Significance of low water—solid ratio and temperature on the physico‐mechanical characteristics of hydrates of tricalcium aluminate

Abstract

Abstract Hydration characteristics are reported of tricalcium aluminate studied at 20 and 80 °C using water‐solid ratios of 0.2 and 1.0. Hydration products were subjected to differential thermal analysis, thermogravimetric analysis, scanning electron microscopy, length change, porosity and pore size distribution, and micro‐hardness measurements. Hydration proceeds faster at 80 °C than at 20 °C and the cubic C 3 AH 6 phase is detected in the first few seconds. At 20 °C hydration occurs with the initial formation of the hexagonal phases and expansion is continuous. At higher temperatures and a water‐solid ratio of 0.2, after an initial small expansion, the dimensional change is low. The product at 80 °C develops more than fourfold the hardness value developed at 20 °C. After 2 days of hydration, porosity, per cent C 3 AH 6 and microhardness are 15.2%, 83% and 38.9 kg/mm 2 ; corresponding values for the product obtained at 20 °C are 21.5%, 75% and 9.1 kg/mm 2 . Microstructural examination of the material formed at 80 °C indicates a closely welded and continuous network of the cubic phase. These results reveal that at a low water‐solid ratio and higher temperatures the formation of the cubic phase from C 3 A results in an enhancement of strength.