The alkali-silica reaction: The surface charge density of silica and its effect on expansive pressure

Abstract Electrical double-layer theory has been used successfully to explain the expansion caused by the alkali-silica reaction. The net proton surface charge density of the reactive aggregate is a critical parameter for this approach. However, little work has been done to measure the surface charge density of silica as a function of pH at background electrolyte concentrations that are relevant to the conditions existing in concrete pore solution. We therefore measured the net proton surface charge density of silica gel, opal, and quartz as a function of pH in 0.7 mol·L −1 electrolyte solution (NaCl and KCl). The effects of electrolyte concentration and pH on the electrical double-layer estimate of expansive pressure caused by the alkali-silica reaction are significant.