Study of the hydration of calcium zirconium aluminate (Ca7ZrAl6O18) blended with reactive alumina by calorimetry, thermogravimetry and other methods

The reactivities of hydratable alumina, calcium zirconium aluminate and their binary mixtures were investigated by calorimetric method, X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), differential thermal/thermogravimetric analysis (DTA–TG) and scanning electron microscope observations. The rate of heat evolution illustrates only one distinct exothermic peak in the mixtures containing calcium zirconium aluminate which corresponds the subsequent precipitation of hydrated material mainly in the form of amorphous CaO–Al2O3–H2O phases and crystalline C4AH19 occurs simultaneously after wetting of Ca7ZrAl6O18 grains. Nevertheless, coexistence of both unstable calcium aluminate hydrates (CAH10, C2AH8, C4AH19) and thermodynamically more stable C3AH6 detected by FT-IR and DTA–TG in the paste cured at 20 °C may have originated in the thermally induced partial conversion reaction due to the considerable amount of heat generated by the Ca7ZrAl6O18 hydration. It is also found that curing temperature affected the hydration products formed in the hydration products of both Ca7ZrAl6O18 and Ca7ZrAl6O18/Al2O3 blends. Reactive alumina influences the hydration behavior of Ca7ZrAl6O18 facilitating the nucleation and growth of hydration products, causes characteristic changes in the microstructure of hardened blended pastes and favors recrystallization of dehydrated calcium aluminates.