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

Electrical double-layer theory has been used successfully to explain the ex pansion caused by the alkali-silica reaction. The net proton surface charge density of the reactive aggregate is a critical parameter for this approac h. However, little work has been done to measure the surface charge density of silica as a function of pH at background electrolyte concentrations tha t are relevant to the conditions existing in concrete pore solution. We the refore 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 an d KCl). The effects of electrolyte concentration and pH on the electrical d ouble-layer estimate of expansive pressure caused by the alkali-silica reac tion are significant. (C) 1999 Elsevier Science Ltd. All rights reserved.