Ion-specific effects influencing the dissolution of tricalcium silicate

It has been recently demonstrated that the dissolution kinetics of tricalcium silicate (C3S) is driven by the deviation from its solubility equilibrium. In this article, special attention is paid to ions relevant in cement chemistry likely to interact with C3S. In order to determine whether specific effects occur at the interface C3S-water, particular efforts have been made to model ion activities using Pitzer's model. It has been found that monovalent cations and monovalent anions interact very little with the surface of C3S. On the other side, divalent anions like sulfate slow down the dissolution more strongly by modifying the surface charging of C3S. Third, aluminate ions covalently bind to surface silicate monomers and inhibit the dissolution in mildly alkaline conditions. The formation and the breaking of these bonds depend on pH and on [Ca2+]. Thermodynamic calculations performed using DFT combined with the COSMO-RS solvation method support the experimental findings. (C) 2014 Elsevier Ltd. All rights reserved.