Euradwaste '08 - EU Bookshop - Europa
Euradwaste '08 - EU Bookshop - Europa Euradwaste '08 - EU Bookshop - Europa
the case of the long plug elaborated in Grimsel (Switzerland), more suitable aggregates were used, made of natural siliceous gravel and river sand. To determine the relative proportions of each aggregate fraction, the reference grading limits of the Sprayed Concrete Association (SCA) were used, slightly adapted to the actual maximum size of the coarse fraction selected. Basic low-pH concrete design and main properties The integration of concrete components was made by means of the absolute volume method using the aggregates and the paste components selected. A cement content of approximately 300 kg/m 3 was determined and the water was adjusted in trial mixes for a slump in the range 12–17 cm. During experimental trials, a formulation based on CAC showed variations and instability (strong thyxotropic behaviour) at the fresh state, and thus it was rejected for further studies. The nominal compositions of the low pH concretes suitable for pumping and shotcreting are given in Table 4. Cement formulation Table 4: Nominal composition of basic concrete types Short Plug (aggregate from the excavation) Long Plug (convent. aggregates) 70%CAC+20 %SF+10%FA 60%OPC+40 %SF 282 35%OPC+35%S F+30%FA 60%OPC+40%SF Water (kg/m 3 ) 262 277 237 230 Binder (kg/m 3 ) 310 307 316 275 Water/binder 0.85 0.9 0.75 0.84 Filler (kg/m 3 ) - - - 70 Gravel (kg/m 3 ) 621 615 635 - Fine Gravel (kg/m 3 ) 201 200 205 588 Sand (kg/m 3 ) 825 818 843 1045 Super plasticizer (kg/m 3 ) Air-entraining admixture (kg/m 3 ) 5.58 5.5 5.7 5.7 - 0.6 0.6 The main parameters analyzed in the concretes made using these nominal compositions were: � In fresh concretes: unit weight (kg/m 3 ), consistency (slump), cohesion and aspect (qualitative assessment). � In the hardened state: compressive strength, elastic modulus and pH, determined at different ages (time of curing). Results obtained in basic concretes with super plasticizer are given in table 5 and figures 1 & 2.
Properties Table 5: Properties of basic concretes at the fresh state 70%CAC+20%S F+10%FA Short Plug (aggregate from the excavation) 60%OPC+40%SF 35%OPC+35%SF +30%FA Unit weight (t/m 3 ) 2.23 2.23 2.25 2.27 Slump (cm) 17 12 13 15 Cohesion Good Good Good Good Aspect Good Good Good Good Comp. Strength (MPa) 40 35 30 25 20 Basic concretes 15 70CAC/20SF/10FA sp 10 60OPC/40SF sp 5 0 35OPC/35SF/30FA sp 60OPC/40SF lp 0 20 40 60 80 100 Curing time (days) 283 Long Plug (conventionalaggregates) 60%OPC+40%SF Figure 1: Evolution of compressive strength over curing time (sp: short plug; lp: long plug) pH 12,2 12 11,8 11,6 11,4 11,2 11 10,8 10,6 Basic concretes 70CAC/20SF/10FA sp 60OPC/40SF sp 35OPC/35SF/30FA sp 60OPC/40SF lp 10,4 0 20 40 60 80 100 Curing time (days) Figure 2: Evolution of pH vs. curing time. (sp: short plug; lp: long plug) Other properties of the low-pH concrete The hydraulic conductivity of the low-pH concrete was determined using granitic water from Äspö in order to simulate the real conditions of an underground repository. The mean value obtained from cored shotcrete samples was 1.03·10 -10 m/s, which is similar to that of the surrounding rock (which is in the order of 1·10 -10 m/s) and this value does not increase with time [2]. Besides, the pH
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the case of the long plug elaborated in Grimsel (Switzerland), more suitable aggregates were used,<br />
made of natural siliceous gravel and river sand. To determine the relative proportions of each aggregate<br />
fraction, the reference grading limits of the Sprayed Concrete Association (SCA) were<br />
used, slightly adapted to the actual maximum size of the coarse fraction selected.<br />
Basic low-pH concrete design and main properties<br />
The integration of concrete components was made by means of the absolute volume method using<br />
the aggregates and the paste components selected. A cement content of approximately 300 kg/m 3<br />
was determined and the water was adjusted in trial mixes for a slump in the range 12–17 cm. During<br />
experimental trials, a formulation based on CAC showed variations and instability (strong<br />
thyxotropic behaviour) at the fresh state, and thus it was rejected for further studies. The nominal<br />
compositions of the low pH concretes suitable for pumping and shotcreting are given in Table 4.<br />
Cement formulation<br />
Table 4: Nominal composition of basic concrete types<br />
Short Plug (aggregate from the excavation) Long Plug (convent. aggregates)<br />
70%CAC+20<br />
%SF+10%FA<br />
60%OPC+40<br />
%SF<br />
282<br />
35%OPC+35%S<br />
F+30%FA<br />
60%OPC+40%SF<br />
Water (kg/m 3 ) 262 277 237 230<br />
Binder (kg/m 3 ) 310 307 316 275<br />
Water/binder 0.85 0.9 0.75 0.84<br />
Filler (kg/m 3 ) - - - 70<br />
Gravel (kg/m 3 ) 621 615 635 -<br />
Fine Gravel (kg/m 3 ) 201 200 205 588<br />
Sand (kg/m 3 ) 825 818 843 1045<br />
Super plasticizer<br />
(kg/m 3 )<br />
Air-entraining admixture<br />
(kg/m 3 )<br />
5.58 5.5 5.7 5.7<br />
- 0.6 0.6<br />
The main parameters analyzed in the concretes made using these nominal compositions were:<br />
� In fresh concretes: unit weight (kg/m 3 ), consistency (slump), cohesion and aspect (qualitative<br />
assessment).<br />
� In the hardened state: compressive strength, elastic modulus and pH, determined at different<br />
ages (time of curing).<br />
Results obtained in basic concretes with super plasticizer are given in table 5 and figures 1 & 2.
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