THERMAL PROPERTIES OF A SUSTAINABLE CEMENT MATERIAL: EFFECT OF CURE CONDITIONS

The effect of curing temperature and curing time on the thermal properties of wollastonite-based calcium phosphate cement, a sustainable cement material, was studied. Mass losses of 11.7% at 105-220 C and 1.8% at 380-500 C, as seen by TGA, were attributed to brushite to monetite and monetite to calcium pyrophosphate conversion, respectively, which was further confirmed by FTIR. TGA also indicated that the mass loss can be minimised by increasing the curing time and decreasing the curing temperature. Deformation values recorded from the first heating cycle of thermomechanical analysis (TMA) results revealed a linearly decreasing trend with increase in curing time. CTE values, as obtained from the second heating cycle of TMA results, remained more-or-less constant with variation in curing time and slightly increased with increase in curing temperature, possibly due to changes in moisture content. The rate of hydration at different curing temperatures were evaluated from the (exothermic) DSC curves using the linear slope in the accelerating period of cement hydration and the data were matched with a model-free Friedman analysis. The activation energy was found to be 57.8 kJ/mol. This type of cement with a lower heat of hydration and lower setting time could be a sustainable alternative to conventional cement materials.