Research On Concrete Shrinkage And Cracking Control

In this paper, the influences on concrete shrinkage and splitting tensile strength by the varieties and contents of the raw materials, such as cement, sand, fly ash, water-reducer and expansion agents, are studied. The possibility of the prevention of the concrete cracking by proper concrete proportion design is discussed. Results showed that the brand and content of cement greatly effect the concrete shrinkage. If the cement content is higher than 470kg/m3,the concrete shrinkage would be higher than 400x10-6, inevitably result in concrete cracking under restrained circumstances. When the fine sands are adopted, the water content would increase greatly, causing shrinkage increasement. Qualified fly ash can reduce the concrete shrinkage, the reducement is very clear when excessive substitution is adopted. But the cohesiveness of fly ash concrete is not very good, so the cure should be enhanced to avoid cracking by speedy water emission. The accelerating admixture and retardening water-reducer can also increase the concrete shrinkage. The expansion agents can only make up the shrinkage to some extent, and the compensation effects would be reduced when the retardener and fly-ash are used. The expansion agents are not panaceas to avoid the shrinkage cracking as expansion can also reduce the concrete soundness. Under bad curing condition, the polypropylene fibrillated film fiber can improve concrete's anti-crarking property, while the nominal steels have very unobvious effects.To reduce the concrete shrinkage thus avoid the cracking, the former factors must all be taken into account in concrete proportion design to develop sound concrete.