Analytical Model for Square Root Increase of Surface Chloride Concentration and Decrease of Chloride Diffusivity

An analytical model of chloride diffusion in concrete structures is derived mathematically for a condition with a square-root increase of surface chloride concentration and a decrease of chloride diffusivity in the initial exposure period. This model is validated with four sets of chloride profiles measured by other researchers on concrete samples containing a few types of cementitious materials. The validation results indicate that the new model is accurate and suitable for the abovementioned diffusion condition with the average coefficient of determination (R2) between the modeled results and the measured chloride profiles being very close to 1 (i.e., >0.971). The model can be used to predict the chloride concentration profile after undergoing diffusion for a certain period in the initial exposure period, which can then be integrated with the profile outcomes modeled for the subsequent exposure periods with different diffusion conditions to determine the corrosion initiation period as a main part of concrete structure’s service life.