Influence of superplasticizer, plasticizer, and silica fume on the drying shrinkage of high-strength concrete subjected to hot-dry field conditions

The effects of adding condensed silica fume (10% of cement weight) on the concrete mix, and those of adding either superplasticizer or plasticizer on the drying shrinkage (DS) of 12 high-strength concrete prisms exposed to either controlled laboratory or hot-dry field conditions, were monitored for over 3 years. The results indicate that for specimens cured under controlled laboratory conditions, inclusion of silica fume in the concrete mix reduces the 3-year DS by 25%, the induced shrinkage stress by 36% and the first month rate of DS by 21%. The corresponding reduction in the 3-year DS, the induced shrinkage stress, and the first month's rate of DS for the counterpart specimens cured under hot-dry field conditions are 13%, 26%, and 24%, respectively. The results also show that for specimens cured under laboratory conditions, replacing the superplasticizer by plasticizer increases the 3-year DS by 21%, the induced shrinkage stress by 27%, and the first month's rate of DS by 32%. The corresponding increase in the DS, the induced shrinkage stress, and the first month DS for the counterpart specimens cured under the hot-dry field conditions are 27% and 34%, and 35%, respectively. Furthermore, test results indicate that the range of the maximum recorded DS strains in 3-year exposure period is between 450 to 650 mu m/m and is dependent on the concrete content of admixtures. On the other hand, depending on the curing conditions, 75 to 80% of the 3-year DS occurs within the first 3 months of exposure. (C) 1998 Elsevier Science Ltd.