Non-ideal solid solution aqueous solution modeling of synthetic calcium silicate hydrate

New data relevant to calcium silicate hydrate (C-S-H) gels prepared at room temperature have been obtained over a time period of up to 112 weeks. X-ray diffraction (XRD) indicates equilibrium was attained after 64 weeks. Coupled with fourier transform infrared (FT-IR) spectroscopy, a phase change in C-S-H gel at Ca/Si approximate to 1.0 was identified and the occurrence of portlandite as a distinct phase for Ca/Si > 1.64. The incongruent dissolution of C-S-H gel was modeled as a non-ideal solid solution aqueous solution (SSAS) between the end-member components CaH2SiO4 (CSH) and Ca(OH)(2) (CH) using equations defining the solidus and solutus curves on a Lippmann phase diagram. Despite being semiempirical, the model provides a reasonable and consistent fit to the solubility data and can therefore be used to describe the incongruent dissolution of C-S-H gels with compositions Ca/Si >= 1.0. (c) 2006 Elsevier Ltd. All rights reserved.