HYDRATION OF CALCIUM ALUMINATE CEMENTS IN THE PRESENCE OF CALCIUM-CARBONATE

The hydration reactions of mixtures of calcium aluminate cements with calcium carbonate have seen studied at 25 degrees C and 60 degrees C u sing X-ray diffraction methods, conduction calorimetry and SEM. It is shown that the degree of conversion to the cubic phase is directly pro portional to the available reactive SiO2. Hydration of calcium alumina te cements low in SiO2 leads to nearly quantitative formation of monoc arbonate C(3)A . CaCO3 . 11H(2)O in the presence of CaCO3. The resulti ng phase assemblage gibbsite-monocarbonate is stable up to 90 +/- 5 de grees C at 1CO % relative humidity. In cements containing SiO2 bound i n phases with hydraulic activity as glass, C2S, gehlenite or related c ompounds, a hydrogrossular stable in the presence of CaCO3 will be for med. The minimum SiO2-concentration in this hydrogarnet is close to th e composition 3CaO . Al2O3 . 0.4Si0(2) . 52H(2)O.