Experiment and simulation of chloride ion transport and binding in concrete under the coupling of diffusion and convection

Diffusion and convection are the main factors affecting chloride ion transport in unsaturated cementitious materials. In this study, capillary salt absorption experiment and steady-state migration experiment were used to investigate the chloride ion migration in unsaturated concrete, and a modified chloride ion diffusion-convection model was established for concrete considering curing age, initial water saturation and the combined effect of chloride ion. The results show that the chloride ion migration in unsaturated concrete can be divided into six stages: safety stage, initial stage, convection stage, deceleration stage, diffusion stage and stablilization stage, the chloride ion binding coefficient is approximately linear with the initial saturation, and the concrete with fly ash content of 40% or sand content of 60% has the best blocking effect on chloride ion migration.