Thermodynamic modeling of the CaO-SiO2-CaCO3-H2O closed and open system at 25ºC

Abstract

This paper reports on a thermodynamic calculation-based study of the CaO-SiO2-CaCO3-H2O closed system at 25 °C, conducted to determine the range of carbonate ion concentrations at which each phase of the system is stable. Portlandite (CH) and the CSH gel were found to be stable for carbonate ion concentrations of less than or equal to 7.62 X 10-3 mM/kg and 1.62 x 10-2 mM/kg, respectively. The CSH gel was found to remain stable in the system at pH values ranging from 10.18 to 10.48. In the CaO-SiO2-H2O open system at 25 °C, likewise studied, with PCO2 held constant at atmospheric values, only hydrated silica (SH) and calcite were found to be stable.

Keywords

• cement
• carbonation
• thermodynamic modeling