A thermodynamic model for the calcium silicate hydrate gel, modelled as a non-ideal binary solid solution

Solubility calculations have been performed on the CaO-SiO2-H2O system. A modified version of the program SOLISOL was used to model the C-S-H gel as a non-ideal binary solid solution. To account for the non-ideality a mixing model of Margules type, expressing the Gibbs excess free energy of a solid solution as a function of the composition was used. The model indicates that the calcium rich gel coexists with almost pure Ca(OH)(2)(s). A program PAS-SIPHIC has been written to handle the solubility calculations in the region where the C-S-H phase coexists with Portlandite. (C) 1997 Elsevier Science Ltd.