Thermal analyses of cement components hydrated in the presence of calcium carbonate

Abstract

Tricalcium silicate, tricalcium aluminate and tricalcium aluminate + gypsum were hydrated in the presence of 5–50% CaCO 3 for different lengths of time (a few minutes to 28 days) and the products were examined by differential scanning calorimetry (DSC), differential thermo-gravimetry (DTG), differential thermal analysis (DTA) and conduction calorimetry. The hydration of tricalcium silicate was accelerated by CaCO 3 and there was evidence of incorporation of CaCO 3 into the calcium silicate hydrate phase. In the hydration of tricalcium aluminate, carboaluminate complex was identified and the formation of the cubic calcium aluminate hydrate phase was found to be retarded. In the tricalcium aluminate + CaSO 4 · 2H 2O + CaCO 3+ H 2O system the rate of formation of ettringite (high calcium sulphoaluminate hydrate) and its conversion to the monosulphoaluminate hydrate was accelerated by CaCO 3. On the basis of these results a mechanism has been proposed to explain the effect of CaCO 3 on the hydration of cement.