Numerical and experimental investigation of coupled capillary suction and chloride penetration in unsaturated concrete under cyclic drying-wetting condition

Understanding the simultaneous transport mechanism of water and chloride in unsaturated concrete under cyclic drying-wetting condition plays a crucial role in assessing the service life of concrete structure. This paper presents an experimental investigation and mesoscale numerical modeling of chloride penetration coupled with capillary suction in unsaturated concrete exposed to cyclic drying-wetting condition. The hydraulic diffusivity modeling considering the effects of gaseous and liquid water for drying and wetting periods was first developed. Combining with the extended Darcy’s law and the convection-diffusion model, the coupled model of capillary suction and chloride penetration in unsaturated concrete under cyclic drying-wetting condition was further proposed. Aiming at obtaining some model parameters for numerical model validation, the laboratory tests of drying-wetting cycles and mercury intrusion porosimetry (MIP) test of samples after different drying-wetting cycles were conducted. C30 and C50 specimens were exposed to the chloride attack environment in a self-designed automatic marine tidal chamber with two kinds of drying-wetting cycle ratio (αt = 3:1 and 85.4:1) for the exposure durations of 30 and 90 days. The results indicate that the established model can accurately predict the coupled transport of water and chloride in unsaturated concrete under cyclic drying-wetting condition. Furthermore, the effects of drying-wetting ratio and initial saturation degree on the behavior of water and chloride transport in concrete were discussed.