Electrokinetic properties and mechanism of chloride binding in 42-month cured cement pastes with fly ash and ground granulated blast furnace slag exposed to seawater

Abstract

To understand the mechanism of chloride binding of mature cement pastes exposed to seawater, the electrokinetic properties of the paste/solution interface have been investigated. Powders were made from 42-month cured paste of ordinary Portland cement, fly ash cement, and ground granulated blast furnace slag cement. The suspensions were prepared by mixing the paste powders into various solutions of Ca(OH)2, CaCl2, NaCl, Na2SO4, MgCl2, MgSO4 and artificial seawater with a solid-to-solution ratio of 0.1 g/L. The measurement of zeta potentials of paste suspensions was carried out. The chloride binding capacities of the pastes exposed to seawater were compared to pastes exposed to NaCl solution. The results indicated that Mg2+ and Ca2+ can reverse the negative surface charge of paste particles in aqueous solution to positive, except Mg2+ dissociated from solely MgSO4 solution, leading to the higher chloride binding capacities for the pastes exposed to seawater compared to NaCl solution. Furthermore, the important impacts of Van der Waals interaction and hydrotalcite-like phase in the paste composition on chloride binding were confirmed.