Solubility Behavior of the Hydration Products in the Pore Solution of Hydrated Cement Pastes

The concentrations of Ca, Al, Si, Na, K, SO42- and pH value in the pore solution of Portland cement were measured during the first 28 days of hydration at room temperature. A thermodynamic analysis of the elemental concentrations was used to predict saturation indices of various solid phases known to form in normal cement system. During the first 4 h the composition of pore solution is dominated by K+, Na+, SO42- and OH-. Large and rapid changes in the concentrations of Ca2+, SO42- and hydroxyl occurred between 4 h and 24 h, and thereafter the pore solution is essentially one of alkali hydroxides. Portlandite and calcium monosulfoaluminate was slightly supersaturated after the first few hours. Saturation indices calculations for ettringite and C-S-H indicate the high levels of supersaturation until 28 days.