 

indicator to predict the efficiency of the cement in concrete mixes. 

3.2 Mineral Additions 

Mineral additions can be incorporated into concrete either with the cement (blended 

cements) or directly, batched as a component, at the concrete plant. 

The convenience of one or the other procedure is a matter of arguments between cement 

and concrete producers [2]. For obvious commercial reasons, the former support the 

introduction of the addition at the cement plan, on the following grounds: 

a) Better control of the quality and quantity of the addition at the cement plant 

b) Avoidance of handling, storing and batching another component at the concrete plant 

c) Better uniformity in the distribution of the addition when it is incorporated into the 

cement 

The first two reasons are generally valid, whilst practical experience and some investigations 

[3] have shown that it is possible to introduce the addition at the concrete plant without 

negative effects on its performance. 

The concrete producer, as long as he can find mineral additions of good and uniform quality 

and at a reasonable price, will prefer in general to add them at his plant. Indeed, this 

procedure will enable him to vary the dosage of the addition according to the characteristics 

of the concrete to be produced, thus widening his range of products and optimising costs. 


Cement 

Concrete 

The use of a mineral addition might lead to cost reductions, depending on its hydraulic 

contribution and price; it will be profitable if: 

$m dC 

---- £ ---- (3) 

$c M 

where dC is the reduction in Portland cement content achieved by using a quantity M of 

mineral addition. 

There is an interesting potential to reduce costs through the judicious use of mineral 

additions, when such materials of good quality are available at the concrete plant at 

convenient prices [4,5]. 


In 1976/77 HMC carried out a comparative study, COMBET, among 44 RMC plants of the 

'Holderbank' Group [6]. Among other aspects, the quality of the aggregates used in each 

plant was compared. Representative samples were taken from each plant, observing the 

proportion of the different fractions used, with which mixes with the same composition were 

prepared at HMC laboratories (350 kg/m3 of the same cement and a w/c ratio of 0.55). 

Figure 4 

Compressive Strength (MPa) 

40 

35 

30 

25 

20 

15 

10 

5 

0 

Reference concrete - Cement: 350 kg/m 3 , w/c= 0.55 

f’cm = 30 ± 3.1 MPa 

Slump < 50 mm 

Slump = 50 - 250 mm 

Aggregates used in 38 RMC GCs 

Fig. 4 shows the results of cube strength at 28 days of such mixes; it can be seen that the 

direct effect of aggregate quality on the compressive strength is not very significant. It must 

be mentioned, however, that those mixes are not strictly comparable because, as indicated 


Cement 

Concrete 

in the graph, the mixes had different consistencies. From the consistencies actually 

measured it is possible to calculate the consumption of cement required to achieve concretes 

of similar consistency and w/c ratio (strength). 

Figure 5 

Reference concrete – Slump = 70 mm, w/c= 0.55 

600 

No. of aggregate fractions in use: 

2 3 = 4 

Cement Consumption (kg/m 3 ) 

500 

400 

300 

200 

100 

0 


Fig. 5 shows the cement consumption calculated for the 33 aggregates studied, to produce 

mixes of slump = 70 mm and w/c = 0.55; they vary along a very large range: 310 to 500 

kg/m3. Moreover, it can be observed that the aggregates composed by just two fractions 

tend to give the worse results, whilst the cement content tends to decrease when more 

fractions are used. The explanation is that, with more fractions available, a better design of 

the aggregate grading is possible. 


Cement 

Concrete 

Figure 6a 

Reference concrete – Slump = 70 mm, w/c= 0.55 

600 

DIN Grading Zone: 

< C B-C A-C A-B 

Cement Consumption (kg/m 3 ) 

500 

400 

300 

200 

100 

0 


Figure 6b 

100 

% Passing 

90 

80 

70 

60 

50 

40 

30 

20 

10 

C 

B 

A 

too fine 

usable 

optimum 

too coarse 

0 

0.15 

0.3 

0.6 

2.4 

1.2 

4.8 

Sieve Opening (mm) 

9.6 

12.5 

19 

25 


Cement 

Concrete 

Fig. 6 shows the calculated cement consumption of the equivalent mixes, indicating the 

location of the aggregate grading with respect to the limits established in DIN Standards. In 

general, aggregates laying within the more favourable zones require less cement. 

One of the conclusions of COMBET study was that in about 30% of the plants investigated, it 

would have been possible to improve the grading by a better proportioning of the fractions 

actually available in them; in general, these cases corresponded to mixes with rather high 

cement consumption. 

3.4 Chemical Admixtures 

Chemical admixtures have become a common component of RMC mixes. The more 

widespread ones are the water reducers/plasticizers (conventional or of high 

range/superplasticizers), retarders, air entraining agents, and combinations of them. 

Given their high unit price, its utilisation is often confined to the purpose of conferring special 

characteristics to the mixes, rather than in reducing costs. In principle, the admixtures with 

highest potential for cost reductions are the plasticizers. In a first analysis, a saving in costs 

will be feasible if : 

$q 1 1 

---- £ ---------------- . ----- (4) 

$c 1 - dW/W0 Q/C 

where dW/W0 is the reduction in water content of the mix generated by the use of the 

plasticizer in the doses Q/C. According to [6] a superplasticizer that, used in doses of 1% of 

the weight of cement, allows a water reduction of 10%, will be economical only if its price is 

less than 11 times that of the cement. In many countries the price of the admixture exceeds 

that relation and, thus, they do not allow a reduction in costs. 

As the water reduction capability of the plasticizers is very variable and depends also on the 

characteristics of the other components and of the mix itself [7] and also as the price varies 

widely from country to country, it is difficult to generalise on their potential for cost 

optimisation. 

4 Optimisation trough Refinement in Strength Level 

The strength of concrete is specified on the basis of statistical criteria. This means that, when 

a customer is specifying a given compressive strength, he is prepared (or should be) to 

accept that a certain proportion p of the concrete delivered is 'defective', i.e., of a strength 

below the specified value (Fig. 7). That proportion p varies according to the codes and 

standards of every country: 

p = 2 % in Switzerland 

p = 5 % in the rest of Europe, Australia, New Zealand, Brazil and Argentina 

p = 10 % in North-America , most of Latin-America and partially in France 


Cement 

Concrete 

Figure 7 

Mean 

Frequency 

Specified 

“defective” 

Concrete 

p 

Margin 

15 20 25 30 35 40 45 


This means that the producer must design his mixes to reach a mean strength exceeding the 

specified strength by a certain Margin. This Margin must compensate the unavoidable 

variations of quality during production. As shown in Fig. 8, the higher his variability, the 

higher the Margin the producer has to adopt and, consequently, the higher the cost of his 

mixes. 

Figure 8 

Means 

Low Variability 

Frequency 

Specified 

High Variability 

M 

15 20 25 30 35 40 45 50 55 



Cement 

Concrete 

Approximately, a reduction of 1 MPa in the standard deviation s of the strength will allow a 

reduction in cement content of: 

Percentage of 'Defectives' 

p 

Cement Savings through 

1 MPa reduction in s 

2% ~ 14 kg/m3 

5% ~ 11 kg/m3 

10% ~ 9 kg/m3 

50% (mean strength) 0 

Therefore, the potential for cost reductions by increasing the production controls so as to 

diminish the variability is higher in countries where the proportion of 'defectives' accepted is 

lower. Obviously, a reduction in the variability often has a cost, due to more controls, better 

installations, more components to process, etc. 

100 

90 

Figure 9 

Swiss RMC Plant, 1980 

% of Total Variability 

80 

70 

60 

50 

40 

30 

20 

10 

Operation 

Cement 

Aggregate 

Testing 

0 

Consistency 

Strength 

The question that arises is: how can we diminish the variability in concrete quality?. An 

investigation carried out at HMC in 1980 [8], allowed an evaluation of the contribution of 

different factors to the variability in consistency and strength in RMC production. Fig. 9 

summarises the results obtained; it can be seen that the variability of the components 

(cement + aggregates) contributed some 10% of the total variability of strength. It is obvious 

that the main source of variability in concrete quality lies in the production process and, in 

particular, in the uncompensated variation in moisture of the aggregates. 


Cement 

Concrete 

Figure 10 

50 

Mean of 6 tests conducted in 39 Holcim RMC Plants 

45 

Actual Strength (MPa) 

40 

35 

30 

25 

20 

15 

15 20 25 30 35 40 

Required Strength (MPa) 

Moreover, the comparative study COMBET (1976/77) also showed that many of the 

investigated mixes were overdesigned in strength (Fig. 10), indicating that there is an 

interesting potential for cost reduction there. 

Probability of accepting the lot 

(%) 

100 

80 

60 

Figure 11 

Mean strength for fck= 30 MPa and s= 4 MPa 

40.3 38.2 36.6 35.1 33.4 30.0 

AFNOR P18-305 

ASTM C94 

40 

20 

0 

0.1 0.5 1 2 5 10 20 50 

0.1 1 10 100 

Actual % of 'defectives' in the lot 


Cement 

Concrete 

In defining the right Margin, it is useful to know the O-C Curves of the particular acceptance 

criterion by which the concrete supplied is to be judged. More information on the concept of 

the O-C Curve can be found in [9]. As an example, Fig. 11 presents the O-C curve for 

criterion of AFNOR P 18-305 (10% of defectives) [10] which is based on the fulfilment of the 

following two conditions (for non-certified production, fck£ 30 MPa): 

where: 

fm3 ³ fck + 4 MPa (1) 

fi ³ fck - 1 MPa (2) 

fm3 : moving average of 3 test results 

fck 

fi 

: specified strength (characteristic strength) 

: each individual test result 

The O-C curve must be understood as follows. Along the x-axis the actual percentage of 

'defectives' (% of concrete with strength below the specified strength fck) is plotted and in the 

y-axis the probability of accepting a lot with such amount of 'defectives' is indicated. To make 

the graph more meaningful, the mean strength of the lots is plotted on the top x-axis, 

assuming an fck= 30 MPa and a standard deviation of 4 MPa. 

It can be seen that, if the supplier designs the concrete with exactly the right Margin for 10% 

"defectives" (Margin= 1.28*s ) he will still get a relatively high proportion of his concrete 

rejected (about 20%). If he wants to ensure a lower proportion of rejections , say 5%, he has 

to overdesign his mix to a Margin= 1.75*s. For s=4 MPa this means about 2 MPa more of 

mean strength and some extra 15 kg/m3 of cement in his mix. If plants are automated, one 

can imagine a scenario where the Margin can be adapted to the characteristics of the client. 

A client that carries out a strict quality control will receive concrete designed with a higher 

margin to avoid rejections, whilst another one that does not, will receive the strictly minimum 

margin of 1.28*s (going below this margin will constitute a dishonest practice and must not 

be done). 

As a comparison, Fig. 11 shows also the acceptance criterion of ASTM C94, which is based 

on the fulfilment of the following two conditions [11]: 

fm3 ³ fck (3) 

fi ³ fck - 3.4 MPa (4) 

It can be seen that the ASTM C94 criterion is more favourable to the producer (less risk of 

rejection of lots with up to 10% 'defectives') but is a bit unfair to the customer (higher risk of 

acceptance of lots with more than 10% 'defectives'). This illustrates the consequences that 

the acceptance criterion has on the risks for both the producer and the consumer of 

concrete. 


Cement 

Concrete 

5 CONCLUSIONS 

Several factors known for their potential in achieving cost reductions in ready-mix concrete 

mixes have been discussed. 

It has been seen that the cement type may have a significant influence on the cement 

consumption and, therefore, on the cost of the mixes. 

Certain potential also exists in adding mineral additions at the concrete plant (when they are 

suitable and available), which also opens possibilities in products differentiation. 

It is considered that the aggregates, given their enormous incidence in the cement 

consumption of the mixes, offer the best potential for mix optimisation and cost reductions. 

The potential of achieving cost reductions through the utilisation of chemical admixtures 

depends strongly on their efficiency and price. 

Important savings can be achieved by fine-tuning the mix design to strict margins that cover 

the production variability and certain unforeseeables. A good knowledge of the risks implied 

in the compliance criteria applicable to RMC is essential to that end. 

Appendix A shows the result of a BCM (Better Cost Management) initiative undertaken by St. 

Lawrence Group in Canada, with the support of HMC, to find ways to reduce costs in Ready- 

Mixed Concrete production. Huge potential for cost savings was detected in many of the 

areas discussed in this paper. 

6 REFERENCES 

[1] Torrent, R. and Jornet, A., "Covercrete Study, Part I", MA Report 90/3815/E, 1990. 

[2] Braun, H., "Composite cements and hydraulic additives for ready-mixed concrete", 

5th Stone & Ready-Mixed Concrete Conference, paper No. 14, Lucerne, 1983. 

[3] Longo, A. and Torrent, R., "Methods of addition of blast-furnace slag: their effect on 

the compressive strength of mortars and concretes", ACI SP-91, 1986, v.2, pp.1381-1400. 

[4] Frenzer, G., "Reduction of Portland cement in concrete - how far can we go?", 11th 

Stone & Ready-Mixed Concrete Conference, San José de Costa Rica, Nov. 1995. 

[5] Ruiz Rico, Enrique, "Substitution of cement by fly ash in concrete and mortars",11th 

Stone & Ready-Mixed Concrete Conference, San José de Costa Rica, Nov. 1995. 

[6] "Comparative study on ready-mixed concrete 1976/77", MA Report 77/2486/E, 1977. 

[7] Gebauer, J., "Chemical admixtures - Essential constituents of concrete. Prospects 

and limitations", 6th Stone & Ready-Mixed Concrete Conference, paper No.2, Mons, 1985. 

[8] Dratva, T., Gebauer J. et al., "Study on material and operating factors in the readymixed 

concrete production", MA Report 81/2810/E, 1981. 

[9] Torrent, R., "Concrete quality control: compressive strength. Producer's and 

consumer's approach and risks", Workshop on Concrete Technology, St. Lawrence Cement, 

Canada, February 8-12, 1988. MA Report 88/3524/E. 

[10] AFNOR P 18-305: "Béton prêt a l'emploi", Normalisation Française, Dec. 1994. 

[11] ASTM C94: "Standard Specification of Ready-Mixed Concrete", May 1994. 


Cement 

Concrete 

Concrete Admixtures 

KEY COMPONENTS OF MODERN CONCRETE 

P.-C. AITCIN 

Université de Sherbrooke, Sherbrooke, Canada 

M. BAALBAKI 

Holcim Group Support - Corporate Product Development 

1. ABSTRACT..................................................................................................................... 100 

2. INTRODUCTION............................................................................................................. 100 

3. AN ARTIFICIALLY COMPLICATED TERMINOLOGY................................................... 101 

4. DISPERSING ADMIXTURES KEY COMPONENTS FOR CONCRETE 

DURABILITY................................................................................................................... 103 

4.1 Durable concrete.................................................................................................... 103 

4.2 Why cement needs to be dispersed?..................................................................... 105 

5. CEMENT/ADMIXTURE COMPATIBILITY...................................................................... 106 

6. ENTRAINED AIR ............................................................................................................ 109 

7. CONCLUSIONS.............................................................................................................. 110 

8. REFERENCES................................................................................................................ 111 


Cement 

Concrete 

1 Abstract 

Concrete admixtures are still too often perceived as mysterious ingredients for making 

concrete. Their unseen chemical nature, their mysterious modes of action too often cast 

them as the results of alchemy rather than high-tech chemistry. While some admixtures 

were originally industrial by-products and only marginally beneficial, more and more modern 

products are specially prepared or synthecized for the concrete industry. Their action is 

more specific and more engineered, making them more efficient. We can now state that the 

most recent technological developments in concrete technology rely on enhanced admixture 

efficiency rather than on improvements in cement manufacturing. 

Amongst all the admixtures currently used by the concrete industry, superplasticizers play a 

major role: it is now possible to make workable or flowing concretes with reduced 

water/cement ratios with the mix containing just enough, or even less, water needed to fully 

hydrate all the Portland cement particles. The microstructure of the resulting hydrated 

cement paste is very compact, which does away with the weak transition surrounding the 

aggregates, increases significantly the compressive strength, and drastically reduces 

concrete permeability to outside aggressive agents. 

However, it should be emphasized that these improvements in the quality of concrete are 

only achieved if admixtures are correctly used and if the concrete is placed and cured 

properly. Modern admixtures will not transform a poor mix, that has been badly placed and 

not cured, into a high-performance concrete. There are no miraculous products, only 

chemical ingredients that must be used judiciously to transform an already good concrete 

into a better one. 

Keywords: admixture, cement/superplasticizer compatibility, concrete, curing, dispersing 

admixtures, durability, flowing concrete, microstructure, permeability, superplasticizer 


The idea to introduce chemicals when making concrete is not new in itself; Latin authors 

reported that a hundred years before Christ, blood or eggs were used to improve concrete 

properties [1]. This practice was still in use during the Middle Ages since Villard de 

Honnecourt, a cathedral builder, was recommending ca 1230 to moisten cement with linseed 

oil to make a vessel that could hold water [2]. Closer to the present day, it was just before 

the Second World War that the beneficial use of chemical admixtures was re-emphasized 

accidentally in the USA: a dispersant used to thoroughly disperse some carbon black to 

differentiate the color of the concrete of the center line of a 3-lane concrete highway, 

entrained as a secondary effect some tiny air bubbles, which made the concrete easier to 

place and more durable to freezing and thawing. This fortuitous discovery led to the birth of 

a successful business in cement and concrete technology, the admixture business. 

In spite of the fact that admixture business is a multimillion dollar business, it is then 

surprising to find very few comprehensive books about them [3][4][5][6][7], similarly there are 

very few international conferences on admixtures [8][9] and even in 1994 a great number of 

engineers and scientists are still questioning the beneficial use of achnixtures in cement and 

concrete technology. 

Is there actually a science of admixtures? Would it not be better to simply ban the use of 

admixtures in modem concrete technology rather than to face all the compatibility problems 

that field engineers increasingly have to deal with? Would it not be better to simply add more 

cement and more water in modern concrete rather than trying to complicate the 


Cement 

Concrete 

manufacturing and placing of such a simple material as concrete by introducing in it "minute" 

amounts of mysterious chemicals? 

However, when the role played by admixtures on concrete properties is well understood, it is 

better appreciated that admixtures are essential components of modern concrete. Of course, 

the chemical system that results from the simultaneous use of a very complex mineral 

system (Portland cement) and several organic polymers is very complex but this system can 

be mastered when the mode of cement/admixtures and admixtures/admixtures interaction is 

well understood. 

Concrete technology recently evolved more rapidly than cement, concrete, and admixtures 

standards, so that it is now urgent to correct the situation if problems are not likely to be 

created artificially and if we want to benefit from the opportunities to drastically improve 

concrete technology and concrete durability by adequately using admixtures. Admixtures are 

no longer made from cheap by-products but rather composed of elaborate polymers. No 

longer is it simply a matter of business; it is a matter of technology and a matter of science. 

3 An artificially complicated terminology 

A major source of confusion in the field of admixture is the artificially complicated terminology 

that has developed through the years not only in the commercial literature but also in 

standards. It can be agreed that this abundance of terms to describe the multitude of 

admixtures offered to the concrete industry is perhaps being artificially created to fulfill 

marketing strategies. For example, in the booklet Design of Concrete Mixtures edited by the 

Portland Cement Association in chapter 6: Admixtures for concrete [10], the following types 

of admixtures are listed: accelerators, air detrainers, air entraining admixtures, alkalireactivity 

reducers, bonding admixtures, coloring agents, corrosion inhibitors, dampproofing 

admixtures, finely divided mineral admixtures (cementitious, pozzolans, pozzolanic and 

cementitious and nominally inert) fungicides, germicides, insecticides, gas formers, grouting 

agents, permeability reducers, pumping aids, retarders, superplasticizers, water reducers, 

and workability agents. 

French technical literature in the admixture field is also very rich. In his book on Concrete 

Admixtures VENUAT [6] lists: plasticizers, water reducers, fluidizers, air entraining agents, 

mass dampproofing admixtures, set accelerators, hardening accelerators, set retarders, 

foam formers, gas formers, admixtures for grouting, coloring agents, stiffeners for shotcrete. 

This very rich terminology is also found in standards, for example ASTM C494 [11] 

recognized seven different types of water reducers identified by specific letters from A to G 

as shown in Table 1, and the new European standards EN934-2 recognize nine types of 

admixtures listed in Table 2. 


Cement 

Concrete 

Table 1 — Different types of water reducers according to ASTM C494 standard 

Type Function Effect 

A 

B 

C 

D 

E 

F 

G 

Water reducer 

Retarder 

Accelerator 

Water reducer and retarder 

Water reducer and accelerator 

Water reducer - high range 

Water reducer - high range - 

and retarder 

Reduce water demand at least 5% 

Retard setting time 

Accelerate setting and early-strength 

development 

Reduce water (minimum 5%) and retard 

set 

Reduce water (minimum 5%) and 

accelerate 

Reduce water demand (minimum 12%) 

Reduce water demand (minimum 12%) 

and retard set 

This very rich terminology creates confusion rather than clarification so that for many people 

admixture terminology is still more related to alchemy rather than physico-chemistry. 

This situation is the result of different factors: the secrecy of admixtures formulation brought 

to a paroxysm by admixture companies, and the use of industrial by-products as the main 

source of chemicals admixtures. As these industrial by-products most of the time contain 

several active chemical components with respect to cement hydration, their action is a 

multifunctional one rather than a specific one. Finally, it should be recognized that such a 

situation prevails due to a lack of scientific understanding of the mode of action of these 

admixtures. 

If this very complicated terminology is scrutinized more closely it is very easy to radically 

simplify, if admixtures are classified according to the main physicochemical effects they 

produce on the reaction of hydration and the properties of fresh and hardened concrete. For 

example, DODSON [5] proposes to group all concrete admixtures into four different 

categories. 

Admixtures can function by several mechanisms. 

1. Dispersion of the cement in the aqueous phase of concrete. 

2. Alteration of the normal rate of hydration of the cement, in particular the tricalcium 

silicate phase. 

3. Reaction with the by-products of the hydrating cement, such as alkalies and calcium 

hydroxide. 

4. No reaction with either the cement or its by-products." 


Cement 

Concrete 

This presentation will only deal with dispersing and air entraining admixtures that play a key 

role on concrete durability. 

Type 

Table 2 — Different types of admixtures proposed by EN 934-2 standard 

Action 

Water reducing/plasticizing Admixture which without affecting the consistence, permits 

a reduction in the water content of a given concrete mix, or 

which, without affecting the water content increases the 

slump/flow or which produces both effects simultaneously. 

High range water 

reducing/ 

superplasticizing 

admixture 

Water reducing admixture 

Air entraining admixture 

Admixture which, without affecting the consistence, permits 

a high reduction in the water content of a given concrete 

mix, or which, without affecting the water content increases 

the slump/flow considerably, or which produces both effects 

simultaneously. 

Admixture which reduces the loss of water by reduction of 

bleeding 

Admixture that allows a controlled quantity of small 

uniformly... 

Set accelerating admixture Admixture which decreases the time to commencement of 

transition of the mix from plastic to rigid state 

Hardening 

admixture 

accelerating 

Admixture which increases the rate of development of early 

strength in the concrete, with or without affecting the setting 

time 

Set retarding admixture 

Water resisting admixture 

Multifunction admixture 

Admixture which extends the time to commencement of 

transition of the mix from the plastic to rigid state 

Admixture which reduces the capillarity absorption of 

hardened concrete 

Admixture that affects several properties of fresh and/or 

hardened concrete by performing more than one of the 

main functions 

4 Dispersing admixtures key components for concrete 

durability 

4.1 Durable concrete 

When concrete is subjected to external aggression the most effective way to decrease the 

intensity of this aggression is to reduce its porosity and permeability [12]. This is why the 

water/cement ratio has always been the controlling factor of concrete durability. The 

water/cement ratio, and not strength has to remain the pivotal controlling criterion for 

designing durable concrete structures [13]. 

Concrete durability is becoming a subject of major concern in many countries, a great 

number of international conferences are held regularly on this subject, a great number of 


Cement 

Concrete 

papers analyze the causes of these repeated failures but there are very few papers dealing 

with the crucial question — how to make a durable concrete that could be used either to 

repair or rehabilitate damaged structures or to build new durable ones. 

A durable concrete structure is built with workable low water/cement concrete. A workable 

low water/cement concrete is made using appropriately an efficient dispersing admixture. 

Experience shows that, for most of the time, it is impossible to make a workable concrete 

having a slump higher than 100 mm by simply mixing water and cement at a water/cement 

ratio lower than 0.40, while it is possible to make an almost fluid concrete having a slump 

higher than 200 mm having a water/cement ratio below 0.30 when using a superplasticizer. 

When the microstructure of a high and low W/C concretes are observed under a scanning 

electron microscope it is possible to visualize the drastic consequence of the reduction of the 

water/cement ratio on concrete microstructure and consequently on concrete durability [14]. 

Figure 1 depicts schematically the microstructure of 0.65 and 0.25 W/C cement pastes. In 

this schematic representation, the surface representing the water (pale grey) and the surface 

representing the cement (dark grey) are in the same proportions as the water/cement ratio by 

mass. 

Fresh Cement Paste 

Anhydrous 

cement 

grains 

Water 

C-S-H 

0.65 0.25 

Ettringite 

Lime 

Hydrated Cement Paste 

Fig. 1 — The impact of water-cement ratio on concrete paste microstructure 

The cement particles are far from each other in the 0.65 W/C paste and very close to each 

other in the 0.25 one. In the latter paste hydration products fill the gap between cement 

particles very rapidly and achieve a strong and dense microstructure. On the other hand, in 

the case of the 0.65 water/cement ratio paste, hydration products have to develop over long 

distance before reaching the hydration products from another cement particle. Moreover, as 


Cement 

Concrete 

there is more water than necessary to fully hydrate all the cement particles, this remaining 

water constitutes a continuous medium through which aggressive agents will penetrate and 

attack concrete. If for any reason this 0.65 concrete dries, the network of empty pores 

constitute a pathway for the penetration of gas, bacterias, fluids, etc. 

This difference in microstructure has two very important consequences on strength and 

permeability: concrete strength increases greatly and permeability decreases when the W/C 

decreases. However, a 0.25 water/cement ratio concrete is not totally impervious: when 

such a concrete is tested for rapid chloride ion permeability in accordance with AASHTO T- 

277 (Standard Method of Test for Rapid Determination of the Chloride Permeability of 

Concrete) it is found that chloride ions can pass through such low water/cement concrete but 

at a very low rate when compared to 0.65 W/C concrete. Figure 2 gives a correlation 

between W/C and chloride ion permeability for some concretes [15]. 

4.2 Why cement needs to be dispersed? 

Cement particles have a surface containing a great number of unsaturated electrical charges 

so that they have a strong tendency to flocculate when they are in contact with water [16]. 

Cement flocs trap a part of the mixing water which is no longer available to fluidify the mix 

with the practical result that it is not possible to make a workable concrete having a 

water/cement ratio lower than 0.40. 

Rapid chloride permeability 

(coulomb) 

8000 

6000 

4000 

2000 

1d cure 

7d cure 

0 

0.20 0.30 0.40 0.50 0.60 0.70 0.80 

Water/cement ratio 

Fig. 2 — Rapid chloride permeability of concrete as a function of w/c and the length of 

curing 

Water dispersing admixtures are polymers that reduce this flocculation, so that more or all 

the water introduced initially in the mix is available to make the concrete workable [5]. Water 

dispersing molecules, as it will be seen, also contributes to lubrication process of the 

concrete. The most efficient polymer, presently used as water dispersing admixtures are the 

so-called superplasticizers or high range water reducers [17]. 

Of course, the superplasticizer/cement interaction depends on the physicochemical 

parameters of the superplasticizer and of the cement. In general terms, this interaction can 

be divided into two main effects: a physical effect that is also found when a superplasticizer 

is used to disperse a non cementitious fine powder, and a chemical effect related to the 

reaction of the superplasticizer with the most reactive sites of the hydrating cement particles. 

The physical effect is a three fold one [18]: 

1. adsorption of the superplasticizer molecule by Van der Waals and electrostatic forces on 

cement particles. 


Cement 

Concrete 

2. surface charging which induces long range interparticle repulsive forces 

3. steric hindrance between adsorbed polymer molecules and neighboring particles. 

All these physical actions tend to defloculate and disperse cement particles [18]. 

However, the action of superplasticizer molecules is not only physical. Their sulfonate sites 

can react with C 3 A. It has been found that the shorter polynaphthalene molecules have a 

greater tendency to react with C 3 A so that an efficient superplasticizer must contain the 

minimum amount of short polymers (di and trimers). 

This double action of a superplasticizer on cement particles reveals itself when observing the 

shift of heat development curves under increasing dosages of superplasticizers. Upon first 

addition of a superplasticizer the heat flux peak is shifted substantially to shorter times due to 

improved water/cement contact upon deflocculation and a more homogeneous dispersion of 

the cement particle occurs. Upon further addition of superplasticizers some retardation is 

observed; retardation that increases with superplasticizer dosage. This retardation is 

observed for both the beginning of the accelerated phase and the maximum of the thermal 

peak. This is another point which makes low molecular weight superplasticizer not at all 

interesting from a practical point of view. This retardation is the result of the adsorption of 

superplasticizer molecule on C3S sites as the superplasticizer dosage increases. It has 

been found that low molecular weight molecules induce more pronounced retardation [18]. 

From this brief discussion about the mode of action of superplasticizer molecules it can be 

concluded that an efficient superplasticizer must have a high degree of sulfonation to offer 

many electrically active sites in order to disperse all the cement particles. Moreover, it has 

been found that among the two positions that the SO3 -- sites can occupy in the naphthalene 

rings, the so-called β site is more efficient to disperse cement particles. Secondly, a 

superplasticizer should contain as few short polymers (di and trimers) as possible and as 

many high molecular weight chains as possible without too much crossliriking in order to 

confer to the polymeric chain as a large covering effect as possible [19]. 

In order to control the quality of commercial superplasticizers, standards have been 

developed. Most of these standards are in fact extensions of standards developed for water 

reducers, there are not always best suited to evaluate objectively the actual efficiency of a 

superplasticizer. 

5 Cement/admixture compatibility 

It is somewhat surprising that cement/admixture compatibility problems are becoming more 

and more frequent, especially in the field of superplasticizers. In the past, few cases of poor 

compatibility between a cement and a water reducer were reported. This kind of problem 

was quite rare. In the few cases reported in the literature [20][21][22] it was found that the 

rapid slump loss observed in the field were most of the time associated with the presence of 

anhydrite as a source of calcium sulfate to control Portland cement setting. Where such 

cements were used in conjunction with a lignosulfonate based water reducer the anhydrite 

did not pass into solution fast enough so that not enough SO4 -- ions were available to react 

with the C3A to form ettringite. In such a case, the slump loss was due to a flash set 

situation i.e. the rapid formation of hydrogarnet, in spite of the fact that the total SO3 content 

of the cement complied to cement standards. 

The first documented cement/superplasticizer compatibility problems reported in the 

literature have been explained in the same way [23], when it was not a specific deficiency of 

the commercial superplasticizer that was the principal cause of the compatibility problem (low 


Cement 

Concrete 

degree of sulfonation, high percentage of cc site sulfonated, high percentage of di or trimers, 

low degree of crosslinking). 

It has been also observed that cement/superplasdcizer compatibility problems seem to be 

more frequent in low water/cement ratio concretes [24]. This type of concrete contains per 

unit volume more C3A and less water where SO4 -- ions from the calcium sulfate bearing 

minerals can dissolve. In some cases the initial hydrating conditions are such that there are 

not enough SO4 -- ions dissolved in water, or the calcium sulfate bearing minerals do not 

dissolve fast enough to neutralize the available C3A. Such a situation can occur because 

the optimization of the calcium sulfate content of Portland cement is done at the cement plant 

in conditions that are quite different from the ones that prevail in low W/C concrete. The 

calcium sulfate content is presently optimized on a paste or a mortar having a W/C ratio of 

about 0.50 using only pure water [25]. 

In such a system there is less C3A and more water by unit volume than in a low W/C 

concrete and the admixture could interfere with the solubility rate of the different sources of 

SO4 -- . 

Moreover, a system having a W/C = 0.50 is rich enough in water so that the water in fact 

controls most of the rheological properties of the mix. In such a system hydrating cement 

grains are far enough from each other so that they do not interfere very much and affect the 

rheological properties of the system. 

