on the stabilization of cohesive soil by means of cement and ...

O
Qu
h LIBRARY
^AL AIRCRAFT FSTADN. REPORT 79
—^—^_______________________________________.-
ADVISORY GROUP FOR AERONAUTICAL
RESEARCH AND DEVELOPMENT
REPORT 79
ON THE STABILIZATION OF COHESIVE SOIL
BY MEANS OF CEMENT AND BITUMINOUS
BINDING AGENTS
by
RUDOLF KLEIN
AUGUST 1956
NORTH ATLANTIC TREATY ORGANIZATION
PALAIS DE CHAILLOT. PARIS 16
A

NORTH ATLANTIC TREATY ORGANIZATION
ADVISORY GROUP FOR AERONAUTICAL RESEARCH AND DEVELOPMENT
ON THE STABILIZATION OP COHESIVE SOIL BY MEANS OF
CEMENT AND BITUMINOUS BINDING AGENTS
by
Rudolf Klein
REPORT 79
This Report was presented at the Ninth Wind Tunnel and Model Testing Panel, held from
27th to 31st August, 1956, in Brussels, Belgium.

SUMMARY
This Report defines the purpose of soil stabilization and explains the
basic principles involved. A brief historical review is given of work on
soil stabilization carried out mainly in Germany, in which two kinds of
binding agents were used, viz., bituminous materials and cements. It is
shown that soils - at least those involved in the experiments described -
have optimal ranges of stabilization which lie within relatively small
limits and the conclusion is drawn that for good results machinery for
soil stabilization should be specially designed.
SOMMAIRE
Au cours de ce rapport, 1'auteur definit le but de la stabilisation au
sol et en expose les principes de base. II retrace un bref apercu
hlstorique des travaux de recherche sur la stabilisation au sol men4s
prindpalement en Allemagne, travaux pour lesquels deux sortes d'agents
agglutinateurs furent utilises: materiaux bitumineux et ciment. II
demontre que les sols, d& raoins ceux dont il s'agit dans les experiences
dlcrites, presentent des etendues de stabilisation optima aux limites
relativement restrdntes, et il conclut que, pour obtenir de bons
re'sultats, on devrait mettre au point des machines spedalement destinees
a la stabilisation au sol.
624.138
3g3b2c
ii

CONTENTS
Page
SUMMARY i i
LIST OF FIGURES iv
1. PURPOSE OF SOIL STABILIZATION 1
2. HISTORICAL REVIEW 1
3. BASIC PRINCIPLES OF SOIL STABILIZATION 3
4. PROCESS OF SOIL STABILIZATION 6
4.1 Preliminary Work 6
4.2 Mixture 7
4.3 Control of Water Conservation 7
4.4 Consolidation 7
5. CONCLUSIONS
REFERENCES 10
TABLE I : Mixture ratio and granulometric composition of
soils A, B, C, D, E and F 12
TABLE II Characteristics of Base Soils 12
FIGURES 13
ill

LIST OF FIGURES
Pig.l Distribution of airfields on which use was made of soil stabilisation
by Germany during the period 1936 - 1945 13
Fig.2 Graphical representation of grain distribution of soils A - F 14
Pig.3 Position of soils in the coordinate system 15
Fig.4 Specific gravity of various mixtures in relation to water content
(The underlined percentages indicate the water content selected) 16
Pig.5(a) 7 and 28 day compressive strength for 120 kg/m 3 cement mixture,
various qualities of cement and the soils A - F 17
Fig.5(b) 7 and 28 day compressive strength for 200 kg/m 3 cement mixture,
various qualities of cement and the soils A - F 18
iv
Page

ON THE STABILIZATION OF COHESIVE SOIL BY MEANS OF
1. PURPOSE OF SOIL STABILIZATION
CEMENT AND BITUMINOUS BINDING AGENTS
Rudolf Klein*
The stabilization of soil consists of altering site soil in such a manner that it
will withstand the strain caused by traffic without being damaged. The stabilization
can be achieved only by the admixture of certain types of soil and it depends on the
structure of the soil whether or not it is favourable to stabilization - referred to as
the corrective material. It can also be achieved by mixing and consolidating, in situ,
the locally available or improved soil with binding agents.
A binding agent added in order to increase the stabilizing effect of the cohesive
elements of the soil must fulfil two functions: (i) it must cement together the various
parts of the soil and (ii) it must envelop the component parts of the soil in order to
regulate the water content of the mixture.
Binding agents of many types are suitable for soil stabilization. Besides cement and
bituminous binding agents, cold glue, ajid natural and artificial resins are, inter alia,
suitable. The stabilization, by means of resins in particular, appears to be of considerable
value despite its great expense, because satisfactory stabilization can be
achieved within a few hours 1 .
Stabilized soils for roadway pavements are, in principle, satisfactory as a temporary
solution, but if the pavements are to last, they may be used only for moderate traffic
and loads. Consequently, soil stabilization for the construction of improved soil bases
for road use is being investigated to an increasing extent because of the sometimes
heavy loads of modern traffic 2 ' 3 •'*. This, however, does not affect their suitability
for traffic of less heavy loads and as a temporary measure.
2. HISTORICAL REVIEW
Rather more than twenty years ago, methods for soil stabilization were separately
developed, particularly in the USA and in Germany. The reasons for their employment
differed. The problem in the USA was to create, within the shortest possible time and
at the lowest possible cost, an extensive net of highways in this vast territory for the
rapidly increasing motor vehicle traffic. There was no need to put forward such high
quality requirements as are necessary for today's traffic since traffic then was less
dense and loads less heavy: on the contrary, the deliberate intention was to build highways
at low cost and within the shortest possible time. In order to reduce movement of
material to a minimum, the object to be achieved was to stabilize the soil in such a
manner that it offered a sufficiently compact roadway under all weather conditions.
The soil stabilization developed in such a manner and now employed to such a considerable
extent has proved to be satisfactory. The work done in the USA, which in particular
was described by Winterkorn 5 , covered the stabilization of many types of soil, using
every suitable kind of binding agent.
*Professor Dr. Ing., Darmstadt.

