Concrete Water Transport Law Under The Dry-wet Circulation And Sulphate Erosion Research

Concrete structures are subjected to the environmental corrosions such as drying-wetting cycles, sulfate erosion etc under the sea or acid rain, which reduce its durability and shorten the service lifetime. Sulfate attack is the main factor causing the degradation of the concrete durability, while the drying-wetting-cycle actions accelerate the corrosion process of concrete caused by sulfate attack. Research on concrete durability under the couplings of sulfate attack and drying-wetting cycles is of great significance to carry out long-lifetime design and to improve the security of concrete structures.To solve this problem, numerical simulation and experiments were used to investigate the moisture transport under the drying-wetting-cycle actions, the ionic transport caused by sulfate attack and the salt crystallization in pore solution. The main contents and conclusions are as follows:(1) Based on the moisture transport mechanism in concrete, using Fick’s law and Darcy’s law, the moisture transport equation in concrete, which is associated with vapor diffusion and liquid water penetration, was established under the drying-wetting cycles. The equation is a nonlinear partial differential equation, and it is solved by one-point subdomain high precise integration method to obtain an one-dimension semi-analytical solution, and an analytical program is completed by MATLAB language.(2) Some mortar samples with different water-cement ratios were designed and cut into groups of slices in accordance with one-dimension transport of moisture. the transport experiments of moistures in the slices, such as the wetting, drying and drying-wetting cycles were carried to verify the established moisture model. The result indicates that the results from the moisture transport model agree well with that of experiments, thus it can be used to analyze the process of the moisture transport in concrete.(3) A two-dimension transport equation of moisture in concrete was set up to analyze the moisture transport in concrete beam and column, and one-point subdomain high precise integration method was used for obtaining the semi-analytical solution of the equation. Numerical simulations were carried out to investigate the moisture transport in Concrete prism under the wetting, drying and drying-wetting cycles. The results show that, the moisture transport rate in concrete decreases from the surface to the interior of specimens, and it is higher in the diagonal of the cross-section of the column than the other.(4) Based on the convection transport of sulfate solution in concrete, the transport model of sulfate ions under the wetting-drying cycles was given. Numerical simulations were carried out to investigate the sulfate ion transport and sulfate’s crystallization volume in concrete after the moisture evaporates. The result shows that, the concrete specimen surface is significantly influenced by drying-wetting conditions, and the sulfate ion concentration in pore solution increases with the cycle numbers. the drying time or wetting time have an obvious effect on the distribution of sulfate ion in concrete. The amount of sulfate crystals in concrete increases with the drying-wetting cycle numbers.