Accelerating effect of Li2CO3 on formation of monocarbonate and Al-hydroxide in a CA-cement and calcite mix during early hydration

QXRD, calorimetry and pore water analysis were performed, to gain insight into accelerating mechanism of Li2CO3 on CA-cement with CaCO3 (filler and reactant) and investigate its impact on phase formation. Data were combined with thermodynamic modeling (PhreeqC and GEMS) to gain the equilibrium phase assemblage for comparison. Acceleration was reached by adding 0.05 wt% Li2CO3 to a CA-CaCO3 mix. Early increase of pH during hydration and higher pH after the main reaction were observed by adding Li2CO3. Total heat of hydration after 20 h was higher in the sample without Li2CO3. The determined crystalline hydrate content disclosed significant differences. The reference mixture showed 8 wt% CAH(10) while there was none in the mixture accelerated by Li2CO3. The detected amount of mono carbonate (CO2 center dot AFm) after 20 h was doubled when accelerated by Li2CO3. Formation of a layered double hydroxide, formula [Al2Li(OH)(6)](2)center dot X center dot nH(2)O (with X = 1/2 center dot CO32- or OH-), acting as catalyst was considered.