Numerical modeling of chloride diffusion in cement-based materials considering calcium leaching and external sulfate attack

Abstract

Chloride-induced corrosion of steel bars can shorten the service life of concrete structures in marine environment. Therefore, a numerical model that can accurately characterize the chloride diffusion in marine concrete can help to evaluate the service durability of structures. In this paper, a novel chloride diffusion model considering the coupling effect of calcium leaching and sulfate attack in cement-based materials is proposed. The model can not only simulate the increase of porosity structure and the desorption of bound chloride caused by calcium leaching, but also characterize the competitive antagonism between sulfate and chloride salts in cement-based matrix, which produces expansive products to fill pores and promotes the desorption of bound chloride. The proposed model was further developed in COMSOL, and verified by two groups of literature experimental data. Then, the verified model was applied to investigate the coupling effect of calcium leaching and external sulfate attack on chloride diffusion process in cement-based materials. The results show that the proposed model can effectively reproduce the chloride diffusion process in both groups of tests well. In contrast to the single influencing factor, the coupling effect of calcium leaching-sulfate attack on the chloride diffusion process in cement-based materials shows that there is a phenomenon of inhibiting chloride diffusion in the early stage of erosion, but it shows a promoting effect in the later stage. Compared with sulfate attack, calcium leaching always dominates the influence of chloride diffusion in cement-based matrix. Furthermore, considering the coupled effect of leaching-sulfate attack, the initial corrosion time of reinforced concrete is about 24.5% earlier than that without considering the coupling effect. Increasing the thickness of steel bar cover layer and reducing the initial porosity of matrix can effectively delay the occurrence of steel bar corrosion in cement-based matrix.