The situation in the beginning, in Germany, was entirely different. Here with the
increasing motor vehicle traffic, a relatively close net of highways was already in
existence. At that time, there was no need for the construction of additional highways
like the previously-mentioned low-cost roads in the USA. Stabilization of soil
has been employed on airfields since about 1934. Before that time, turf was regarded
as the ideal airfield surface. Its satisfactory qualities are based on the living
and growing conditions of the grass. The entanglement caused by the roots, together
with the gra&s, creates a surface layer which offers a certain amount of protection
against mechanical damages. In addition, the moisture content which is preserved in
the ground by the turf causes, even during dry periods, a certain elasticity and flexibility
of the manoeuvring area which was then demanded for flying operations.
At that time, sufficient surface stability of manoeuvring areas had to be created
within relatively short periods. But normally it took at least one or two years to
obtain a turf having the required stability. It was also often Impossible to maintain
the turf in good condition and to secure sufficient surface stability under all weather
conditions. In the face of heavy ground traffic the drainage, though at other times
satisfactory, was insufficient to prevent the formation of surface sludge during the
rainy season.
The use of a constantly increasing number of aircraft, which, moreover, were heavier
and faster, as well as the need for keeping the airfields operational also during lengthy
rainy periods and thaw, in conjunction with the need for short construction periods,
necessitated the replacement of turf by other surface stabilization methods. Primarily,
the attempt was made to improve the granulometric composition of the soil by the
admixture of gravel, sand or clay. But experience showed that a soil stabilization
sufficient to meet the exacting requirement of flying operations cannot be achieved by
the addition of other soils alone.
As a certain elasticity and flexibility of the stabilized soil was expected from a
mixture of tar and bitumen as binding agents, these two materials were used at first.
After completion of the soil subgrade and drainage, the local site soil was loosened by
means of special appliances, mixed with added binding agents and thereafter consolidated
with light rollers. In this way the soils could be stabilized so as to meet the
requirements of flying operations. At that time, tyre pressures for aircraft were only
about 3 to 4 kg/cm 2 , and individual loads about 6 tons at most.
When the undercarriages of aircraft were provided with stronger springs, elasticity
and flexibility for the stabilized soil corresponding to that of turf was no longer
required. Furthermore, as bitumen had to be imported, soil stabilization using cement
was preferred and, for reasons connected with the raw material problem, this method
was used to a greater extent in Germany than the method employing bituminous binding
agents 6 .
By the end of the war the methods of soil stabilization, in particular those employing
cement, had been developed to a high degree. With the aid of organized air force
construction teams and runway construction units as well as contractors, it became
possible by the end of the war to achieve in a 10-hour day an output of up to 8000 sq
metres of stabilized soil with the aid of specialized, efficient plant. Altogether,
an area of nearly 100 million sq metres of stabilized surface for flying operations
has been produced on airfields distributed nearly all over Europe (Fig.1). For this,
cement was primarily used as a binding agent. At the end of the war, the constructional
organization collapsed and the plant was destroyed, abandoned or removed.

