Electrokinetic potential of hydrated cement in relation to adsorption of chlorides

In this study, surface charge mechanism of cement hydrates and its relations to adsorption of chloride ions are investigated. Hydrated cement paste (HCP) shows net positive surface charge by dissociation and adsorption. In HCP, chlorides bind as Friedel's salt (chemical binding) as well as adsorb on the surface of hydrates (physical binding). A surface complexation model is used to predict the adsorption of chlorides on calcium silicate hydrates (C–S–H). A good agreement between experimental and predicted chloride adsorption isotherm clearly demonstrate that the chlorides adsorb on the surface of C–S–H and bringing additional negative surface charge (SiOHCl−). However, chloride ions neutralize the positively charged surfaces of portlandite and Friedel's salt by physical adsorption. From the results, it can be concluded that C–S–H is the dominant phase in terms of chloride adsorption in HCP.