Abstract
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.
Highlights
Hydraulic bonding via calcium aluminate cement (CAC) is the most applied mechanism due to both castable fluidity and green mechanical strength [1,2,3,4,5]
Particle size distribution of the synthesized calcium zirconium aluminate revealed the most of the powder is in micron level and around 50 vol% of the material was below lm
The X-ray diffraction (XRD) study obtained from the synthesized sample revealed that Ca7ZrAl6O18 was identified as the major crystalline phase as well as very small peaks related to impurity of CaZrO3
Summary
Hydraulic bonding via calcium aluminate cement (CAC) is the most applied mechanism due to both castable fluidity and green mechanical strength [1,2,3,4,5]. Absence of any major peak belonging to Ca7ZrAl6O18 suggests that transformation of this phase is complete in the hardened binder paste containing 50 mass% Al2O3 cured at 50 °C (50A50C7A3Z-H-T50), while at the lower curing temperature remains present in the unhydrated form (50A-50C7A3Z-HT20) The spectra of hydrated pastes prepared using different curing temperatures showing different absorption bands indicate not the same hydration products for these samples.
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