After the war, it was primarily the late Professor Dr. Ing. Reinhold of the Technische
Hochschule (Polytechnic Academy) at Darmstadt, (he incidentally, died, in 1955),
who worked on the problem of soil stabilization, and it is essentially due to him that
the work of soil stabilization in Germany has continued.
3. BASIC PRINCIPLES OF SOIL STABILIZATION
The load bearing capacity of a soil depends on internal friction and cohesion. The
internal friction depends on the grading of the soil, on the form of the grain, and on
the degree of compactness of the soil. Non-cohesive soils show considerable internal
friction, cohesion being of minor importance. The load bearing capacity of cohesive
soils, on the other hand, depends less upon internal friction than on cohesion, and
this increases as the grains become smaller. Cohesion is due to the adherence of the
various parts due to surface tension, and for this to be effective, the hygroscopic
water surrounding the soil particles is essential. With a certain water content,
depending on the grading of the individual soil, the load bearing capacity of the soil
reaches an optimum. It is the function of the binding agent to secure maximum stabilization
and to increase the amount of stabilization obtainable with an optimum water
content in the soil. The suitability of the soil is of fundamental importance, and
arising from the statement just made this should be considered under conditions in
which no special binding agents have been added. 7 This aspect will therefore be discussed
first.
Satisfactory sand-clay and gravelly sand-clay mixtures should have as few cavities
as possible and should contain such an amount of fine particles of a colloidal nature
as is necessary for optimum stabilization. The amount of such fine particles which
will constitute an optimum will depend on the grading of the entire mixture. This
grading would have to be determined through laboratory tests in each individual case,
as it is not yet possible to make general statements. Since the load bearing capacity
of such cohesive soils is to a considerable extent dependent on the water content, all
methods of soil treatment must provide for such quantity of moisture to be contained
in the mixtures as will develop good stability. To find a practicable range, the
Proctor-test 8 , should be employed; with this test the degree of compactness resulting
from given test conditions is determined in relation to the water content. The highest
degree of compactness of the soil resulting from the prescribed test conditions is
called the Proctor-compactness and it is measured in terms of dry bulk density. The
more cohesive the soil, the greater the water content associated with the highest degree
of compactness.
For any further valuation of the soils the Atterberg consistency limits are used: these
are the liquid limit; the plastic limit; and the plasticity 9 resulting from these two
limits. Under the prescribed test conditions, the liquid limit designates the limit
between the liquid and the plastic stage, and the plastic limit that between the plastic
and the semi-solid stage. The plasticity is due to the difference in water content
between the liquid limit and the plastic limit. It is the range within which the soil
can be regarded as plastic. The greater the plasticity index of the soil, the larger
the proportion of cohesive material. The plasticity index therefore allows conclusions
to be drawn as to the cohesive properties of the soil.

As roadways are required to be largely moisture resistant, the ability of binding
agents to envelop and agglutinate individual or aggregate hygroscopic particles,
thereby preventing any change in their water content, is utilized. In this respect,
the bituminous binding agents have an effect slightly different from that of cement.
While bituminous binding agents envelop the soil particles, make them water repellent,
and glue them together more or less elastically, cement on the other hand, because of
its settipg qualities, although providing the soil particles with less moisture resistance,
achieves a better binding effect. With regard to the water conservation aspect
of the problem, the conditions are rather complicated, insofar as on the one hand a
relatively limited water content must be associated with the cohesive parts of the
soil, while on the other hand the same applies to the cement, which, for its part,
requires a specific quantity of water for the process of setting and hardening. If the
total water content is either insufficient or excessive, for the two purposes, the
resulting strength is decreased. It must therefore be determined very carefully in
each case what total water content is required for the cement-soil mixture, and this
water content must be maintained accurately during the working process.
It is not possible to draw conclusions as to the suitability of soils for stabilization
with or without binding agents merely on the basis of their grading. The suitability
of the total mixture will depend in fact on definite special properties of the
fine particles. On a very large surface exchangeable cat-ions are bound by adsorption.
According to the chemical composition of the fine particles, these ions possess varying
water absorbing capacities, which decide the suitability of the soils for stabilization.
This applies to clays as well as to humus, with more or less considerable quantitative
differences existing between various types of clay and humus. Nevertheless, care must
be taken, depending on the effect of the binding agent, that the humus content is kept
within safe limits.
It is understandable that, due to these complicated inter-relations, no firm, generally
accepted rules for pre-determining the suitability of cohesive soils for stabilization
can be made, and that for the time being we must, generally, confine ourselves
to selecting the soils according to our judgment, leaving it to the stabilization test
to determine their suitability 10 .
In order to understand the problem properly, it is necessary first to consider the
influence of the grading on soils containing clays of similar chemical composition.
For that purpose, 6 soils, A, B, C, D, E and P, were mixed from two base soils A and F
- as shown in Table I - in the Test Laboratory for Road Construction and Municipal
Engineering of the Technische Hochschule, Darmstadt.
Soil A is a fine, non-cohesive, but at the same time non-angular type of sand of a
yellow-brownish colour, as is found for instance near Grlesheim in the vicinity of
Darmstadt. Soil F is the so-called Heppenheim clay, which accumulates in the manufacture
of roofing tiles and was available in finely-ground form. The properties and
analysis of the two base soils are given in Table II.
The grading curves of the base and mixed soils are given in Figure 2. Figure 3 shows
the position of soils in a triangular diagram. Three separate test series were carried
out, in which, basically, 120, 160 or 200 kg of Portland cement of the quality classes
225, 325 and 425 were added individually to one cubic metre of a consolidated soil-cementwater
mixture. The water contents, dissimilar for the various soil mixtures and cement

