Closed-form solutions for modeling chloride transport in unsaturated concrete under wet-dry cycles of chloride attack

This study proposes a set of new closed-form solutions for a linearly cyclic surface chloride function for predicting the transport of chloride ions in unsaturated concrete. The proposed solutions are validated, and their generality is also tested. From the study, the constant surface chloride calculated by the existing simple closed-form solution is found to be an average of the linearly cyclic surface chloride proposed in this study. Their diffusion coefficient is consistent despite using different closed-form solutions. The chloride content in unsaturated concrete is very sensitive to the time-dependent surface chloride which is cumulatively imposed. The proposed solutions are further applied to concrete with combined actions of chloride attack and compressive loading. A bilinear model for each parameter in the proposed solutions is developed. Apparently, the initial attack and the time-dependent attack of chloride ions is higher, if the stress level is higher than 41% and 19.9%, respectively. Moreover, the resistance of concrete to chloride ions is lower, if the stress level is higher than 29%. In some example, the increase of the surface chloride tends to be to the power of two, this is expected to be the reason of faster deterioration of unsaturated concrete.