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The solution that surrounds hydrating cement particles contains dissolved species which are important in the overall process. A method, based on the Gibbs‐Duhem equation for a three‐component system, has been developed for computing the composition of one phase from values for its equilibrium solubility in a second phase. The method has been used to compute the CaO:SiO 2 ratio for two types of calcium silicate hydrate (C‐S‐H) gel, one of which is thought to form from hydrating tricalcium silicate (Ca 3 SiO 5 ), and the other by precipitation from appropriate solutions. The results agree well with measured values reported in the literature. They have also been used to help define the probable composition of the C‐S‐H layer which forms on tricalcium silicate surfaces during the early stages of hydration when the reaction is slow. A chemical potential phase diagram is constructed from which thermodynamic quantities can be computed directly. The free energies of formation have been estimated for two types of C‐S‐H formed from CaO, SiO 2 , and H 2 O, These results provide insight into the structure and composition of C‐S‐H, which is the most abundant product in portland cement systems.
Gartner et al. (Thu,) studied this question.