In some cases, the rapid rate of consumption of water during the formation of ettringite (C3A 

. 3 CaSO4 . 32 H2O) decreases drastically the already quite low amount of mixing water. To 

be more specific, typical HPC concretes are mixed using 125 to 145 L/m 3 water, that is 20 to 

40 liters less than a typical 0.50 W/C ratio air-entrained concrete or 40 to 60 liters less than a 

typical 0.50 W/C ratio non air-entrained concrete. Therefore any rapid consumption of water 

can lead to a situation where there is not enough water to ensure a proper workability in a 

low W/C ratio concrete. 

From a practical point of view four typical situations can be found when studying the rheology 

of a low W/C grout with a Marsh cone. Figure 3a, b, c and d illustrate these different 

situations where the superplasticizer dosage and the Marsh cone flow time have been 

reported respectively along x and y axes [26]. 

Figure 3a represents the case of a perfectly compatible combination of cement and 

superplasticizer, the superplasticizer dosage at the point of saturation is low and the 60 

minutes curve is close to the 5 minutes one. Figure 3b on the contrary represents a case of 

incompatibility, the superplasticizer dosage at the saturation point is quite high and the 60 

minutes curve is far up the 5 minutes. Very often in such a case the grout stops to flow very 

rapidly, often as fast as 15 minutes after the beginning of the mixing. 

Figure 3c and 3d represent intermediate cases. In Fig. 3c the 5 minutes curve is similar to 

the 5 minutes curve presented in Fig. 3a but the 60 minutes curve is similar to the 60 minutes 

curve presented in Fig. 3b. In Fig. 3d the 5 minutes curve is similar to the 5 minutes curve 

presented in Fig. 3b and the 60 minutes curve has a relative position to the 5 minutes curve 

similar to the situation prevailing in Fig. 3a. 

In another paper [26] each typical case has been explained in greater detail and some 

solutions involving mainly the addition of an appropriate amount of retarder have been 

proposed so that the cement and superplasticizer combinations presented in Fig. 3b, 3e and 

3d behave, in the best cases, as similarly as possible to the combination presented in Fig. 


Cement 

Concrete 

3a. Unfortunately it is not always possible to adequately correct the situation to achieve the 

flow time curves as those presented in Fig. 3a. 

Presently it is not possible to develop polynaphthalene or polymelamine sulfonates that work 

with any Portland cement at any water/cement ratio due to the too great a variability of the 

solubility rate of the different calcium sulfates used to control the setting of the commercial 

cements [24]. However, when some attention is given to this important characteristic at low 

W/C ratio, it is possible to manufacture Portland cement that is perfectly compatible with 

good polynaphthalene or polymelamine superplasticizers. If such an ideal situation does not 

exist it is better to develop a blended superplasticizer whose composition is adjusted to the 

particular cement [27][28]. The development of such a superplasticizer should be done 

through a cooperative development program involving the admixture manufacturer, the 

cement producer and the user. 

120 

100 

(a) 

W/C = 0.35 

T = 22 °C 

120 

100 

(b) 

W/C = 0.35 

T = 22 °C 

Marsh flow time (sec) 

80 

60 

40 

0.0 

120 

100 

0.8 

1.6 

(c) 

2.4 

60 min 

3.2 

5 min 

W/C = 0.35 

T = 22 °C 

4.0 

80 

60 

40 

0.0 

120 

100 

0.8 

1.6 

(d) 

2.4 

60 min 

5 min 

3.2 

W/C = 0.35 

T = 22 °C 

4.0 

80 

60 min 

80 

60 min 

60 

5 min 

60 

5 min 

40 

0.0 

0.8 

1.6 

2.4 

3.2 

4.0 

40 

0.0 

0.8 

1.6 

2.4 

3.2 

4.0 

Percent superplasticizer (by wt. solids) 

Fig. 3 — Rheological characteristics of different cement/superplasticizer combinations 

Up to now, there have been very few incentives to invest time, effort and money to solve this 

kind of problem, as HPC still represents a very small part of the concrete market. However, 

when the concrete will be designed essentially for durability and not uniquely for strength, 


Cement 

Concrete 

this situation may change and it will be possible to see more and more people involved in this 

tricky business: trying to optimize a cement/superplasticizer combination at low W/C ratio 

values. Cement producers will find that it is not too difficult or too costly to adjust the 

solubility rate of the sulfates and to control it [25]. 

To acheive such an ideal situation, it is only necessary to recognize that admixtures in 

general and superplasticizers in particular are, when properly used, essential constituents of 

durable concrete as important as cement or water. In fact, due to the very efficient 

dispersant properties of polynaphthalene and polymelamine superplasticizers it is possible to 

make flowing concretes having very low W/C ratios in the order of 0.30, or even lower, that 

are particularly impermeable [14]. These concretes are not penetrated easily by aggressive 

agents so that they will last longer than 0.50 to 0.70 W/C ratio concretes that are indirectly 

specified when designers are designing their structures with 20 to 40 MPa concretes. 

It would be unwise to be over-confident on the durability of low W/C concretes and take 

advantage of their low permeability to decrease the thickness of the concrete cover or to 

eliminate early curing. Admixtures are not miraculous products, they will never transform a 

bad concrete poorly cured into a good one, but they can transform a good concrete properly 

cured into a better and more durable one. 

It is amazing to see that as the 21 st century approaches, there are still engineers 

recommending the use of high W/C ratio concretes which are porous and permeable, and 

later they complain that these concretes are subjected to carbonation, that they do not 

protect adequately reinforcing steels from corrosion, and that they are not resistant to 

freezing and thawing. Would it not have been better to start specifying a impermeable 

concrete having a low W/C ratio and try to use efficiently the extra megapascals brought by 

this type of concrete? This is the future of concrete. 

6 Entrained air 

The intentional entrainment of air bubbles in an ordinary concrete is always associated with 

the idea to improve its durability to freezing and thawing. However, there are still some who 

do not accept this idea. But, generally, it is accepted that when the bubble system has some 

well defined characteristics (spacing factor, specific surface, diameter, total volume) it is a 

necessary condition but not always sufficient because, and that is often forgotten, these 

characteristics have to be developed in a concrete having a W/C ratio lower than a given 

value depending on the harshness of the environmental conditions. These maximum W/C 

ratios values vary from one country to another and usually they are in the 0.40 to 0.55 range. 

Of course, the introduction of a certain amount of air in a concrete results in a decrease in its 

compressive strength. It is usually admitted as a rule of thumb that each per cent of air 

decreases compressive strength by 5 per cent. This means that a given non air entrained 

concrete that contains 2 per cent of entrapped air and that tests 40 MPa will not test more 

than 32 MPa if its air content is increased to 6 per cent by the addition of an appropriate 

amount of air entraining admixture. This means that as long as concrete structures are 

designed on a strength basis, an air entrained concrete must always have a lower W/C ratio 

than a non air entrained concrete having the same design strength. This is a valid point for 

the purpose of durability. 

A second interesting effect of entrained air is that its beneficial effect on concrete rheology 

and workability is all too often forgotten. Air entrained concretes are more creamy and less 

prone to breeding. Moreover, the entretainment of air bubbles in the concrete results in an 

increase of the slump, or in the use of less mixing water if the slump has to remain constant. 

For example, ACI standard 211 "Standard Practice for Selecting Proportions for Normal, 

Heavyheight and Mass Concrete" [29] recommends to reduce by 15 to 25 liters the amount 


Cement 

Concrete 

of water to produce a concrete of a given strength made with a coarse aggregate having a 

given maximum size and a sand of a given fineness modulus. This reduction in the amount 

of mixing water necessary to obtain a given slump has a positive effect on the water/cement 

ratio needed to obtain a given strength. 

The presence of a discontinuous air bubble system has also a positive action on the 

capillarity of concrete and on the development of microfissures within the hydrated cement 

paste. All these secondary effects of entrained air contribute to some extent to make air 

entrained concrete of a given strength more durable than a non air entrained concrete of the 

same strength. But, is this well established situation still valid when dealing with very low 

W/C concretes? Is it appropriate to add entrained air in low W/C concretes to make them 

more durable? 

Presently it is not clearly accepted by all the scientific community that HPC with low W/C 

ratios needs any air at all to be freeze thaw resistant [30]. Of course, it is found when 

performing procedure A of ASTM C 666 Standard, that HPC having W/C higher than 0.25 

needs entrained air to pass successfully the 300 freezing and thawing cycles under water 

[31], but there are more and more people questioning the severity of this test to decide if a 

field concrete is freeze thaw resistant [32]. 

However, field experience developed during the construction of several high performance 

concrete bridges have shown an unexpected advantage of entrained air when making HPC 

[26][27]. The workability of RPC is considerably improved by the addition of entrained air, as 

well as its finishability. Air entrained mixes are sheared much more easily, they are less 

sticky, they can be placed much more easily and are less thixotropic, which is translated in 

the field by significant gains in productivity during placing. Up to now it has not been 

possible to quantify this type of improvement but it is hoped that with the recent development 

of different workabilimeters by different researchers it will be possible to designate numbers 

on this qualitative appreciation. 

The authors are convinced that in the future HPC will increasingly contain some entrained air 

(3 to 5 per cent) not to improve their durability, but to improve their workability. This 

improvement in the workability of HPC will have beneficial effects, particularly on the quality 

of the covercrete and indirectly on HPC durability. 

7 Conclusions 

Concrete's resistance to exterior aggressive agents is intimately linked to the facility with 

which it can be penetrated by these aggressive agents. This facility of penetration depends 

among other factors directly on the compactness of the hydrated cement paste. It is also 

directly linked to the water/cenient or water/cementitious ratio of the concrete mixture. Due 

to the very efficient dispersing properties of polynaphthalene and polymelamine 

superplasticizers it is now possible to make durable concretes having W/C equal to 0.30 or 

even lower; as such concretes are almost impervious they will be much more durable than 

normal concrete. They are, of course, stronger than normal strength concrete and designers 

will have to learn how to use efficiently these extra megapascals needed to insure better 

durability to concrete structures. 

Unfortunately, not all current commercial cements have been optimized in terms of the 

solubility rate of their SO4 so that so-called cement/superplasticizer compatibility problems 

are more likely to occur in the future as the W/C ratio of concrete used decreases. However, 

this situation can be easily corrected when the actual cause of the incompatibility has been 

found. Most of the time, it is found that there is a discrepancy between the quantity and the 

reactivity of the C3A present in the mixture and the amount of SO4 -- ions going into solution 

within the mixing water. 


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Concrete 

Air entraining agents will be more and more incorporated intentionally in low W/C concretes 

not to specifically improve their freeze thaw durability, but rather to improve their workability. 

As soon as a HPC concrete having a W/C ratio of 0.30 or less contains 3 to 5% of entrained 

air a marked change in its workability appears. Experience shows that when high quality 

admixtures are used with a cement well balanced in terms of C3A and soluble sulfates there 

is no problem to entrain the desired amount of air in a superplasticized low W/C ratio 

concrete. 

Admixtures, and more specifically superplasticizers, are not miraculous products. They will 

never transform a bad concrete mixture into a good one, but can be used to transform a 

good concrete into a better one; a concrete that can be placed more easily, a more compact 

and more impermeable concrete that will offer greater resistance to the penetration of 

aggressive agents in as much as this concrete is cured properly. 

8 References 

1. Mindess, S., Youg, J.F., (1981) "Concrete", Prentice Hall Englenwod Cliffs NJ, pp. 15. 

2. Garrison, E.G. (1991) A History of Engineering and Technology, CRC Press, Boca 

Raton FA, pp. 106. 

3. Ramachandran, V.S. (1984) Concrete Admixture Handbook, Noyes Publications, Park 

Ridge, NJ, U.S.A., 626 pp. 

4. Rixon, M.R. and Mailvaganam, N.P. (1978) Chemical Admixtures for Concretes, E & 

F.N. Spon, New York, U.S.A., 306 pp. 

5. Dodson, V. (1990) Concrete Admixtures, Van Nostraud Reinhold, New York, U.S.A., 211 

pp. 

6. Venuat, M. (1984) Adjuvants et Traitements, Edited by M. Venuat, 66 avenue C. 

Perrière, 92320 Chatillon-sous-Bagneux, France, 830 pp. 

7. Joisel, A. (1973) Admixture for Cement - Physico Chemistry of Concrete and its 

Reinforcement, Published by the author, 3 avenue André, 95230 Soisy, France, 253 pp. 

8. Malhotra, V.M. 1 st , 2 nd , 3 rd and 4 th International Conferences on Superplasticizers 

organized in 1978 (ACI SP-62), 1981 (ACI SP-68), 1984 (ACI SP- 1 19) and 1994 held 

in october 1994. 

9. Admixture for Concrete — Improvement of properties (1990) Edited by Vasquez, 

Published by Chapman and Hall, London, U.K., 486 pp. 

10. Design and Control of Concrete Mixtures (1990) Published by Portland Cement 

Association, 5420 Old Orchard Road, Skokie, Ill, U.S.A., pp. 63-76. 

11. ASTM C494 (1990) Standard Specification for Chemical Admixtures for Concrete, pp. 

250-257. 

12. Aïtcin, P.-C. (1994) Durable Concrete — Current Practice and Future Trends. Edited by 

P.K. Mehta, ACI SP-144, pp. 85-104. 

13. Neville, A. (1981) Properties of Concrete, Pitman, London, U.K., 779 pp. 

14. Aïtcin, P.-C. and Neville, A. (1993) High-performance Concrete Demystified. Concrete 

International, ACI Journal, Vol. 15, No. 1, January, pp. 21-26. 


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Concrete 

15. Gagné, R. and Aïtcin, P.-C. (1993) Superplasticizers for Durable Concrete. Concrete 

Durability, Edited by R.R. Villarreal, Universidad Autonoma de Nuevo Leon, Monterrey, 

N.L. Mexico, pp. 201-217. 

16. Kreijger, P.-C. (1980) Plasticizers and Dispersing Admixtures. Admixtures Concrete 

International, the Construction Press, London, U.K., pp. 1-16. 

17. Aïtcin, P.-C., Jolicoeur, C., and MacGregor, J.G. (1994) Superplasticizers: How They 

Work and Why they Occasionally Don't, ACI Concrete International, Vol. 16, No. 5, May, 

pp. 45-52. 

18. Jolicoeur, C., Nkinamubanzi, P.-C., Simard, M.-A., and Piotte, M. (1994) Progress in 

Understanding the Functional Properties of Superplasticizer in Fresh Concrete, 4 th 

CANMET/ACI International Conference on Superplasticizers and Other Chemical 

Admixtures in Concrete, Montreal, October. 

19. Piotte, M. (1993) Caractérisation du poly (naphtalènesulfonate) et interactions de ce 

superplastifiant dans une suspension de ciment. PhD Thesis, Chemical Department, 

Université de Sherbrooke, 205 pp. 

20. Paillère, A.-M., Alègre, R., Ranc, R., and Buil, M. (1984) Interaction entre les réducteurs 

d'eau-plastifiants et les ciments, Lafarge / Laboratoire central des ponts et chaussées, 

Bd. Lefebvre, Paris, France, pp. 105-108. 

21. Dodson, V.H., and Hayden, T.D. (1989) Another Look at the Portland Cement Chemical 

Admixture Incompatibility Problem. Cement, Concrete and Aggregate, Vol. 11, No. 1, 

pp. 52-56. 

22. Manabe, T. and Kawada, N. (1960) Abnormal Setting of Cement Paste Owing to 

Calcium Lignosulfonate. Semento Konkunto, No. 162, pp. 24-27. 

23. Ranc, R. (1990) Interactions entre les réducteurs d'eau-plastifiants et les ciments. 

Ciments, bétons, plâtres, chaux, No. 782, pp. 19-20. 

24. Tagnit-Hamou, A., Baalbaki, M., and Aïtcin, P.-C. (1992) Calcium-sulfate Optimization in 

Low Water/Cement Ratio Concretes for Rheological Purposes, 9 th International 

Congress on the Chemistry of Cement, New Delhi, India, Vol. 5, pp. 21-25. 

25. Tagnit-Hamou, A. and Aïtcin, P.-C. (1993) Cement and Superplasticizer Compatibility. 

World Cement, Vol. 24, No. 8, August, pp. 38-42. 

26. Lessard, M., Gendreau, M., Baalbaki, M., and Pigeon, M. (1993) Formulation d'un béton 

à hautes performances à air entrainé. Bulletin de liaison des laboratoires des ponts et 

chaussées, Paris, No. 188, Novernber-December, pp. 41-51. 

27. Aïtcin, P.-C. and Lessard, M. Canadian Experience With Air-entrained, Highperformance 

Concrete. ACI Concrete International, to be published. 

28. Lessard, M., Dallaire, E., Blouin, D., and Aïtcin, P.-C. High-performance Concrete for 

MacDonald's. ACI Concrete International, to be published. 

29. ACI Standard 211. Standard Practice for Selecting Proportions for Normal, Heavyheight 

and Mass Concrete. ACI Manual of Concrete, Part 1, pp.211.1-1 211.1-38. 

30. Hammer, T.A. and Sellevold, E.J. (1990) Frost Resistance of High-strength Concrete, 

2 nd International Symposium on Utilization of High-strength Concrete, University of 

California, Berkeley, ACI SP-121, 1990, pp. 457-487. 


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Concrete 

31. Gagné, R., Pigeon, M., and Aïtcin, P.-C. (1991) The Frost Durability of High-performance 

Concrete, 2 nd Canada/Japan Meeting on the Effect of Low Temperature on Concrete, 

Edited by J.G. Litvan/K. Sakai, Japan, pp. 57-87. 

32. Phileo, R.E. (1986) Freezing and Thawing Resistance of High-strength Concrete. 

National Cooperative Highway Research Program Synthesis of Highway Practice 129. 

T.R.B., Washington DC, December, 31 pp. 


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Concrete 

Concrete Production Practices 

1. GENERAL....................................................................................................................... 115 

2. BATCHING OF MATERIALS.......................................................................................... 115 

3. MIXING............................................................................................................................ 116 

3.1 Types of mixers...................................................................................................... 116 

3.2 Uniformity of mixing................................................................................................ 117 

3.3 Mixing time ............................................................................................................. 117 

4. HANDLING, TRANSPORTING, PLACING..................................................................... 117 

5. COMPACTING................................................................................................................ 118 

5.1 Internal vibrator ...................................................................................................... 119 

5.2 External vibrator ..................................................................................................... 119 

5.3 Vibrating table ........................................................................................................ 120 

5.4 Surface vibrator...................................................................................................... 120 

6. CURING OF CONCRETE ............................................................................................... 120 

6.1 Length of curing period .......................................................................................... 120 

6.2 Curing methods...................................................................................................... 121 

6.3 Curing Compounds ................................................................................................ 122 

6.4 Steam curing .......................................................................................................... 123 

7. HOT WEATHER CONCRETING .................................................................................... 123 

8. COLD WEATHER CONCRETING.................................................................................. 126 

9. READY-MIXED CONCRETE .......................................................................................... 129 

10. PUMPED CONCRETE.................................................................................................... 130 

11. SPECIAL CONCRETING PROCESSES ........................................................................ 133 

12. LITERATURE.................................................................................................................. 134 

12.1..Concrete Technology ............................................................................................. 134 

12.2..Concrete practice ................................................................................................... 134 

12.3..Testing of Concrete................................................................................................ 134 


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Concrete 

1 General 

Characteristics and properties of fresh and hardened concrete depend to a great extent upon 

mix design and quality of the constituent materials. 

However, the importance of mixing, transporting, placing and curing techniques should not 

be neglected. 

Improved production practices and techniques will then contribute considerably to achieving 

a good concrete. Each stage of concrete production is important and has an influence on the 

final concrete serviceability. 

2 Batching of Materials 

To produce concrete of uniform quality, the ingredients must be measured accurately for 

each batch. Most new specifications require that batching be done by weight rather than by 

volume because of the inaccuracies in measuring solid materials (especially damp sand) by 

volume. The weight system for batching provides greater accuracy, simplicity and flexibility. 

Flexibility is necessary because changes in the aggregate moisture content require frequent 

adjustments in batch quantities of water and aggregates. Water can be measured accurately 

by either volume or weight. 

ACI specifications generally require that materials be measured within this percentage of 

accuracy: 

cement ± 1% 

aggregates ± 2% 

water ± 1% 

admixtures ± 3% 

The ERMCO (European Ready Mixed Concrete Organisation) Code of good practice for 

Ready-Mixed Concrete gives recommendations for batching tolerance as listed in Table 1. 

Table 1: Accuracy of batching acc. ERMCO 

Material 

Tolerance 

Cement ± 3% 

Coarse aggregate ± 3% 

Fine aggregate ± 3% 

Admixtures ± 5% 

Water ± 3% 

Equipment should be capable of measuring quantities within these tolerances for the 

smallest batch regularly used, as well as for larger batches. 

The accuracy of batching equipment should be checked periodically and adjusted when 

necessary. Admixture dispensers should be checked daily since errors in admixture 

batching, particularly overdosing, can lead to serious problems in both fresh and hardened 

concrete. 


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Concrete 

3 Mixing 

The objective of mixing is: 

♦ to coat the surface of all aggregate particles with cement paste 

♦ to blend all the ingredients of concrete into a uniform mass 

♦ to maintain uniformity of concrete at the discharging from the mixer 

All concrete should be mixed thoroughly until it is uniform in appearance, with all ingredients 

evenly distributed. Mixers should not be loaded above their rated capacities and should be 

operated at approximately the speeds for which they were designed. If the blades of the 

mixer become worn or coated with hardened concrete, the mixing action will be less efficient. 

Badly worn blades should be replaced and hardened concrete should be removed 

periodically, preferably after each day’s run of concrete. 

3.1 Types of mixers 

The method of discharging is one of the criteria for the classification of concrete mixers. 

Tilting Mixer: Mixing chamber (drum) it tilted for discharging (see Figure 1). 

Figure 1: 

Tilting mixer 

Drum (non-tilting) mixer: The axis of the mixer is always in a horizontal position, and 

discharge is effected by inserting a chute into the drum or by reversing the direction of 

rotation of the drum, as applied in the truck mixer used in the ready-mixed concrete 

production (see Figure 2). 

Figure 2: 

Drum (non-tilting) mixer 

Pan mixer: consists of a circular pan rotating about its axis, with one or two stars of paddles 

rotating about a vertical axis not coincident with the axis of the pan (see Figure 3). 


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Concrete 

Figure 3: 

Pan mixer 

The capacity of tilting and drum mixers is usually large (up to 6 m 3 ), whereas the pan mixer is 

smaller (up to 2 m 3 ) and is particularly efficient for stiff and cohesive mixes often used in 

precast concrete industry. 

Bowl-and-stirrer Mixer (cake mixer): works according to the same principle as the pan mixer 

and is sometimes used for mixing of mortar. 

3.2 Uniformity of mixing 

The efficiency of the mixer can be determined by the variability of the mix discharged into a 

number of samples without interrupting the flow of concrete. 

The values given in Table 2 are the highest acceptable values for a ‘satisfactory’ mixer. 

Table 2: 

Variability of concrete in a ‘satisfactory’ mixer 

Compressive strength 4 - 6% 

Percentage of coarse aggregate 6 - 8% 

Percentage of fine aggregate or 5 - 8% 

cement 

3.3 Mixing time 

The mixing time varies with the type of mixer and, strictly speaking, it is not the mixing time 

but the number of revolutions of the mixer that is the criterion of adequate mixing. Generally 

about 50 revolutions are sufficient. 

4 Handling, transporting, placing 

Each step in handling, transporting and placing concrete should be carefully controlled to 

maintain uniformity within the batch and from batch to batch so that the completed work is 

consistent throughout. It is essential to avoid separation of the coarse aggregate from the 

mortar or of water from the other ingredients. 

Concrete is handled and transported by many methods. These include the use of chutes, 

buggies operated over runways, buckets handled by cranes or cabinways, small railroad 


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Concrete 

cars, trucks, pumping through pipelines, and pneumatically forcing the concrete or dry 

concrete materials through hoses. 

Preparation prior to placing includes compacting, trimming and moistening the subgrade; 

erecting the forms; and setting the reinforcing steel. A moist subgrade is especially important 

in hot weather to prevent extraction of water from the concrete. 

Forms should be clean, tight, adequately braced, and constructed of materials that will impart 

the desired texture to the finished concrete. Sawdust, nails and other debris should be 

removed before concrete is placed. Wood forms should be moistened before placing 

concrete; otherwise they will absorb water from the concrete and swell. Forms also should be 

treated with a releasing agent such as oil or lacquer to facilitate their removal. For 

architectural concrete, lacquer or emulsified stearates are used since they are non-staining. 

Reinforcing steel should be clean and free of loose rust or mill scale at the time concrete is 

placed. Any coatings of hardened mortar should be removed from the steel. 

5 Compacting 

The process of compacting concrete consists essentially of the elimination of air voids. 

The oldest means of achieving this is by ramming or punning the surface of concrete. The 

most common method for compacting is by vibration. The use of vibration makes it possible 

to work with drier mixes, so that concrete with a lower water/cement ratio and a lower cement 

content can be manufactured. Whether or not vibrators can be employed is determined by 

the consistency of the mix. Mixes which are very wet should not be vibrated as separation 

may result. Each type of vibrator requires a different consistency. 

Various types of vibrators have been developed (see also Figure 4): 


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Concrete 

Figure 4: 

Various types of vibrators 

5.1 Internal vibrator 

Of the several types of vibrators this is perhaps the most common one. It consists essentially 

of a poker, housing an eccentric shaft driven through a flexible drive from a motor. The poker 

is immersed in concrete and thus applies approximately harmonic forces to it; hence, the 

alternative names of poker- or immersion vibrator. 

The frequency of vibration varies up to 12’000 cycles of vibration per minute. 

The poker is easily moved from place to place, and is applied at 50 to 70 cm centers for 5 to 

30 sec., depending on the consistency of the mix. 

5.2 External vibrator 

This type of vibrator is rigidly clamped to the formwork resting on an elastic support, so that 

both the form and the concrete are vibrated. As a result, a considerable proportion of the 

work done is used in vibrating the formwork, which also has to be strong and tight so as to 

prevent distortion and leakage of grout. 

The principle of an external vibrator is the same as that of an internal one, but the frequency 

is usually between 3000 and 6000 cycles. 


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Concrete 

5.3 Vibrating table 

This can be considered as a case of formwork clamped to the vibrator instead of the other 

way round, but the principle of vibrating the concrete and formwork together is unaltered. 

The source of vibration, too, is similar. Generally a rapidly rotating eccentric weight makes 

the table vibrate with a circular motion. With two shafts rotating in opposite directions the 

horizontal component of vibration can be neutralized so that the table is subjected to a 

simple harmonic motion in the vertical direction only. 

5.4 Surface vibrator 

A surface vibrator applies vibration through a flat plate direct to the top surface of the 

concrete. In this manner the concrete is restrained in all directions so that the tendency to 

segregate is limited; for this reason a more intense vibration can be used. 

6 Curing of concrete 

Properties of concrete such as resistance to freezing and thawing, strength, watertightness, 

wear resistance, and volume stability improve with age as long as conditions are favorable 

for continued hydration of the cement. The improvement is rapid at early ages but continues 

more slowly for an indefinite period. Two conditions for such improvement in quality are 

required: 

♦ the presence of moisture 

♦ a favorable temperature 

Excessive evaporation of water from newly placed concrete can significantly retard the 

cement hydration process at an early age. Loss of water also causes concrete to shrink, thus 

creating tensile stresses at the drying surface. It these stresses develop before the concrete 

has attained adequate strength, surface cracking may result. All exposed surfaces, including 

exposed edges and joints, must be protected against moisture evaporation. 

Hydration proceeds at a much slower rate when the concrete temperature is low; from a 

practical standpoint there is little chemical action between cement and water when the 

concrete temperature is near or below freezing. It follows that concrete should be protected 

so that moisture is not lost during the early hardening period and the concrete temperature is 

kept favorable for hydration. 

6.1 Length of curing period 

Since all the desirable properties of concrete are improved by curing, the curing period 

should be as long as practicable in all cases. 

The length of time that concrete should be protected against loss of moisture is dependent 

upon the type of cement, mix proportions, required strength, size and shape of the concrete 

mass, weather and future exposure conditions. This period may be a month or longer for 

lean concrete mixtures used in structures such as dams; conversely, it may be only a few 

days for richer mixes, especially if Type III of high-early-strength cement is used. Steamcuring 

periods are normally much shorter. 

For must structural uses, the curing period for cast-in-place concrete is usually 3 days to 2 

weeks, depending on such conditions as temperature, cement type, mix proportions, etc. 

More extended curing periods are desirable for bridge decks and other slabs exposed to 

weather and chemical attack. 


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Concrete 

6.2 Curing methods 

There are different methods to cure concrete: 

1) Methods that supply additional moisture to the surface of the concrete during the early 

hardening period. These include sprinkling and using wet coverings. Such methods afford 

some cooling through evaporation, which is beneficial in hot weather. 

2) Methods that prevent loss of moisture from the concrete by sealing the surface. This may 

be done by means of waterproof paper, plastic sheets, liquid membrane-forming 

compounds, and forms left in place. 

3) Methods that accelerate strength gain by supplying heat and moisture to the concrete. 

This is usually accomplished with live steam or heating coils. 

Sprinkling (see Figure 5) 

Continuous sprinkling with water is an excellent method of curing . If sprinkling is done at 

intervals, care must be taken to prevent the concrete from drying between application of 

water. A disadvantage of sprinkling may be its cost. The method requires an adequate 

supply of water and careful supervision. 

Figure 5: 

Sprinkling 

Wet coverings 

Burlap, cotton mats, or other moisture-retaining fabrics are used for curing. Treated burlaps 

that reflect light and are resistant to rot and fire are available. Coverings should be placed as 

soon as the concrete has hardened sufficiently to prevent surface damage. Care should be 

taken to cover the entire surface, including the edges of slabs such as pavements and 

sidewalks. The coverings should be kept continuously moist so that a film of water remains 

on the concrete surface throughout the curing period. 

Waterproof paper (see Figure 6) 

Waterproof curing paper is an efficient means of curing horizontal surfaces and structural 

concrete of relatively simple shapes. One important advantage of this method is that periodic 

additions of water are not required. 


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Concrete 

Figure 6: 

Waterproof paper 

Plastic sheets (see Figure 7) 

Certain plastic sheet materials (polyethylene films) are used to cure concrete. They are 

lightweight, effective moisture barriers and easily applied to simple as well as complex 

shapes. 

In some cases, the use of thin plastic sheets for curing may discolor the hardened concrete. 

This may be especially true when the concrete surface has been steel-troweled to a hard 

finish. When such discoloration is objectionable, some other curing method is advisable. 

Figure 7: 

Plastic sheets 

6.3 Curing Compounds 

Liquid membrane-forming curing compounds retard or prevent evaporation of moisture from 

the concrete. They are suitable not only for curing fresh concrete, but also for further curing 

of concrete after removal of forms or after initial moist curing. 

The concrete surface should be moist when the coating is applied. Normally only one 

smooth, even coat is applied, but two coat may be necessary to ensure complete coverage. 

A second coat, when used, should be applied at right angles to the first. 

Curing compounds used in hot weather should be white colored. 

Curing compounds are applied by hand-operated or power-driven spray equipment (see 

Figure8) immediately after the disappearance of the water sheen and the final finishing of the 

concrete. 


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Concrete 

Figure 8: 

Curing compounds 

6.4 Steam curing 

Of the methods in Group 3, accelerating the strength development, the most common is 

steam curing. It can be used to advantage where early strength gain in concrete is important 

or where additional heat is required to accomplish hydration, as in cold-weather concreting. 

Two methods of steam curing for early strength gain are used today: 

♦ curing in live steam and atmospheric pressure (for enclosed cast-in-place structures and 

manufactured precast concrete units) 

♦ curing in high-pressure steam autoclaves (for small manufactured units). 

A steam-curing cycle consists of: 

1) an initial delay prior to steaming 

2) a period for increasing temperature 

3) a period for holding the maximum temperature constant 

4) a period for decreasing temperature 

A typical atmospheric steam-curing cycle is shown in Fig. 11, chapter ‘Concrete Categories’, 

paragraph 3.6. 

Steam curing at atmospheric pressure is generally done in a steam chamber or other 

enclosure to minimize moisture and heat losses. 

High-pressure steam curing in autoclaves takes advantage of temperatures in the range of 

160 to 190°C and corresponding pressures. Hydration is greatly accelerated and the 

elevated temperatures and pressures may produce additional beneficial chemical reactions 

between the aggregates and/or cementitious materials that do not occur under normal steam 

curing. 

