Comparison of calcium aluminate cements on hydration and strength development at different initial curing regimes

Abstract

This paper examines the influence of CA2 (monocalcium dialuminate, CaAl4O7) in calcium aluminate cement (CAC) on strength development relevant to conversion reaction in the hydration process. to ensure the different phase compositions at early ages, a curing temperature of 5 and 65 °C was applied to fabricating cement paste with two types of CAC for the first 24 h. The hydration behavior of the specimen was investigated by isothermal calorimetry, X-ray diffraction, and thermogravimetry. Simultaneously, the development of pore structure was analyzed by mercury intrusion porosimetry. The results showed that CAC containing CA2 exhibits a gradual increase in strength with no drop during test periods, regardless of initial temperature, while the typical CAC paste treated at 5 °C suffers from a strength loss due to conversion. The performance of refractory CAC may arise from CA2 hydration, producing amounts of crystalline gibbsite and thus mitigating/restricting the transformation of metastable hydrates into stable ones in order to preserve their chemical balance in the cement matrix. This phenomenon could be supported by a variation in hydrate composition and pore volume derived from the present works. However, conversion reaction should be verified in the temperature-fluctuated environment and over long-term stability in future work.