Effect of transitional aluminas on Portland cement hydration, phase assemblage and the correlation to ASR preventing effectiveness

This study reveals the impact of transitional aluminas on the hydration kinetics, phase assemblage of Portland cement, and ASR preventing effectiveness. Transitional aluminas were obtained by annealing reactive alumina mainly consisting of γ-Al2O3 at various temperatures. Their impacts on hydration kinetics at early age and phase assemblage were examined on a Portland cement blended with 7 wt% transitional aluminas. The increase in annealing temperature reduces the reactivity of transitional aluminas, manifesting into a decreasing dissolution rate in stimulated pore solution. The rapid dissolution of transitional aluminas annealed below 600 °C prolonged the induction period and inhibited the dissolution of C3S. Their continuous dissolution contributes to the formation of monosulfate, (SO4-OH) AFm, and katoite. As a result, the incorporation of these transitional aluminas prevents ASR effectively. In contrast, transitional aluminas annealed above 600 °C present as fillers due to their decreased reactivity, hence promoting the hydration process and exerting little effect on phase assemblage.