A model for dissolution of CaO-SiO2-H2O gel at Ca/Si > 1

Abstract Calcium silicate hydrate (CaO-SiO 2 -H 2 O) gel is the principal hydration product of Portland cement. Experimental data show that the dissolution of CaO-SiO 2 -H 2 O (C-S-H) gel is strongly dependent on Ca/Si (C/S) ratio in the range of C/S > 1. A model for dissolution of C-S-H gel is presented by considering a nonideal mixture of binary solid solutions of Margules type. Guggenheim and Prausnitz equations are applied to represent the activities of model solids as a function of mole fractions. The Gibbs-Duhem equation, incorporating the activities of model solids, is then used to express the conditional solubility products of model solids in terms of C/S ratio. The determination of Guggenheim's empirical parameters is performed with geochemical code PHREEQE on experimental data. By these procedures, a dissolution model of C-S-H gel is described. The solubility results predicted by the proposed model are comparable with experimental data.