7 Hot weather concreting 

Hot weather for concreting is defined as any combination of high air temperature, low relative 

humidity and wind velocity, tending to impair the quality of fresh or hardened concrete or 

otherwise resulting in abnormal properties. Hot weather can adversely affect the properties 

and serviceability of concrete. 


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Concrete 

Concrete mixed, placed and cured at elevated temperatures normally develops higher early 

strength than concrete produced at normal temperatures, but the 28 day or later strength is 

generally lower (Figure 9). 

Figure 9: 

Influence of curing temperatures on strength at day and 28 days 

Plastic shrinkage cracking is usually associated with hot weather concreting. High concrete 

temperature, high air temperature, high wind velocity and low humidity, or combinations 

thereof, cause rapid evaporation which significantly increases the probability that plastic 

shrinkage cracking will occur. 

As shown in Figure 10, the amount of mixing water required to make a concrete of a certain 

consistency, increases considerably as the temperature of fresh concrete increases. 


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Concrete 

Figure 10: 

Water requirement of a concrete mix increases with an increase in 

temperature 

For the common, non-massive types of structure a maximum concrete temperature of 32°C 

is recommended by ACI as a reasonable upper limit. For the massive types of construction a 

temperature of 16°C or even lower would be desirable. 

The most practical method of maintaining low concrete temperatures is to control the 

temperature of the materials. 

The equation given below shows that, for concrete of conventional properties, a reduction of 

the concrete temperature by 1°C requires reducing either the cement temperature by about 

8°C or the water temperature by about 4°C or the aggregate temperature by about 2°C. 

Equation: 

T = temperature of freshly mixed concrete (deg. C) 

T a , T c , T w , T wa = temperature of aggregate, cement, mixing water 

and water on aggregate respectively (deg. C) 

W a , W c , W w , W wa = weight of aggregate, cement, added mixing water 

and water on aggregate, respectively (kg) 

Of the materials contained in concrete, water is the easiest to cool. It can be cooled by 

refrigeration or by adding ice which is used as part of the mixing water, provided that it is 

completely melted by the time mixing is completed. 


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Concrete 

Cement temperature has only a minor effect on the temperature of the freshly mixed 

concrete because of the low specific heat of cement and the relatively small amount of 

cement contained in the mix. Fresh hot cement from the plant can cause difficulties. 

Aggregates have a pronounced effect on the fresh concrete temperature because they 

represent 60 to 80% of the total weight of concrete. Aggregate stockpiles should be shaded 

from the sun and kept moist by sprinkling. Before concrete is placed, the forms, the 

reinforcing steel, and the subgrade should be cooled by sprinkling as well. 

Transporting and placing of concrete should be done as quickly as practicable. During 

extremely hot periods improved results may be obtained by restricting the placing of concrete 

to the early morning or evening hours. 

In order to prevent concrete from drying out, curing should be started as soon as the 

concrete surface is finished. In special cases of concreting during hot weather a retarding 

admixture may be used to delay the setting time. 

8 Cold Weather Concreting 

Concreting in cold weather requires special precautions. Concrete sets slowly in cold 

weather and development of strength is delayed. At low temperatures (at +5°C or lower 

during placing and the early curing period), one or more of these recognized protective 

measures should be used: 

♦ Heating the area where concrete is placed 

• The presence of ice and the possibility of ice formation during concreting must be 

avoided. Temperature of the concrete forms should be raised to above freezing, as 

well as that of adjacent concrete and subgrade, through the use of heated 

enclosures. 

♦ Heating the water and concrete materials 

• In cold weather, freshly placed concrete should be at least 10°C and not more than 

32°C when poured in the forms. In addition to heating water, it may be necessary to 

heat aggregates. 

♦ Use of chemical accelerators 

• During low temperatures, the use of chemical accelerators can speed up the set of 

concrete. Calcium chloride is the most commonly used and may be used up to 2% by 

weight of cement. 

♦ Calcium chloride or admixtures containing soluble chlorides must not be used: 

• in reinforced and prestressed concrete 

• in concrete containing embedded aluminium 

• in lightweight insulating concrete place over metal decks 

• in concrete that will be in contact with soils, or water containing sulfates 

♦ Maintaining concrete temperatures 

• Concrete slabs lose heat and moisture rapidly in cold weather. They need protection 

against wind and cold. A heated enclosure or insulation should be provided to keep 

concrete temperature above 10°C. The following Time-Temperature Chart shows 

minimum periods in which concrete temperatures should be maintained: 


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Concrete 

20°C 10°C 

plain concrete 3 days 7 days 

plain concrete with 

calcium chloride 

2 day 3 days 

• Note: After the periods shown above, concrete temperature should be maintained 

above 5°C for at least four days. Concrete should not be allowed to dry out. 

♦ Special provisions for curing 

• Cold weather air acts like a sponge to draw moisture from concrete in both its fresh 

and hardened state. This rapid drying-out process must be avoided. Curing and 

protection from start to finish should be continuous and uninterrupted until the 

concrete attains its designed strength. At the end of the curing period (see Time- 

Temperature Chart above), protection should be removed in such a way that the 

temperature of the concrete will not drop faster than 5°C in 24 hours. 

The following figure 11 illustrates the precautions that should be taken for cold weather 

concreting. 


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Concrete 

Figure 11: 


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9 Ready-Mixed Concrete 

If, instead of being batched and mixed on the job site, concrete is delivered ready for placing 

from a central plant, it is referred to as ready-mixed concrete. 

This type of concrete is used extensively in many countries as it offers numerous advantages 

as compared to the job-site-mixed concrete (Table 3). 

Table 3: 

Production of ready-mixed concrete in W. Europe (from ERMCO Annual 

Report 1976/77 and 1995/96) 

Country 

Cement consumption 

in ready-mixed 

concrete in % of total 

cement consumption 

Ready-mixed concrete 

production in mio m 3 

1976/77 1995/96 1976/77 1995/96 

Austria 19.5 44.0 4.3 8.6 

Belgium 30.9 39.0 6.34 9.1 

W. Germany 44.6 55.0 49.8 68.3 

Finland 57.7 40.0 3.4 1.6 

France 26.3 40.6 25.2 29.7 

Great Britain 42.1 50.0 24.8 22.3 

Italy 23.1 43.8 31.7 54.0 

Spain 19.0 36.6 15.6 36.2 

Holland 36.4 52.0 6.8 8.0 

Sweden 48.4 61.7 5.2 2.4 

Switzerland 40.7 57.0 5.6 9.0 

USA 60.0 71.5 130.0 192.0 

Ready-mix concrete plants use precision scales to weigh the ingredients as the producer is 

responsible for delivering concrete of the required quality. 

There are three types of mixing: 

♦ Transit mixed concrete is mixed completely in a truck mixer. The batching of ingredients 

is carried out in a dry-batch plant. 

♦ Central mixed concrete is batched and mixed completely in a stationary batching and 

mixing plant (premix-plant) and is delivered in a special dump truck (tipper) without 

mixing or agitating, or in a truck mixer at agitating speed. 

♦ Shrink-mixed concrete is mixed partially in a stationary mixer and then completed in a 

truck mixer. 

Because of the many advantages offered by ready-mixed concrete, this industry has shown 

a phenomenal growth in recent years. These advantages can be summarized as follows: 

♦ Use of modern precision batching equipment assures an accurately proportioned mix and 

allows the use and modification of different mix designs. 

♦ Thorough mixing of each batch helps to produce uniform concrete. 

♦ More efficient operation on the job site (no space problems with respect to storage of 

ingredients, etc.). 


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Concrete 

♦ Delivery at the time required. 

♦ Delivery in the exact quantity desired, thus eliminating waste. 

♦ Equipment on the building site not necessary. 

♦ Possibility to use different chemical admixtures. 

♦ Possibility to use special concretes. 

♦ Clear and easy base for delivery contracts; no problems with estimates of concrete cost. 

The basis for the purchase of ready-mixed concrete is the concrete volume (m 3 , cubic yard) 

and required concrete quality. To attain the desired concrete quality, different types of 

concrete mixes (mix design) can be used (see also paper on "Concrete Mix Design"): 

♦ Designed mix (performance mix): concrete is designed by the ready-mix producer and 

should fulfill all requirements as stated by the purchaser. 

♦ Codified mix: mix proportions are established in a National Code and are usually suitable 

for a restricted range of concrete strength classes and applications (for example in CEB- 

Code only for mixes with strength ≤ 25 N/mm 2 ). 

♦ Prescribed mix: the purchaser is responsible for designing the concrete mix and specifies 

the mix proportions and the materials to be used by the ready-mix producer. 

In recent years the ready-mixed concrete industry has gained considerable influence on the 

development of concrete standards and specifications. Several new developments in the 

concrete technology have been introduced by the ready-mixed concrete industry, e.g. 

♦ flowing concrete 

♦ ready-mixed mortar 

♦ developments of new accelerated testing methods, etc. 

10 Pumped Concrete 

Pumped concrete may be defined as concrete conveyed by pressure through either a rigid 

pipe or flexible hose and discharged directly into the desired area. 

Pressure is applied by (see Figures 12 to 14): 

♦ Piston pumps 

♦ Pneumatic pumps (compressed air) 

♦ Squeeze pressure pumps 


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Concrete 

Figure 12: Schematic drawings of the various pump types - 

piston type concrete pump 

Inlet valve opens while outlet valve is closed and concrete is drawn into cylinder by gravity 

and piston suction. As piston moves forward inlet valve closes, outlet valve opens, and 

concrete is pushed into pump line. 

Figure 13: 

Pneumatic type concrete pump 

Compressor builds up air pressure in tank, which forces concrete in placer through the line. 


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Concrete 

Figure 14: 

Squeeze Pressure Type Concrete Pump 

Pumping may be used for most concrete constructions, but it is especially useful where 

space for construction equipment is limited. 

Very often the ready-mixed concrete companies include a pumping division. The portion of 

pumped concrete as compared to the total ready-mixed concrete production in various 

countries is shown in Table 4. 

Table 4: 

Pumped concrete in proportion to the total ready-mixed concrete 

production (1996) 

(Ready-mix concrete companies affiliated with the Holcim Group) 

Country No. of Plants Pumped concrete 

in % of the total 

production 

Belgium 55 30 

France 116 7 

Switzerland 18 15 

W. Germany 38 49 

Greece 3 74 

Colombia 29 37 

Costa Rica 13 33 

Mexico 62 32 

Brazil 40 30 

Ecuador 7 70 

South Africa 38 16 

The concrete pumps can be: 


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Concrete 

♦ Truck-mounted or 

♦ Stationary 

Ease of operation, safety and economy is required of a good pump. Today the most widely 

used diameter of a pipe for pumping is 125 mm; the usual maximum grain size is 32 mm, the 

minimum cement content about 300 kg and the consistency should be plastic (slump 7 to 12 

cm). 

Pumping jobs over heights of more than 200 m and with volumes of up to 110 m 3 /hour are 

quite common in today’s concrete practice. 

11 Special Concreting Processes 

The various special concreting processes will not be discussed in detail. However, some of 

them are briefly explained in the following: 

♦ Vacuum-processed concrete: concrete from which, after compaction and before 

hardening, water is extracted by a vacuum process. The w/c ratio is thus reduced so that 

concrete with higher strength, higher density, lower permeability and better durability can 

be obtained. 

♦ Preplaced-aggregate concrete: concrete produced by placing coarse aggregate into a 

mould and later injecting a cement-sand grout, usually with admixtures to fill the voids. 

♦ Dry-packed concrete: concrete mixture sufficiently dry to be consolidated by heavy 

ramming. 

♦ Spun concrete: concrete compacted by centrifugal action, e.g. in the manufacture of 

pipes (centrifugal process, roller-suspension process). 

♦ Tremie concrete: concrete placed under water through a pipe or tube. 

♦ Shotcrete: mortar or concrete conveyed through a hose and projected at high velocity 

onto a surface; also known as air-blown mortar, pneumatically applied mortar or 

concrete, sprayed mortar and gunned concrete (gunite). 


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Concrete 

12 LITERATURE 

12.1 Concrete Technology 

1) A.M. Neville - Properties of Concrete, 4th Edition - Longman Group Ltd. 

2) Lea’s Chemistry of Cement and Concrete, 4th Edition - Arnold Ed. 

3) Ghosh - Cement and Concrete Science and Technology - abi Books Private Ltd. 

12.2 Concrete practice 

1) W.H. Taylor - Concrete Technology and Practice 

2) Ramachandran - Concrete Admixtures Handbook - Noyes Publications 

3) ACI Manual of Concrete Practice - aci Publications 

4) Properties of Fresh Concrete, Proceedings of the Rilem Colloquium - Chapman & Hall 

12.3 Testing of Concrete 

1) Bartos - Fresh Concrete, Properties and Tests - Elsevier Ed. 

2) Concrete Test Methods. 

RILEM, Secrétariat Général, 12 rue Brancion, 75737 Paris CEDEX 15 


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Concrete 

Concrete Shrinkage 

1. DEFINITION AND DESCRIPTION OF SHRINKAGE ............................................136 

2. TYPES OF SHRINKAGE AND SIGNIFICANCE....................................................136 

2.1 General .........................................................................................................136 

2.2 Plastic shrinkage ...........................................................................................137 

2.3 Drying shrinkage ...........................................................................................139 

2.4 Autogenous shrinkage ..................................................................................141 

2.5 Carbonation shrinkage ..................................................................................143 

3. FACTORS INFLUENCING CONCRETE SHRINKAGE.........................................145 

3.6 Overview .......................................................................................................145 

3.7 Concrete composition ...................................................................................145 

3.8 Type and Grading of Aggregate....................................................................147 

3.9 Cement characteristics..................................................................................148 

3.10 Mineral components......................................................................................149 

3.11 Chemical Admixtures ....................................................................................150 

3.12 Curing and Storage Conditions .....................................................................150 

3.13 Dimension of Structural Member...................................................................151 

3.14 Reinforcement...............................................................................................152 

3.15 Combined Effect on Individual Factors .........................................................152 

4. CONTROL OF CRACKING DUE TO SHRINKAGE ..............................................153 

4.16 Introduction ...................................................................................................153 

4.17 Reduction of Cracking Tendency ..................................................................154 

4.18 Reinforcement...............................................................................................154 

4.19 Joints.............................................................................................................155 

4.20 Shrinkage-Compensating Concrete ..............................................................156 


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1 Definition and description of shrinkage 

Shrinkage and the contrary effect of swelling, is a seemingly simple phenomenon of 

contraction which is defined as the reduction in the outer volume without the influence of an 

external force. Strictly speaking, shrinkage is a three-dimensional deformation but it is 

usually expressed as a linear strain because in the majority of exposed concrete elements 

one or two dimensions are much smaller than the third dimension, and the effects of 

shrinkage are greatest in the largest dimension. 

In common usage, the term shrinkage is a shorthand expression for drying shrinkage 

of hardened concrete but there are several other types of shrinkage deformation in 

concrete which, depending on circumstances, may or may not occur simultaneously 

or be independent of one another [A6]. 

Volume changes due to changes in temperature are not to be covered by the terms 

shrinkage and swelling, although stresses created through the release and flowing off of heat 

of hydration are often called thermal shrinkage or thermal contraction. 

For practical purposes, shrinkage is usually described by the amount of shrinkage in one 

dimension as expressed by the following formula: 

ε (t) = (l t - I 0 )/I 0 = ∆l/l 0 

being: 

I 0 : initial length 

l t :length at time t 

The dependence of time shows that shrinkage deformations vary with time. For constant 

ambient conditions, the amounts of shrinkage tend towards a corresponding final state 

(designated as final shrinkage value ε s,00 ) the amount of shrinkage depends mainly on the 

relative humidity and temperature of the ambient air, the dimensions of the structural element 

and the concrete’s composition. In case of water storage, the shrinkage will show positive 

values (swelling). 

2 Types of shrinkage and significance 

2.1 General 

All shrinkage phenomena occurring in concrete systems are basically caused by changes in 

the water balance within the porous matrix of the concrete. According to the time of 

occurrence and the origin of the change in this water balance, four different types of 

shrinkage for concrete can be distinguished. 

• Shrinkage due to capillary forces in the fresh and still plastic concrete. This kind 

of shrinkage is called “plastic shrinkage” or early shrinkage. 

• Shrinkage due to drying out of the hardened concrete (“drying shrinkage”). 

• Shrinkage in connection with the chemical volume reduction during cement hydration 

called “autogenous shrinkage”. 

• Shrinkage due to carbonation of the hardened concrete called “carbonation shrinkage” 


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2.2 Plastic shrinkage 

Plastic shrinkage cracking is a constant source of concern in the concrete industry. It is a 

frequent cause of anxiety, yes conflict, between the concrete supplier and the client when 

cracks are observed on a freshly placed concrete surface. It also causes concern to the 

designers as “long-term durability” comes into question. 

After placement and compaction of the fresh concrete, the concrete surface is usually 

covered by a film of water. The thickness depends mainly on the bleeding tendency of the 

concrete. At this stage the concrete is still in a plastic state and hence reference is made to 

plastic shrinkage. 

The most important factor influencing plastic shrinkage and plastic shrinkage cracking is the 

rate of evaporation of water from the concrete surface. A similar loss can occur by suction by 

the underlying dry concrete or soil (placing concrete on a dry subgrade should be avoided). 

If the rate of evaporation exceeds the rate at which bleeding water rises to the surface, then 

plastic shrinkage and cracking are likely to occur . 

The state is easily visible by the disappearance of the sheen from the surface of concrete. 

But it has been observed that cracks also form under a layer of water and merely become 

apparent on drying. 

Another type of cracking on the surface of fresh concrete is caused by differential settlement 

of fresh concrete due to some obstruction to settlement, such as large particles of aggregate 

or reinforcing bars. This plastic settlement cracking can be avoided by the use of a dry mix, 

good compaction and by not allowing too fast a rate of build-up of concrete. Plastic 

shrinkage cracking and plastic settlement cracking are sometimes confused with one 

another. 

The temperature, relative humidity and wind velocity of the air and the temperature of the 

concrete influence the rate of evaporation. It should be remembered that evaporation is 

increased when the temperature of the concrete is much higher than the ambient 

temperature; under such circumstances, plastic shrinkage can occur even if the relative 

humidity of the air is high. 

The ACI 305R-91 nomograph (Figure 2.1) is still the preferred method for predicting the 

evaporation rate of bleed water from the surface of freshly placed concrete. Precautionary 

should be taken when the rate evaporation is expected to approach 0.2 [psf/h] (1.0 kg/m²/hr). 

The Canadian code [C1] nominates 0.75 kg/m 2 /hr as the critical value while Australian 

references quote 0.5 kg/m 2 /hr as a value at which precautions should be taken. Such 

conditions mainly occur during hot weather concreting, but any atmospheric condition 

resulting in an excessive evaporation rate can lead to plastic shrinkage cracks. According to 

ACI 305R-91, the risk of plastic cracking is the same at the following combinations of 

temperature and relative humidity: 

• 41°C and 90% 

• 35°C and 70% 

• 24°C and 30% 

Recently Paul J. Uno has developed a “single operation” equation which can be used on a 

simple hand-held calculator and is very appropriate for on-site quick checks to see if 

evaporation is going to be a critical factor in plastic shrinkage cracking. 


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Concrete 

E = 5[(T c +18) 2.5 – r (T a +18) 2.5 ][V+4]x10 -6 

Where 

E = evaporation rate, kg/m 2 /hr 

T c = concrete temperature, °C 

T a = air temperature, °C 

r = (RH percent)/100 

V = wind velocity, kph 

Under favourable climatic conditions, the amount of plastic shrinkage for concrete can reach 

up to 400 µm/m. According to experience, the width of the individual crack amounts to about 

0.1 to 3 mm and the cracks can extend in thick concrete members down to a depth of 10 cm. 

A typical feature of the plastic shrinkage cracks is that they are relatively wide at the surface 

and then rapidly decrease in width towards the interior of the concrete. The pattern of cracks 

is generally irregular (“map” pattern). For concrete slabs, also patterns with a series of 

parallel lines at very approximately 45° to the edge of the slab are observed. 

The most notable characteristic of plastic shrinkage cracks in slabs is that they normally do 

not extend to the edge of the slab, because the edge can shrink without restraint. 

Plastic shrinkage and the above described crack formation is most likely to take place are the 

hours after compaction and finishing of the concrete up to the beginning of the hardening, 

which is typically the period of 2 to 8 hours after concrete placement. According to a study 

carried out at HGRS on restrained concrete slabs, a very critical period for cracking seems to 

be 2 to 4 hours after mixing and placing. Retarders, which maintain the concrete workable for 

a longer time, can intensify or occasionally even initiate the plastic shrinkage cracking. 

To prevent the cracks, the site personnel must be aware of the factors that will cause 

cracking and be prepared for adverse conditions. In some case, not pouring at all could be 

the best choice. 


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Concrete 

Figure 2.1 – Effect of air temperature, relative humidity, wind velocity and concrete 

temperature on rate of evaporation of surface moisture from concrete. 

To effectively avoid these cracks from forming, the golden rule is not to let the concrete dry 

out too rapidly. This means that it is crucial to finish the concrete as quickly as possible and 

to start curing immediately. In severe conditions, such as very hot, dry and windy, it may be 

necessary to apply an evaporation retarder to the fresh concrete. These compounds are 

alcohol-based and are not substitutes for normal curing compounds. They are specifically 

designed to be applied to fresh concrete and are very effective in preventing excessive water 

loss during the initial stage of strength gain. 

Concrete composition is of importance insofar as water rich fresh concrete with high water 

retention ability is more susceptible to shrinkage and cracking than other concrete, so that 

certain improvement is also possible by adaptations in concrete characteristics. 

2.3 Drying shrinkage 

As a result of a disequilibrium in the relative humidity between concrete and its environment, 

any concrete loses water when exposed to an environment whose relative humidity is lower 

than that existing in the capillary network in the concrete. As a result of this water loss, 

concrete shrinks. The magnitude of drying shrinkage depends on many factors, including the 

properties of the materials, temperature, relative humidity of the environment, the age at 

which concrete is first exposed to a drying environment and the size of the concrete element 

that is drying. 


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The driving force for drying shrinkage is the evaporation of water from the capillary network 

in the concrete at the menisci which are exposed to air with a relative humidity lower than 

that within the capillary pores. As the free water contained in the capillary pores is held by 

forces that are inversely proportional to the diameter of the pores, the loss of water is 

progressive and proceeds at a decreasing rate. Researchers still disagree about the 

fundamental mechanism responsible for drying shrinkage. These mechanisms include the 

capillary tension, the surface adsorption, and the interlayer water removal. 

Drying shrinkage occurs first at the surface of concrete, and indeed only at a surface 

exposed to dry air; this could be a single surface or all external surfaces of a concrete 

element. Drying shrinkage then progresses toward the core of the element so that the loss 

of water expressed as a percentage of the apparent volume of concrete is smaller for 

concrete elements with a lower surface/volume ratio. Factors influencing the magnitude of 

the loss of water are the porosity of the concrete and the characteristics of the capillary pore 

network such as the size and shape of the pores and their continuity. 

Typical basic shrinkage values of structural members according to the location and climatic 

condition respectively are shown in Table 2.1. As hardened concrete has a very low tensile 

elongation at rupture of 0.1 to 0.2 x 10 -3 [G1], structural members are susceptible to cracking 

if the deformation is hindered by external restraint. If the tensile stresses, caused by the 

external restraint, exceed the tensile strength of the concrete, continuous cracks are formed 

(Figure 2.2). These cracks can affect the function of the corresponding structural members. 

Table 2.1 – Basic shrinkage value in dependence of location of structural member 

Location of structural member Average rel. 

humidity about (%) 

Basic shrinkage 

value (µm/m) 

IN WATER 100 +100 

In very humid air, e.g. directly above 

water 

90 -130 

Generally in the open air 70 -320 

In dry air, e.g. in dry interior rooms 50 -460 

A further consequence of the drying shrinkage is loss of the pretension in pre-stressed 

structural members. Also warping of concrete slabs is directly related to the amount of drying 

shrinkage. Finally, significant time-dependent bending of structural members is possible due 

to drying shrinkage, similar to effects observed under load by means of creep. 


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Figure 2.2 – Cracking of concrete due to drying shrinkage under restraint 

To summarise, it can be stated that drying shrinkage of concrete can not be avoided, but the 

amount of shrinkage can be controlled to a certain extent by adjusting some influencing 

factors in a favourable manner. The shrinkage deformation depends mainly on the time, the 

dimensions of the structural member, the storage conditions and the concrete composition. 

2.4 Autogenous shrinkage 

As far as concrete with low water/binder ratios is concerned, high levels of autogenous 

shrinkage are generally associated with self-desiccation. For ordinary concrete, autogenous 

shrinkage is negligible (typical value are 40 µm/m at the age of one month and 100 µm/m 

after five years). This difference in the behaviour of these two types of concrete can be 

explained in terms of differences in the size distribution of the pore and capillary networks. 

According to Aïtcin the expression autogenous shrinkage was first mentioned in the literature 

in 1934 and positively defined by Davis as a macroscopic volume change caused by the 

hydration of cement. The expression chemical shrinkage is also found in the literature 

because autogenous shrinkage is a consequence of the decrease in the absolute volume of 

the hydrated cement paste during its hydration. 

It may be worth noting that, because the products of hydration can form solely in water-filled 

space, only a part of the water in the capillary system can be used in hydration. Thus, for 

hydration to take place there must be enough water present both for the chemical reactions 

and for filling of gel pores. These gel pores are formed by the reactions of hydration of 

cement. They are much finer than capillary pores so that they drain water from the coarsest 

capillary pores. As a consequence in the absence of any external water supply, the coarsest 

capillary pores start to dry in a manner similar to drying by evaporation. This is why this 

phenomenon is called self-desiccation. 


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The causes of autogenous shrinkage are the same as the causes of drying shrinkage 

because it is the same physical phenomenon that is developing within concrete: the creation 

of menisci within the capillary system and the resulting tensile stresses. Nevertheless, there 

are some major differences between autogenous shrinkage and drying shrinkage: 

• autogenous shrinkage develops without any mass loss, unlike drying shrinkage; 

• autogenous shrinkage develops isotropically within the concrete while drying shrinkage 

progresses from the drying surface to the core of the element; 

• autogenous shrinkage does not develop any relative humidity gradients, drying shrinkage 

does; 

Autogenous shrinkage is linked directly to cement hydration and starts to develop uniformly 

and isotropically only few hours after the casting of concrete (practically always before 24 

hours), whereas drying shrinkage starts to develop a little slower and at the surface when 

hardened concrete is exposed to a dry environment which is usually a matter of days rather 

than hours (Figure 2.3). 

Less than one day 

Several days 

Figure 2.3 – Typical plot of change in temperature versus concrete shrinkage. 

Autogenous shrinkage can be avoided if the coarse capillaries are refilled by an external 

supply of water (water curing). As long as the gel pore system and capillary pore systems 

are connected to this external supply of water, no menisci are formed within the capillary 

system, so that there are no induced tensile stresses and no autogenous shrinkage. 

The ingress of external water favours further hydration of the still unhydrated parts of cement 

particles and at this stage, hydration results in an increase in the absolute volume because 

the added water from outside the concrete. As a consequence, the gel pore system and the 

capillary pore system may become disconnected, depending on the local pore size 

distribution in the hardening concrete. As soon as the water phase has ceased to be 

continuous, water ingress from outside stops and conditions for the development of 

autogenous shrinkage are created. 


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Hydration 

Volumetric contraction 

Self desiccation 

Menisci 

Autogenous 

shrinkage 

No 

External 

supply of 

water 

No autogenous 

shrinkage 

No 

Yes 

Pores 

and capillaries 

connected? 

Yes 

No menisci 

Autogenous shrinkage tends to increase at higher temperatures, with a higher cement 

content, and possibly with finer cements and with cements which have a high C 3 A and C 4 AF 

content. At a constant content of blended cement, a higher content of fly ash leads to lower 

autogenous shrinkage . 

Research at CSIRO shows that during the first 24 hours after casting, some high strength 

concrete exhibits total shrinkage values of 600-800 µm/m under standard temperature 

conditions. Autogenous strains of this magnitude translate to a total deformation of between 

6 and 8 mm for every 10 m length of concrete element. This amount of autogenous 

shrinkage in the first 24 hours is equivalent to the total drying shrinkage measured over a 

period of 1 year for the same concrete. According to Mak these autogenous deformations 

may cause a real risk of early age cracking in in-situ, precast and composite members. 

2.5 Carbonation shrinkage 

The absorption of CO 2 from the air significantly changes the chemical and physical 

characteristics of the cement stone. Not only the free Ca(OH) 2 is transformed to CaCO 3 

under release of water, but also the hydration products of the cement are decomposed under 

the influence of CO 2 . This carbonation process is accompanied by an increase in weight of 

the concrete and by an increase in the irreversible shrinkage. The reversible shrinkage, 

however, is reduced considerably, which can be explained by the formation of relatively 

coarse crystals of calcium carbonate. 

The mechanisms of carbonation shrinkage are not very clear and can not be explained by 

the liberation of previously bound water alone. Carbonation shrinkage is possibly caused by 

the dissolution of crystals of Ca(OH) 2 while under compressive stress (imposed by the drying 

shrinkage) and depositing of CaCO 3 in spaces free from stress; the compressibility of the 

paste is thus temporarily increased. Carbonation of the hydrates present in the gel does not 

contribute to shrinkage, as the reaction does not involve dissolution and re-precipitation. 


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The effect of carbonation depends a lot on the relative humidity and drying state of the 

concrete. Carbonation increases shrinkage mostly at the intermediate humidities of about 

50%. Water saturated or very dry concrete absorbs practically no CO 2 and accordingly do not 

have higher shrinkage values. An additional factor playing an important role is the sequence 

of drying and carbonation. Simultaneous shrinkage and carbonation (which usually happens 

in practice) produces lower total shrinkage than when drying is followed by carbonation 

(Figure 2.4). 

For the amount of shrinkage of whole structural members, the carbonation shrinkage is not 

significant, since in general it only affects a very small part of the total cross-section. 

Conditions under which carbonation shrinkage can be noticed are encountered on vertical 

surfaces of exposed structural members, which are seldom exposed to rain-showers and 

which often get sunshine. In the edge zones of these members, the carbonation shrinkage 

can lead to internal (tensile) stresses in the surface area, creating a dense net of fine 

unevenly distributed cracks. 

Figure 2.4 - Influence of the sequence of drying and carbonation of shrinkage 


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3 Factors Influencing Concrete Shrinkage 

3.1 Overview 

Among the four types of shrinkage described in the previous section, drying shrinkage is 

most common and important in the present concrete construction practice. As stated before, 

autogenous shrinkage is relatively important only for high performance concrete (HPC) 

having a low water/cement ratio (< 0.40) and in large mass concrete structure. HPC 

represents only a small volume of concrete that is used in the present market (but is 

expected to be more important in the future for reasons of durability). 

Plastic shrinkage can usually be controlled effectively by an adequate curing procedure, so 

that cracking of concrete in its plastic state can be avoided. 

The literature lists many factors that have an influence on shrinkage of concrete (mostly 

drying shrinkage). The following list gives an overview of the most commonly mentioned 

variables: 

• Concrete composition (aggregate, water and cement content, w/c-ratio) 

• Cement characteristics (composition, fineness) 

• Type and grading of aggregate 

• Mineral admixtures 

• Chemical admixtures 

• Curing and storage conditions 

• Dimensions of structural member (size and shape) 

• Reinforcement 

3.2 Concrete composition 

The most important influence on the shrinkage of concrete is exerted by the aggregate, 

which restrains the amount of shrinkage that can actually be realised. Cement paste in 

concrete, if unrestrained, would shrink from 5 to 15 times as much as concrete. The ratio of 

shrinkage of concrete (S c ) to shrinkage of neat paste (S p ) depends on the aggregate content 

in the concrete, a, and is 

S c = S p (1 – a) n 

The experimental values of n vary between 1.2 and 1.7. The paste content of concrete is 

thus one of the main factors governing shrinkage. It is controlled by the total amount of 

cement and water in the concrete. In practical terms, at a constant water/cement ratio, drying 

shrinkage increases with an increase in the cement content because this result in a larger 

volume of hydrated cement paste that is liable to shrinkage. However, at a given workability, 

which roughly means a constant water content, shrinkage is unaffected by an increase in the 

cement content, or may even decrease, because the water/cement ratio is reduced and the 

concrete is, therefore, better able to resist shrinkage. The overall pattern of these influences 

on drying shrinkage is shown in Figure 2.5. 

The dual influences of water/cement ratio and aggregate content are shown in Figure 2.6, 

but it must be remembered that the shrinkage values given are not more than typical for 

drying in a temperate climate. 


