Thermodynamic properties of C-S-H, C-A-S-H and M-S-H phases: Results from direct measurements and predictive modelling

How cement-based materials behave in storage operating conditions is important in the context of a radwaste deep geological repository. In particular, we need missing thermodynamic data for ternary and low-pH cementitious materials that have high aluminum oxide content. This work reports calorimetric measurements performed on calcium silicate hydrate (C-S-H), calcium aluminate silicate hydrate (C-A-S-H) and magnesium silicate hydrate (M-S-H) gel phases. Coupled with solubility experiments and vapor adsorption isotherms, a complete set of thermodynamic parameters for C-S-H, C-A-S-H, and M-S-H is provided. The measurements are complemented by a model predicting thermodynamic properties, which is parameterized using results from this work. Predominance diagrams allow us to confirm the relation between M-S-H and low C/S phases. The diagrams support a discussion on kinetics that may play a role in relations with other Al-and Mg-bearing phases.