admixtures, were found in accordance with the Proctor-test anc" so regulated that they
showed maximum volume weights of fresh mixtures (cf. Pig.4). The 7-day and 28-day
compressive strengths obtained by the admixture of 120 and 200 kg/m 3 of cement are
shown graphically in Figures 5a and 5b.
It is seen that the maximum compressive strength increased with the increased
admixture of cement and higher-quality cement, and when cement of increasingly better
quality was used, and is also associated with soils containing less fine particles.
It was shown that the range of soils especially suitable for stabilization became
smaller in the direction of those containing less fine particles.
In general the most favourable compressive strengths were obtained with soil C.
Moreover it was shown that the water content associated with the respectively highest
volume weight of fresh mixtures proved to be, for all cohesive soils, that with which
the maximum compressive strengths of the test cubes were obtained. Furthermore, the
samples of soil C provided the best results in respect of the relation between strain
and stress.
It will be necessary to extend this knowledge of the suitability of soils for stabilization
by means of cement with further research and, in particular, to investigate
whether the knowledge gained is also valid in the case of soil mixtures containing clays
of other chemical composition. Tests of this kind have been initiated. The investigations
should also provide a definition for irregular soils, i.e. such soils to which
the above mentioned regularities do not apply.
In order to avoid misunderstandings it must be pointed out that certain types of
stabilization, as is shown in the case of soils B, D and E, can of course be achieved
with soils of very dissimilar grading. There are no objections to the application of
stabilization methods also in the case of less suitable soils, provided that the compressive
strength obtained meets the individual requirements. The knowledge of the
really favourable range is essential, however, in all cases where great compressive
strength is required, as for instance in airfield construction, as well as in connection
with the economy of soil stabilization, as in the less favourable ranges it is
necessary to add greater quantities of binding agents. The increase of the cement
admixture is limited only by the increasing trend of shrinking.
The detailed fundamental aspects which must be considered in respect of stabilization
methods, apply analogically to the use of bituminous binding agents. Modifications are
necessary insofar as the bituminous agents are liquids 1 , and therefore possess other
properties than does cement. The quantity of the binder must, however, be limited more
than in the case of cement, as otherwise the internal friction of the mixture will be
reduced. The required quantity is conditional upon various characteristics of the soil
and the binding agent. Inter alia, the quantity grows with increasing viscosity. Independently
thereof, on the other hand, there exists an automatic but highly involved
relationship between the water content of the soil and the liquid matrix quantity, as
excessive liquid reduces the cohesion. The most favourable water content is higher for
soils containing a greater proportion of fine particles. It therefore requires a
greater quantity of matrix. In order to stabilize such soils, tars of high viscosity
or suitable bitumina may be added at sufficiently high temperatures. A certain quantity
of water in the soil is necessary where the hot-binding material is mixed with the soil.
The reason for this is that owing to the rapid cooling of the binding material on

6
contact with the cooler moist soil, the binding material is unable to envelop the soil
particles completely. Thus, an especially intimate cohesion of the soil particles with
the binding material is not effected. It is the water which must exercise the function
of enveloping the particles in order to secure the cohesive effect. Emulsions may also
be added to these cohesive soils, and the water conservation most favourable to the
stabilization of the mixture can be achieved by means of such added emulsion liquids.
In this case, as the quantity of bituminous binding material used increases, more time
is required-to obtain the required strength because a greater amount of liquid must
evaporate.
These considerations show that, when bituminous binding materials are used, soils
are no longer suitable for stabilization if the high content of fine particles would
require such a quantity of binding material to be used that it would be Impossible to
obtain sufficient internal friction of the mixture. This limit of the suitability of
soils is higher when cement is used as a binding material.
Stabilization by means of bituminous binding material raises the practical question
as to the quantitative relation between the fine particles, the water content and the
content of binding material. Definite, generally accepted rules on this matter have not
been published. However, a certain amount of experience is available. The decisions
are made on the basis of test methods, as for instance, the 'Konus Test' 12 and the
'Hubbard-Field-Test' 13 . The test methods are based on the determination of the energy
which is required for the penetration of certain substances into the stabilized material.
4. PROCESS OF SOIL STABILIZATION
The following things are of fundamental importance for any process of soil stabilization:
(a) Preliminary work before a decision on the stabilization method to be employed.
(b) A mixture of the soil with the water and the binding agent, which should be as
thorough as possible,as well as the corrective material to be added if necessary.
(c) Control of the water content required for the stabilization.
(d) Consolidation of the mixture.
4.1 Preliminary Work
In order to obtain especially good results in soil stabilization it is necessary to
determine carefully, in the laboratory, the quantity and quality of the corrective
material to be added. The same applies to the apportioning of the binding material and
the water content 14 . Such procedure, however, is possible only if there is enough time
available. If cement is used for the stabilization, the period of time required is
greater than if bituminous binding material is use 1; it amounts to several weeks. It is
urgent, in fact, that test methods should be developed which will make it possible to give
reliable forecasts on the attainable compressive strengths within the shortest possible
time. As long as this is not the case, however, in view of the need to make immediate
decisions, construction orders should be given in accordance with such results as are

