Temperature-dependent reactive-transport simulation of chloride binding in cementitious materials with kinetic Friedel salt formation

A reactive-transport model for chloride binding in cementitious materials is developed and validated over four temperatures (5, 21, 35, and 80°C) and three chloride concentrations (5, 10, and 20 g.L−1). Diffusive transport is coupled with surface complexation reactions (SCRs), in which the equilibrium constants (logK) are described by a nonlinear temperature-dependent formulation, and with kinetic laws for Friedel salt precipitation and dissolution that depend explicitly on temperature and chloride activity. Compared with equilibrium-only approaches, the proposed model avoids over-prediction of early-age bound chloride at elevated temperature. The nonlinear logK formulation provides a more consistent representation of SCR behavior from 5 to 80°C, while the chloride-activity-dependent Friedel salt kinetics is required to capture the delayed precipitation observed at 80°C under high chloride exposure. . The simulations further show that Friedel salt should be retained as the governing chloride-binding AFm phase in the final model formulation, whereas Kuzel salt does not reproduce the observed bound-chloride level satisfactorily under the investigated high-temperature conditions. In addition, kinetic Portlandite dissolution regulates Ca2+ supply and shifts the balance among competing phases. An additional assessment using CEM V indicates that the framework remains applicable up to 35°C, whereas the discrepancy at 80°C reveals a binder-specific limitation of the current high-temperature mineralogical submodel.