A numerical study of chloride migration in concrete under electrochemical repair

Electrochemical repair (ECR) is one of the most effective methods of removing chloride from offshore engineering structures to improve their durability. The diffusion of chloride and electrochemical migration are key stages in this process. In this work, a new numerical chloride migration–diffusion model was established using the Nernst–Planck equation. The distributions of free chloride ions in concrete in the stages of free chloride diffusion and ECR were simulated and the effects of the external potential and cathode position on ECR efficiency were analysed. The results showed that ECR can effectively remove chloride ions from concrete. After 12 weeks of ECR, the chloride removal efficiency was more than 66%. With an increase in the repair time, the ECR efficiency decreased gradually. In the initial stage of ECR, the chloride concentration on the rebar surface decreased rapidly. After 4 weeks of ECR, the chloride concentration tended to stabilise. The ECR efficiency also improved with an increase in external potential increases, with the chloride concentration on the reinforcing bar surface decreasing rapidly. When cathodes are set on both sides of the concrete, the ECR time should be extended and the external potential should be increased to achieve a better repair effect.