available, on the basis of the grading curves, which are readily obtainable, on the
Atterberg consistency limits and on a chemical study of the soil 15 . If fine particles
are abundant, cement will be given preference over bituminous binding material, as a
successful soil stabilization will then be possible in many cases even without soil
correction. Vice versa, bituminous stabilization will be given preference in cases
where the proportion of fine particles is relatively small. In the apportioning of the
binding materials, the fundamental aspects outlined in Section 3 must be observed.
4.2 Mixture
The mixing of cohesive soils with each other, as well as with the binding material
and the water, is rendered difficult through the cohesion of these soils. It is therefore
a pre-requisite for the mixture that the soil is pulverized as far as possible;
this is effected with rotary hoes cutting the soil at considerable speed. The greater
the cutting resistance, the greater the power which is required. The soil must be
milled in such a manner that the required degree of pulverization is reached. When the
binding material is added to the soil before its pulverization, mixing is already
effected to a certain degree during the pulverizing process. Normally, the mixture is
fully enriched with the necessary moisture only after the pulverization has been carried
out to the required extent, the purpose being to facilitate the mixing, and in particular,
fully to secure the desired water content. In order to intensify the mixture,
either the rotary hoe is used consecutively several times or, in the case of high power
machinery, a special mixing plant ft used, operating in combination with the rotary hoe -
but separate from it - by which the soil mixture is intimately mingled by means of two
or three counter-rotating mixing rollers. In this case, the machine need roll over the
area to be stabilized only once, so that the entire mixing process is carried out in
one operation.
A really thorough mixture is of considerable importance for the strength of the ready
laid mixed material. For this reason it is necessary to control this mixture very carefully
in the course of the mixing. Visual inspection suffices to control the uniform
composition of the mixture reliably.
4.3 Control of Water Conservation
In order to attain the optimal water content, the inherent moisture content of the
soil must be determined during the construction. The so-called CM-apparatus is suitable
for this purpose 16 . It is expedient to add the amount of water necessary to attain the
optimal water content not at once, but at intervals during the mixing process, so that
the required water will remain within the mixture instead of seeping into the subgrade.
In order to prevent the premature drying of the ready laid mixture in the case of cementstabilized
soils, either the concrete pavement construction methods are employed, or the
surface is coated with a cold-processed binding material,
4.4 Consolidation
The thoroughly kneaded mixture must be consolidated in such a manner that the maximum
compactness mentioned in Section 3 is attained. The consolidation of the mixture is
effected by using a similar technique as in the case of cohesive soils. The sheepfootroller,
the rubber wheel roller and the vibrator are particularly satisfactory as consolidators.
The two borders of the consolidated strip processed in one operation must

8
be properly supported, otherwise the border zones may give way laterally. The consolidation
must be examined from time to time by means of cut samples. The required surface
levelling is effected in the usual way, for instance with light glazing rollers.
With regard to the performance of the work, distinction is made between methods in
which the mixing process is carried out directly on the soil, and such methods in which
the soil to be stabilized is lifted. Hitherto, the first method is generally preferred,
as it is cheaper, and the required equipment simpler. It is, however, sensitive to wind
and rain. In the case of this so-called mix-in-place method, all operations may be
distributed over the entire area to be stabilized, or the material to be mixed may be
concentrated in a limited area. The latter method of course is part-way to the socalled
lifting or pre-mix method, and consequently possesses the advantages of the premix
method to a certain extent. The more corrective material and water are to be added,
the better is the pre-mix method.
An advantage of the pre-mix method is that the corrective material, the water and the
binding material can be measured out with greater accuracy, and thereby climatic
effects eliminated to a considerable extent. A special advantage of the pre-mix method
is the fact that the water content can be regulated most exactly, as the seeping of
water into the subgrade during the mixing process is prevented. In order to reduce the
amount of work necessary for the transport of the lifted soil, machines have been constructed
which, while steadily proceeding over the area to be stabilized, lift, pulverize,
irrigate the soil, mix it with the binding material, and thereafter lay the mixture.
This method appears to be the best one, as it combines the advantages of small
transport work with precision of construction.
It follows from these explanations that the attainable compressive strength is greater
and can be guaranteed better, the more carefully the preliminaries and the main work
are carried out. It is clear that better stabilization is achieved by methods which
offer great regularity and reliability in the performance of the individual operations.
This is, however, only the case If large machines, which have especially been created
for soil stabilization, are available. They have the advantage that they not only perform
work of the highest quality, but also prove to be inherently most efficient, thereby
guaranteeing the quickest progress of the work.
An attempt was made to concentrate on one advantage of soil stabilization, viz.
inexpensiveness, by using machinery of the simplest nature - equipment originally designed
for other purposes, but which could be used for soil stabilization as well. In
this case the machinery used did not consist of big plant capable of performing all or
at least a major part of the operations of soil stabilization, but of separate equipment
with which the functions needed for stabilization could be carried out in several
operations. With regard to the special tasks of soil stabilization on airfields which
are to be carried out with the least delay and, in general, as a provisional arrangement,
it appears to be particularly necessary to use big plant, because it is only in this
way that the advantage of reliable work and good efficiency are obtained. Thus, it is
more or less indispensable that, for stabilization purposes on airfields, efficient big
machinery is available, whose work is prepared and currently controlled by mobile
laboratories.
It may be mentioned that this statement is in accordance with earlier German experiences
17 . The successful work on many airfields was only possible because the air force

