Properties and microstructures of limestone calcined clay cement (LC 3 ) mortars subjected to elevated temperatures

This research aims to study the thermal performance of limestone calcined clay cement (LC3) mortars with various strengths at elevated temperatures. Key physical and mechanical properties, including ultrasonic pulse velocity, explosive spalling behavior, flexural, and compressive strength, were systematically evaluated. Furthermore, phase transformations and microstructural changes were analyzed using TG, XRD, MIP, and SEM. The results demonstrate that replacing cement with LC3 has little effect on high-temperature explosive behavior, but reduces the mechanical strengths at high temperatures. High-temperature explosive spalling is observed to be mitigated with increasing water/binder ratio. The compressive and flexural strengths show a slight increase or gradual decrease up to 200 °C, but exhibit a sharp decline beyond 200 °C. Elevated temperatures lead to increased total porosity and average pore diameter, accompanied by microstructural degradation, which can mainly be attributed to the decomposition of ettringite, mono-carboaluminate (Mc), C–(A)–S–H, hemicarboaluminate (Hc), CH, and CaCO3 at high temperatures.