Low-carbon expanded clay mortars for enhanced thermal and heat resistance

The use of expanded clay as a supplementary cementitious material in mortar offers potential for reducing carbon dioxide (CO2) emissions and improving thermal insulation, but is limited by reduced mechanical performance. This study investigates combined effects of expanded clay incorporation (0%, 10%, 20%, 30% cement replacement) and elevated temperature exposure (25°C–800°C) on quarry sand-based mortars. Mechanical properties, mass loss, and microstructural changes were evaluated, along with statistical and sustainability assessments. Results show increasing expanded clay content reduced bulk density by 1.27%–2.14% and improved thermal insulation by 13.47%. Compressive and flexural strength decreased by 2.88%–6.97% at ambient temperature for 30% replacement. After high-temperature exposure, expanded clay mortars showed improved thermal stability, retaining 47.3%–61.21% of original strength at 800°C against 32.6%–33.3% for control. Performance declined significantly at 800°C due to cracking, void formation, and microstructural damage, with ultrasonic pulse velocity values below 3000 m/s. Elastic modulus variation was similar across all mortars. Statistical analysis confirmed significant effects of both variables (p < 0.05). Partial cement replacement reduced carbon dioxide emissions by 15%–30%. Overall, optimised expanded clay use balances mechanical performance, thermal resistance, and sustainability for low-carbon, temperature-resistant mortar systems.