construction teams and runway construction groups had high performance power plant at
their disposal. Moreover, the conclusion drawn is also in accordance with experiences
in the United States and in England, where high-quality plant has also been built to
meet the requirements of modern stabilization methods 18 .
It has already been mentioned that the soil texture indicates to a certain extent
whether cement or bituminous binding material is preferable. Apart from this, it may
be said that bituminous binding material generally allows an earlier use of the stabilized
areas. A further advantage worth mentioning is the fact that the maintenance of
the water content after completion is practically certain, i.e. that the stabilized
area is resistant to precipitation. On the other hand it must be noted that the utilisation
of hot-plant mixing becomes more difficult as the temperature decreases. Adaptation
to lower temperatures through the use of low-viscosity binding material is
indeed possible to a certain extent. However, it is always desirable to use binding
materials of the highest possible viscosity in order to obtain solid pavements also at
peak temperatures. When temperatures are low, it would be natural to use emulsions or
bituminous material which can be worked cold. But their disadvantage consists of the
fact that, particularly in the case of pavements having a relatively high percentage
of fine particles, and possessing considerable strength, the drying or evaporation of
the vapourizable oils causes additional work and takes a long time.
5. CONCLUSIONS
This paper constitutes an attempt to explain, in a general way, the essence and
characteristics of soil stabilization, with particular reference to work carried out in
Germany. The experiments described were limited to soil stabilization by means of
cement and bituminous binding material. It appears that the desired systematic order
involves many problems, whose quantitative solution is still unsolved. Consequently, to
be able to carry out any stabilization project reliably it is necessary to conduct
extensive systematic research, to supplement the special knowledge already in existence.
Finally, it may be said that the possibilities of rapid and cheap construction of
road pavements based on soil stabilization are significant in two respects; on the one
hand with regard to its suitability for the creation of a stabilized subgrade for
supporting high-quality, heavy load-carrying pavements and, on the other, with regard
to its suitability for the creation of temporary pavements for lighter loads, such as
advanced airfields. It has been shown that the soils have optimal ranges of stabilization,
which often lie within relatively small limits. But this does not exclude the
possibility of satisfactory stabilization results being achieved also within a larger
range. The demand for accuracy and precision in respect of the individual operations,
inherent in the peculiarity of the stabilization process, clearly reveals the advantage
of using heavy machinery specially constructed for soil stabilization, and justifies the
investment of large funds for this purpose.

10
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2. Lammlein, 'A.
3. Mittmeyer, H.
4. Herion, E.
5. Winterkorn, H.P.
et al.
6. Bilfinger, R.
7.
8.
9.
10.
11. Kirschmer, 0.
12. Patzhold. H.
13. Schmidt, H.
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Strasse und
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Berticks ichtigung der Ergebnisse der WASHO-Versuchsstrasse .
Strasse und Autobahn 1956, p. 118-124.
Bodenverfestigung mit Teer, Ausfuhrung auf den Deckenlosen
Sl and _S2 der Bundesautobahn Hamburg-Hannover. Strasse
und Autobahn 1955, p. 421-425.
Bodenstabilisierung. Strasse und Autobahn 1952, p.207-210
and 254-258.
Engineering Properties of Clay Soils, Winterkorn Research
Inst., Princeton, N.Y. 1950.
Bodenvermorte lung mit bitumin'dsen - 5 - Bindemitte In und
Zement. Volk und Reich Verlag, Berlin 1943.
Anleitung fur den Bau und die Unterhaltung mechanisch verfestigter
Trag- und Verschleisschichten der Forschungsgesellschaft
fur das Strassenwesen e.V. Koln 1952.
Merkblatt fur bodenphysikalische Priifverfahren der Porschungsgesellschaft
fiir das Strassenwesen e.V. Koln 1955,
p. 17.
Merkblatt fiir bodenphysikalische Priifverfahren der Forschungsgesellschaft
fiir das Strassenwesen e.V. Koln 1955,
p. 4.
Vorlaufiges Merkblatt fur den Bau von zementverfestigten
Erdstrassen der Porschungsgesellschaft fur das Strassenwesen,
Kbln 1940 und Neubearbeltung 1955.
Die mechanischen und rheologischen Eigenschaften von Bitumen.
Bitumen 1956, p.86. ff.
Uber die Stabilisierung von Sanden durch Zumischung von
Teer, Strassenbau und Bautenschutz mit Steinkohlenteer.
Vft-Mitteilungen 1956, p. 20-23.
Die verschiedenen Verfahren zur PrufUng der Stabilitdt von
Bitumen-Mineralgemischen in den USA. Bitumen 1952, p.159-160.

