Thermal and mechanical performance of cement paste under high temperature thermal cycles

Concrete is identified in the literature as a suitable material for thermal energy storage applications, with even innovative application potentials such as storage media in concentrating solar power plants. To ensure a suitable heat transfer among concrete components, the binder material of concrete (cement paste) require further research and understanding to this aim. In particular, the thermal stability of cement paste under temperature cycled conditions arises as a research gap. In this study, ordinary Portland and calcium aluminate cement types were selected using a low water-cement ratio. Thermo-mechanical properties were studied before and after 1, 10, and 25 or 50 thermal cycles at 200 °C, 400 °C, 600 °C, and 800 °C. Although ordinary Portland cement paste showed micro-cracking propagation after 25 thermal cycles from ambient temperature to 200 °C and 400 °C, both cement pastes preserved their integrity, being compressive strength higher in ordinary Portland cement. On the contrary, after 25 or 50 thermal cycles at 600 °C and 800 °C, only calcium aluminate cement preserved its integrity, while ordinary Portland cement revealed a fragmentation status. Despite the compressive strength decrease in calcium aluminate paste at 600 °C and 800 °C, as a result of porosity increase, the properties were maintained after 10 thermal cycles. However, thermal conductivity in calcium aluminate paste was reduced nearly 50% after the first cycle at temperatures higher than 200 °C.