Simulation of chloride ion transport and erosion in fractal porous media under multi field coupling

Concrete is an important part of submarine building structure, which is eroded by hydrostatic pressure and chloride ion. In this study, concrete is regarded as a dually-porous structure composed of pores and fractures. Considering hydrostatic pressure and fractal characteristics of concrete structure, a fractal model is established for chloride ion diffusion under the dual drive of concentration and pressure. Considering the effective stress caused by water pressure in pores of concrete, a fluid–solid model for chloride ion migration is proposed. The fluid–solid coupling fractal model for chloride ion migration was verified by comparing with the experimental data. The numerical simulation results show that: (1) the influence of fractal dimension on the chloride ion diffusion coefficient and chloride ion concentration is nonlinear; (2) compared with low hydrostatic pressure, high hydrostatic pressure has more significant effects on chloride ion concentration and diffusion coefficient; (3) when the effective stress and water pressure in pores are not considered, the diffusion coefficient of chloride ion is always a constant.