14.
15. Leadabrand, J.A.
Norling, L.T.
Vorlaufiges Merkblatt fur den Bau von zementverfestigten
Erdstrassen der Porschungsgesellschaft fur das Strassenwesen,
Koln 1940 und Neubearbeitung 1955.
Wartime Road Problems, Nr. 7. Use of Soil-Cement Mixtures
for Base Courses. Highway Research Board 1949.
Current Road Problems, No. 12. Soil-Bituminous Roads.
Highway Research Board 1946.
Soil-Cement Test-Data Correlation in Determining Cement
Factors for Sandy Soils. Highway Research Board, Bulletin
69. 1953, P. 29-44.
16. Baier,' W. Bodenfeuchtigkeitsbestimmung mit dem CM-Gerdt. Gas- und
Wasser-Fach 1955, p. 677.
17. Bilfinger, W. Bodenvermbrtelung mit bituminosen Bindemitteln und Zement.
Volk und Reich Verlag, Berlin 1943, p. 172-195.
18. Garbotz, G. Mascliinelle Hilfsmittel bei der Bodenvermortelung in
Amerika. Strassen- und Tiefbau 1952, p. 345-348.
Eindrucke vom amerikanischen Strassenbau. Strassen- und
Tiefbau 1955, p. 294-296.
11

12
Soil
A
B
C
D
1
P
Mixture of
A (%)
100
90
75
50
25
0
F (%)
0
10
25
50
75
Properties
Specific weight
Liquid limit
Plastic limit
Plasticity
100
(electrometric) pH-value
(hydrogen-ion concentration)
Humus content
Chloride content
Sulphates
TABLE I
Mixture ratio and granulometric composition of
soils A, B, C, D, E and F
Percentage of Sand
(0,09-2 mm)
91,8
83,3
70.3
49.0
27,6
6.2
TABLE II
Percentage of Dust
(0,002-0,09 mm)
8.2
15,6
26,7
45.1
63.6
81,9
Characteristics of Base Soils
g/cm 3
% by weight
% by weight
% by weight
% by weight
% by weight
A
2,668
cannot be determined
because of
non-cohesiveness of
soil
6.81
0
0
0
Percentage of Clay
(0.002 mm)
0
1.1
3.0
5,9
8.8
11.9
F
2.580
38,50
20,98
17.52
7.65
0
0,0058
0,058

• Zement verfestigte Boden
0 Bituminos verfestigte Boden
• Cement stabilised soils
0 Bitumen stabilised soils
Pig.l Distribution of airfields on which use was made of soil stabilisation by
Germany during the period 1936 - 1945
13

OmW%
•D
1
5 JO
H
0
Ton
(Fuxstm) fan-
Schldmmkorn
tchluff
Mitttt-
F/
.A
/ / y
s ,
7 /
f~
irvb-
j
/
D
t
y.
y
/
/
aaC
/
/
Ftin-
yy
71
' &
7 +§
* III
* \ ii
Sand
Mitttlz_
i
m
Siebkorn
liroO- Fmn-
ojooi ajon a oos a.01 aoe ai a* to
Schlammkorn: Washed grain
Siebkorn: Sifted grain
Ton: Clay
Schluff: Poor clay
Sand: Sand
korndurcnmesser a [mm]
Ordinates: Wt. % of grains < d(left)
Wt. % of grains > d(right)
Abscissae: Grain diameter d(mm)
Hies
Mititi- Oroe-
Kies: Gravel
Feinstes: Very fine
Fein: Pine
Mittel: Medium
Grob: Coarse
Fig.2 Graphical representation of grain distribution of soils A- F
6*9xW%
0
to
»
to
S
I
to V
10
10
90
no
Cl

10 20 30 to 50 eo
Staub
Sand
Rohton
Rohfon (untirr 0.002mm) -
dust
sand
crude clay (less than 0.002 mm)
Fig.3 Position of soils in the coordinate system
70 80 90 >00
15

A
1
5
.8 '
4
i/?/./mV
/
s
_
WJSsergehnlt [%J 6 8 K) B » W 6 8 10 B_ W fl 10 12. II 16
D |
Boden •• >.»
•v.
1
I
1 '••"
i I.BO
.RH/n J'1
/
t
1
/
1
N V
\ >
E
/
/
y
y
/
/
f
/
/
/
/
r "
N
\ >
c
F
/
/
7 /
7
/
J
/
I
V • V
/ ^ r
W*ssergehaltl°/a] 8 to 12 m^ W m 16 l± 22 16 18 20 22_ 2U 26
Boden: Soil Ordinates:
Abscissae:
Specific gravity
Water content %
Fig.4 Specific gravity of various mixtures in relation to water content
(The underlined percentages indicate the water content selected)

