Potassium dawsonite formation in calcium aluminate cements

The carbonation of calcium aluminate in the presence of alkali has been the subject of many investigations. The process, termed "alkaline hydrolysis", has been associated with external alterations produced in calcium aluminate cement (CAC) materials: dark stains, surface peeling etc, and the final consequence of this process is an important loss in mechanical strength of the material. However, there was no evidence of an intermediate compound, unlike carbonation of calcium aluminate cement without alkalis, where compounds do form. The formation of an intermediate compound, the formula of which is close to potassium dawsonite, KAl(CO3)(OH)(2), has been observed in calcium aluminate cement specimens with moderate alkali contents. In the present investigation the compound is characterised by XRD, FTIR, SEM/EDX and TEM/EDX.