Calculation of critically supersaturated domains with respect to ettringite in the CaO-Al2O3-CaSO4-H2O system at 20°C^

摘要

The conditions of ettringite formation are very important factors to understand cement hydration but also sulfate attacks. The determination of the solubility of ettringite but also of the solubility of the phases usually found in a cement paste, made it possible to know, thanks to a thermodynamic approach, the stability domain of ettringite. However thermodynamics does not allow to know the rates of precipitation of ettringite. Thus a method has been developed to calculate the aqueous phase compositions, named critically supersaturated domains, leading to very fast nucleation rate, and thus quasi instantaneous precipitation of ettringite. From the knowledge of the aqueous phase at the boundary of the critically supersaturated domains, it is possible to assess the inhibiting or catalyzing effects of the ions on the rate of ettringite precipitation. Then typical kinetics equation can be used to simulate the precipitation rate of ettringite.