Hydration of calcium aluminate cements in the presence of calcium carbonate

The hydration reactions of mixtures of calcium aluminates with CaCO (sub 3) have been studied at 25 and 60 degrees C using XRD, conduction calorimetry and SEM techniques. It is shown that the degree of conversion to the cubic phase is directly proportional to the available reactive SiO (sub 2) . Hydration of aluminate cements low in SiO (sub 2) leads to nearly quantitative formation of monocarbonate C (sub 3) ACaCO (sub 311H) (sub 2) O in the presence of CaCO (sub 3) ; the resulting assemblage gibbsite-monocarbonate is stable to up to 90 + or - 5 degrees C at 100% relative humidity. In cements containing SiO (sub 2) bound in phases with hydraulic activity as glass, C (sub 2) S, gehlenite or related compounds, a hydrogrossular stable in the presence of CaCO (sub 3) will be formed. The minimum SiO (sub 2) concentration in this hydrogarnet is approximately 3CaOAl (sub 2) O (sub 30.4SiO) (sub 25.2H) (sub 2) O.