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The water content of concrete affects shrinkage in so far as it reduces the volume of 

restraining aggregate. Thus, in general, the water content of a mix would indicate the order 

of shrinkage to be expected, following the general pattern of Figure 2.7, but the water content 

per se is not a primary factor. In consequence, mixes having the same water content, but 

widely varying in composition, may exhibit different values of shrinkage. An important factor, 

which influences the water requirement of the concrete at given consistency, is the 

temperature of the fresh concrete. Particularly in hot climates, measures have to be adopted 

to keep this temperature at a reasonably low level. 

Figure 2.5 - Shrinkage as a function of cement content, water content, and w/c ratio; 

concrete moist-cured for 28 days, thereafter dried for 450 days. 

Figure 2.6 - Influence of w/c ratio and aggregate content on shrinkage 


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Figure 2.7 - Relation between the water content and drying shrinkage 

3.3 Type and Grading of Aggregate 

Considerable variation in concrete shrinkage can result from the type of aggregate used, 

even within the range of ordinary aggregates (Figure 2.8). This is mainly attributed to the 

different elastic properties of the aggregates, which determine the degree of restraint 

provided. Aggregates with a higher modulus of elasticity and lower compressibility 

respectively give a lower shrinkage. The presence of clay in aggregate lowers its restraining 

effect on shrinkage, and since clay itself is subject to shrinkage, clay coatings on aggregate 

can increase shrinkage by up to 70%. 

Figure 2.8 - Shrinkage of concrete of fixed mix proportions but made with different 

aggregates, and stored in air at 21° and a relative humidity of 50 %. 


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Beside their compressibility, the shrinkage of the aggregates themselves may be of 

considerable importance in determining the shrinkage of the concrete. Shrinking rocks have 

usually high absorption (see Table 2.2) rates, so that this can be treated as a warning sign 

that the aggregate should be carefully investigated for its shrinkage properties. Sandstone 

and slate are typical examples for aggregates, which show already on their own considerable 

volume changes upon wetting and drying. 

Table 2.2 – Effect of type of aggregate of a single size on concrete shrinkage *[C3] 

Lightweight aggregate usually leads to higher shrinkage, largely because the aggregate, 

having a lower modulus of elasticity, offers less restraint to the potential shrinkage of the 

cement paste. 

Size and grading of aggregate per se do not influence the magnitude of shrinkage, unless 

water requirement is affected to a greater extent (e.g. in sand rich aggregate mixes). A larger 

aggregate, however, permits the use of a leaner mix and hence results in lower shrinkage. 

The larger aggregate also tends to restraint the concrete more, and as this may result in 

internal microcracking, such internal cracking may be harmful. The particle shape of 

aggregate has little effect on concrete shrinkage except if it determines the amount of mixing 

water that must be used to obtain a certain workability. 

3.4 Cement characteristics 

Finer Portland cements show a tendency towards greater concrete shrinkage, but the 

increase is normally not very large. In some cases, finer cements produce even concrete 

with lower shrinkage. Fineness of cement seems to be a factor as it can change the water 

demand of the concrete and because they contain less very coarse cement particles, which 

hydrate comparatively little, and can function as restraining bodies along with the aggregate 

particles. 

Regarding Portland cement composition, there are certain indications that shrinkage is 

increased for aluminate and alkali rich cements. Reduced drying shrinkage has been 

observed for alite rich cement, which is probably due to a coarser structure of the hydration 

product. Carlson found that among the potential compounds in Portland cement their relative 

contribution to shrinkage increases in the order C 3 S, C 2 S and C 3 A. 

The gypsum dosage in the Portland cement has a major effect on shrinkage. According to 

Lerch, drying shrinkage values can be up to 50% higher for cement deficient in gypsum. The 


Cement 

Concrete 

optimum gypsum content for minimum shrinkage is more or less equal to the one for 

adequate retarding action and strength development, thus primarily depends on C 3 A and 

alkali content of the cement. The importance of gypsum dosage to minimise contraction of 

concrete was also confirmed by Pickett. 

In practice, the shrinkage of concrete of same consistency will vary but little for a wide range 

of cement contents, because a richer mix will have a lower water/cement ratio and these 

effects offset each other. At constant water content, the amount of shrinkage is more or less 

in the same order of magnitude for mixes which are rich or poor in cement (see again Figure 

2.5), independent of the water/cement-ratio applied. This phenomenon is explained by the 

fact that mixtures with high w/c ratio give off the water more easily, but under lower 

development of shrinkage forces, whereas at low w/c-ratio less water evaporates under the 

release of higher shrinkage forces. 

3.5 Mineral components 

Relatively little data is available on the influence of mineral components on the shrinkage 

behaviour of concrete. It is believed that the effect of mineral components on drying 

shrinkage depends mainly on their influence on the concrete water requirement. In general 

those mineral components which increase the water requirement, will increase drying 

shrinkage and those, which decrease the water requirement, will decrease it. 

Due to the higher water demand, natural pozzolans in the cement will therefore usually 

increase the drying shrinkage of concrete. The replacement of clinker by limestone, fly ash 

and blast furnace slag does apparently not influence the drying shrinkage behaviour to an 

appreciable degree, since the water demand for same workability remains virtually 

unchanged compared to Portland cement concrete. Silica fume, when used together with a 

superplasticizer to maintain the workability, appears to have also no major effect on drying 

shrinkage. 

For HPC, where relatively high binder contents and low water/binder ratios are adopted, the 

rate of hydration may be so high as to cause severe shrinkage and cracking specially at an 

early age. Some work has illustrated that the use of mineral components such as silica fume 

and pulverised fuel ash results in increased autogenous shrinkage. Research workers have 

also observed that using metakaolin or silica fume at certain water/binder ratios as partial 

cement replacement materials may lead to reduced autogenous shrinkage. The authors 

attributed the reduction in shrinkage to the resulting pore refinement and improved particle 

size distribution of the blend, together with early strength development. 

Recently it has been shown that autogenous shrinkage may be negligible by using triple 

blend cement with 10% metakaolin and 20% fly ash. Such compositions could have 

significant commercial application in controlling and eliminating cracking. 

This dual role of mineral components on autogenous shrinkage probably explains why there 

is some disagreement between researchers on the influence of certain mineral components 

on shrinkage in general. 

The situation is further complicated by variations in environmental conditions, curing 

procedure and period, cement type and content, use of superplasticizers, mineral 

components type and content, and specimen size and shape. It is also possible that a 

particular mineral component may reduce one form of shrinkage whilst increasing another. 

Within the framework of ESCOCEM-low shrink cement it has been decided to focus on the 

use of mineral components for such a development. 


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Concrete 

3.6 Chemical Admixtures 

The effect of water reducing admixtures on shrinkage can not be correlated with the 

reduction in the water content of the concrete. Actually, the influence of plasticizers or 

superplasticizers on drying shrinkage is in general negligible despite the substantial water 

reduction achieved. The use of such admixtures is thus no guarantee that concrete 

shrinkage will be reduced. The only way to know if a certain water-reducing admixture will 

result in lower shrinkage is to test it with the corresponding concrete mix. 

The entrainment of air by means of corresponding chemical admixtures has been found to 

have virtually no influence on shrinkage. Set-retarding admixtures can have a varied effect, 

but do generally not influence the shrinkage values to a greater extent. Special attention has 

to be given to the accelerators calcium chloride and triethanolamine. The increase of 

shrinkage is disproportionally large with small amounts of these admixtures. 

Several chemical admixtures designed for the purpose of drying shrinkage reduction are 

available in the market (shrinkage reducing admixture). These admixtures are claimed to be 

effective measures to minimise shrinkage, but the exact mechanisms are not known. 

Possible explanations for the reduced shrinkage could be the weakening of the capillary 

tensions or improved water-retaining properties of the concrete. 

To keep a watching brief and be aware of this HGRS carried out several studies on concrete 

to establish the shrinkage reducing potential of such admixtures. The results of these 

different studies are compiled in reports RMP 96/13135/E, PDA 97/17026/E and HC 

98/18009. It has been revealed that the potential for shrinkage reduction admixture seems to 

be quite limited (30%) with a negative side effect on strength development. It should also be 

noted that the use of these admixtures increases the cost of concrete. 

3.7 Curing and Storage Conditions 

The length of moist curing is relatively unimportant in the control of shrinkage. After a curing 

period to achieve adequate strength development of the concrete, additional moist curing will 

not help to reduce shrinkage. Prolonged moist curing only delays the onset of shrinkage, but 

the final shrinkage values reached remain virtually the same. The amount of shrinkage may 

be slightly reduced by the swelling experienced in course of the curing process. 

The relative humidity of the medium surrounding the concrete after curing greatly affects the 

magnitude of shrinkage (Table 2.1 and Figure 2.9). The smaller the relative humidity of air to 

which the concrete is exposed, the higher is the final shrinkage of the corresponding 

structural member. Figure 2.9 also illustrates the greater absolute magnitude of shrinkage 

compared to swelling in water. 

The effect of wind on drying shrinkage of concrete is not significant. As the moisture 

conductivity of hardened concrete is so low that only a small rate of evaporation is possible, 

this rate cannot be increased by movement of air. 


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Concrete 

Figure 2.9 - Relation between shrinkage and time for concrete stored at different 

relative humidities. 

3.8 Dimension of Structural Member 

The dimension of the structural member is a very important factor regulating drying shrinkage 

of concrete as the magnitude of shrinkage varies considerably with the size and shape of the 

specimen. A part of the size effect may also be due to the pronounced carbonation of small 

specimens. For practical purposes, shrinkage thus cannot be considered as purely an 

inherent property of the concrete and has always to be related to the size of the concrete 

member. 

Both the rate and the final values of shrinkage decreases as the concrete member becomes 

larger, but above some value the size effect are no longer apparent. Although the 

volume/surface ratio does not perfectly reflect variations of both size and shape, there is a 

satisfactory correlation with the shrinkage for design purposes. There appears to be a linear 

relation between this ratio and the logarithm of shrinkage (Figure 2.10). 

Figure 2.10 - Relation between ultimate shrinkage and volume/surface ratio. 


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Concrete 

Accordingly it can be concluded that drying shrinkage in mass concrete is not of major 

importance, unless the surface drying contributes to the beginning cracks that may otherwise 

not form. Thin structural members and structures with large exposed surfaces (e.g. slabs and 

walls) will always have a higher shrinkage and are thus more prone to cracking, particularly if 

they are not free to move. 

3.9 Reinforcement 

In reinforced concrete drying shrinkage results in a compressive stress in the bars, which 

themselves resist and reduce the overall drying shrinkage in the reinforced concrete 

member. The actual value of shrinkage reduction is obviously dependent on the amount of 

reinforcement used. 

The addition of discrete fibres such as polypropylene, glass and steel to the concrete can 

reduce drying shrinkage to a certain extent. More than for the purpose of shrinkage reduction 

itself these fibres are, however, added to prevent cracking of the concrete due to shrinkage. 

3.10 Combined Effect on Individual Factors 

It is believed that the combined effect of various influencing factors on concrete shrinkage is 

the product and not the sum of the individual effects of the concerned factors. This 

cumulative effect on shrinkage of making poor choices in the selection of materials and 

construction practices has been emphasised by Powers and Tremper. 

To illustrate the effect of combination of influencing factors, the shrinkage results of Powers 

are presented in Table 2.3. It shows the cumulative and individual effects of the most 

unfavourable versus the most favourable choices with regard to six factors influencing the 

amount of shrinkage. He concluded from his data that wrong choices of alternatives with 

respect to volume change could result in about seven time as much shrinkage as would 

result from the best choices. 

It is of course not very likely that all negative factors occur at the same time. Nevertheless, it 

is worthwhile to note the magnitude of increase in shrinkage that can occur if several 

unfavourable choices are made. 

Table 2.3 – Individual and cumulative effects of various factors on 

shrinkage 


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Concrete 

4 Control of Cracking due to Shrinkage 


The reason why cracks can be formed by drying shrinkage has already been illustrated in 

Figure 2.2. If hardened concrete could shrink without any restraint, it would not crack. 

However, in a real structure the concrete is always subject to some degree of restraint either 

by the foundation or another part of the structure or by the reinforcing steel embedded in the 

concrete. The combination of shrinkage and restraint develops tensile stresses and if these 

exceed the tensile strength of the concrete, cracks will be formed. 

The magnitude of tensile stress developed during drying of hardened concrete is not only 

influenced by the amount of shrinkage, but also by other factors such as: 

• degree of restraint 

• modulus of elasticity of the concrete 

• creep or relaxation of the concrete 

As far as cracking is concerned, a high extensibility of concrete (low modulus of elasticity and 

high creep) is generally desirable, because it permits concrete to withstand greater volume 

changes. 

The importance of cracking due to drying shrinkage and the minimum width at which a crack 

is considered significant depend on the conditions of exposure of the concrete. A general 

guide for the tolerable crack width in reinforced concrete is given in Table 2.4. Since under 

given physical conditions, the total crack width per unit length of concrete is constant and the 

cracks should be as fine as possible, it is desirable to have more cracks. Accordingly, the 

restraint to cracking should be uniform along the length of the member. 

The measures adopted for the control of cracking due to drying shrinkage comprise the 

reduction of the cracking tendency of the concrete to a minimum, the use of adequate and 

properly positioned reinforcement and the use of control joints. Cracking can also be 

minimised by the application of expansive cements to produce shrinkage compensating 

concrete. 

Table 2.4 – Tolerable crack width in reinforced concrete according to exposure 

condition 


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Concrete 

4.2 Reduction of Cracking Tendency 

As mentioned previously, the cracking tendency is due not only to the amount of shrinkage, 

but also to the degree of restraint, the modulus of elasticity and the creep or relaxation of the 

concrete. Some factors, which reduce the shrinkage at the same time may decrease the 

creep and relaxation and increase the modulus of elasticity, so that they offer only little help 

to reduce cracking tendency. Nevertheless, in a general way, the measures that can be 

taken to reduce the shrinkage of concrete should also decrease the cracking tendency. 

In accordance with the influencing factors described in section 2.3, corresponding measures 

can be derived to reduce the amount of drying shrinkage of concrete. For least shrinkage, 

the concrete mix proportioning should incorporate those factors that contribute to the lowest 

paste and water content respectively, which means: 

• largest practical maximum size of aggregate 

• lowest practical sand content 

• lowest practical slump 

• lowest practical temperature of fresh concrete 

Regarding the materials used for concreting, the following selections have to be preferred: 

• cement with low C 3 A and alkali and high C 3 S content, optimum gypsum dosage and not 

too high fineness (preferably no ASTM type III cement or equivalent) 

• aggregate of low compressibility and absorption, free of clay, dirt and excessive fines. 

The use of calcium chloride and triethanolamine containing admixtures should be avoided. In 

how far the reduction in water content by means of water reducers will result in a net 

shrinkage reduction must be tested on trial mixes. The use of shrinkage reducing chemical 

admixtures may also be taken into consideration. 

Another way to reduce the cracking tendency, which is seldom used, is to apply a surface 

coating to the concrete, that will prevent the rapid loss of moisture. Effective coatings are for 

instance chlorinated rubber and waxy or resinous materials. The slowing down of the rate of 

evaporation and thus the rate of shrinkage will be beneficial, because concrete has a 

remarkable quality of relaxing under sustained stress. Concrete may be able to withstand 

without cracking two or three times as much slowly applied shrinkage as it can rapid 

shrinkage. 

4.3 Reinforcement 

Properly placed reinforcement in adequate amounts not only reduces the total amount of 

shrinkage, but prevents also unsightly cracking. By the distribution of the shrinkage strains 

along the reinforcement through bond stresses, a larger number of very fine cracks will occur 

instead of few wide cracks. 

The placement of reinforcement to limit crack width can be mainly foreseen for relatively thin 

structural members. In massive structures, reinforcement may be placed in the 20 to 40 cm 

thick surface zone, since in the interior massive concrete will shrink only to a little extent. 

The addition of discrete fibres to the concrete matrix is a further alternative to reduce 

cracking tendency. The fibres increase the tensile strength of the concrete, so that it can 

withstand higher shrinkage without cracking. 


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Concrete 

4.4 Joints 

The use of joints is the most effective method of preventing formation of unsightly cracking. If 

no joints are provided in large surface structures such as walls, slabs or pavements, the 

concrete will make its own “joints” by cracking. 

Contraction joints in walls are made, for example, by fastening wood or rubber strips to the 

forms, which leave narrow vertical grooves in the concrete on the inside and outside of the 

wall. Cracking of the wall due to shrinkage should occur at the grooves, relieving the stresses 

and preventing formation of unsightly cracks. The grooves should be sealed on the outside of 

the wall to prevent penetration of moisture. Sawed joints are commonly used in pavements, 

slabs and floors. 

Some guide values for the distances of contraction joints in structural concrete members are 

given in Table 2.5. For further indications on the placing and formation of joints, it is referred 

to the relevant literature. 

Table 2.5 – Guide values for the maximum permissible distance an of contraction 

joints in some structural concrete members. The values vary 

considerably according to insulation, heat insulation, reinforcement or 

anchorage. 


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Concrete 

4.5 Shrinkage-Compensating Concrete 

A possible way to minimise or reduce shrinkage cracking is shrinkage compensation by the 

use of expansive cements. General guidelines for the use of such shrinkage-compensating 

concrete have been established in the ACI Manual of Concrete Practice. 

The basic concept of shrinkage compensation by means of expansive cements is to increase 

the concrete volume before the commencement of shrinkage, so that the concrete will attain 

after the shrinkage process its original volume. The use of expansive cement in shrinkagecompensating 

concrete does not accordingly prevent the development of shrinkage; the early 

expansion just balances the subsequent normal shrinkage. 

There exist several types of expansive cements to be used in shrinkage compensating 

concrete. The specific features and characteristics of these cements and their application will 

be described in the subsequent section. 


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Concrete 

Concrete Durability 

1. INTRODUCTION ............................................................................................................... 158 

2. DEFINITION ...................................................................................................................... 158 

3. DELETERIOUS PROCESSES AFFECTING CONCRETE............................................... 158 

3.1 Sulfate Attack......................................................................................................... 158 

3.2 Chloride Attack ....................................................................................................... 159 

3.3 Acid Attacks............................................................................................................ 159 

3.4 Carbonation ............................................................................................................ 159 

3.5 Alkali-aggregate Expansive Reactions ................................................................... 161 

3.6 Abrasion.................................................................................................................. 161 

3.7 Biodeterioration....................................................................................................... 161 

3.8 Freeze-Thaw........................................................................................................... 161 

4. CHOOSING THE MATERIALS AND MIX DESIGN PARAMETERS TO 

GUARANTEE CONCRETE DURABILITY...................................................................... 162 

4.1 Cement ................................................................................................................... 162 

4.2 Aggregates ............................................................................................................. 162 

4.3 Water ...................................................................................................................... 162 

5. MIX DESIGN ..................................................................................................................... 163 

5.1 Water Cement Ratio ............................................................................................... 163 

5.2 Compressive Strength ............................................................................................ 166 

6. CONCLUSIONS ................................................................................................................ 166 

7. REFERENCES.................................................................................................................. 167 


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Concrete 


During many years the strength was considered the most important property of the concrete 

and the parameter to access its quality. However, nowadays the durability of the concrete is 

gaining importance, particularly due to the high costs involved on repairs and maintenance of 

structures of concrete incorrectly proportioned or applied. In UK, for example, around 40% of 

the total invested on civil construction is destined to repairs and maintenance (Neville 1997) 

and in Europe the values spent on repairs of bridges grew approximately 65% between 1985 

and 1990. According to the Federal Highway Administration (USA) (in Nmai 2000), 42% of 

the 575600 American bridges can be considered structurally deficient or unsafe due to the 

corrosion of their reinforcements. It is also estimated that, from 1981 to 2000, 102 billions 

dollars were spent on repairs of these bridges and that, from this total, 1 billion dollars could 

have been saved only with the improvement of concrete quality. 

Studies carried on all over the world show that the majority of the durability problems are 

related to bad execution, but the decline of concrete quality is also related to the use of nonappropriated 

materials and mix design, with water to cement ratio higher and higher. 

According to Wischers (1984) to produce a concrete with compressive strength of 30MPa, at 

28 days, on the 40's in England, it was necessary to work with w/c equal to 0.47 and cement 

content of 300kg/m 3 . Thirty years later, that means in the 70's, this same concrete could be 

produced with w/c equal 0.72 and cement content of 250kg/m 3 . What is apparently an 

advantage, i. e., the decrease of cement content and the increase of water to cement ratio, 

is, in fact, one of the main causes of the augmentation of durability problems and of losses 

due to repairs and maintenance of concrete structures. 

2 Definition 

Durability is the capacity that the concrete has to resist the weathering (freeze-thaw), 

abrasion or chemical processes, such as sulfate and chloride attack, acid attack, carbonation 

and reactions involving alkalis and aggregates. These processes may lead to the formation 

of expansive products with consequent concrete cracking or to the decomposition of the 

hydrated components of the cement paste. 

3 Deleterious Processes Affecting Concrete 

3.1 Sulfate Attack 

The sulfate attack occurs through the reaction between the sulfates, in general from external 

sources, such as polluted water or soil, and the C 3 A presents on the Portland clinker and/or 

the Ca(OH) 2 generated by cement hydration. It results on ettringite and gypsum formation, 

with consequent expansion and fissures. 

The sulfate attack also promotes deterioration of the hydrated cement products, causing 

losses of concrete mass and strength. 

This type of pathology can be prevented by using sulfate resistant cements (normally with 

low C 3 A) or cements with high amounts of active mineral components (slag, fly ash or 

pozzolan). 


Cement 

Concrete 

3.2 Chloride Attack 

Chloride ions can be introduced into the concrete by its mixing water, by the use of 

contaminated aggregates, de-icing salts or chloride-based accelerators (whose usage is 

forbidden in several countries). 

In alkaline environments the concrete reinforcement is covered by a thin, impermeable and 

adherent film of iron oxide that protects it from corrosion. In this case, the reinforcement is 

"passivated". The chloride ions can destroy this layer de-passivating the rebars. This process 

that can be described according to the reactions 1 and 2 generates iron hydroxide. As this 

compound has volume 600% higher than the reagents, its formation is accompanied by 

expansion. 

(1) Fe 2+ + 2Cl - ⇒ FeCl 2 

(2) FeCl 2 + 2H 2 O ⇒ Fe(OH) 2 + 2HCl 

The effects of chloride attack are twofold - losses of rebar section due to the iron 

decomposition and fissures caused by the expansion. 

The chloride attack is minimized by decreasing the permeability of the cement paste, a 

characteristic that can be achieved by the adoption of low w/c and by the use of cements 

with high amount of active mineral components. 

3.3 Acid Attacks 

The cement paste constituents are compounds stable in alkaline environment, with low 

resistance to acids. Thus, when the concrete pH decreases reaching values lowers than 6.5, 

the calcium hydroxide produced during cement hydration reacts with the acids, generating 

water-soluble compounds that are then lixiviated, increasing the concrete permeability. 

These acids have diverse origin, being derived, for example, from the combustion of fuels 

with sulfur (sulfuric acid), from the metabolism of microorganisms and animals (organic 

acids) and industrial residues. 

3.4 Carbonation 

In alkaline environment the concrete rebars are protect from corrosion. However when the 

pH changes in direction to more acid values, this protection is destroyed and corrosion can 

take place. 

The carbonation - a chemical process that involves the reaction of the calcium hydroxide 

from the cement paste and the CO 2 from the atmosphere - modifies the pH of the concrete, 

favoring the corrosion of its reinforcement. 

The carbonation is accelerated in concretes exposed to environments with relative humidity 

between 50% and 70% also increasing with the increase of CO 2 supplied and the w/c. 

Although the carbonation is an inevitable process, it can be reduced with the use of cements 

with low amount of mineral components, with adequate cement content and with the increase 

of concrete strength and curing period (Figures 1 and 2). 


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Concrete 

10 

9 

8 

Depth of Carbonation (mm) 

7 

6 

5 

4 

3 

humid cure 

dry cure 

2 

1 

0 

35 40 45 50 55 60 


FIGURE 1 - Influence of curing on concrete compressive strength and carbonation 

depth of concrete (after Neville 1995). 

140 

TIME OF CORROSION INITIATION (days) 

120 

100 

80 

60 

40 

20 

0 

0 5 10 15 20 25 30 

CURING PERIOD (days) 

FIGURE 2 – Influence of curing duration on corrosion initiation (after Neville 1995) 

Corrosion can also be prevented by protecting the reinforcement with a layer of concrete 

thick enough to guarantee that the carbonation front will not reach the rebar. This thickness 


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Concrete 

of concrete cover is a parameter included in many national concrete standards. The ACI 

Manual of Concrete Practice 2002, Part 1 (201.2R-19) consider that for concrete exposed to 

moderate-to-severe corrosion environments, the concrete covering the rebars should be at 

least 38mm and preferably, 50mm thick. 

3.5 Alkali-aggregate Expansive Reactions 

The alkali-aggregate reactions are chemical processes that involve some types of 

aggregates and sodium or potassium ions. They generate expansive products that filling up 

porous and discontinuities of concrete paste, cause fissures and its disintegration. 

Once started, these reactions cannot be stopped, but they can be prevented by using inert 

aggregates or cements with high amount of active mineral components. 

3.6 Abrasion 

The concrete abrasion leads to its disintegration. Abrasion effects can be minimized by the 

densification of the cement paste, which is achieved by adopting low w/c. Experience shows 

that the resistance to abrasion of a concrete with w/c around 0.30 is comparable to the one 

of good quality rocks. 

3.7 Biodeterioration 

The biodeterioration process is, essentially, an acid attack process to the concrete. Some 

bacteria and fungi can grow on concrete surface and through the acids released during their 

metabolism, decompose the cement hydrated compounds. 

The reduction of the w/c results in hardened cement pastes with low porosity, making difficult 

the proliferation of microorganisms and concrete degradation. 

3.8 Freeze-Thaw 

When the temperature of a saturated concrete decreases, the water present in its porous can 

freeze and the augment of volume that accompanies this phenomenon causes concrete 

expansion. 

The repetition of this process due to successive cycles of freeze-thaw can lead to 

disintegration of the concrete. 

The resistance of the concrete to freeze-thaw can be improved by decreasing its 

permeability, which is obtained by using low water to cement ratio, and also by using air 

entraining agents: the voids they create in the hardened cement paste allow the water 

expansion without damaging the concrete. 


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Concrete 

4 Choosing the Materials and Mix Design Parameters to 

Guarantee Concrete Durability 

The processes that lead to concrete deterioration can be avoided or minimized with the right 

choice of its constituents, rational mix design and careful preparation and application. 

4.1 Cement 

In many markets it is possible to find several cement types, whose difference may be due to 

the kind of additions (MIC) their contain. In general, it could be said that the cements can be 

divided in 2 groups, namely: OPC, which is composed essentially by Portland clinker and 

gypsum, composite cements, which can have active mineral components such as slag, fly 

ash and pozzolan as addition, or limestone. 

The addition of active mineral components has as main consequence, the improvement of 

the durability of the cement products. This is achieved through the reaction between the MIC 

and the Ca(OH) 2 , with formation of C-S-H, and by the dilution of the C 3 A of the clinker, 

minimizing the potentially deleterious actions of these two compounds in the hardened 

concrete. As seen, the C 3 A can, for example, react with sulfates and chlorides generating 

expansive products, being also responsible for expressive amount of the heat released 

during cement hydration. 

The Ca(OH) 2 can also react with sulfates, resulting in expansion, can suffer carbonation, 

favoring rebar corrosion, being lixiviated by water, generating efflorescence and increasing 

concrete permeability, as well acting as a catalytic for alkali-aggregate reaction. 

The active mineral components decrease or avoid the deleterious effect of these processes, 

producing concretes with lower heat of hydration and permeability and therefore, more 

durables. 


The coarse and fine aggregates should have characteristics compatible with the standards 

requirements and free of harmful substances or compounds that can take part on deleterious 

reactions. The most common harmful substances present in aggregates are organic material, 

like leaves for example, organic substances such as sugar and high content of very fine 

material or clay. Additionally, the aggregate should be preferably inert face to alkalis, in order 

to prevent expansive reactions. 

4.3 Water 

The concrete mixing water should be potable and free of substances that may be harmful to 

the concrete, as for example, sugar, acids or citrates. It should also have limited sulfate, 

chloride and alkali content. 

However, as important as the quality is the quantity of water added to the concrete. If in 

excess it creates voids that decreases its strength, increases its permeability and facilitates 

deleterious attack driven by the ingress of aggressive agents into its cement paste. 


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Concrete 

5 Mix Design 

5.1 Water Cement Ratio 

The w/c is one of the most important parameters regarding concrete quality. Since Abrams' 

studies in 1919, it is known that there is an inversely proportional relation between w/c and 

concrete compressive strength (Figure 3). Nowadays, it is also known that the w/c has a 

fundamental role on concrete quality and durability. 

45 

CONCRETE COMPRESSIVE STRENGTH (MPa) 

40 

35 

30 

25 

20 

15 

10 

5 

0 

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 

FIGURE 3 - Relation between w/c and concrete compressive strength 

The quantity of water required for the complete hydration of the cement added to the 

concrete is equivalent to a w/c around 0.30. Therefore, higher values indicate water excess 

and available to create voids and channels of percolation on the hardened cement paste, as 

can be seen on Photo 1. Naturally, these voids and discontinuities cause decrease of 

concrete strength and as they are interconnected, favor the ingress of deleterious agents into 

the concrete. 

Aiming guaranteeing a long service-life for concrete structures, the European standard EN 

206/1 - Concrete - Part 1: Specification, performance, production and conformity, establishes 

maximum w/c according to the environment to what concrete will be exposed. It is 

summarized on Table 1. 

w/c 


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Concrete 

PHOTO 1 - Concrete observed under petrographic microscope, showing interconected 

voids created by water in excess 

TABLE 1 - Exposure conditions and requirements of EN 206/1 (simplified) 

Type of attack 

Chloride-induced 

corrosion 

Carbonatio 

n-induced 

corrosion 

Sea water 

Chloride 

other than 

from sea 

water 

Freezethaw 

attack 

Aggressive 

chemical 

environment 

Exposure class XC1 XC4 XS1 XS3 XD1 XD3 XF1 XF4 XA1 XA3 

Maximum w/c 0.65 0.50 0.50 0.45 0.55 0.45 0.55 0.45 0.55 0.45 

Minimum cement 

content (kg/m 3 ) 

260 300 300 340 300 320 300 340 300 360 

The maximum value permitted, equal to 0.65 is justified by studies that show that in 

hardened cement pastes with w/c higher than 0.70 all porous are connected, 

increasing significantly its permeability and decreasing its durability. 

It means that the higher the aggressiveness of the environment, the lower has to be the w/c. 

Photos 2 and 3 show concretes with w/c equal to 0.30 and 0.50 and highlight the 

microstructural differences due to the decrease of the water content in concrete. With w/c 

equal to 0.30 the cement paste is more compact and therefore, more resistant and durable. 


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Concrete 

1.1 

1.1 

PHOTO 2 – Concrete with w/c = 0,50 at 28 days, showing the aggregate 

(G) and the cement paste (P) with high porosity. Scanning electron 

microscope; magnification 1500x (in Vieira 1998). 

1.1 

1.1 

PHOTO 3 – Concrete with w/c = 0,30 at 28 days, showing aggregate (G) 

and cement paste (P) compact, without porous. Scanning electron 

microscope; magnification 1500x (in Vieira 1998). 


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Concrete 

5.2 Compressive Strength 

Although in many countries minimum compressive strength values are not a required in the 

concrete standards, nowadays there is a trend in the sense of including it in the 

specifications and normally values around 20MPa - 25MPa are being adopted. 

The explanation for this resolution is that concretes prepared with the maximum w/c ratio and 

minimum cement content determined by the standards (for example the European one - EN 

206/1), will have compressive strength higher than 20MPa - 25MPa. Therefore the 

compressive strength can be used as a indirect mean of verification the compliance with the 

standards, concerning durability. 

6 Conclusions 

The durability of the concrete is one of the fundamental aspects that should be considered 

since the project phase and materials selection, until the final stages of its application. 

Regarding materials, the quality of the concrete depends on the quality of the 

aggregates and mixing water, on the right choice of the cement type and when using 

chemical admixtures, on the selection of products compatibles with the cement 

selected. 

The proportioning of theses materials has to be rationally defined: particularly important in 

this phase, are the definitions of the optimums cement content and w/c. 

