Reducing Shrinkage and Improving Cracking Resistance of Concrete by Using Fly Ash

Cracking in concrete is one of the main reasons to decreasing both the quality and the service life of buildings. This study mainly evaluated the effect of fly ash on the length changes and the cracking resistance of concrete. High CaO fly ash was used as a replacing cement material by decreasing the cement in the ratio of 30% by weight. Concrete mixtures with a controlled slump were tested in this study. The experiment programmes included on a compressive strength, length changes under free and internal restrained conditions and a cracking resistance according to ring test of concrete in the laboratory. Compressive strength of concrete is decreased by using fly ash. However, the compressive strength of concrete containing fly ash continually increases until later ages when compared to that of concrete without fly ash. Both free shrinkage and restrained shrinkage of concrete were reduced in the case of fly ash concrete. Especially, the use of fly ash significantly delayed a cracking age of concrete under the external restrained condition according to ring test as compared to cement only concrete.