Modeling of bidirectional chloride convection-diffusion for corrosion initiation life prediction of RC square piles under drying-wetting cycle

Modeling chloride penetration mechanism in unsaturated concrete is essential for corrosion initiation life prediction of marine reinforced concrete (RC) structures. This paper presents a bidirectional chloride convectiondiffusion model for the chloride concentration distribution of RC square piles in the tidal and splash zone. The finite difference numerical method is used to solve the convection-diffusion governing equations with the drying-wetting cycle. The numerical model is validated by two experimental results and the analytical solution with constant surface chloride conditions. The peak value and convection depth in the chloride distribution curve of RC square piles are investigated. The results show that the periodic drying-wetting chloride environment is the dominant factor of the convection effect formed in the surface layer of the square piles. Moreover, a coupling effect is observed in the diagonal areas of square piles. The corrosion initiation life under a periodic dryingwetting chloride environment is shorter than that with constant surface chloride concentration. Furthermore, the sensitivity analysis results show that the diffusion coefficient, the concrete cover depth, and the variable rate of drying-wetting cycles are the critical parameters for predicting the corrosion initiation life of RC square piles under the drying-wetting cycle.