The compressive strength specified in the project has to be compatible with the solicitations 

to what the concrete will be subject to and in case of reinforced concrete the concrete layer 

that covers the rebars have to have the thickness required by the standards in order to 

guarantee their protection against corrosion. 

Finally, the execution, application and cure of the concrete have to be carefully made. 


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Concrete 

7 References 

NEVILLE, A. M. (1995) Properties of Concrete. Longman Group Limited. 4 th Ed. 844p. 

NEVILLE, A. M. (1997) Maintenance and durability of structures. Concrete International 

v. 19, n. 11, p: 52-56. 

NMAI, C.K. Recent developments in the design of reinforced concrete structures for 

long service lives from a corrosion perspective. In: CONGRESSO BRASILEIRO DO 

CONCRETO, 42, 13-18 de agosto 2000, Ceará. Anais... 

VIEIRA, S. R. S. S. Concretos comum e de alto desempenho: análise do 

comportamento através da microscopia eletrônica de varredura. (Ordinary concrete and 

high performance concrete: A behaviour analysis through scanning electron microscopy). In: 

CONGRESSO BRASILEIRO DO CONCRETO, 40, Rio de Janeiro, 1998, Rio de Janeiro. 

Anais... (in Portuguese). 

VIEIRA, S. R. S. S. Vida longa às estruturas de concreto: o concreto de alto 

desempenho como garantia da durabilidade. (Long life to the concrete structures: the 

high performance concrete as guarantee of durability). Revista Engenharia, Ciencia & 

Tecnologia, Vitória, ES, v. 4, n.1, p.51-56, jan/fev. 2001 (in Portuguese). 

WISCHERS, G. (1984) The Impact of the Quality of Concrete Constructions on the 

Cement Market. "Holderbank" Group Meeting 1984. 


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Alkali-Aggregate Reactions in Concrete 

1. INTRODUCTION AND DEFINITIONS .............................................................................. 169 

2. ALKALI-AGGREGATE REACTION: REQUIREMENTS .................................................. 169 

3. TYPICAL FEATURES FROM ALKALI-AGGREGATE REACTION................................. 169 

4. HISTORY........................................................................................................................... 174 

5. TYPES OF ALKALI-AGGREGATE REACTION .............................................................. 175 

5.1.1 Alkali-silica reaction.................................................................................. 175 

5.1.2 Alkali-silicate reaction............................................................................... 175 

5.1.3 Alkali-carbonate reaction.......................................................................... 175 

6. PREVENTING THE ALKALI-AGGREGATE REACTION................................................. 175 

7. AGGREGATE REACTIVITY ............................................................................................. 176 

8. TESTING METHODS ........................................................................................................ 178 

8.1 Evaluation of the potential reactivity of the aggregate ............................................ 178 

8.1.1 Petrography.............................................................................................. 178 

8.1.2 Accelerated Test (ASTM C 1260/94) ....................................................... 178 

8.2 Evaluation of the efficiency of a cement or MIC to inhibit the alkaliaggregate 

reaction ................................................................................................. 179 

8.2.1 Accelerated Test (ASTM C 441) .............................................................. 179 

8.3 Evaluation of the potential reactivity of a certain cement-aggregate 

combination............................................................................................................ 179 

8.3.1 Accelerated method (ASTM C227) .......................................................... 179 


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1 Introduction and Definitions 

Alkali-aggregate reactions are complex chemical processes that occur in concrete, involving 

soluble alkali, namely sodium and potassium, and reactive aggregates. The result of the 

alkali aggregate reactions are expansive products - amorphous or crystallised - which filling 

up discontinuities of the hydrated paste, can cause fissures (Photo 1) and structural 

displacements. 

The source of alkalis is, normally, the cement, but they can also be derived from some 

chemical admixtures used in concrete, from aggregate contamination, concrete mixing water, 

etc. 

The reactivity of the aggregates is determined by the presence of some specific compounds 

or by textural characteristics, which denote stress. 

2 Alkali-Aggregate Reaction: Requirements 

Besides the soluble alkalis and reactive aggregates, the occurrence of the alkali-aggregate 

reactions also depends on the availability of water, even in very small amounts, percolating 

the hardened cement paste. Thus, the permeability of the concrete is also an important factor 

in the process: the more permeable the concrete, the more susceptible to damages due to 

these expansive reactions. 

The presence of construction defects, shrinkage fissures or other discontinuities increases 

the permeability of the concrete, favouring the alkali-aggregate reactions. 

3 Typical Features from Alkali-Aggregate Reaction 

The alkali-aggregate reactions can be recognized by cracks with a very typical "map" pattern 

(Photos 1 to ) and by the presence of gel, as a white, glassy or porcelain-like material around 

the aggregates or filling up porous or cracks in the cement paste. . 

In a microscopic level, crystallized products from alkali-aggregate reactions can also be 

identified under different shapes: filaments, flowers or leaves-like (Photos ). 

Both, the gel and the crystallized products are compounds of silica, calcium and alkalis, most 

commonly, potassium (Figure 1). 


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Map cracks 

PHOTO 1: Cracks due to alkali-aggregate reaction 

F 

PHOTO 2: Crack in concrete, due to alkali-aggregate reaction, partially filled up with 

expansive product (white). 


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PHOTO 3: Gel white-bluish disperses on the cement paste and around aggregate 

evidencing alkali-aggregate reaction. Stereoscopic microscope; magnification 6x. 

PHOTO 4: White-bluish gel contouring aggregate in concrete affected by alkaliaggregate 

reaction. Stereoscopic microscope; magnification 12x. 


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PHOTO 5: Micro-crack in concrete, generated by expansions due alkali-aggregate 

reaction. Concrete observed under transmitted light microscope; magnification 50x. 

PHOTO 6: Crystallized product from alkali-aggregate reaction, growing on the 

aggregate surface. Concrete observed under scanning electron microscope; 

magnification 750x. 


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PHOTO 7 – Filament-like alkali-aggregate reaction product, identified in concrete. 

Scanning electron microscope; magnification 500x. 

PHOTO 8 – Alkali-aggregate reaction product identified in concrete. Scanning electron 

microscope; magnification 750x. 


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PHOTO 9 – Gel produced by alkali-aggregate reaction, observed under scanning 

electron microscope (magnification 125x). In the box, it is represented 

its chemical composition. 

4 History 

The alkali aggregate reaction was first described in the early 40's by Stanton, in California, 

and since then, several occurrences have been reported all over the world. Dams are the 

most common structure affected by alkali-aggregate reactions that have been also found in 

concrete pavements, bridges, railway sleepers, etc. 


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5 Types of Alkali-Aggregate Reaction 

The alkali-aggregate reactions can be divided in three groups, according to the mineral or 

compound responsible for the expansion. There are: 

5.1.1 Alkali-silica reaction 

The fastest and better known reaction. 

Occurs between alkalis and some varieties of amorphous or cryptocrystalline silica, such as, 

volcanic glass, found in some basalts (photo 1), opal and chalcedony. 

(1) SiO 2 + Na+ or K+ + H 2 O → (Na or K) 2 SiO 3 .2H 2 O 

Expansive gel 

Derived from the aggregate 

Derived from the cement, chemical 

admixtures, water, etc 

5.1.2 Alkali-silicate reaction 

This reaction is similar to the alkali-silica one, occurring between some silicates, specially 

deformed or microcrystalline quartz, present in rocks as gneiss, granites, milonites, etc. 

Some textural and structural features of the rocks are indicative of its potential reactivity face 

to alkalis. The most important are: 

Presence of quartz with undulatory extinction, presence of minerals in fine or very fine grains, 

and minerals strongly oriented according to preferential directions, due to shear. 

5.1.3 Alkali-carbonate reaction 

The mechanism that leads to alkali-carbonate reaction is not very well understood yet, but it 

seems to be consensus that it involves calcareous rocks with both calcite and dolomite 

(calcite-to-dolomite ratio = 1) and 5% to 25% of clay minerals. One of the mechanisms 

proposed to explain the alkali-carbonate reaction is the dolomite decomposition, with 

formation of brucite, according to the reaction 2. Nevertheless some authors believe that the 

expansion is due to the clay constituents of the rock, and, therefore, an alkali-silicate 

reaction, in fact. 

(2) CaMg(CO 3 ) 2 + 2(K or Na)OH → CaCO 3 + Mg(OH) 2 + (Na or K) 2 CO 3 

6 Preventing the Alkali-Aggregate Reaction 

The alkali-aggregate reactions are process that, once started cannot be paralysed, and 

therefore their prevention is fundamental. It can be done using inert aggregates, cement with 

low alkali content (Na eq. < 0.60%) or high amount of active mineral components or limiting 

the amount of soluble alkalis in concrete, which according to the general recommendations 

should not exceed 3.0kg/m 3 . 

The Ca(OH) 2 presents in the hardened cement paste contributes, as a catalyst, to the alkaliaggregate 

reactions; the pozzolans, fly ashes, slags and silica fume consume the calcium 

hydroxide, thus inhibiting the process. 


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7 Aggregate reactivity 

The aggregate reactivity depends on the presence of some specific constituents and 

structural/textural aspects derived from the rock genesis. Some reactive compounds are: 

Volcanic glass, present in some basalts (Photo 10) 

 

 

Strained, deformed quartz, a common constituent of granites, gneiss and 

quartzites (Photo 11) 

Varieties of amorphous or micro-crystalline silica, such as opal and chalcedony, 

found e.g., in gravels. 

Some textural and structural aspects are also indicative of rock reactivity. They are: 

Very fine silicates, as fine-grained quartz, 

Very pronounced foliation produced by shear processes (Photo 12). 

V 

PHOTO 10: Volcanic glass (V) as a constituent of a basalt rock. Its presence indicates the 

reactivity of the aggregate to alkalis. Optical microscope, magnification 25x. 


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Q 

PHOTO 11: Quartz (Q) with undulatory extinction evidencing stress and the potential 

reactivity of this aggregate. Optical microscope, magnification 25x. 

PHOTO 12: Aggregate showing minerals strongly oriented due to shear. This feature 

suggests its reactivity when in contact with alkalis. Optical microscope; magnification 25x. 


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8 Testing Methods 

Several methods have been proposed to access the reactivity of aggregate and the 

performance of a cement or cement-aggregate combination with respect to alkali-aggregate 

reaction. Here only some of them - the most commonly used ones are presented. 

8.1 Evaluation of the potential reactivity of the aggregate 

8.1.1 Petrography 

Petrography is a technique that allows the identification of the mineral composition of the 

aggregate and the way these compounds are distributed (structure/texture). In order to 

evaluate its potential reactivity to soluble alkalis, a thin section of the aggregate is analysed 

under the petrographical microscope, where features such as: 

 

 

 

Presence of volcanic glass, opal, chalcedony, etc, 

Deformed quartz with undulatory extinction, 

Very fine to fine grained silicates, 

Minerals strongly oriented, as result of shear 

can be recognized. 

8.1.2 Accelerated Test (ASTM C 1260/94) 

The method prescribed in the ASTM C 1260/94 access the potential reactivity of the 

aggregate through the measurement of the expansions showed by mortar bar prepared with 

the studied aggregate and a no-inhibitor cement, after curing for 14 days in a solution of 

NaOH, at 80 o C. 

According to this procedure, if at 14 days curing, the expansions are: 

Lower than 0.10%, the aggregate is considered inert, 

Higher than 0.20%, the aggregate is considered reactive and 

 

Between 0.10% and 0.20%, the aggregate is considered potentially reactive, but 

additional tests are necessary. 


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8.2 Evaluation of the efficiency of a cement or MIC to inhibit the alkaliaggregate 

reaction 

8.2.1 Accelerated Test (ASTM C 441) 

In this method the expansion of mortar prepared with the studied cement or MIC and Pyrex 

glass used as aggregate, cured in water at 38 o C, during 16 days is measured. 

Expansions lower than 0.02% indicate that the cement or MIC is able to prevent the 

occurrence of alkali-aggregate reaction, even when using reactive aggregates. 

8.3 Evaluation of the potential reactivity of a certain cement-aggregate 

combination 

8.3.1 Accelerated method (ASTM C227) 

Mortar bars prepared with a certain cement-aggregate pair is stored in water at 37.8 o C, and 

eventual expansions after 3 and 6 months can be used as indicators of its reactivity. 

Although the limit between a reactive and non-reactive combination is not clearly defined, 

expansions higher than 0.05% after 3 months and 0.10% after 6 months, can be considered 

indicatives of potential reactivity. 


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Self-compacting Concrete 

1. DEFINITION .................................................................................................................... 181 

2. SELF-COMPACTING CONCRETE DEVELOPMENT .................................................... 181 

3. SELF-COMPACTING REQUIREMENTS........................................................................ 183 

4. MATERIALS FOR MANUFACTURING SELF-COMPACTING CONCRETE................. 184 

4.1....Powder 184 

4.2....Superplasticizers.................................................................................................... 184 

4.3....Viscosity agents ..................................................................................................... 185 

5. MIX PROPORTION DESIGN METHOD.......................................................................... 187 

5.1....JSCE Method ......................................................................................................... 187 

5.2....Okamura’s Method................................................................................................. 190 

6. TEST METHODS FOR SELF-COMPACTABILITY EVALUATION................................ 191 

6.1....Slump flow.............................................................................................................. 191 

6.2....Test Method for passability through spaces using U or Box-shaped 

apparatus ............................................................................................................... 192 

6.3....Flow-through test method using V-funnel .............................................................. 115 

6.4....L-Box test ............................................................................................................... 115 

6.5....Ring test ................................................................................................................. 116 

6.6....Acceptance test at jobsite ...................................................................................... 116 

7. PRODUCTION AND PLACEMENT OF SELF-COMPACTING CONCRETE ................. 117 

7.1....Storage of aggregate ............................................................................................. 117 

7.2....Plant facilities ......................................................................................................... 117 

7.3....Transportation ........................................................................................................ 118 

7.4....Placing 119 

7.5....Finishing and curing ............................................................................................... 119 

7.6....Formwork and supports ......................................................................................... 120 

8. QUALITY CONTROL AND INSPECTION DURING CONSTRUCTION ......................... 120 


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1 Definition 

It is not possible to make only one definition of Self-Compacting Concrete. According to the 

most widely definition SCC is: 

High fluidity concrete with significant increase in fluidity that can be placed under its own 

weight and can fill the form work without vibration and achieve good consolidation without 

exhibiting any segregation nor bleeding. A SCC should present high deformability and great 

stability, without risk of blockage. See 3.3. [A1] 

2 Self-compacting concrete development 

The first prototype of SCC was developed by Ozawa et. al. [1988] by using granulated blast 

furnace slag and fly ash together with superplasticizer according to three states: 

‣ Fresh state: self-compactable with high resistance to segregation 

‣ Early age: avoidance from initial defects caused by heat generation of 

hydration, hardening or drying shrinkage and settlement 

‣ Hardened: protection against external factors (low permeability and frost 

resistance when required) 

Due to heat generation (limitation with the type and content of cement) and hardened 

concrete properties (low porosity) it was very difficult to achieve a flowable and at the same 

time stable concrete without the use of mineral components as well as chemical admixtures. 

Further development continues in Japan, especially in the research institute of large 

construction companies. As a result, Self-compacting has been applied into many practical 

structures over the last few years for the main following reasons: 

‣ To shorten construction period [Kashima et. al.1998] 

‣ To ensure compaction in confined zone which makes vibration difficult or 

impossible 

‣ To reduce noise due to vibrating compaction especially at pre-fabrication plants 

[Uno, 1998] 

The construction of the two anchorages of Akashi-Kaikyo bridge, one of the longest 

suspension (1’991 meters) in the world, is one of the typical applications where SCC was 

used. The use of SCC shortened the anchorage construction period by 20%, from 2.5 to 2 

years [Kashima et. al.1998]. 

In another application, high strength (60 MPa) self-compacting concrete was used to 

fabricate Osaka Gas’ new prestressed concrete outer tank for liquefied natural gas storage 

(12’000 m 3 of concrete), which accommodates the world’s largest capacity of 180’000 kl. As 

a result, the construction period was reduced from 15 to 11 months. [Kitamura et. Al. 1998]. 


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Figure 1 – Application to anchorage of Akashi-Kaikyo 

Figure 2 – Application to LNG tank 

Nowadays, the interest for Self-compacting concrete has rapidly increased world-wide 

following the pioneering work done in Japan. We should note that outside Japan, that has 

successfully experienced this technology mainly in huge and sophisticated construction 

projects, self-compacting concrete is still in a development phase with very few experimental 

projects. 


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3 Self-compacting requirements 

How do requirements differ between conventional and self-compacting concrete? The 

essential difference in requirement concerns the fresh properties of SCC which must display 

a substantial flowability (filling capacity) between small gaps of reinforcements and achieve 

full compaction without vibration, while possessing high resistance to segregation during 

transportation, pumping and placing into formwork. When a shorter period of concreting is 

required, SCC must flow with a lower inclination even if the depositing speed is high. 

Apart from fresh concrete requirements all other requirements for conventional concrete such 

as curing must be fulfilled. 

Figure 3 – Essential requirements for self-compacting concrete 

The level of filling capacity required for SCC depends on the conditions not only of the 

structural detailing of formwork and reinforcements but also of the concreting practices such 

as speed and volume of concrete deposited. Self-compacting concrete with the same mix 

proportion and the same rheological properties may show the different filling capacities under 

the different conditions, therefore SCC should be designed to satisfy the level of filling 

capacity required according to the condition [Noguchi et. al. 1998]. 

The following three ranks has been established as levels of self-compactability by the Japan 

Society of Civil Engineers [Concrete engineering series 31]: 

‣ Rank 1: Self-compactability into members or portions having complicated 

shapes and/or small cross-sectional areas with a minimum steel clearance in 

the range of 35 to 60 mm. 

‣ Rank 2: Self-compactability into reinforced concrete structures or members with 

a minimum steel clearance in the range of 60 to 200 mm. This normally 

corresponds to a steel content of 350 to 100 kg/m 3 . 

‣ Rank 3: Self-compactability into members or portions having large crosssectional 

areas and a small amount of reinforcement (less than 100 kg/m 3 ) with 

a minimum steel clearance of more than 200 mm. 


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4 Materials for manufacturing self-compacting concrete 

The self-compacting characteristic of concrete requires a high fluidity with sufficient 

segregation resistance. The two features, high fluidity and sufficient segregation resistance, 

are in general contrary to each other. In order to attain the both contradictory factors at the 

optimal level, a large quantity of powder is required with help of superplasticizer. It is not 

clear, however, what kind of powder is the most suitable and what of physical properties of 

powder control the amount of water. In any case a trial an error technique is in fact applied 

to find out a satisfactory mix proportion. Following are examples of materials for SCC for 

which sufficient field experience has been acquired in Japan. 

4.1 Powder 

Powder is a generic term for cement and other solid concrete materials having a fineness 

equal to or higher than cement. These include cement, ground granulated blast-furnace 

slag, fly ash, silica fume, and limestone powder. 

1) Belite-rich Portland cement: this is a type of Portland cement developed for 

concrete proportioned to have a high binder content. The belite content is 40 to 

70%, which is higher than moderate-heat cement. It is used where high 

strength and/or low heat are required. 

2) Binary/ternary system low-heat cement: this type of cement is a normal or 

moderate-heat Portland cement mixed with ground granulated blast-furnace 

slag and/or fly ash. It is used where low heat is required without reducing the 

powder content 

3) High-fineness ground granulated blast-furnace slag: it has been reported 

[Nawa et. al., 1998] that the thixotropicity of paste incorporating fine-fineness 

blast furnace slag powder (greater than 10'000 cm 2 /g) decreases compared to 

ordinary Portland cement. 

4) Fly ash: concrete flowability is enhanced by the “ball-bearing” effect of spherical 

form of fly ash. 

5) Limestone powder: consists primarily of CaCo 3 (calcite) pulverised to a specific 

surface area by Blaine of 2500 to 8000 cm 2 /g. It is used where desired low 

heat and/or strength be reduced without reducing the powder content. 

4.2 Superplasticizers 

Superplasticizers used in SCC are of two types. High range water reducing agent (HRWR) 

and high range AE water reducing agent (HRAE). As show in figure 4, currently used 

superplasticizers include naphthalene sulfonate, polycarboxylate, melamine sulfonate, and 

amino sulfonate-based agents. The type of superplasticizer to be used in SCC is decided 

considering the level of retention characteristics required and the existence of interaction with 

cement and admixture (viscosity agent). 


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Figure 4 – Classification of superplasticizers 

4.3 Viscosity agents 

The viscosity agents used in SCC may be broadly divided into four groups: 

1) Cellulose-based water-soluble polymers 

2) Acrylic-based water-soluble polymers bio-polymers 

3) Glycol-based water-soluble polymers 

4) Inorganic viscosity agents 

The standard addition quantity, characteristics, and interaction effects of viscosity agents 

vary depending on the type. For instance, cellulose-based water-soluble polymers and 

acrylic-based water-soluble polymers are used in viscosity-agent type SCC and combined 

type SCC. On the other hand, bio-polymers and inorganic viscosity agents are used only in 

the combined type SCC. In addition to the above, admixtures possessing both reducing 

action and viscosity action, have also been developed. 


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The action of mechanisms in viscosity agents that impart ingredient segregation resistance 

varies largely depending on the type. As shown figure 5, mechanisms in viscosity agents 

that impart ingredient segregation resistance may be broadly divided into two types [Nawa et. 

al.,1998]: 

Mechanisms that act in powder grains as cement 

1) Mechanisms that act in water in the concrete 

Figure 5 – Mechanisms imparting material segregation resistance 

Almost, all viscosity agents used in concrete have one or more functional groups in their 

molecular structures and are consequently adsorptive. In the case of adsorptive viscosity 

agents, the decline of the flow value is presumed to form the bridge structure by adsorbing 

on the surface of cement particles. As the dosage of the non-adsorptive viscosity agents 

increases, apparent plastic viscosity of mortar increases, yet the flow value does not change. 

Therefore, it becomes possible to control the viscosity keeping the flowability constant by 

using non-adsorptive agents. Also, non-adsorptive viscosity agents do not contest with 

superplasticizer for adsorption sites and the amount of adsorbed superplasticizer stays 

same. Therefore, non-adsorptive agents can lead to an adequate fluidity and viscosity of 

mortar. It is expected that the unique property of non-adsorptive viscosity agents is good for 

self-compacting concrete. 

Viscosity agents that act in cement grains include cellulose-based water-soluble polymers 

and acrylic-based water-soluble polymers. Glycol-based water-soluble polymer does not 

adsorb at all on to the surface of cement. From the bio-polymers, polysaccharide polymers, 

micro-organisms, and inorganic viscosity agents do not dissolve in water, but the polymers 

themselves adsorb the water, swell, and impart viscosity. 

Glycol type and water-soluble amide type, liquid viscosity agents are beginning to be used in 

place of conventional powder types, such as the cellulose type, acrylic type, polysaccharide 

polymers, biopolymers and inorganic viscosity agents. 

There is affinity between viscosity agents and superplasticizers. If the affinity becomes poor, 

a conspicuous slump loss or coagulation occurs, and the flowability of concrete degrades. 

This affinity is well known from experience, but the mechanism between them is still not 

clear. For instance, it has been reported that if cellulose-based water-soluble polymer, which 

has a poor affinity, is combined with naphthalene sulfonate, the interaction between the two 

becomes extremely weak because of the conversion of sodium naphthalene sulfonate to 

calcium naphthalene sulfonate. 


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5 Mix proportion design method 

Self-compacting concrete is not only a concrete but a whole family of concrete types exactly 

as the situation is today for conventional concrete. With SCC two normally incompatible 

properties of deformability and segregation resistance are both realised to achieve selfcompactability. 

A typical mix proportion design method for SCC consists of three stages: 

1. Proportioning condition examination: The performance requirements of 

concrete are selected on the basis of the structural, construction and 

environmental conditions, and the target performance requirements then are 

determined. 

2. Proportioning examination: The concrete materials are selected and a tentative 

mix proportion is determined. 

3. Proportioning verification: The initial proportion is checked by trial mixing if it 

satisfies the performance requirements. If it fails in any area, the initial mix 

proportion is modified and tested again. 

A wide variety of formulas are possible for self-compacting concrete satisfying the selfcompactability 

requirements as well as performance requirements. SCC is therefore, 

proportioned by selecting an adequate combination of materials in consideration of the 

restricting conditions at production plants and economical efficiency including their availability 

and transportation cost. Two major methods – one by the Japanese Society of Civil 

Engineers (JSCE) and another described by Prof. Okamura et. al. – are introduced here 

[Nawa et. al., 1998]. 

5.1 JSCE Method 

Although various classification systems are possible for SCC, this method classifies it 

roughly into three categories, i.e., the powder type, viscosity agent type and combination 

type. The mix proportioning procedure is illustrated in figure 6. 

Figure 6 – JSCE mix design method for SCC 


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5.1.1 Powder-type self-compacting concrete 

This type of SCC is proportioned to provide the required self-compactability not by using a 

viscosity agent but primarily by reducing the water/powder ratio (in effect increasing the 

powder content) to impart adequate segregation resistance and using air-entraining and 

high-range water-reducing admixture or superplasticizer to impart high deformability. The 

type of powder to be used should be adequately selected in consideration of the purpose of 

use of the concrete. This type of SCC has generally high strength and good durability. 

a) Maximum size of coarse aggregate and coarse aggregate content: the 

standard maximum size of coarse aggregate should be 20 mm or 25 mm. The 

content should be selected to provide the required self-compactability ranks are 

as follows: 

Self-compactability 

Unit absolute volume of coarse aggregate 

Rank 1 280 – 300 L/m 3 

Rank 2 300 – 330 L/m 3 

Rank 3 320 – 350 L/m 3 

b) Unit water content: It is desirable that the unit water content be 

minimised, as it affects the qualities of hardened concrete. It should 

normally be in the range of 155 to 175 kg/m 3 . 

c) Water/powder ratio: It should be in the range of 28% to 37% by mass of 

cement or 0.85 to 1.15 by volumetric ratio to cement, though dependent 

on the type and composition of powders. 

d) Powder content: It should normally be in the range of 160 to 190 L/m 3 , 

though dependent on the type and composition of powders. 

e) Air content: The standard air content of fresh concrete requiring high 

resistance to frost damage should normally be 4.5%. 

f) Unit fine aggregate content: Should be determined from the unit coarse 

aggregate content, unit water content, unit powder content and air 

content. 


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5.1.2 Viscosity agent-type self-compacting concrete 

This is a type of SCC considered to be an extension of the anti-washout underwater 

concrete. Segregation resistance is increased by the use of viscosity agent with the powder 

content being low compared with the powder-type. The mixture proportions of such concrete 

are relatively similar to those of conventional concrete except that a viscosity agent and an 

air-entraining and high-range water-reducing admixture or superplasticizer are used. It may 

be manufactured even at the construction site by using truck agitators. 

a) Maximum size of coarse aggregate and coarse aggregate content: the 

standard maximum size of coarse aggregate should be 20 mm or 25 mm. The 

content should be selected to provide the required self-compactability ranks are 

as follows: 

Self-compactability 

Unit absolute volume of coarse aggregate 

Rank 1 280 – 310 L/m 3 

Rank 2 300 – 330 L/m 3 

Rank 3 300 – 360 L/m 3 

b) Unit water content: The unit water content should be the minimum 

required to attain the specified self-compactability, as it produces strong 

effects on the qualities of hardened concrete. 

c) Water/binder ratio and water/powder ratio: 

‣ It is recommended that the minimum water/binder ratio be selected 

from among those determined by the performance items required of 

the concrete, such as strength, durability, water-tightness and steelprotecting 

capacity. 

‣ When the required self-compactability cannot be obtained by the 

water/binder ratio determined in above, it is recommended that the 

water/binder ratio be reduced, by increasing the binder content or that 

the water/powder ratio be reduced, by using a non-binder powder. 

d) Air content: The standard air content of fresh concrete should generally 

be 4.5% of the volume of concrete. However, a value higher by 

approximately 1% point may be recommended for certain proportioning 

conditions. 

e) Chemical admixture dosage: The dosages must be determined in the 

ranges of not adversely affecting the qualities, such as the specified timerelated 

quality changes of fresh concrete, setting time and strength 

development. 

f) Unit fine aggregate content: Should be determined from the unit coarse 

aggregate content, unit water content, unit powder content and air 

content. 


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Concrete 

5.1.3 Combination-type self-compacting concrete 

This type of SCC has a reduced water/powder ratio and contains a viscosity agent. The 

difference from the viscosity agent-type is that the purpose of using a viscosity agent is to 

alleviate the fluctuation of fresh concrete properties due to the fluctuation of surface moisture 

content, aggregate grading, etc. The addition of small amount of specified viscosity agent to 

powder-based SCC minimises variation in flowability not only due to the changes in surface 

moisture ratio or grading of fine aggregate, but also the changes in concrete temperature. 

The mixture proportion of this type of SCC is similar to the powder-type except for the use of 

a viscosity agent. 

5.2 Okamura’s Method 

This method (Fig. 7) is based on the assumptions that moderate-heat Portland cement or 

belite-rich Portland cement is the only source of powdered materials. With this method, 

therefore, if the requirement for self-compactability is satisfied, the required performance of 

the hardened concrete is generally achieved. Considering the variability that arises during 

manufacturing, such as variations in material quality and weighing errors, the target selfcompactability 

is determined in advance at a higher level than required. The method is 

explained below. 

Figure 7 – Okamura’s mix design test method for SCC 

a) Air content: this should be determined at 4 – 7%, dependent on the 

environment to which the content structure will be exposed. 

b) Unit coarse aggregate content: the relative volumetric coarse aggregate ratio 

(G/Glim, a ratio of coarse aggregate volume to solid volume of coarse 

aggregate in concrete volume excluding air) should be 0.50. At levels higher 

than 0.50, self-compactability suddenly falls. 

c) Unit fine aggregate content: the volumetric fine aggregate ratio (V s /V m , 

volumetric ratio of fine aggregate with particles larger than 90 µm to mortar 

volume excluding air) should be 0.40. This value is determined on the safe side 


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one for self-compactability considering the variability in material quality level 

during manufacturing. 

d) Volumetric water/powder ratio: value at which the relative flow area (T m ) is 5 

and the relative funnel speed (R m ) is 1 in mortar tests (flow test and V-funnel 

test). 

e) Superplasticizer dosage: dosage at which the relative flow area (T m ) is 5 and 

the relative funnel speed (R m ) is 1 in mortar tests (flow test and V-funnel test). 

6 Test methods for self-compactability evaluation 

Relevant test methods are essential during mix design development and at the actual site 

delivery. Many different test methods for SCC are reported all over the world. 

6.1 Slump flow 

The slump flow is one of the most popular methods of evaluating the consistency of 

concrete, both in the laboratory and the construction sites due to its ease of operation. This 

is a conventional method widely used for evaluating the flowability of concrete §(Fig.8). The 

flowability is characterised by the final diameter and the T50-value. The final diameter, the 

slump-flow value, describes the yield stress and the T50-value describes the plastic 

viscosity. Normally a slump-flow of approximately 600 – 700 mm is found appropriate, with 

stability evaluated by observing coarse aggregate distribution at the very periphery of the 

concrete, while no segregation border of water, paste or fine mortar should be evident. Until 

today no recommendations for appropriate T50-values exist, a too low value always indicates 

too low plastic viscosity and thus a segregating mix [Billberg, 1999]. 

Slump-flow being a very simple method is suitable both for plant or laboratory development 

as well as site delivery. The only property slump-flow does not measure is the blocking 

behaviour. 

Figure 8 – Slump-flow test 

Note: A mortar flow test (Fig. 9) is used to evaluate materials for mix proportioning. 


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Figure 9 – Mortar flow test 

6.2 Test Method for passability through spaces using U or Boxshaped 

apparatus 

The requirements for self-compactability can be different from one another depending on the 

structure to be compacted. From the point of view of rationalising quality control, Okamura 

and Ozawa proposed the so-called “Box-type test” (Fig. 10), modified version of U-shaped 

test (Fig. 11), whose bottom part is flat. Box-test is more sensitive to concrete with low 

segregation resistance and can therefore, detect such concrete easily. 

Concrete with the height of over 300 mm can be judged as self-compactable to practical 

structures. To stiff concrete cannot fill enough in the opposite tower due to its low 

deformability and too flowable concrete also cannot fill due to segregation between coarse 

aggregate and mortar in front of the obstacle. 

