Calcium silicate hydrate (C-S-H) gel solubility data and a discrete solid phase model at 25 °C based on two binary non-ideal solid solutions

Modeling the solubility behavior of calcium silicate hydrate (C-S-H) gel is important to make quantitative predictions of the degradation of hydrated ordinary Portland cement (OPC) based materials. Experimental C-S-H gel solubility data have been compiled from the literature, critically evaluated and supplemented with new data from the current study for molar Ca/Si ratios = 0.2-0.83. All these data have been used to derive a discrete solid phase (DSP) type C-S-H gel solubility model based on two binary non-ideal solid solutions in aqueous solution (SSAS). Features of the DSP type C-S-H gel solubility model include satisfactory predictions of pH values and Ca and Si concentrations for all molar Ca/Si ratios = 2.7 → 0 in the C-S-H system, portlandite (CH) for Ca/Si ratios > 1.65, congruent dissolution at Ca/Si ratios = 0.85, and amorphous silica (SiO2(am)) for Ca/Si ratios < 0.55 as identified in the current study by IR spectroscopy.