Study On Shrinkage Characteristic Of Concrete At Early Age

The project was supported by the National Natural Science Foundation of China, the research on the early age shrinkage deformation and stress development law of concrete. Concrete crack is one of key factors to affect engineering quality and durability. With the compliction of hydraulic structure design, and the diversification of materials and the service environment, the concrete crack at early age has become increasingly severe, which influences the security and lifetime of projects. Limited by traditional test methods and techniques,it is difficult to quantitively reflect the early-age cracking of concrete. so it is necessary to study the shrinkage deformation characteristics of concrete at early age.The shrinkage of concrete is composed of chemical shrinkage, autogenous shrinkage and drying shrinkage and shrinkage of concrete is mainly autogenous shrinkage and drying shrinkage, the drying shrinkage of concrete is one of the main reasons which cause cracks on the concrete and it mainly occurres in concrete at early age.This paper discussed and analyzed the cracking time of net grouts,the shrinkage of mortar and the shrinkage deformation change rule of concrete at early age in different kinds of cement, different water cement ratio, different admixture and its compound admixture, different coarse aggregate,which was fromed three levels of the net grouts, mortar, concrete. The net grouts, mortar experimental test and concrete analysising results showed that the concrete shrinkage at early age increased with age, but the contraction deformation slowed down, and it significantly slowed down at the vicinity of a certain age, so the concrete shrinkage deformation mainly occurred at the early age; Different kinds of significantly effected concrete shrinkage deformation at the early age, the concrete shrinkage deformation at early age of low heat cement was less than the one of moderate heat cement; Different kingds of water cement ratio markedly influenced concrete shrinkage deformation at early age, increasing the water cement ratio can reduced the concrete shrinkage deformation at early age; adding admixture can reduce the concrete shrinkage deformation at early age, but when the mineral aggregate amount of more than 15%, increasing to add the content of the one cannot obviously influence the shrinkage deformation at early age; Different kinds of aggregate also greatly impacted on concrete shrinkage and shrinkage rate at early age.Applying the grey correlation degree and GM(1, N) model to analyze the influence factors of concrete shrinkage deformation at early age. At the early age, the concrete shrinkage deformation changed fastest by age. When the total amount of admixture was more than 40%, the content of fly ash most influenced concrete shrinkage deformation among all kinds of the admixture.