According to JSCE, when Rank 2 self-compactability is required, the concrete is judged as 

satisfying the requirement, if its filling height is not less than 300 mm by a filling tester with 

obstacle R2. When Rank 1 self-compactability is required, the concrete is judged as 

satisfying the requirement, if its filling height is not less than 300 mm using obstacle R1. The 

methods for concrete of Rank 3 include testing by a filling tester without any obstacle 

(obstacle R1 with five D10 deformed bars and obstacle R2 with three D13 deformed bars). 


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Figure 10 – Box-shaped test 

Figure 11 – U-shaped test 

6.3 Flow-through test method using V-funnel 

The viscosity of mortar and concrete are proposed to be evaluated through V-funnel tests 

(Figure 12). It is known that the apparent flow-through time is elongated after a certain rest 

period. Concrete with a low segregation resistance can lead to a large difference in flowthrough 

time between two tests. The degree of segregation can be judged by this test to a 

certain extent. 

Mortar 

Figure 12 – V-funnel tests 

Concrete 


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6.4 L-Box test 

The L-box test provides information regarding flowability, blocking and segregation (Figure 

13). The following parameters are measured [A2]: 

a) The time for the front to reach 200 mm marking 

b) The time for the front to reach 200 mm marking 

c) When the concrete stops, the distances H1 and H2 are measured. Acceptable 

values of the so-called blocking ratio, H2/H1, can be >0.80. 

Figure 13 – L-box test [A2] 


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6.5 Ring test 

The Ring test has a diameter of 300 mm with a fixed spacing of the vertical bars (Fig. 14). 

The blocking is assessed as a ratio of the average height of the concrete retained inside the 

ring at an approximately 200 mm diameter to the average height of the concrete outside of 

the ring [A3]. 

Figure 14 – Ring test 

6.6 Acceptance test at jobsite 

Since the degree of compaction into the structure mainly depends on the self-compactability 

of concrete and poor self-compactability cannot be compensated by the construction work, 

self-compactability have to be checked for all concrete just before casting at the jobsite. 

However, conventional testing methods for self-compactability require sampling and then this 

can be laborious if acceptance test is to be carried out for all the concrete. Testing method 

was developed by [Ouchi et. al., 1996]: 

1) Testing apparatus is installed between agitator truck and pump at the jobsite. 

All the concrete is poured into the apparatus (Fig. 15) 

2) If the concrete flows through the apparatus, the concrete is considered as selfcompactable 

for the structure. If not the mix-proportion have to be adjusted. 

This apparatus was successfully used at the construction site of LNG tank of Osaka Gas 

and saved labour for the acceptance test (Fig. 16) 


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Figure 15 – Outline of acceptance testing apparatus at jobsite 

Figure 16 – Acceptance test at construction site 

7 Production and placement of self-compacting concrete 

There are some significant differences in production of SCC compared to conventional 

concrete. The most obvious is that the rheological properties of fresh SCC can be allowed to 

vary only to a very limited extent. For conventional concrete, any quality variation can be 

handled by varying the compaction work. Therefore, the production of SCC should be 

carried out in plants where the equipment, operation and materials are properly controlled. 

7.1 Storage of aggregate 

SCC is generally more susceptible to fluctuation of unit water content than normal concrete. 

For this reason, it is necessary to control fluctuation of the surface moisture ratio of 

aggregate, particularly fine aggregate. The surface moisture should be measured by an 

adequate method and its correction should be made accurately and promptly. 

Where the fluctuation of aggregate grading can have adverse effects on the fluctuation of 

SCC, aggregates with different grading should be stored separately. Thus, variation in 

aggregate grading is more difficult to handle during production. 

7.2 Plant facilities 

Both pan-mixers as well as free-fall mixers can be used to produce SCC (worn-down and old 

types of free-fall mixers are excluded). The type and status of mixer though has an impact 


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on mixing efficiency, thus affecting mixing time. Therefore, the method of mixing SCC should 

be adequately established on the basis of field experience. The mixing time should be as a 

rule not less than 90 seconds. 

For instance, the mixing sequence is very important. SCC that should be frost resistance 

and thus have a controlled air-pore system, an optimum addition time of air entraining agent 

during mixing and a slightly prolonged mixing time is needed, but of course this also depends 

on mixer efficiency. 

7.3 Transportation 

SCC should be transported to the site within an adequate time in consideration of time 

required for placing so that placing can be completed while the required self-compactability is 

retained. The time limit from mixing to the end of placing should be as a rule 120 minutes. 

7.4 Placing 

The maximum distance of free drop should be as a rule not more than 5 meters. The 

maximum lateral flow distance should be as a rule 8 meters and must not exceed 15 meters. 

The point of depositing shall be shifted to avoid segregation due to lateral flow of concrete. 

When more than one layer is placed, the upper layer must be placed within the time during 

which the previous layer retains its fluidity, so that both layers can be monolithically 

integrated. If the second layer of SCC is placed on the existing layer which, has begun to 

set, cold joints or colour difference may occur (Fig. 17). 

Figure 17 - Colour difference on surface of SCC 

More or less perfectly continuous casting results in a completely defect free surface which is 

necessary to attain perfect concrete surfaces. In the case of architectural concrete, it is 

better to lower the free fall height to reduce generation of air bubbles on the surface of 

concrete (Figure 18). In vertical element a better finishing has been obtained when the 

concrete were placed from bottom to top. 


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Figure 18 – Air bubbles on the surface of SCC 

7.5 Finishing and curing 

In comparison with ordinary concrete, the setting time of SCC tends to be delayed according 

to the type of powder and superplasticizer and time of concrete placing. Therefore, care 

should be exercised when finishing the surface. 

The viscosity of SCC is high and bleeding is almost non-existent. When monolithic surface 

finish is required, measures to spray water, etc. must be taken during finish work. Since 

there is almost no bleeding in SCC, the surface tends to dry earlier than ordinary concrete, 

easily causing plastic cracks. Therefore, the top of concrete slabs, etc. must be covered or 

sprayed with water after placing so as to prevent drying. 

7.6 Formwork and supports 

a) Although some results show smaller lateral pressure than liquid pressure 

[Billberg, 1999 and Orsa Béton, 1999], the lateral pressure of concrete should 

as a rule be regarded as liquid pressure when designing formwork and 

supports. Quantitative calculation of lateral pressure based on the properties of 

fresh SCC, frame conditions, and placing conditions has not been made yet. 

When formwork is broken and SCC begins to flow out, it is almost impossible to 

stop it and a lot of labour is necessary to handle concrete that has flowed out. 

There will be no alternative but to suspend concrete placing scheduled for the 

day. 

b) In confined spaces, vent holes should be provided at adequate positions in the 

top forms. 

c) Formwork should be accurately constructed to prevent loss of concrete. When 

there is a gap in shuttering, paste or mortar in SCC flows out easily, and the 

outflow may continue for a long time (Fig. 19) 


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d) Where the aesthetic appearance of concrete surface is of particular 

importance, the materials for sheathing and type of form remover should be 

suitably selected to minimise air-voids on formed surfaces. 

Figure 19 – Outflow of paste or mortar 

8 Quality control and inspection during construction 

The performance of produced and transported SCC to the construction site can differ from 

that designed and tested at the laboratory. It is, therefore, important to control before placing 

that produced and transported concrete attains the established self-compactability for 

ensuring reliability of the structure. Since the changes in the temperature and transportation 

time during the construction can alter the self-compactability from the designed level, it has 

to be confirmed by a suitable method by the time the placing begins. 

The deformability, segregation resistance and self-compactability should be controlled at the 

point of unloading taking into account the quality changes during conveyance from the 

unloading point to the placing point. Self-compactability may be inspected by passability 

tests with a filling tester (see section 2.5.2) used at the verification stage. The obstacle 

conditions corresponds to the established self-compactability rank should be used for testing. 

The inspection shall be carried out at least once for each 50 m 3 . 

Whether the concrete attains the required self-compactability at the point of unloading can 

also be judged by placing a passability apparatus (see section 2.5.6) between the agitator 

truck and the mobile pump, with which the passability of the whole truckload can be 

automatically tested. 


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Concrete 

Concrete Technology: Current Situation and Future Trends 

Pierre-Claude Aïtcin 

Université de Sherbrooke, Québec, Canada 

Moussa Baalbaki 

Holcim Group Support - CPD 

1. CONCRETE THE MOST WIDELY USED CONSTRUCTION MATERIAL ..................... 201 

2. THE DEVELOPMENT OF CONCRETE IN A SUSTAINABLE 

DEVELOPMENT PERSPECTIVE................................................................................... 202 

2.1 Sustainable development....................................................................................... 202 

2.2 Concrete technology status.................................................................................... 202 

2.3 Modern concrete technology is still ignored in several parts of the 

world....................................................................................................................... 203 

2.4 Life cycle of concrete structures............................................................................. 203 

3. NEW PROMISING TECHNOLOGIES IN THE DOMAIN OF CONCRETE ..................... 205 

3.1 Cheap concrete or expensive concrete.................................................................. 205 

3.2 Some recent technological break though in the domain of concrete 

materials................................................................................................................. 205 

4. HIGH PERFORMANCE CONCRETE ............................................................................. 207 

5. SELF LEVELING CONCRETE ....................................................................................... 208 

6. ROLLER COMPACTED HIGH PERFORMANCE CONCRETE ..................................... 209 

7. REACTIVE POWDER CONCRETE................................................................................ 210 

7.1 Increase of the homogeneity.................................................................................. 210 

7.2 Increasing of the compactness .............................................................................. 210 

7.3 Improvement of the microstructure by thermal treatment ...................................... 211 

7.4 Ductility of reactive powder concrete ..................................................................... 211 

8. THE CHALLENGES OF THE CEMENT AND CONCRETE INDUSTRY IN 

THE 21 ST CENTURY....................................................................................................... 212 

9. REFERENCES................................................................................................................ 214 


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Concrete 

1 Concrete the most widely used construction material 

During the twentieth century, concrete became the most widely used construction material. 

Total concrete production in 1997 exceeded 7 billion cubic meters, which is just over 1 cubic 

meter or 3 tons per capita. 

How did concrete attain this status in 100 years? There is no single reason that accounts for 

its success, but rather a conjunction of facts : 

• concrete is not expensive; 

• concrete technology is simple; 

• concrete is primarily made from local materials; 

• concrete materials are widespread all over the globe; 

• concrete has high compressive strength; 

• concrete stays plastic long enough to be transported and placed; 

• concrete is a versatile construction material; 

• concrete is durable; 

• concrete is environmentally friendly. 

During the same period of time, most countries experienced general urbanization. As history 

teaches us, urbanization has consistently been the source of wealth since the times of the 

Sumerians and the Egyptians or the Incas and the Aztecs. It is not our intention to develop 

the socioeconomic reasons behind this fact; we only call attention to it and show that the use 

of cement and concrete has increased as the urbanization process has developed during the 

twentieth century. 

Any construction of streets, buildings, houses, schools, hospitals, water supply systems, and 

wastewater treatment plants in modern cities involves the use of concrete. The land, water, 

air, and even airwave links between cities needed to promote trade between urban areas 

and create the wealth of a nation or a continent have been built on concrete. We aren't 

overly optimistic or enthusiastic in stating that concrete is one of the foundations of wealth in 

modern civilization. 

While the urbanization process has plateaued in most industrialized nations, it will continue 

to develop during the first part of the 21 st century in many countries and result in an overall 

increase in the consumption of cement and concrete. 


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2 The development of concrete in a sustainable 

development perspective 

2.1 Sustainable development 

Sustainable development is presently more than reality, it is a serious commitment towards 

the future. We must understand it and deal with it specially in relation to its globalization. 

The highest socioeconomic output at the lowest environmental impact must be searched for 

in any human activity. Compatibility between production, consumption, national and 

international trade and environmental issues must be permanently looked for. The linkage 

between all the parameters that may affect sustainability is one of the greatest challenges of 

our times; it is more than simply looking for decreasing industrial polluting emissions or 

energy saving, it is optimizing any activity so that its environmental impact will be the lowest 

possible. 

Sustainability is largely influenced by : economy and evergrowing social demands and 

welfare, energy availability such as fossil fuel, renewable resources, technological 

development, existing infrastructure, educational level, country size/population density, 

urbanization level, standard of living, new geopolitical and commercial barriers, among other 

parameters. 

In spite of the fact that concrete is well accepted to be for its own nature a material having a 

low energy content causing a low impact on the global environment, it is important to see 

what can be done to improve the situation in a sustainable development approach because 

great amounts of concrete are used every year all around the world. 

Production processes must be energy saving and should not generate harmful by-products 

or emissions in the production. Adaptation of a community to the principles of sustainable 

development leads to a need of a remarkable increase in the lifespan and quality of different 

products. Durability will be a key factor in the future from economical and environmental 

point of views in building as well as in road programs. Maintenance is expensive from any 

point of view. 

2.2 Concrete technology status 

The author is deeply convinced that presently : 

• concrete is not used at its best not only from a sustainable development point of view but 

also from an economical one; 

• putting into practice on a worldwide basis what is already a well established technology in 

some parts of the world would result in a more efficient use of cement and aggregates; 

• the impact of concree use on the environment is very limited when compared to other 

human activities. 

There are presently too many countries making too much concrete with a very low 

compressive strength of about 15 MPa to 20 MPa which results not only in a waste of 

cement but also in an increase of the rate of aggregate depletion in many urban areas. 

It is very easy to show that ecologically and economically the use of low strength concrete is 

equally harmful. A lot of engineers, contractors and owners are only concerned with the unit 

price of 1 m 3 of concrete when they should rather look at the cost of the Megapascal they 

need for structural purpose or at the life cycle cost of a concrete structure. 


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In order to illustrate this point let us consider the concrete columns of the structural 

laboratory of the University of Sherbrooke which have been built 30 years ago with a 25 MPa 

concrete, that should have contained about 300 kg of cement per cubic meter of concrete. In 

1998 these columns could have easily been built with a 75 MPa HPC containing 450 kg of 

cement per cubic meter of concrete, corresponding to a 50% increase in the cement dosage 

of the concrete. However, if we consider the amount of concrete per m 3 , the cross section 

area of the high strength columns would be 1/3 of that of the present columns. Therefore, 3 

times less HPC would be used for each column and the quantity of cement necessary to 

achieve the same structural performance would be half the one used 30 years ago (C × 1/3 × 

1.5 = 0.5 C). This significant saving in cement is also concomitant with an even greater 

saving in the quantity of aggregates used to build these columns. Less than 1/3 of the 

aggregates used 30 years ago would be necessary to build in 1998 high performance 

concrete columns having the same structural performance. 

Moreover, if we look further in the future it is easy to realize that when the present 25 MPa 

concrete will be recycled, it could only be used as a road base aggregate, while a 75 MPa 

concrete could be used once or twice as a source of recycled aggregate to make concrete of 

a lower compressive strength before being used as a road aggregate. 

Of course the saving in cement and aggregate is not as significant in structural member 

made of high performance concrete working in flexure. 

2.3 Modern concrete technology is still ignored in several parts of the 

world 

First, for too many people concrete is still a mixture of cement, water and aggregates. The 

use of admixtures that improves so much the efficient use of cement in concrete is ignored 

so that large amounts of cement are presently wasted. 

Portland cement particles tendency to flocculate when mixed with water resulting in the 

addition of an unnecessary increase of mixing water and cement to achieve a workable 

mixture, can be overcome by the use of organic molecules known as dispersants, water 

reducers or superplasticizers. Unfortunately the use of water reducers is not the general rule 

so that at the dawn of the twenty first century it can be estimated that the same amount of 

concrete having the same compressive strength and the same durability could be made in a 

worldwide basis using about 10 percent less cement, which means that between 100 and 

200 million tonnes of cement are wasted by ignorance every year. 

Second, the selection of the type of concrete to be used to build a structure is too often made 

only by taking into account structural aspects without considering the environmental 

conditions to which this concrete will be exposed during its service life. The result is that too 

many concrete structures cannot perform their socioeconomic function for a very long period. 

The premature failure of 20 MPa to 30 MPa external parking garages in Canada is a good 

example of such an inadequate use of concrete. When an external parking garage has to be 

built the selection of concrete must not be done based only on structural criteria, but rather 

on durability criteria. A similar situation has been faced in Midle-East because the peculiar 

environmental conditions that concrete would have to face were not given enough 

consideration. Even in Europe too many concrete structures suffer a premature failure due 

to carbonation : the skin of a low strength concrete is more prone to carbonate than that of a 

higher strength concrete. 

2.4 Life cycle of concrete structures 

Increasing the life cycle of concrete structures is essential in a sustainable development 

approach but this analysis of the cycle life cast must include the evaluation of the impact in 


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the environment of a system that includes the whole activities associated to a product or 

service from raw meal extraction until the waste elimination. This evaluation must be 

performed all over the duration of the infrastructure. 

Moreover, presently, the construction industry is too fractionated which is very unfortunate, 

and very few people have an integrated view of the whole construction process. The 

decisions taken by each partners are taken on an individual basis without taking into account 

the final cost of the project. Too often, in order to save a penny at one step of the 

construction a subcontractor will oblige one of the next subcontractors to spend a dollar to 

overcome a difficulty that could have been solved for much less than one dollar, if the 

solution of the problem had been more wisely shared between the two subcontractors. As 

an example let us consider the increase in the C 3 S content in modern Portland cement. This 

has been the response of the cement industry to the demand of contractors who wanted to 

speed up the construction process. Not only the 24-hours compressive strength of the 

concrete has been increased but also the 28-day one, but with the result that after 28 days 

such concretes do not increase their compressive strength very much while former concretes 

made with a cement having a lower C 3 S content were still developing a significant amount of 

strength after 28 days, years ago. Therefore, the durability rules established for these former 

concretes made with a low C 3 S cement are no more valid for concretes made with high C 3 S 

cements because the concrete is practically not gaining anymore strength after 28 days. 

Concrete durability does not depend on compressive strength but rather on the water/cement 

ratio which dictates the porosity of the hydrated cement paste and the progression rate of 

aggressive agents within concrete. On that respect a given 28-d compressive strength can 

be achieved with a modern cement at a much higher water/cement ratio than some years 

ago, which is not so good from the durability point of view. 

These are only a few examples of what can be done to improve the performance of concrete 

in a sustainable development approach. 


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3 New promising technologies in the domain of concrete 

3.1 Cheap concrete or expensive concrete 

At the dawn of the 21 st century there are some promising concrete technologies that are 

already confirmed or emerging in some countries that should be used increasingly in the first 

part of the 21 st century, but, given the limitated allocated time, it is my intention to limitate my 

presentation to four of them with which I am familiar and confident to see spreading all over 

the world. 

Before presenting these technologies I think that is important to analyze why in the last 

twenty years, concrete has found an increasing use in some niche markets instead of staying 

uniquely a commodity product. A few recent technological developments in the domain of 

admixtures and supplementary cementitious materials or filler, have resulted in the 

development of new types of efficient concretes that are already competing steel on some of 

its traditional construction markets. 

Concrete efficiency has to be considered in a broader view then simply the decrease of its 

unit price. The future of the concrete industry is not linked to the development of less 

expensive concretes but rather in the development of more expensive concretes, the use of 

such expensive concrete will result in a decrease of the final cost of concrete constructions, 

because the cost of concrete represents always only a small part of whole cost of a concrete 

structure, and, great savings can be realized in the other steps of the construction process, if 

concrete composition is optimized according to its final use. What is important is not the 

price of 1 m 3 of concrete but rather the cost of for example 1 MPa or of 1 more year in the life 

cycle of a concrete structure. As we will see later on in the three of the four new concrete 

technologies that will be presented the use of a concrete having a more expensive unit cost 

resulted in significant decrease of the initial cost of some concrete structures. 

It is hoped that a new philosophy in the use of concrete will emerge in the first part of the 21 st 

century as part of the growing tendency to deliver built key projects or BOOT (Build-Own- 

Operate-Transfer) infrastructures. For having been involved in a BOOT project, I can assure 

you that not only the working philosophy of the contractor is becoming more integrated but 

also that his decisions are taken in the perspective of a minimization of maintenance work. 

The philosophy of the lowest bidder has been and still is catastrophic in too many cases for 

the concrete industry, with the result that concrete present world wide a poor image. As long 

as maintenance and replacement costs are not integrated in tenders, concrete will be abused 

in the sake of making a fast and easy dollar. Our societies are not rich enough to base their 

development on such an attitude. 

3.2 Some recent technological break though in the domain of concrete 

materials 

In too many parts of the world, oncrete is still essentially a mixture of cement, water and 

aggregates but modern concrete always contains one or several admixtures. It is not wrong 

to say that most of the recent advances in concrete technology are rather due to an 

innovative use of admixtures rather than in an improvement of cement manufacturing. 

Portland cement is a wonderful building material, but from a physico chemical point of view it 

suffers from one intrinsic weakness : during its final grinding too many electric charges are 

developed at the surface of cement particles, with the result that, when concrete is mixed 

with water, cement particles have a strong tendency to flocculate. The poor dispersion of 


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portland cement particles in water is definitely limiting the binding potential of portland 

cement, because, in order to improve concrete workability, non-stochiometric water has to be 

added in concrete in order to obtain a sufficient workability to be able to place concrete 

without having to develop too much vibration energy. This extra water succeeds in 

dispersing cement particles, but at the same time pull apart individual cement particles so 

that hydrates must bridge larger gaps to create binding links. The resulting hardened 

microstructure is therefore very porous and weak and prone to favor the ingress of 

aggressive agents within the structure. 

Fortunately, very few amounts (usually less than 1 percent of cement mass) of so-called 

water reducers or superplasticizer can be used to neutralize these electrical charges and 

increase the dispersibility of portland cement particles in water. Therefore, presently, it is 

possible to make flowing concrete having a slump of 200 to 250 mm and containing less 

water that the amount necessary to hydrate all the cement particles present in the mix. 

Moreover, the characteristicts of these polymeric materials have been optimized so that the 

retention of such a high slump during 1 or 2 hours does not cause any problems and does 

not result any more in a decrease of the 24-h strength due to some hydration retardation, as 

it was observed with the first generation of superplasticizers. 

A second technological break through in the domain of concrete technology, that occurred in 

the last twenty year, has been the use of silica fume, a by-product of the silicon and 

ferrosilicon industry. In fact, silica fume is composed of very fine spherical particles (one 

hundred time finer than a cement particle) of amorphous silica. Silica fume can be 

considered as a superpozzolan. In spite of the fact that limited amounts of silica fume are 

presently available, the discovery of the particular properties of this material has given a 

momentum to the research of the effects of the use of very fine powders in concrete. In that 

domain, the last word has not yet been said and in the first part of the 21 st century, it will not 

be surprising to see all kind of very fine powders being used when making concrete, rice 

husk ash and metakaolin can be such products. 

Finally, colloïdal agent, initially developed for underwater concreting, are finding new uses in 

self leveling concrete as it will be seen later. 

Due to time limitation it will not be possible to cover corrosion inhibitors and shrinkage 

reducing admixtures and some other admixtures that begin to be used. 


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4 High performance concrete 

High performance concrete should be rather called low water/cement ratio (W/C) or low 

water/binder ratio (W/B) concretes. In fact, the high performance W/C or W/B ratio is usually 

comprised, at present time, between 0.25 and 0.35, but, concretes having a lower W/C or 

W/B have been used. These low W/C or W/B ratios traduce in 28-d compressive strengths 

comprised between 50 and 100 MPa, but, concretes with a higher 28-d compressive strength 

have been made. 

The compressive strength of high performance concrete, among other factors, is a function of: 

• the WC or W/B, of the amount of entrained air it contains, 

• the efficiency of the selected cementitious combination used, 

• the "strength of the coarse aggregates", of the efficiency of the superplasticizer 

used among other factors. 

When making high performance concrete one of the most important factor is to find a cement 

or a cementitious combination which is compatible with one of the commercially available 

superplasticizer. A cement or cementitious combination is said to be compatible when a low 

W/C or W/B ratio concrete having an initial slump higher than 200 mm is able to maintain this 

slump during 1 hour or 1 hour and half and still have a high 1-d compressive strength. 

The compatibility between a cement and a superplasticizer is governed by quite complex 

physico-chemical parameters and is still more or less well understood from a scientifical point 

of view. However, several empirical methods can be used to find if a particular 

cement/superplasticizer is compatible or not. When a particular combination is found to be 

non compatible or poorly compatible several tricks can be used to try to improve the 

compatibility like : adding a slight amount of retarder, a slight amount of alkali sulfate, using 

the so-called double introduction technique. 

The use of silica fume is not mandatory to make high performance concrete, but when it is 

available at an economical price it is suggested to use it because it facilitates the fabrication 

of high performance concrete. Several cementitious combinations have been used to make 

high performance concrete depending on the local availability of supplementary cementitious 

materials. 

When making high performance concrete it is important to select a "strong" coarse aggregate 

because in some cases it has been found that the coarse aggregate was in fact limiting the 

compressive strength that could be achieved. Moreover, it is found that the elastic properties 

of the coarse aggregate are influencing very strongly the elastic properties of high 

performance concrete so that the usual empirical formulas used to predict the elastic 

modulus from the compressive strength should be used with great care. 

Generally speaking it is admitted that the durability of high performance concrete is greater 

than that of ordinary concrete. There is still one controversial point concerning the durability 

of high performance concrete, it is its freeze-thaw durability. Should high performance 

concrete contains entrained air like ordinary concrete to be freeze thaw resistant or not? 

Presently, in Canada, the rule is that high performance concrete must be air entrained to be 

freeze thaw resistant, however the usual spacing factor requirement for ordinary concrete 

has been relaxed by some institutions. For example, the department of transportation of the 

Province of Quebec accept that the spacing factor of high performance concrete be lower 

than 350 m and not lower than 230 m like for ordinary concrete. 


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One major difference between the behavior of high performance concrete and ordinary 

concrete is their shrinkage pattern. High performance concrete develops a very rapid and 

strong autogenous shrinkag, while autogenous shrinkage is perfectly negligible in ordinary 

concrete. Therefore, in order to minimize the development of the potential autogenous 

shrinkage of a high performance concrete it is important and necessary to water-cured high 

performance concrete before hydration reaction begins, that is 3 to 6 hours after placing. If a 

high performance concrete is not water-cured as early as that, it can be badly cracked, which 

in turn will affect the durability of the concrete structure. 

Depending on the compressive strength that is loked for 1 m 3 of high performance concrete 

can be 30 to 100% more expensive than a 25 to 30 MPa concrete. But, when properly used 

high performance concrete can be used to build less expensive concrete structures because 

the savings in the amount of concrete used, in the form work, in the reinforcing steel, in the 

footings etc. result in a an initial cost decrease. If the maintenance savings, and the initial 

socio-economical costs are taken into account it is found that building with high performance 

concrete is building cheaper. 

High performance concrete has been used to build outstanding structures but also to solve 

day-to-day problems like the reconstruction of a MacDonald's restaurant entrance. High 

performance concretes will be used more and more used in the 21 st century because of their 

durability or their rapid hardening rather than their final strength. 

5 Self leveling concrete 

Self leveling concretes have been developed in Japan, but start to be used in several 

countries. Self leveling concrete is a type of expensive concrete which use can result in a 

significant saving of the initial cost of some specific structures where placing cost of ordinary 

concrete could be very high. This is particularly the case of highly reinforced concrete 

elements in seismic zones. 

But, it has been found that self leveling concretes can be used also for another reason : it is 

a noiseless concrete that don't need to be vibrated to be placed, therefore, in urban areas 

self leveling concrete can be placed any time without disturbing the neighborhood : 

particularly late in the evening or during the night or early in the morning. For example, in an 

urban area, a contractor can wait till 6 o'clock to close his form instead of rushing to close 

them at 4 o'clock, therefore, every day if beneficiate of 2 more working hours from his crew. 

The self leveling concrete could be placed after 6 o'clock without any disturbance for the 

neighborhood under the supervision of a foreman assisted by a helper. 

Self leveling concretes have a composition that is altered from that of an ordinary concrete, 

they are made with a smaller size coarse aggregate, they contain more sand, more 

cementitious material, more superplasticizer and a colloïdal agent to control their viscosity, 

their segregation and their bleeding. 

Self leveling concretes have been used to build some huge structures but also to repair small 

unaccessible structural element. 

Without any doubt there is a niche market for self leveling concrete in the 21 st century. 


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6 Roller compacted high performance concrete 

Roller compacted concrete is not per se a new type of concrete, roller compacted concretes 

have been extensively used for dam construction. When used to build a dam roller 

compacted concrete in a very lean mix which compressive strength is quite low, 15 to 20 

MPa, in order to develop the lowest amount of heat. Roller compacted concrete increases 

the construction rate of a dam and decreases significantly the amount of material to be used 

to build it because of the steeper slopes that can be used. 

This placing technique is now used in richer mixes that can achieve a 50 to 60 MPa 28d 

compressive strength. Roller compacted high performance concretes are dry mixes which 

workability is measured in term of so-called Vebe time. The placing is done using standard 

asphalt placing equipments, with the great difference for the working crew that it is a cold mix 

rather than a hot one that has to be placed. 

The batching of high performance roller compacted concrete can be done either in any 

concrete batching plant or in an asphalt plant which has been slightly modified. Instead of 

adding the hot liquid asphalt as a binder, portland cement is added. 

High performance roller compacted concrete are quite economical mixes, it has been 

possible to achieve a 50 MPa compressive strength with 290 kg of cement per m 3 . 

Moreover, recently it was found that high performance roller compacted concrete can be air 

entrained using a new type of air entraining agent. 

Roller compacted high performance concrete has already found a use in a certain number of 

industries to build unreinforced large working areas (metallurgical plant, pulp and paper mills, 

warehouses, lumber mills, saw mills, scrap yards etc). What makes roller compacted high 

performance concrete attractive for such applications is the simplicity of use the rapidily of 

the construction time frame, the high wear resistance of the concrete surface, and also 

economics if the life cycle of such a strongs lab is taken into account. Interestingly, most of 

the projects have involving the use of high performance roller compacted concrete been 

done by asphalt companies which have found a very interesting new market for their placing 

equipment. 

There is no need for joints, usually roller compacted high performance concrete is let free to 

crack, the presence of fine cracks being of no concern for the users. In the case of the 

Domtar paper mill near Sherbrooke 86 000 m 2 of two 150 mm layers of high performance 

roller compacted concrete were cast in less than 6 weeks (such a surface represents the 

surface of 16 adjacent soccer fields). Very fine transversal cracks were observed every 30 m 

and compressive strength measured on cores was found to be about 50 MPa. 

It is sure that this placing technique will be widely used during the 21 st century in all kind of 

industrial applications. For example, a roller compacted high performance concrete was sold 

to increase the cleanliness of a log yard in order to increase the afternoon output of a saw 

mill because the logs could be washed and be less sandy before being sawed. As the wear 

of the saws was significantly decreased, the afternoon output was greatly improved, every 

evening the sharpening of the saws took less time and the saws lasted longer. 

It will be the rôle of the marketing people to find markets for high performance roller 

compacted concrete for economical reasons that very often will be very indirectly related to 

the traditional qualities of concrete. 


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7 Reactive powder concrete 

Reactive powder concrete is a new type of cement based material. Reactive powder 

concrete does not contain any coarse aggregate, the maximum size of particles used to 

make it is usually comprised between 300 and 600 m. Therefore, some people argue that 

reactive powder concrete should not be called concrete since from a particle size point of 

view it is rather a mortar. However, when a reactive powder is reinforced with long and fine 

steel fibers it is easy to demonstrate, when considering the scale effect, that these fibres are 

acting in the reactive powder concrete as reinforcing bars in an ordinary concrete. 

Three principles are at the base of the development of reactive powder concrete : 

• an increase of the homogeneity of the material by eliminating the coarse aggregate, 

limiting the sand content, improving the mechanical properties of the paste and 

suppressing the transition zone around the aggregate; 

• an increase of the compactness of the mix by optimizing the grain size distribution of the 

different constituents and by pressing the mix before and during the setting (optional); 

• a refinement of the microstructure by a special heat treatment. 

7.1 Increase of the homogeneity 

The elimination of the coarse aggregate and its replacement by a fine sand tends to reduce 

considerably the size of the microfissures of mechanical, thermal and chemical origins that 

are linked, in an ordinary concrete to the presence of an inclusion (aggregate) in a matrix that 

is homogeneous (the hydrated cement paste). This reduction of the size of the 

micrrofissures is accompanied by an improvement of the properties of the RPC on their 

compressive and tensile strength. The sand content is reduced in order to pass from a rigid 

skeleton of aggregates that are adjacent and which present a large area in contact which 

each other, to a set of inclusions within a continuous matrix. This modification of the 

organization of the material results in a reduction of the negative effects on the porosity that 

can result from a partially restrained shrinkage when the aggregate skeleton is too stiff. 

