Transport model and simulation of chloride ion in unsaturated concrete

In order to study the circulation and accumulation of chloride ion in concrete under the condition of dry-wet alternation, the water and chloride ion transport equations were respectively established based on Darcy's law and Fick's second law. Then the convection-diffusion equation of chloride ion in unsaturated concrete was obtained according to the coupling relationship between water and chloride ion transport. This model was tested and verified, and the parameters analysis was used to summarize the temporal and spatial variation law of chloride ion concentration in dry-wet alternation environment. The results show that the model of convection-diffusion is in good agreement with the engineering practice and the model test results, and can reflect the temporal and spatial variation characteristics and rules of chloride concentration under the alternating dry-wet conditions. The temporal and spatial distribution of chloride concentration under unsaturated and saturated conditions is significantly different in curve shape and numerical value. The number of dry-wet cycles, the ratio of dry-wet cycle time, the saturation of concrete at the boundary of drying process and the initial saturation of concrete are crucial parameters of convection-diffusion equation. The content of chloride ions in shallow depth of concrete accumulate gradually with the increase of the number of cycles of drying and wetting. The larger the number of dry and wet cycles, the higher the cumulative chloride content and the higher the concentration peak.