Effect of micro-sized alumina powder on the hydration products of calcium aluminate cement at 40 °C

In this work, the effect of different micro-sized alumina powders on the hydration products of calcium aluminate cement (CAC) during hydration at 40 °C is studied. The cement hydration at the designated times is terminated by the freeze-vacuum method. The phase development and microstructure evolution during the cement hydration are investigated by XRD and DSC, and SEM, respectively. It is found that 3CaO·Al2O3·6H2O (C3AH6) is the dominant product of the pure CAC after hydration at 40 °C for 3.5 h. But 2CaO·Al2O3·8H2O (C2AH8) is the dominant hydrate and C3AH6 is not found in the mixtures of CAC and micro-sized alumina powder under the same condition. The results indicate that the addition of alumina powders promotes the formation of C2AH8 and retards the conversion of C2AH8 to the C3AH6 phase. Moreover, such phase development with alumina addition is discussed.