A COMPARISION BETWEEN PLASTIC SHRINKAGE OF CONCRETE CONTAINING SILICA FUME AND THE NORMAL CONCRETE

Plastic shrinkage is one of the most important parameter which must be considered in hot weather concreting. If plastic shrinkage is not prevented, cracking will be significant, especially if silica fume is used in the mix. In this paper, the effect of silica fume in bleeding and evaporation was investigated in laboratory. The results showed that in restrained shrinkage, beside relative humidity, temperature and wind velocity, sun radiation also is very important factor in evaporation rate. It is found that under solar radiation condition, the evaporation was much larger than the estimated value in ACI 305 Nomogram. The rate of evaporation under solar radiation was about two folds of evaporation rate under shade condition.The results showed that in terms of crack initiation time, crack width and total cracking area, concrete containing silica fume is more severe than concrete with no silica fume. Reduction of water cement ratio in concrete with silica fume makes the concrete more sensitive in cracking. The results of this project also showed that the severity of the cracking is not related only to rate of bleeding but all environmental factors including like sun radiation or shading and also mix compositions have important roles.