How C12A7 influences the early hydration of calcium aluminate cement at different temperatures

Abstract

Calcium aluminate cement (CAC) can contain mayenite (C12A7) as a minor phase which can influence the early hydration. Since CAC hydration is known to be extremely temperature dependent, this study presents the valuable effect of C12A7 dissolution on the early hydration at different temperatures (10, 23 and 35 °C). A reference system without C12A7 and a mixture with 4 wt% C12A7 in the cement phase was investigated using heat flow calorimetry, QXRD and pore solution measurements. In the reference system, a clear induction phase without reactions was observed at all three temperatures, whereas with C12A7, heat flow and reactions were observed at each temperature, as C12A7 was observed to dissolve instantly after water addition accompanied by C2AH8 precipitation. Saturation indices of C2AH8 are slightly higher with the addition of C12A7, which indicates a higher supersaturation of C2AH8 and explains the measured precipitation before the actual CAC main reaction.