Theoretical model for the coupling effect of moisture transport on chloride penetration in concrete

Concrete's internal pore structure crucially influences the rate at which moisture and chemicals, e.g., chloride, move through concrete. This paper explores the coupling effect of moisture transport on the chloride penetration in both saturated and non-saturated concrete, which arises because moisture carries chloride ions as it moves through the pores. To characterize simultaneous moisture and chloride movement in general, a modified Fick's first law can be used for the flux of chloride ions as well as the flux of moisture. A mathematical model is developed based on a multiscale approach for the effective humidity diffusion coefficient, accounting for different moisture diffusion mechanisms in different sizes of pores: Molecular, Knudsen, and Surface diffusions. Based on the results for humidity diffusion coefficient, a material model for the coupling parameter was developed. Validation based on available experimental results demonstrated excellent agreement in predicting pore relative humidity and chloride content profiles.