The increase of the mechanical properties of the paste, more particularly of its elastic 

modulus, and, at the same time the reduction of the gap between the rigidity of the paste and 

that of the aggregates tend to reduce the effects related to the modification of the stress field 

around the aggregates. 

The increase of the compactness of the aggregate skeleton by the use of constituents having 

complementary grand size distribution and by the use of a high dosage of a very fine material 

like silica fume, result in the elimination of the transition zone between the paste and the 

sand particles increasing the transfer of the mechanical properties between the aggregates 

and the paste. 

7.2 Increasing of the compactness 

The increase of the compactness of an aggregate mix tend to minimize the voids between 

the particles and to reduce the amount of mixing water necessary to achieve a certain 

degree of workability. A theoretical approach associated with laboratory experiments has 

been used to select the best commercial components of the RPC and to fix their mixing 

proportions in order to increase its final compactness. Table 1 gives a typical composition of 

a RPC. 

The compactness of a reactive powder concrete can be increased even more if during 

setting a load is applied on the fresh concrete. The application of such a load results in the 


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elimination of entrapped air that can developed during mixing, in the extraction of a part of 

the mixing water, in reducing the amount of water occupied in the fresh reactive powder 

concrete, in reducing the water/binder ratio and finally in compensating for a part of the 

chemical shrinkage. The pressing of a fresh reactive powder concrete can result in a gain of 

more than 5% on the relative density. 

7.3 Improvement of the microstructure by thermal treatment 

The heating in water of reactive powder concrete at a temperature comprised between 70 

and 90°C after its setting results in an acceleration of the pozzolanic reaction of the silica 

fume while modifying the structure of the hydrates already developed. This heat treatment 

results in a mechanical strength that is much higher than that of untreated samples. A heat 

treatment at 400°C can even alter further the microstructure of the reactive powder concrete 

and result in compressive strength gains that are much more significant (over 500 MPa, and 

even over 800 MPa have been obtained when doing this). In this last case RPC was 

confined with a pressure of 50 MPa and contained metallic aggregates. This type of curing is 

more difficult to realize, particularly for large structural elements. 

The curing in water between 90 to 100°C over a period of 48 hours is quite easy to do, this is 

the type of curing that has been used during the experimental works done at the Université of 

Sherbrooke. Reactive powder concretes having a 200-MPa compressive strength are 

fabricated on a daily basis in this way by technicians and graduate students. However, such 

reactive powder concrete is not a ductile material. The improvement of the ductility of this 

type of concrete is essential in order to make its use more interesting. 

7.4 Ductility of reactive powder concrete 

Reactive powder concrete matrices have a purely linear elastic behavior and their rupture is 

brittle. Their ductility is greatly improved by the addition of fibers or by their confinement in a 

steel tube. 

As it can be seen in the Figure 1, the addition of 140 kg/m 3 (1.8% volumetric fraction) of steel 

fibers having a length of 12 mm gives to reactive powder concrete some ductility in 

compression. The positive effect of the fibers on the ductility is more evident in the case of 

the flexural strength as it can be seen in Figure 2. The flexural behavior of a reactive powder 

concrete containing steel fibers is similar to that of reinforced concrete. In fact, adding 12mm 

long fibers having a diameter of 0.2 mm in a material where the maximum size of the 

coarsest sand grain is about 200 m correspond at ordinary concrete scale to add 

reinforcing 20 mm bars 1.2m long in a concrete made with a coarse aggregate having a 

maximum size of 20 mm 

It is known for a long time that the confinement of concrete in a steel tube result in an 

increase of the ultimate strength and of the ductility of the concrete when it is submitted to a 

compressive load. This strength increase is very interesting when the basic compressive 

strength of concrete is high. In the case of reactive powder concrete the improvement 

brought by the confinement is even more significant as it can be seen in Figure 1. In this 

figure, it is seen that according to the thickness of the steel tube, the fiber dosage and even 

the pressure applied on the concrete during its setting it is possible to obtain compressive 

strength varying from 250 to more than 350 MPa, but, what is more impressive is the ductility 

obtained when confining the RPC. During a study done at the Université de Sherbrooke on 

100-mm diameter specimens, the most interesting results were obtained with a reactive 

powder concrete containing steel fibers pressed during the setting and confined in a steel 

3mm thick tube. The ultimate compressive strength that was measured on such specimens 

was over 350 MPa. 


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Reactive powder concretes have been used, up to now, in a limited number of structural 

application where its high strength, its light weight high ductility and great durability and low 

maintenance cost can be used advantageously. Reactive powder concrete can be perceived 

as a very expensive concrete when considering its unit price per m 3 , which is comprised 

between 750 to 1000$ CDN, but, as reactive powder concrete in most its present 

applications compete with steel due to its very high compressive strength and pseudo plastic 

behaviour its price should be considered by the tonne rather than by the m 3 . The price of 

reactive concrete relate to its mass is 300 to 400 $ CDN/tonne in comparison to 1 000 to 1 

500 $CDN for structural steel. 

For sure reactive powder concrete market will always be a very specialized and lucrative 

markets. In the author's opinion the pig iron market should be considered as a potential 

market for reactive powder concrete, because as Pierre Richard, the inventor of the reactive 

powder concrete concept, says reactive powder concrete can be seen as a pseudo plastic 

cold ceramic. 

These four examples of new concrete technologies that were presented are only a few 

examples of successful uses or of new promising technologies developed recently in the 

domain of concrete. Another author could have selected other examples to show that 

concrete is a versatile material that will continue to be widely used in the 21 st century, in its 

traditional markets, but also, in unforeseen new markets. But, it is also sure that successful 

concrete technologies of the 21 st century will have to integrate a sustainable development 

perspecttive. 

8 The challenges of the cement and concrete industry in 

the 21 st century 

The main challenge of the cement and concrete industry in the 21 st century is to obtain the 

highest socioeconomic out put of each cubic meter of concrete at the lowest environmental 

cost. 

The author is deeply convinced that education is one of the biggest challenge of the concrete 

industry in the 21 st century. For to long concrete has been perceived as a low tech 

commodity product, and, competition based on price. This attitude was encouraged by the 

quite universal lowest bidder philosophy and has definitely tarnish the image of concrete in 

the public. 

Moreover by tradition in most parts of the world concrete production is fragmented in 

numerous small organizations operating locally in an artisanal mode rather than as a modern 

and efficient industry. Concrete making is still considered as a low tech activity that does not 

demand any particular technical knowledge, so that anyone who has some entrepreneurship 

can be in business with a small investment. Therefore, it will be difficult to have a rapid and 

significant impact on the concrete industry development. 

Therefore, the real chalenge is not what has to be done, it is rather how to do it and how fast 

it can be done. 

It will be a pity if the development of the concrete industry in developing countries during the 

first half of the 21 st century does not take advantage of the present state of the art technology 

in cement and concrete manufacturing developed in industrialized countries but rather 

repeats the errors of the past. 

However, it is not a hopeless situation, because the technology to obtain the most efficient 

technological and environmental output of each cubic meter of concrete exists already; it is 

only a matter of education to put it into application. When considering the existing 

communication means that are presently available to develop a worldwide educational 


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system, it is time to take advantage of this situation to develop a worldwide concrete industry 

that will direct its efforts to improve its performance in a sustainable development approach. 

Following a significant research effort concrete image has been revamped and now in some 

applications concrete is directly competing steel : high rise buildings, offfshore platforms, 

large bridges, etc. 

Well advanced concrete technologies is already available, the challenge is to make these 

technologies available all over the world. 

Efficient use of newly developed admixtures should be strongly and rapidly promoted in order 

to be able to make more durable concrete out of the same amount of cement. 

The use of supplementary cementitious materials, natural pozzolans, artificial pozzolans and 

fillers should be promoted rapidly in order also too to make more concrete out of the same 

amount of cement. 

Increasing the life cycle of concrete structure is another goal that must be rapidly 

implemented, concrete structure should be designed based on durability criteria and not 

uniquely on structural criteria. 

There is still a great future for concrete as a construction material in the commodity market in 

the 21 st century but it is sure that a great number of niche markets will erode gradually the 

usual commodity market. Concrete in the 21 st century will be a sophisticated mixture of 

minerals and organic polymers which performances will atonish us. 


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9 References 

1. Aïtcin, P.-C., “Concrete the Most Widely Used Construction Material”, Adam Neville 

Symposium on Concrete Technology, Edited by V.M. Malhotra, Second CANMET/ACI 

International Symposium on Concrete Technology, Las Vegas, June 12, 1995, pp. 257 – 

266. 

2. Aïtcin, P.-C., “Cement and Concrete Development from an Environmental Perspective”, 

International Workshop on Concrete Technology for a Sustainable Development in the 

21 st Century, Solvacr, Lofoten Island, Norway, June 1998, to be published by E und FN 

SPON in 1999. 

3. Aïtcin, P.-C., Marciano, E., “The Future of the Cement and Concrete Industry According 

to a Sustainable Development Approach”, Wabe International Symposium on Cement 

and Concrete, Montréal, Canada, May 1998, 10 p. 

4. Aïtcin, P.-C., Baalbaki, M., “Chemical Admixtures. Key Components for Durable 

Concretes, Wabe International Symposium on Cement and Concrete, Montréal, Canada, 

May 1998, 9 p. 

5. Aïtcin, P.-C., Jolicoeur, C., MacGregor, J.G., “Superplasticizers: How They Work and 

Why They Occasionally Don’t”, Concrete International, Vol. 16, No. 5, May 1994, pp. 45 – 

52 (available in Spanish and Portuguese). 

6. Aïtcin, P.-C., “Durable Concrete – Cement Practice and Future Trends”, ACI-SP 144, 

1994, pp. 85 – 104. 

7. Aïtcin, P.-C., “From Gigapascals to Nanometres”, Engineering Foundation Conference, 

Potosi, M.D., USA, August 1988, 28 p. 

8. Aïtcin, P.-C., “Condensed Silica Fume”, Edited by P.-C. Aïtcin, Les Editions des 

l’Université de Sherbrooke, ISBN 2-7622-0016-4, 1983, 52 p. 

9. Khayat, K.H., Aïtcin, P.-C., “Silica Fume in Concrete” – An Overview”, ACI SP-132, Vol. 

2, 1992, pp. 835 – 872. 

10. Aïtcin, P.-C., Neville, A.M., “High-performance Concrete Demystified”, Concrete 

International, Vol. 15, No. 1, Jan. 1993, pp. 21 – 26. 

11. Aïtcin, P.-C., “The Art and The Science of High-performance Concrete”, Mario Collepardi 

Symposium and Advances in Concrete and Science and Technology, Edited P.K. Mehta, 

Rome 1997, pp. 107 – 126 (Translation in French, Portuguese and Italian are available). 

12. Aïtcin, P.-C., “High-performance Concrete”, E and FN SPON, London, U.K., 1998, 591 p. 

(Translation in French and Portuguese in progress). 

13. Aïtcin, P.-C., “The Influence of the Spacing Factor on the Freeze-Thaw Durability of 

HPC”, Sherbrooke 98 Symposium on HPC and RPC, Sherbrooke, August 1998, Vol. 4, 

pp. 419 – 434. 

14. Aïtcin, P.-C., Pigeon, M., Pleau, R., Gagné, R., “Freezing and Thawing Durability of Highperformance 

Concrete”, Sherbrooke 98, Symposium on HPC and RPC, Sherbrooke, 

August 1998, Vol. 4, pp. 383 – 392. 

15. Aïtcin, P.-C., “Non-shrinking Concrete”, CANMET/ACI/JCI, 4 th International Conference 

on Recent Advances in Concrete Technology, Supplementary papers, Tokushima, 

Japan, June 1998, pp. 215 – 226. 


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16. Aïtcin, P.-C., “Autogenous Shrinkage Measurment”, Autoshrink ’98, International 

Workshop on Autogenous Shrinkage of Concrete, Hiroshima, Japan, June 1998, pp. 245 

– 256. 

17. Lessard, M., Dallaire, E., Blouin, D., Aïtcin, P.-C., “High-performance Concrete Speeds 

Reconstruction for McDonald’s”, Concrete International, Vol. 16, No. 9, Sept. 1994, pp. 

47 – 50. 

18. Khayat, K.H., Aïtcin, P.-C., “Use of Self Compacting Concrete in Canada – Present 

Situation and Perspectives”, International Conference on SCC, Kochi, Japan, August 

1998, 10 p. 

19. Richard, P., Cheyrezy, M.H., “Reactive Powder Concrete with High Ductility and 200-800 

MPa Compressive Strength”, ACI SP-144, pp. 507 – 518. 

20. Bonneau, O., Poulin, C., Dugat, J., Richard, P., Aïtcin, P.-C., “Reactive Powder 

Concretes: From Theory to Practice”, Concrete International, Vol. 18, No. 4, pp. 47 – 49. 

21. Bonneau, O., Lachemi, M., Dallaire, E., Dugat, J., Aïtcin, P.-C., “Mechanical Properties 

and Durability of Two Industrial Reactive Powder Concretes”, ACI Materials Journal, Vol. 

94, No. 4, 1997, pp. 286 – 290. 

Table 1. Typical composition of a RPC mixture 

Materials kg/m 3 

Cement 705 

Silica fume 230 

Crush quartz 210 

Sand 1010 

Superplasticizer 17 

Steel fibers 140 

Water 185 

Water/binder 0.26 


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The Art and Science of Durable High-Performance Concrete 

P.-C. Aïtcin 

Synopsis: High-performance concrete can be defined as a low water/binder ratio concrete 

with an optimized aggregate binder ratio to control its dimensional stability. Highperformance 

concrete acts as a true composite material in which coarse aggregates 

contribute to the mechanical properties, therefore, the relationship between elastic modulus 

and strength found in most codes no longer have predictive values for high-performance 

concrete. 

Achieving high performance is not done with a casual approach, all ingredients must be 

carefully selected. It is found that quite often the most difficult thing is to control concrete 

rheology long enough to place a 200-230 mm slump high-performance concrete one hour or 

more after mixing due to compatibility problems between the cement and the 

superplasticizer. 

High-performance concretes are very sensitive to plastic and autogenous shrinkage, so that 

their use demands an immediate water curing. The use of a curing compound which is 

perfectly adequate to cure a concrete having W/B ratio greater than 0.50 is absolutely 

inadequate with high-performance concrete because it does not prevent the development of 

autogenous shrinkage. When a 0.30 high-performance concrete is not water cured before 

setting, it can develop a 200 to 300 microstrains autogenous shrinkage during the first 24 

hours, that will be added to its drying shrinkage. On the contrary when such a highperformance 

concrete is water cured during the first 24 hours, its swells slightly. 

High-performance concrete is definitely more durable than usual concrete. Its increased use 

will be more often linked to its durability than its high strength. Durability will become a key 

issue because we will become more and more concerned with sustainable development. In 

that respect the use of high-performance concrete is more ecological than the use of a usual 

concrete: less cement and less aggregates are needed to sustain a certain load, the life 

cycle of the concrete structure is increased due to the greater intrinsic durability of highperformance 

concrete and, when high-performance concrete will have to be recycled at the 

end of its life, it will be recycled one or two times more than usual concrete because of its 

higher strength. 

Keywords: 

Autogenous shrinkage, durability, fire resistance, heat of hydration, high-performance 

concrete, plastic shrinkage, recycling, sustanable development, water curing, water/binder 

ratio. 

P.-C. Aïtcin, Full Professor, Université de Sherbrooke, Sherbrooke (QC) Canada 


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1.0 INTRODUCTION 

The recent developments in the field of high-performance concrete (HPC) have been a giant 

step in making concrete a high-tech material with enhanced characteristics and durability. 

They have even led to it being a more ecological material in the sense that the component 

admixtures, aggregates, and water are fully used to produce a material with a longer life 

cycle. Be that as it may, we know that concrete will never be a durable material when 

measured against a geological time frame. Any concrete, if we look far enough into the 

future, will end its life cycle as limestone, clay, and silica sand, which are the most stable 

mineral forms of calcium, silica, iron, and aluminium in the earth's environment. Therefore, 

all we can do is to extend the life cycle of this artificial rock as much as possible. 

2.0 WHAT IS HIGH-PERFORMANCE CONCRETE? 

The concrete that was known as high-strength concrete in the late 1970s is now referred to 

as high-performance concrete because it has been found to be much more than simply 

stronger: it displays enhanced performance in such areas as durability and abrasion 

resistance. Although widely used, the expression "high-performance concrete" is very often 

criticised as being too vague, even as having no meaning at all. And what's more, there is 

no simple test for measuring the performance of concrete. 

High-performance concrete can be defined as an engineered concrete in which one or more 

specific characteristics have been enhanced through the selection and proportioning of its 

constituents. This definition is admittedly vague, but it has the advantage of indicating that 

there is no one single type of high-performance concrete, but rather a family of new types of 

high-tech concrete whose properties can be tailored to specific industrial needs. 

While we could devise a slightly more technically rigorous definition of high-performance 

concrete that would still be quite simple, such as it being a concrete with a low w/c (or rather 

a low water/binder ratio), in the 0.30 to 0.40 range. But this would still be inexact because 

high-performance concretes with a water/binder ratio in the 0.20 to 0.30 range have been 

used. 

This definition can be technically refined by stating that a high-performance concrete is a 

concrete in which autogenous shrinkage can develop due to a phenomenon called self 

desiccation when the concrete is not water cured. This technical jargon, however, does little 

to clarify things because very few people are familiar with the terms self-desiccation and 

autogenous shrinkage. 

Since there is no single best definition for the material that is called high-performance 

concrete, I prefer to define it as a low water/binder concrete with an optimised 

aggregate/binder ratio to control its dimensional stability and which receives an adequate 

water curing. 

3.0 WATER/CEMENT OR WATER/BINDER RATIO? 

Both expressions were deliberately used above, either singly or together, to reflect the fact 

that the cementitious component of high-performance concrete can be cement alone or any 

combination of cement with so-called mineral components, such as: slag, fly ash, silica fume, 

metakaolin, rice husk ash, and fillers such as limestone. Ternary systems are increasingly 

used to take advantage of the synergy of some mineral components to improve concrete 

properties in the fresh and hardened states and to make high performance concrete more 

economical. 

In spite of the fact that most high-performance concrete mixtures contain at least one mineral 

component, which should favour the use of the more general expression water/binder ratio, 

the water/binder and water/cement ratios should be used alongside one another. This is 

because most of the mineral components that go into high-performance concrete are not as 

reactive as Portland cement, which means that most of the early properties of high- 


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performance concrete can be linked to its water/cement ratio while its long-term properties 

are rather linked to its water/binder ratio. 

It must be emphasised that the development of high-performance concrete technology has 

taught us what Feret expressed in his original formula giving the compressive strength of a 

concrete mixture: concrete compressive strength is closely related to the compacity of the 

hardened matrix. High-performance concrete has also taught us that the coarse aggregate 

can be the weakest link in concrete when the strength of hydrated cement paste is drastically 

increased by lowering the water/binder ratio. In such cases, concrete failure can start to 

develop within the coarse aggregate itself. As a consequence, there can be exceptions to 

the water/binder ratio law when dealing with high-performance concrete. In some areas, 

decreasing the water/binder ratio below a certain level is not practical because the strength 

of the high-performance concrete will not significantly exceed the aggregate's compressive 

strength. When the compressive strength is limited by the coarse aggregate, the only way to 

get higher strength is to use a stronger aggregate. 

4.0 A COMPOSITE MATERIAL 

Standard concrete can be characterised solely by its compressive strength because that can 

be directly linked to the water/cement ratio, which still is the best indicator of paste porosity. 

Most of the useful mechanical characteristics of concrete can be linked to compressive 

strength with simple empirical formulas. This is the case with elastic modulus and the 

modulus of rupture (flexural strength), because the hydrated cement paste and the transition 

zone around coarse-aggregate particles constitute the weakest links in concrete. The 

aggregate component (especially the coarse aggregate) contributes little to the mechanical 

properties of ordinary concrete. As the strength of the hydrated cement paste increases in 

high-performance concrete, the transition zone between the coarse aggregate and the 

hydrated cement paste practically disappears (Figures 1 and 2). Since there is proper stress 

transfer under these conditions, high-performance concrete behaves like a true composite 

material, as shown by Baalbaki et al. [1]. Stress-strain curves of high-performance concrete 

are influenced by the stress-strain curve of the coarse aggregate, as seen in Figure 3. 

To express this in another way, the elastic modulus (i.e., the rigidity) of a high-performance 

concrete can be tailored to the specific need of the designer simply by selecting the 

appropriate coarse aggregate. Nilsen and Aïtcin [2] have been able to make 100-MPa 

concrete with elastic moduli varying from 27 to 60 MPa. Therefore, the relationships 

between modulus and strength found in most codes have no predictive value with respect to 

high-performance concrete. Recently, however, Baalbaki [3] proposed two simple models 

that take into account the coarse aggregate's elastic characteristics so that the elastic 

modulus of any type of concrete can be calculated. One of the Baalbaki models is presented 

in Figure 4 and the predictive value of his model is presented in Figure 5. 


Cement 

Concrete 

(a) 

Oriented CH 

crystals 

Gap 

(b) 

CH 

(c) 

Figure 1. Microstructure of high water/cement ratio concrete: (a) high porosity and 

heterogeneity of the matrix, (b) orientated crystal of Ca(OH) 2 on aggregate, (c) CH crystal 

5.0 MAKING HIGH -PERFORMANCE CONCRETE 

High-performance concrete can not be made by a casual approach. All ingredients must be 

carefully selected and checked because their individual characteristics significantly affect the 

properties of the final product. What has been said about the coarse aggregate also holds 

true for the cement, the mineral components, the sand, the superplasticizer, and the other 

admixtures. 

Once the materials have been carefully selected, their proportions must also be determined 

meticulously. Particular attention must be paid to water content. Even seemingly 

insignificant volumes of water present in the aggregates or admixtures must be accounted 

for. Increasing the performance of concrete is so difficult and expensive; ruining it is as easy 

as including a little too much water. 


Cement 

Concrete 

Aggregate 

(a) 

C-S-H 

Ca(OH) 2 

(b) 

Figure 2. Microstructure of a high performance concrete: low porosity and homogeneity of 

the matrix 

Compressive strengths of from 50 to 75 MPa can usually be achieved fairly easily with most 

cements. On the other hand, experience has shown that it is more difficult to control the 

rheology long enough to place a 200-mm slump high-performance concrete an hour or more 

after mixing, due to the potential for incompatibility between the cement and superplasticizer. 

6.0 TEMPERATURE RISE 

There is a belief firmly rooted in the concrete community that the heat developed in any 

concrete is a direct function of its cement content. This does not always hold true because 

Portland cement by itself does not develop heat. Since Portland cement develops heat only 

as a result of hydration, it should be rather said that the heat developed in a concrete is a 

direct function of the amount of cement that is hydrating and not a direct function of the total 

amount of cement contained in the concrete. 

The amount of cement hydrating during the first hours can be limited by the amount of 

cement in the mix, such as in mass concrete. But, cement hydration can also be affected by 

the use of a retarder, a high dosage of superplasticizer, or insufficient water to hydrate all the 

cement in the mix. The latter describes the usual situation in high-performance concrete. 


Cement 

Concrete 

45 MPa 

40 

Sandstone Limestone Quartzite 

σ (MPa) 

30 

20 

10 

0 

40 

Rocks 

10 -3 ε 

Sandstone 

σ (MPa) 

30 

20 

Limestone 

10 

Quartzite 

0 

10 -4 

Concretes 

ε 

Figure 3. Stress-strain curves of different rocks and of high-performance concretes made 

with crushed coars aggregates made out of these rocks 

σ1 

σ2 

σ1 

bV1 

aV1 

V2 

aV1 

bV1 

bV1 hydrated cement paste in the 

transition zone 

aV1 hydrated cement paste 

V2 volume of the coarse aggregate 

Figure 4. W. Baalbaki model for concrete 


Cement 

Concrete 

Predicted values (GPa) 

70 

60 

50 

40 

30 

De Larrard & Roy [France, 1992] 

Nilsen [Norway,1992] 

Smeplass [Norway, 1992] 

Alfes [Germany, 1992] 

Giaccio & al. [Argentina, 1994] 

n = 65 

Average deviation = 2.2% 

20 

20 

30 40 50 60 

Measured values (GPa) 

70 

Figure 5. Predictive value of W. Baalbaki model for concrete 

The temperature variation in a concrete due to this development of heat is usually positive 

(temperature rise), but it can be negative (temperature decrease in winter conditions) or 

almost zero (when the amount of heat generated within the concrete equals the heat losses 

through the surface of the concrete and through the forms). 

Consequently, it is not absolutely true that high-performance concrete develops greater heat 

of hydration than plain concrete. In fact, it can be totally false in the case of a particular 

structural element or under specific conditions. This has been confirmed by the work of 

Cook et al. [4], in which three similar columns measuring 1 x 1 x 2.4 m were cast with three 

different concretes with compressive strengths of 30, 80, and 120 MPa. The temperature of 

the concrete was monitored at several places within the columns. The temperature rise at 

the centre of each column, where the temperature was always the highest, was nearly 

identical in the three columns, despite the fact that the cement content varied in the three 

mixes from 355 kg/m 3 for the 30-MPa concrete up to 540 kg/m 3 for the 120-MPa concrete as 

shown in Figure 6. 

Faced with such results, many engineers are surprised that to learn a plain concrete can 

develop as much heat and temperature rise as high-performance concrete, because this 

statement goes against the long-standing myth that the temperature rise in a concrete is 

directly proportional to the cement content. 

Indeed, in this example the 120-MPa concrete evidenced the lowest temperature rise 

because less cement hydrated during the first 30 hours. Less cement had the chance to 

hydrate in the 120-MPa concrete for several reasons: 1) less water was used to make the 

concrete, 2) more superplasticizer was used (it is well-known that naphthalene 

superplasticizers act as retarders when used at high dosages), 3) a retarder was used, and 

4) the hydrates formed in the early stage of hydration in high-performance concrete are so 

compact that hydration kinetics are controlled by diffusion of water through the hydrates 

rather than by chemical processes of dissolution and precipitation, which controls kinetics 

when there is plenty of water in the mixture. 


Cement 

Concrete 

Temperature Rise, °C 

50 

40 

30 

20 

10 

35 MPa column 

90 MPa column 

120 MPa column 

80 

60 

40 

20 

Temperature Rise, °F 

0 

0 

0 24 48 72 96 120 

Age, hours 

Figure 6. Temperature increases at the center of each column 

Moreover, as shown by Lachemi et al. [5], temperature rise is not uniform through the 

structure and the maximum temperature is not reached at the same time. The temperature 

rise depends not only on the amount of heat developed within the concrete, but also on the 

thermodynamic conditions at the boundaries. Of course, the more massive the structural 

element, the higher the temperature rise; the higher the ratio of exposed surface to the 

volume of concrete, the lower the temperature rise. A temperature decrease can be 

observed under severe winter conditions. as shown by Lessard et al. [6] in the reconstruction 

of the sidewalk entrance and by Lessard [7] during the construction of a bridge. 

Using finite-element modelling, Lachemi et al. [8] studied the influence of ambient 

temperature and concrete temperature on the temperature rise in some structural elements 

they monitored during a field experiment. Their main findings were that the highest 

temperature recorded was obtained at the highest ambient temperature when a hot concrete 

mixture was cast, but the more critical conditions for the development of high thermal 

gradients were achieved when a hot concrete was cast on a cold day and then cools. 

7.0 SHRINKAGE 

If water curing is essential to develop the potential strength of cement in plain concrete, early 

water curing is crucial for high-performance concrete in order to avoid the rapid development 

of autogenous shrinkage and to control concrete dimensional stability, as explained below. 

Cement paste hydration is accompanied by an absolute volume contraction that creates a 

very fine pore network within the hydrated cement paste. This network drains water from 

coarse capillaries, which start to dry out. If no external water is added during curing, the 

coarse capillaries empty of water as hydration progresses, just as though the concrete were 

drying. This phenomenon is called self -desiccation. The difference between drying and 

self-desiccation is that when concrete dries water evaporates to the atmosphere, while 

during self-desiccation water stays within concrete (it only migrates towards the very fine 

pores created by the volumetric contraction of the cement paste) [9]. 

In ordinary concrete with w/c greater than 0.50, for example, there is more water than 

required to fully hydrate the cement particles. A large amount of this water is contained in 

well-connected large capillaries so that the menisci created by self-desiccation appear in 

large capillaries where they generate only very low tensile stresses. Therefore the hydrated 

cement paste barely shrinks when self-desiccation develops. 

In the case of high-performance concrete with a w/b of 0.30 or less, significantly more 

cement and less mixing water have been used, so that the pore network is essentially 

composed of fine capillaries. When self-desiccation starts to develop as soon as hydration 

begins, the menisci rapidly develop in small capillaries if no external water is added. Since 

many cement grains start to hydrate simultaneously in high-performance concrete, the drying 


Cement 

Concrete 

of very fine capillaries can generate high tensile stresses that shrink the hydrated cement 

paste. This early shrinkage is referred to as autogenous shrinkage (of course, autogenous 

shrinkage is as large as the drying shrinkage observed in ordinary concrete when these two 

types of drying develop in capillaries of the same diameter). 

But, when there is an external supply of water, the capillaries do not dry out as long as they 

are connected to this external source of water. The result is that no menisci, no tensile 

stress, and no autogenous shrinkage develop within a high-performance concrete that is 

constantly water cured since its setting. 

Thus an essential difference between ordinary concrete and high-performance concrete is 

that ordinary concrete exhibits practically no autogenous shrinkage, whether it is water-cured 

or not, whereas high-performance concrete can experience significant autogenous shrinkage 

if it is not water-cured during the hydration process. Autogenous shrinkage does not develop 

in high-performance concrete if the capillaries are interconnected and have access to 

external water, but, when the continuity of the capillary system is broken, then and only then 

does autogenous shrinkage start to develop within the hydrated cement paste of a highperformance 

concrete, as shown in Figure 7. 

Plastic 

shrinkage 

Self 

dessication 

Drying 

How to cure concrete to minimize its shrinkage 

Curing 

membrane 

or fog 

misting 

Water 

curing or 

fog misting 

Impervious 

film 

Water must be 

prevented from 

evaporating 

Menisci 

formation has 

to be avoided 

Dessication must be 

avoided. Self 

dessication develops 

until hydration stops. 

Figure 7. The most appropriate curing regimes during the course of the hydration reaction 

Drying shrinkage of the hydrated cement paste begins at the surface of the concrete and 

progresses more or less rapidly through concrete, depending on the relative humidity of the 

ambient air and the size of capillaries. Drying in ordinary concrete is therefore rapid because 

the capillary network is well connected and contains large capillaries. Drying shrinkage in 

high-performance concrete is slow because the capillaries are very fine and soon get 

disconnected. 

A major difference between drying shrinkage and autogenous shrinkage is that drying 

shrinkage develops from the surface inwards, while autogenous shrinkage is homogeneous 

and isotropic insofar as the cement particles and water are well dispersed within the 

concrete. 


Cement 

Concrete 

Thus there are considerable differences between ordinary and high-performance concrete 

with respect to their shrinkage behaviour. The cement paste of ordinary concrete exhibits 

rapid drying shrinkage progressing from the surface inwards, whereas high-performance 

concrete cement paste can develop a high isotropic autogenous shrinkage when not water 

cured. This difference in the shrinkage behaviour of the cement paste has very important 

consequences for concrete curing and concrete durability. 

Although the shrinkage of the hydrated cement paste is a very important parameter with 

respect to concrete volumetric stability, it is not the only one. A key parameter is the amount 

of aggregate and, more specifically, the amount of coarse aggregate. Too often it is forgotten 

that the aggregates do more than simply act as fillers in concrete. In fact, they actively 

participate in the volumetric stability of concrete when they restrain the shrinkage of the 

hydrated cement paste: concrete shrinkage is always much lower than that of a cement 

paste having the same w/c. It is common knowledge that concrete shrinkage can be easily 

reduced by increasing the coarse-aggregate content; the shrinkage of the hydrated cement 

paste stays the same, but it is more restrained, so that the volumetric stability of the concrete 

is increased. Restraining the shrinkage of hydrated cement paste by modifying the coarseaggregate 

skeleton may or may not produce a network of microcracks, depending on the 

intensity of the tensile stresses developed by this process with respect to the tensile strength 

of the hydrated cement paste. 

