Moisture Diffusion Coefficient of Concrete under Different Conditions

Humidity change in concrete is the leading cause of concrete shrinkage. Moreover, the moisture diffusion coefficient of concrete is an essential parameter for assessing and predicting the internal moisture content of concrete. However, there is a lack of theoretical construction and experimental studies on the effect of different conditions, especially different constraints, on the moisture diffusion coefficient of concrete. Therefore, the internal humidity, pore structure parameters, and basic mechanical properties of concrete under different strength grades C30, C40, C50, and C60 (C stands for concrete and numbers indicate the strength class of the concrete), curing environments (dry and sealed curing conditions), and constraints were tested in this study. In addition, a calculation model of concrete’s internal humidity and humidity diffusion coefficient was established. The research findings show that the internal humidity of concrete decreased with age due to hydration and drying. External humidity had a significant effect on the moisture change of concrete, and the lower the external humidity, the larger the humidity diffusion coefficient and the faster the internal humidity of concrete decreases. Reinforcement (confinement) changes the pore structure parameters of the concrete, which in turn affects the transport of moisture within the concrete. The higher the reinforcement rate, the larger the pore structure parameters of the concrete, the larger the humidity diffusion coefficient, and the faster the concrete humidity decreases. The method proposed in the study can accurately predict the internal humidity of concrete using the humidity diffusion coefficient. The research results are a reference for preventing concrete shrinkage and cracking in construction.