Influence of zirconia and rice husk ash on residual characteristics of sustainable cement mortar after exposure to elevated temperatures

This study examines the potential of zirconia (ZrO₂) and rice husk ash (RHA) as sustainable alternatives to ordinary Portland cement (OPC) and natural sand in cement mortar. It aims to address environmental concerns linked to cement production and sand extraction. Mortar mixes were prepared by varying ZrO₂ content from 1% to 5% and RHA from 10% to 60%, while keeping a consistent binder-to-sand ratio of 1:3 and a water-cement ratio of 0.5. Extensive tests assessed the mechanical and durability characteristics of the cement mortar, including compressive, tensile, and flexural strength, tensile bond strength, drying shrinkage, water absorption, and capillary water absorption after exposure to elevated temperatures of 100 °C, 200 °C, 300 °C, and 400 °C. The results are compared and analysed to evaluate the behaviour of the mortar under normal room temperature and elevated temperatures, providing detailed insights into its structure, composition, and chemical characteristics, thereby enhancing understanding of its features and durability. The findings indicate that incorporating 20–30% rice husk ash (RHA) with 2–3% zirconia markedly improves the mechanical strength, durability, and thermal stability of cement mortar. The combined effects of zirconia’s nucleation enhancement and RHA’s pozzolanic activity lead to microstructural refinement, reduced porosity, and enhanced performance up to 300 °C.