Moisture diffusion and differential drying shrinkage of concrete

Abstract

Cracks due to differential drying shrinkage occur mainly on exposed surfaces of concrete structures, and appear to be very complicated with time. Thus it is impossible to control the cracks due to differential drying shrinkage by previous researches on average drying shrinkage of concrete which does not consider the non-uniform moisture distribution in concrete. Therefore, based on moisture diffusion of concrete, the differential drying shrinkage of concrete was investigated in this dissertation. The analytical method of moisture diffusion of concrete was firstly developed to estimate the differential drying shrinkage. From the moisture distribution in concrete obtained by analysis of moisture diffusion, the analytical method of differential drying shrinkage was suggested, in which the creep of concrete was also considered. The internal relative humidity in concrete was measured for drying specimen at early ages, and the change of relative humidity due to self-desiccation was also measured for sealed specimen. The effect of concrete strength and initial moist-curing time on relative humidity distribution in concrete was investigated. And the validation of moisture diffusion theory was verified by comparing experimental results with analytical results. In addition, the experiments for differential drying shrinkage were carried out at early ages, in which the autogenous shrinkage due to self-desiccation was also considered. The effect of concrete strength and initial moist-curing time on shrinkage strain distribution in concrete was investigated. And the validation of suggested analytical method was also verified by comparing experimental results with analytical results. The moisture distribution in low-strength concrete is mostly influenced by moisture diffusion of concrete, but the effect of self-desiccation is negligible. The rate of moisture diffusion in low-strength concrete is much higher than that of high-strength concrete, and the relative humidity near t...