720
•oo •
80 •
60
ao
20
Druckfestigkeit
aD [kg/cm 2 ]
Druckfestigkeit: compressive strength
Boden: soils
Pz 425
Pz 325
Pz 225
28 Tage 7Tage
28 Tage: 28 days
7 Tage: 7 days
Pig.5(a) 7 and 28 day compressive strength for 120 kg/m 3 cement mixture, various
qualities of cement and the soils A - F
Bbden

18
Drvckfestigkeit
&D Ikg/cm']
Druckfestigkeit: compressive strength
Bbden: soils
pz 42S
Pz 32S
Pz 22S
28 Tage 7 Tage
Boden
28 Tage: 28 days
7 Tage: 7 days
Fig.5(b) 7 and 28 day compressive strength for 200 kg/m 3 cement mixture, various
qualities of cement and the soils A - F

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AGARD Report 79
North Atlantic Treaty Organization, Advisory Group
for Aeronautical Research and Development
ON THE STABILIZATION OF COHESIVE SOIL BY MEANS OF
CEMENT AND BITUMINOUS BIW.ING AGENTS
Rudolf Klein.
1956
18 pages, incl. 18 refs., 5 figs.
The purpose of soil stabilization and the basic
principles involved are explained. A brief historical
review is given of work on soil stabilization
carried out mainly in Germany, in which two
kinds of binding agents were used, viz., bituminous
materials and cement. It is shown that soils - at
least those involved in the experiments described
P.T.O.
AGARD Report 79
North Atlantic Treaty Organization, Advisory Group
for Aeronautical Research and Development
ON THE STABILIZATION OF COHESIVE SOIL BY MEANS OP
CEMENT AND BITUMINOUS BINDING AGENTS
Rudolf Klein.
1956
18 pages, incl. 18 refs., 5 figs.
The purpose of soil stabilization and the basic
principles involved are explained. A brief historical
review is given of work on soil stabilization
carried out mainly in Germany, in which two
kinds of binding agents were used, viz., bituminous
materials and cement. It is shown that soils - at
least those involved in the experiments described
P.T.O.
624.138
3g3b2c
624.138
3g3b2c
AGARD Report 79
North Atlantic Treaty Organization, Advisory Group
for Aeronautical Research and Development
ON THE STABILIZATION OP COHESIVE SOIL BY MEANS OF
CEMENT AND BITUMINOUS BINDING AGENTS
Rudolf Klein.
1956
18 pages, incl. 18 refs., 5 figs.
The purpose of soil stabilization and the basic
principles involved are explained. A brief historical
review is given of work on soil stabilization
carried out mainly in Germany, in which two
kinds of binding agents were used, viz., bituminous
materials and cement. It is shown that soils - at
least those involved In the experiments described
P.T.O.
AGARD Report 79
North Atlantic Treaty Organization, Advisory Group
for Aeronautical Research and Development
ON THE STABILIZATION OP COHESIVE SOIL BY MEANS OF
CEMENT AND BITUMINOUS BINDING AGENTS
Rudolf Klein.
1956
18 pages, Incl. 18 refs., 5 figs.
The purpose of soil stabilization and the basic
principles involved are explained. A brief historical
review is given of work on soil stabilization
carried out mainly in Germany, in which two
kinds of binding agents were used, viz., bituminous
materials and cement. It Is shown that soils - at
.least those involved in the experiments described
P.T.O.
624.138
3g3b2c
624.138
3g3b2c

- have optimal ranges of stabilization which He
within relatively small limits and the conclusion
is drawn that for good results machinery for soil
stabilization should be specially designed.
Presented at the Ninth Wind Tunnel and Model Testing
Panel, held from 27th to 31st August, 1956, in
Brussels, Belgium.
- have optimal ranges of stabilization which lie
within relatively small limits and the conclusion
is drawn that for good results machinery for soil
stabilization should be specially designed.
Presented at the Ninth Wind Tunnel and Model Testing
Panel, held from 27th to 31st August, 1956. in
Brussels, Belgium.
- have optimal ranges of stabilization which lie
within relatively small limits and the conclusion
is drawn that for good results machinery for soil
stabilization should be specially designed.
Presented at the Ninth Wind Tunnel and Model Testing
Panel, held from 27th to 31st August, 1956, in
Brussels, Belgium.
- have optimal ranges of stabilization which lie
within relatively small limits and the conclusion
is drawn that for good results machinery for soil
stabilization should be specially designed.
Presented at the Ninth Wind Tunnel and Model Testing
Panel, held from 27th to 31st August, 1956, in
Brussels, Belgium.