بررسي جمع شدگي خميري بتن هاي حاوي ميكروسيليس

Evaluation of Plastic Shrinkage in Concrete Containing Silica Fume

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, the sun radiation is also a very important factor in cracking characteristic. But the effect of sun radiation is not considered in ACI 305 R-96 nomogram. 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 ration in concrete with silica fume makes the concrete more sensitive towards cracking. The results of this project also showed that the severity of the cracking is not related only to compressive strength or bleeding of the concrete but all environmental factors like sun radiation and also silica fume in mix, have important role.