8.0 CURING 

High-performance concrete must be cured quite differently from ordinary concrete because 

of the difference in shrinkage behaviour described above. If HPC is not water-cured 

immediately following placement or finishing, it is prone to develop severe plastic shrinkage 

because it is not protected by bleed water, and later on develops severe autogenous 

shrinkage due to its rapid hydration. While curing membranes provide adequate protection 

for ordinary concrete (which is insensitive to autogenous shrinkage), they can only help 

prevent the development of plastic shrinkage in high-performance concrete but they have no 

value in inhibiting autogenous shrinkage. 

The critical curing period for any HPC runs from placement or finishing up to 2 or 3 days 

later, and the most critical period is usually from 12 to 36 hours, as shown in Figure 7. In 

fact, the short time during which efficient water curing must be applied to HPC can be 

considered a significant advantage over ordinary concrete. Those who specify and use HPC 

must be aware of the dramatic consequences of missing early water curing. Initiating water 

curing after 24 hours is too late because, most of the time, a great deal of autogenous 

shrinkage has already occurred and, by this time, the microstructure is already so compact 

that external water has little chance of penetrating very deep into the concrete. 

Water pounding or fogging are the best ways to cure HPC; one of these two methods must 

be applied as soon as possible, immediately following placement or finishing. An 

evaporation retarder can be applied temporarily to prevent the development of plastic. If, for 

any reason, water pounding or fogging cannot be implemented for 7 days, then the concrete 

surface should be covered with wet burlap (hessian) or preferably a prewetted geotextile. 

The burlap or the geotextile must be kept constantly wet with a soaker hose and protected 

from drying by a polyethylene sheet in order to ensure that at no time during the curing 

period is the concrete allowed to dry and experience any autogenous shrinkage. 

Moreover it is observed that when any concrete is water cured during setting it does not 

shrink but rather swell. Figure 8 illustrate the effect of early water curing on the volumetric 

change of concrete. The water curing can be stopped after 7 days because most of the 

cement at the surface of concrete has hydrated and any further water curing has little effect 

on the development of shrinkage. After 7 days of water curing, HPC experiences slow drying 

shrinkage due to the compactness of its microstructure, and autogenous shrinkage has 

already dried out the coarse capillaries pores. Even then, theoretically the best thing to do is 

to paint HPC or to use a sealing agent so that the last remaining water can be retained to 


Cement 

Concrete 

contribute to hydration. There is no real advantage to painting or sealing a very porous 

concrete because it is impossible to obtain an absolutely impermeable coating; painting or 

sealing HPC, however, can be easy and effective. Figure 9 illustrate the curing conditions 

that will result or not into the development of autogenous shrinkage. 

Swelling 

(× 10 -6 ) 

Shrinkage 

(× 10 -6 ) 

100 

0 

-100 

-200 

-300 

-400 

Water 

curing 

7 

Sealed after 7 days 

Age (days) 28 

Air drying 

after 7 days 

2 

No curing 

1 

3 

Figure 8. Length changes according to different curing regimes for the 0.35 W/C concrete 

Hydration 

Volumetric 

contraction 

Self 

desiccation 

Menisci 

Autogenous 

shrinkage 

No 

External 

supply of 

water 

No 

No 

autogenous 

shrinkage 

Yes 

Pores 

and capillaries 

connected? 

Yes 

No 

menisci 

Figure 9. Influence of curing conditions on the occurence of autogenous shrinkage 

Partial replacement of coarse aggregate by an equivalent volume of saturated lightweight 

aggregate has been used to counteract autogenous shrinkage internally. The saturated 

lightweight aggregate particles act as small water reservoirs throughout the mass of 

concrete; they can be emptied into the very fine pores created by hydration reaction. 

Therefore, the water in the lightweight aggregate particles is drained along with that 

contained in the fine capillaries of the HPC. The menisci developed within the cement paste 

are not as small, which means lower tensile stress and less autogenous shrinkage. 

But, it is well known that concrete is never cured properly in the field, if spite of the fact that it 

is always written in the specifications that contractor has to cure concrete. Contractors are 

not curing concrete for a very simple reason: they are not specificallypaid for, therefore, 

concrete curingis always perceived by them as an unprofitable activity or even a source of 

expense and therefore a waste of time. But, when contractors are specifically paid to water 

cure concrete they do it as they do it for any other item that is paid. Since three years now 

the City of Montreal and the Department of Transportation of Quebec are requesting unit 


Cement 

Concrete 

prices for each item directly related to an early water curing. Since the initiation of this new 

policy on the early water curing of concrete, it is amazing to see how zealous contractors are 

in the matter of water curing. For them water curing is now seen as a source of profit. Form 

the first experiences in that matter it has been found that the cost of an early water curing is 

about one tehth of one percent. A very modest price when considering the improved 

durability of the concrete structures that are built like that. 

Therefore the best way to be sure that high-performance concretes are properly and 

efficiently cured in the field is to specifically pay contractors to cure concrete [10]. 

9.0 DURABILITY 

9.1 General matters 

The durability of a material in a particular environment can only be established over time, so 

it is difficult to precisely predict the longevity of high-performance concrete because we do 

not have a track record for HPC exposed to very harsh environments for more than 5 to 10 

years, except perhaps for some North Sea offshore platforms. It must be remembered that 

the first uses of high strength concrete in the late sixties and early seventies were indoor 

applications, mainly in columns in high-rise buildings, which is not a particularly severe 

environment. Outdoor applications of high-performance concrete only date from the late 

eighties and early nineties, which means that not enough time has gone by to properly 

assess the real service life of any high-performance concrete structures under outdoor 

conditions. 

Based on years of experience with ordinary concrete, we can safely assume that high 

performance concrete is more durable than ordinary concrete. Indeed, the experience 

gained with ordinary concrete has taught us that concrete durability is mainly governed by 

concrete permeability and the harshness of the environment [11]. 

It is easy to assess the harshness of any environment with respect to high-performance 

concrete because hydrated cement paste is essentially a porous material that contains some 

freezable water. Assessment involves simply examining how the environment affects each 

of these characteristics. 

On the other hand, it is not always simple to assess how easily aggressive agents will 

penetrate concrete. For example, water flow through a 0.70 w/c concrete is easy to 

measure, but water flow almost stops in a 0.40 w/c concrete, regardless of the thickness of 

the sample and the amount of pressure applied. The gas permeability is also difficult to 

measure. Sample preparation, particularly drying, significantly influences gas permeability. 

Therefore, the critical question remains how to appropriately assess the permeability of a 

concrete with a low w/b and a very compact microstructure. 

Despite all the criticism levelled at it, the so-called "Rapid chloride-ion permeability test" 

(AASHTO T-277) gives a fair idea of the interconnectivity of the fine pores in concrete that 

are too fine to allow water flow. Experience has revealed good correlation between the water 

permeability and rapid chloride ion permeability for concrete specimens with a w/c greater 

than 0.40. Chloride-ion permeability is expressed in coulombs, which corresponds to the total 

amount of electrical charge that passes during the 6-hour test through the concrete sample 

when subjected to a potential difference of 50 volts. 

When the rapid chloride-ion permeability test is performed on concrete samples with lower 

w/c, the number of coulombs passing through the sample decreases. It is easy to achieve a 

chloride-ion permeability of less than 1000 coulombs for a high performance concrete 

containing about 10% silica fume and having a w/b around 0.30. The only other way to 

achieve this would be with latex-modified concrete, which would be much more costly. Much 

lower chloride-ion permeability values can be achieved if the w/b is reduced below 0.25. 

Values as low as 150 coulombs have been reported, far lower than the 5000 to 6000 

coulombs reported for ordinary concrete [12]. 


Cement 

Concrete 

The rapid chloride-ion test also reveals that the connectivity of the pore system decreases 

drastically as the w/b decreases, making the migration of aggressive ions or gas more 

difficult in high-performance concrete than in its plain counterpart. The author believes that 

this is the best indication that the service life of high-performance concrete should exceed 

that of ordinary concrete in the same environment. It is difficult to determine the number of 

years by which the service life would be extended because the predictive models developed 

for ordinary concrete cannot be readily extrapolated to include high-performance concrete. 

However, it can be said that some high-performance concrete structures will outlast the 

average life span of a human being in developed countries. 

9.2 Durability in a marine environment 

9.2.1 Nature of the aggressive action 

Sea water by itself is not a particularly harsh environment for plain concrete, but a marine 

environment can be very harmful to reinforced concrete due to the multiplicity of aggressions 

that it can face [13]. In a marine environment, a concrete structure is essentially submitted to 

four types of aggressive factors: 

• chemical factors related to the presence of various ions dissolved in the sea water or 

transported in the wet air; 

• geometrical factors related to the fluctuation of the sea level (tides, storms, etc.); 

• physical factors such as freezing and thawing, wetting and drying, etc.; 

• Mechanical factors such as the kinetic action of the waves, the erosion caused by sand in 

suspension in the sea water, floating debris and even floating ice in northern seas. 

It is the combination of these different factors that can be harmful to reinforced concrete 

structures. In the following, we will review very briefly the nature of each attack in order to 

show how high performance concrete is the best concrete fitted to resist not only each of 

these particular factors, but also their combined action. 

9.2.2 Chemical attack on concrete 

Sea water is not particularly harmful to plain concrete. Several submerged plain concrete 

blocks and structures exposed for nearly 100 years in different marine environments are still 

in relatively good condition. The only chemical limitation usually recommended for a cement 

to be used in a marine environment is related to its C3A content, which should not be greater 

than 8%. 

Figure 10 represents the different successive altered zones found in a concrete exposed to 

sea water for several years: carbonation, formation of brucite, of monochloroaluminate, and 

sulfatic attack with formation of gypsum, ettringite or even thaumasite . Each of these 

chemical mechanisms is well known and explained in specialized books [13, 14, 15]. 

Zone 1: Carbonated layer 

Zone 2: Magnesia attack 

Zone 3: Sulfatic attack with 

formation of gypsum 

Zone 4: Sulfatic attack 

Sea 

water 

Zone 5: 

leaching 


Cement 

Concrete 

Figure 10. Schematic representation of the different altered layers found in a concrete 

marine structure 

Sea water is very harmful to reinforced concrete. Once chlorine ions are reach the 

reinforcing steel level, resulting in a rapid spalling of the covercrete, it is easier for chlorine 

ions to reach the second level of rebars, and so on. The only way to avoid, or to retard as 

long as possible, the corrosion of the rebars by chlorine ions is: 

• to specify a very compact and impervious concrete, and place and CURE it correctly, 

and; 

• to increase the concrete cover. 

The development of all these mechanisms of aggression is closely related to the facility with 

which aggressive ions can penetrate concrete, therefore it is obvious that a very dense and 

impervious matrix, like the one found in high performance concrete, constitutes the best 

protection that can be presently offered against a marine environment. High performance 

concrete has been used very successfully for more than 20 years to build offshore platforms, 

and more recently to build two major bridges for which the owner had requested a 100-year 

life cycle: the Confederation bridge in Canada and the Tago bridge in Lisboa, Portugal. It is 

interesting to point out that these two bridges have been built in a BOOT mode (Build, Own, 

Operate and Transfer) by consortia of contractors that will have to maintain these two 

bridges during the entire concession time. 

In that respect, it is interesting to note that in the case of these two bridges, the concrete 

cover has been extended to 75 mm to meet the 100-year life cycle requirement. 

It is also very important to point out that it is not sufficient to specify a Type V cement or a 

slag cement to obtain a concrete that will resist to a harsh marine environment. The curing 

of this concrete is as important as the selection of an appropriate cementitious system. The 

rapid deterioration of the precast elements of the Dubaï causeway in the Arabian peninsula is 

a good example of what must not be done. 

9.2.3 Physical attack 

There is still controversy about the necessity of entraining air in high performance concrete to 

make it freeze-thaw resistant. In Canada, any exposed high performance concrete must be 

air entrained, which is the case of the concrete of the Confederation bridge. In Norway, high 

performance concrete can contain a small amount of air, but more to facilitate its placing and 

finishing rather than to improve its freeze-thaw resistance. As freeze-thaw resistance of 

marine structures is not a crucial issue in New Zealand, it is not my intention to insist more 

on this subject which I covered in detail in the original paper from which this one is derived 

[16]. 

9.2.4 Mechanical attack 

In this case also the compactness and the high resistance of the matrix of a high 

performance concrete offers a good protection to the abrasive action of the sand of the 

debris, or even from floating ice. In the case of the Confederation bridge, the concrete used 

to build the conical part of the piles that deflects the ice loads in the tidal zone was a 90 MPa 

air-entrained high performance concrete. This concrete is thought to be able to resist the 

tidal freezing and thawing cycles in winter and the abrasive action of the floating ice which is 

particularly severe in the Northumberland Straight, due to the presence of changing currents 

associated with the tides and winds. 

9.2.5 Conclusion 

It is obvious that high performance concrete is a material of choice fitted to resist the harsh 

environment that is found in coastal areas particularly well. It would be a great mistake to 


Cement 

Concrete 

take advantage of the improved durability of the concrete cover to reduce its thickness, on 

the other hand it would be wise to increase it during the next millenium if we want to start to 

implement an efficient sustainable development policy in civil engineering. Having been 

raised on the shores of the Atlantic Ocean in Biarritz, France, I know how aggressive marine 

environments can be for a reinforced concrete structure built with a poor concrete, that is 

badly cured. I also know how durable are the German blockhaus built at the end of the last 

World War. 

10.0 THE FIRE RESISTANCE OF HPC 

For many years, the fire resistance of HPC has been a controversial subject, some reports 

saying that HPC performed as well as usual concrete, others the reverse [17-26]. Following 

the first fire that occured in a HPC structure, the Chunnel fire [27-28], and from different 

studies in progress in several countries it is clear that the fire resistance of HPC does not 

seem to be as good as that of usual concrete, but that it is not as bad as some alarming 

reports have presented it. As is the case for any concrete, HPC is one of the safest 

construction materials as far as fire resistance is concerned. 

As constructive details, as well as material resistance by itself, could influence greatly the fire 

resistance of a structural element, it is presently impossible to give very simple rules that 

should govern the design of HPC structures that could be exposed to a more or less severe 

fire. Presently, some models have been developed that can be used to forecast the 

structural consequence of a fire on the safety of a HPC structure. Moreover several 

promising avenues are presently being investigated to improve the fire resistance of HPC 

itself. 

Instead of reviewing in detail the controversial literature on the fire resistance of HPC three 

brief presentations on the actual fire resistance of HPC and usual concrete will be done. The 

first one will deal with the violent fire that occured in the Chunnel, based on a report by J.-M. 

Demourieux [28], the second one will deal with the big conflagration that occured in 

Düsseldorf airport and the third one will present the latest fndings of the Brite-Euram 

HITECO BE-1158 research project [29]. 

10.1 The Chunnel fire 

The fire of a truck in the Chunnel did not suprise the safety department of the Chunnel 

administration. The occurence of such a fire had been forecast because each day a truck 

burns in France and another in England [27]. If a fire was to happen in the Chunnel, the 

engine-man of the train was asked to speed up to get the train out of the Chunnel as soon as 

possible. 

It had also been forecast that some hydraulic jacks used to support the access ramp used by 

the trucks to get on the railway platform could be loosened and create a risk of derailment for 

the train. In such a case, the driver could be asked to stop the train and tighten the hydraulic 

jack. But, what had not been forecast was that the two incidents could happen 

simultaneously so that the engine-man could receive two conflicting orders at the same time 

for which no priorization had been included in the safety procedures. 

Facing two contradictory orders the engine-man decided on November 11, 1996 to stop the 

train at 18 km from the French entrance, fortunately in the driest zone of the Chunnel from a 

water seepage point of view. In this area, the blue chalk through which the Chunnel was 

excavated was the most impervious of all the rock formations. When the moles were 

excavating this area they registered their all time speed record and the workers asked for 

some water to be pulverized in the excavated rock to get rid of the fine dry chalk dust 

generated by the moles. 

It is difficult to imagine the damage that could have occured to the Chunnel if the fire had 

taken place a few kilometers further in a fault area where it would not have been possible to 

take advantage of the imperviousness of the chalk layer. 


Cement 

Concrete 

The fire was particularly violent as far as its maximum temperature and length are 

concerned. The maximum temperature that was reached was in the order of 700 to 1000 °C 

and the total duration of the fire was about 10 hours. The concrete lining in the area of the 

fire was composed of precast concrete elements having a design strength of 70 to 80 MPa 

HPC having a water/binder ratio of 0.32 [28]. 

In the most intense zone, the concrete lining was severely damaged and would not have 

been able to counteract the hydrostatic pressure for which it has been designed. An 

extensive survey done after the fire on the unaffected zone has shown that the in-place 

concrete had an average compressive strength comprised between 70 and 80 MPa, a 

modulus of rupture comprised between 7 and 8 MPa, and an elastic modulus comprised 

between 37 and 44 GPa. 

As far as the damaged zone is concerned, it is 480 m long, involving about 300 lining rings 

400 mm thick. It could be divided into six parts that displayed different degrees of damage. 

In the two farthest zones from the centre of the fire, which were 80 and 100 m long on both 

sides, the concrete lining had been only slightly damaged and no steel reinforcement was 

apparent. 

In the next two adjacent zones, which were 70 m long, the concrete lining was more severely 

damaged over a thickness comprised between 50 to 100 mm. In this zone, the first 

reinforcing level can be seen here and there. The more severely damaged section was 

observed on the upper part of the lining. 

The central zone where the fire was the most intense could be divided into two parts, a 50 m 

long area very severely damaged and another one 90 m long slightly less damaged. In the 

most severely damaged zone the concrete lining was completely destroyed all over its 

thickness (400 mm), more specifically in the 3H00 to 8H00 zones. In the less damaged part, 

the residual concrete had a thickness comprised between 50 and 200 mm except in the 

lowest part where its thickness was still 350 mm. In the less damaged zone, the concrete 

lining had a residual thickness of about 200 mm in the upper part and of about 350 mm in the 

lowest part. 

It was observed that in this zone the reinforcing steel arrangement played a very important 

role because the concrete, which was prevented from falling down by the reinforcing bars, 

protected the subjacent concrete. Therefore in such zones, the steel reinforcing bars played 

a key role in protecting the subjacent concrete. In many places in the central zone, the 

reinforcing steel was highly deformed due to the severity of the fire. Under the effect of the 

heat, the restrained dilatation of the lining generated large transversal and horizontal 

stresses in the damaged concrete so that numerous 45° fissures could be observed at the 

edges of the precast elements. Concrete was litterally hollowed out in at the centre of the 

reinforcing mesh over a more or less thick depth depending on its location from the centre of 

the fire. 

Concrete spalled in small pieces having an average thickness of about 10 mm. Some of 

theses pieces were no bigger than a coin. The concrete lining was always more damaged in 

its upper zone than at its bottom end on the track. 

In the two less damaged zones, concrete had spalled over greater surfaces in some places. 

It was possible to see that it happened frequently where nylon spacers had been used during 

precasting to correctly place the reinforcing steel. Most probably the pressure of the gas 

generated during the burning of the nylon spacers was responsible for this spalling. 

All the tests done in the non-damaged part of the lining in the fire zone have shown that the 

residual concrete remaining in the lining was almost intact in the upper part as well as in the 

lower part of the section. SEM observations have shown that the residual concrete had not 

been altered significantly, no permanent strains could be seen even at the surface of the 

residual concrete. In all cases the residual concrete was altered on a very thin layer, and 


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according to petrographical examinations, the maximum temperature reached by the 

concrete in that area was lower than 700 °C. 

The observations and test results conducted on the concrete of the track and at the lower 

part of the lining resulted in the decision to keep them in place during the reconstruction. 

Based on all the observations done and the results obtained, it was decided to rebuild the 

lining using a wet shotcrete after a careful cleaning of the damaged concrete. 

10.2 The Düsseldorf Airport Fire 

On April 16th, 1996 a devastating conflagration broke out at the Düsseldorf Airport, killing 

17 people by smoke inhalation and injuring several hundred. The fire was attributable to 

improper use of combustible insulating material and the plastic cover of the cables laid in the 

hollow ceiling space [29]. 

The fire was triggered by some welding work which had been performed, and developed 

unnoticed for a long time so that the smoke had time to spread into all parts of the building in 

the hollow ceiling and through the ventilation system. 

The highest estimated temperature to which the concrete ceiling was exposed has been 

estimated at 1000 °C. At such a temperature the 25 MPa concrete spalled, but from a 

structural point of view the building elements were not damaged. Moreover, it was found that 

harmful substances such as dioxins did not penetrate into the concrete so that the concrete 

structure was still in serviceable condition. 

Since owners and operators intended to erect an extended and modernized airport facility, 

they decided to demolish the burnt concrete structure. 

10.3 Spalling of concrete under fire conditions 

It is difficult to make a direct comparison between these two major conflagrations but it can 

be pointed out that in both cases, very fortuituously, the initial cause of the fire was the 

burning of some polystyrene, that the maximum temperature reached has been estimated at 

1000 °C, and that the high-performance concrete of the Chunnel and the usual concrete of 

Düsseldorf Airport both spalled. 

Of course, the thickness of the spalling is a function of the maximum temperature that is 

reached during the fire and of the duration of exposure to this temperature, as it has been 

seen in the various zones of the fire area in the Chunnel. 

According to J.-M. Demourieux, a standard ISO 834 fire would have to cause a 30 mm thick 

spalling in the lining of the Chunnel. 

10.4 The Brite-Euram HITECO BE-1158 Research Project 

The preliminary conslusions of this research project, financed by the European Community, 

were presented on March 9th at a meeting of the French Civil Engineering Association 

meeting. All the tests were done in Finland at the V.T.T. Laboratories, one of the best 

equipped European laboratories for fire studies [30]. 

The conclusion of this presentation is: the experimental study undertaken on a 60 MPa highperformance 

concrete without silica fume and a 90 MPa high-performance concrete with 

silica fume have shown an excellent fire resistance, except for a small column that was 

heavily loaded. 

In actual structures more favorable conditions are found : 

• the columns have a bigger size than the one tested; 

• the loading is the service loading and not the maximum loading. 


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The FIREXPO software can be used to predict the thermomechanical behavior of any 

structural element. 

11.0 THE FUTURE 

High-performance concrete is not a passing fad. It is here to stay, not only because of its 

high strength, but also because of its durability. For example, an outdoor concrete parking 

garage can be built with 20-MPa concrete under current codes. Its columns and slabs would 

be somewhat bigger than if an 80-MPa concrete had been used. But the life cycle of the 

garage will be very short in an environment as severe as that in Eastern Canada or in a sea 

coastal area, because 20-MPa concrete cannot adequately protect the reinforcing steel 

against corrosion from chlorine ions. The service life would be somewhat longer in a less 

severe environment, but would still be short due to carbonation. 

Therefore, at the dawn of the twenty-first century, it is not particularly difficult to predict that 

the use of high-performance concrete will increase in order to extend the service life of 

concrete structures exposed to severe environments [11]. The durability of a concrete 

structure depends on several factors, one of which is the durability of the concrete itself. As 

the durability of concrete is essentially linked to its permeability, high-performance concrete, 

with its compact microstructure and very low permeability, should obviously be more durable 

than ordinary concrete. It must be emphasised, however, that good concreting practice, 

including good curing, are essential to creating a durable structure. It would be a pity if 

improper practice and poor curing resulted in a structure with impervious concrete in 

between the cracks. 

We still do not know how to make high-performance concrete with low permeability but 

without the high strength. Therefore, designers have to learn to take advantage of the extra 

strength provided by low w/b concrete. One day, we may be able to make durable concrete 

of lower strength. 

Another reason that will lead to a greater use of high-performance concrete in the 21 st 

century is society's greater interest in ecological concerns [31]. Many others share my 

opinion that we cannot continue the wasteful use of our natural resources and energy that 

characterised the 19 th and 20 th centuries. High-performance concrete is more ecological 

than ordinary concrete. High-performance concrete, with its more compact microstructure, 

provides the sought property with less material. 

Moreover, the 21 st century will be the century of recycling. Recycling paper, cardboard, 

aluminium, steel, and even plastic has already become quite common in many countries. 

The trend towards recycling has already reached the concrete field. We must remember, 

however, that recycling a material leads to a product of lower quality. This is because the 

original purity of the initial materials are lost when different additives are combined in order to 

enhance the final performance of the product. Concrete production has not reached the 

same degree of sophistication as rubber manufacturing, although concrete is becoming more 

complex every day. 

Another new development is reactive-powder concrete, which can have a compressive 

strength of about 200 MPa in an unconfined state and as high as 350 MPa when confined in 

thin steel tubes. Moreover, the addition of steel fibres to reactive-powder concrete produces 

a material with modulus of rupture as high as 25 to 35 MPa in addition to high compressive 

strength [32, 33]. Reactive-powder concrete will pose no threat to the high-performance 

concrete market for years to come. Once we are able to produce and use reactive-powder 

concrete and to design with it at an industrial scale, high-performance concrete will have 

already won over a significant part of the market of ordinary concrete. 

Now that 1000-MPa Portland cement-based materials can be made, only a pessimist could 

refuse to see the future of high-performance concrete. 


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12.0 ACKNOWLEDGEMENT 

This presentation was made possible due to the support of the Canadian Centres of 

Excellence Research Program on High-Performance Concrete. 

The following text was originally presented in a symposium held in tribute to Mario Collepardi 

in Rome in October 1997. It was edited by Leslie Strubble and included as chapter 8 — 

High-Performance Concrete in the book Materials Science of Concrete V published by the 

American Ceramic Society. This present version has been updated. Freeze-thaw resistance 

is not presented and is replaced by Fire Resistance. 

13.0 REFERENCES 

1. Baalbaki, W., Benmokrane, B., Chaallal, O., and Aïtcin, P.-C., "Influence of Coarse 

Aggregate on Elastic Properties of High-Performance Concrete," ACI Mater. J. 88(5) pp. 

499-503 (1991). 

2. Nilsen, A.U., and Aïtcin, P.-C., "Properties of High-Strength Concrete Containing Light- 

Normal- and Heavyweight Aggregate," Cem. Concr. Aggregates 14(1) 8-12 (1992). 

3. Baalbaki, W., PhD. Thesis, Université de Sherbrooke (1997). 

4. Cook, W.D., Miao, B., Aïtcin, P.-C., and Mitchell, D., "Thermal Stress in Large High- 

Strength Concrete Columns,"ACI Mater. J. 89(1) 61-66 (1992). 

5. Lachemi, M., Lessard, M., and Aïtcin, P.-C., "Early-Age Temperature Development in a 

High-Performance Concrete Viaduct," Am. Concr Inst. SP-167 (High Strength concrete: 

An International Perspective, edited by J.A. Bickley) 149 - 174 (1996). 

6. Lessard, M., Dallaire, É, Blouin, D., and Aïtcin, P.-C., "High-Performance Concrete 

Speeds Reconstruction of McDonald's," Concr. Int. 16(9) 47-50 (1994). 

7. Lessard, M., unpublished results, 1995. 

8. Lachemi, M., and Aïtcin, P.-C., "Influence of Ambient and Fresh Concrete Temperature 

on the Maximum Temperature and Thermal Gradient in a High-Performance Concrete 

Structure," ACI Mater. J. 94(2) 102-110 (1997). 

9. Aïtcin, P.-C., Neville, A.M., and Acker, P., "Integrated View of Shrinkage Deformation," 

Concr. Int. 19(9) 35-41 (1997). 

10. Standard Specification for High-Performance Concrete HPC (3VM-20), 19 p. (1998). 

11. Aïtcin, P.-C., "Durable Concrete-Current Practice and Future Trends," Am. Concr. Inst. 

SP-144 (Concrete Technology: Past, Present, and Future, edited by P.K. Mehta) 83-104 

(1994). 

12. Gagné, R., Lamothe, P., Aïtcin, P.-C., "Chloride-ion Permeability of Different Concretes", 

6th Intl Conf. on Durability of Building Materials Components, Omiya, Japan, 1171-1180 

(1993). 

13. Duval, R., Hornain, H., "La durabilité du béton vis-à-vis des eaix aggressoves", La 

Durabilité des Bétons sous la direction de Baron, J., Ollivier, J.-P., Presses de l'École 

Nationale des Ponts et Chaussées, Paris, ISBN 2-85978-184.6, 1992, pp. 376-385. 

14. Neville, A.M., "Properties of Concrete", 4th Edition, Longman, ISBN 0-582-23070-5, 

1995, pp. 514-517. 

15. Mehta, P.K., Monteiro, P., "Concrete - Microstructure, Properties, and Materials", 

McGraw Hill, ISBN 0-07-041344-4, 1993, pp. 167-176. 

16. Aïtcin, P.-C., "The Art and Science of High-Performance Concrete", American Ceramic 

Society, Cements Research Progress, 1996, Edited by L. Struble, ISBN 1-57498-081-5, 

1998, pp. 239-251 


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17. Felicetti, R., Gambavora, P.G., Rosati, G.P., Corsi, F. and Giannuzzi, G., "Residual 

Strength of HSC Structural Elements Damaged by Hydrocarbon Fire or Impact Loading" 

in Utilization of High Strength High Performance Concrete, Paris, ISBN 2 85978 2583, 

579-588 (1996). 

18. Diederich, U., Spitzner, J., Sandvik, M., Kepp, B. and Gillen, M., "The Behavior of High- 

Strength Lightweight Aggregate Concrete at Elevated Temperature" in High Strength 

Concrete, ISBN 82 91341-00-1, 1046-1053 (1993). 

19. Jensen, J.J., Opheim, E. and Aune, R.B., "Residual Strength of HSC Structural 

Elements Damaged by Hydrocarbon Fire on Impact Loading" in Utilization of High 

Strength / High Performance Concrete, Paris, ISBN 2-85978-2583, 589-598 (1996). 

20. Noumowe, A.N., Clastres, P., Delvicki, G. and Costaz, J.-L., "Thermal Stresses and 

Water Vapour Pressure of High-Performance Concrete at High Temperature" in 

Utilization of High Strength / High Performance Concrete, Paris, ISBN 2-85978-2583, 

561-570 (1996). 

21. Sanjayan, G. and Stocks, L.J., "Spalling of High-Strength Silica Fume Concrete in Fire", 

ACI Mater. J. 90(2), March-April, 170-173 (1993). 

22. Chan, S.Y.N., Peng. G.F. and Chan, J.K.W., "Comparison Between High Strength 

Concrete and Normal Strength Concrete Subjected to High Temperature" Mat. Struct. 29 

616-619 (1996). 

23. Khoylou, N. and England, G.L., "The Effect of Elevated Temperature on the Moisture 

Migration and Spalling Behaviour of High Strength and Normal Concretes, ACI SP-167, 

263-268 (1996). 

24. Breitenbücker, R., "High Strength Concrete C105 with Increased Fire Resistance Due to 

Propylene Fibers" in Utilization of High Strength / High Performance Concrete, Paris, 

ISBN 2-85978-2583, 571-578 (1996). 

25. Jensen, B.C., Aarup, B., "Fire Resistance of Fibre Reinforced Silica Fume Based 

Concrete" in Utilization of High Strength / High Performance Concrete, Paris, ISBN 2- 

8597802583, 551-560 (1996). 

26. Phan, L.T., "Fire Performance of High-Strength Concrete: A Report of the State-of-the- 

Art", Res. Rep. NISTIR 5934, NIST, Gaithersburg, Maryland, U.S.A. (1997) 

27. Acker, P., Ulm, F.-J., Levy, M., "Fire in the Channel Tunnel - Mechanical Analysis of the 

Concrete Damage", Concrete Canada - Technology Transfer Day, October 1, Toronto, 

Ontario, 17 p. (1997). 

28. Demorieux, J.-M., "Le comportement des BHP à hautes températures — État de la 

question et résultats expérimentaux", École Française du Béton et le Projet National 

BHP 2000, November 24 and 25, Cachan, France, 27 p. (1998) 

29. Neck, U., Personal communication, March 1999. 

30. Cheyrezy, M., Beloul, M., "Comportement des BHP au feu", French Civil Engineering 

Association Meeting, 7 p., March 9, 1999. 

31. Kreijger, P.C., "Ecological properties of Building Materials," Mat. Struct. 20 248-254 

(1987). 

32. Richard, P., and Cheyrezy, M., "Reactive Powder Concrete With High Ductility and 200- 

800 MPa Compressive Strength," Am. Concr. Inst. SP-144 (Concrete Technology: Past, 

Present, and Future, edited by P.K. Mehta) 507-518 (1993). 

33. Bonneau, O., Poulin, C., Dugat, J., Richard, P., and Aïtcin, P.-C., "Reactive Powder 

Concrete From Theory to Practice," Concr. Int. 18 47-49 (1996). 

(1996).

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