Thermodynamic modelling and experimental investigation on chloride binding in cement exposed to chloride and chloride-sulfate solution

Abstract

This paper mainly investigates the chloride binding capacity of cement paste immersed in chloride and various chloride-sulfate solution. Taking into account the influence of sulfate on the chemically bound and physically adsorbed chloride, a thermodynamic model consisting of hydration model, phase equilibrium model and surface complexation model is established to describe the chloride binding behavior. The formation of Friedel’s salt and ettringite in chloride-sulfate solution are tested by XRD and simulated by the thermodynamic model. The model result of chloride binding behavior in chloride and chloride-sulfate solution are in good agreement with the experimental results. Physically absorbed chloride ions and chemically bound chloride ions are calculated quantitatively. The formation of Friedel’s and Kuzel’s salt are reduced by the presence of sulfate as well as the chloride adsorbed on C-S-H. The evolution of Friedel’s salt and ettringite is closely related to chloride and sulfate concentrations, which is confirmed by the experiment and the proposed model. The thermodynamic model proposed in this paper can be useful to effectively describe the interaction between chloride and sulfate on cement paste.