Using a geochemical model for predicting chloride ingress into saturated concrete

Chloride ingress into concrete was simulated based on a geochemical model that includes Fick's second law for transport phenomena and thermodynamic equilibrium, kinetics treatment and surface complexation for chemical phenomena. The geochemical model was validated by comparing the numerical results and experimental data (extracted from the literature) for CEM II concrete exposed to sodium chloride, potassium chloride, magnesium chloride and calcium chloride solutions. The geochemical model was then applied to investigate the influences of different chloride solutions. The results showed that exposure to magnesium chloride solution led to the greatest amount of Ca²⁺ leaching. Relationships between the total chloride content (TCC) and the free chloride content (FCC) of concrete were established. Increasing the exposure time of the concrete was found to lead to a decrease in chloride binding capacity. The proposed correlations allow determination of the FCC or the TCC of concrete when one of the two is known. The geochemical model was also verified by predicting the chloride content of a CEM III concrete bridge submerged in seawater after 17 and 34 years. With numerous applications, the geochemical model seems a reliable tool for the durability design of concrete structures exposed to chloride environments.