Thermal performance of brick masonry bonded by cement/geopolymer mortar: efficiency of built and repairing

Abstract This study evaluates the thermal resilience of geopolymer-based mortar (GM) compared to conventional cement mortar (CM) in brick masonry. Experiments were designed to investigate the failure behavior of CM and GM composite masonry at 400–800 °C. Physicomechanical performance was assessed through compressive and tensile bond strength, while physical performance was evaluated by crack characteristics and failure modes. Cost and feasibility analysis for a 3 m × 3 m masonry unit included initial construction and post-exposure repair costs. Experimental results showed that CM strength decreased drastically with temperature, losing up to 88% at 800 °C, while GM exhibited a 30.4% strength gain at 400 °C before a moderate decline at higher temperatures. Brick-CM composites experienced debonding above 400 °C, whereas brick-GM maintained bond strengths above 8 MPa (compression) and 0.2 MPa (tension) across all temperatures. The bond strength of GM increases with temperature (400–600 °C), which agrees with its physical performance, where cracks become smaller and less propagate due to autonomous self-healing. Failure modes correlated with strength variations, with GM shifting from cohesive to adhesive failures as temperature increased. CM developed extensive, interconnected cracking, while GM displayed smaller, isolated cracks up to 600 °C. Cost analysis revealed that although GM had the highest initial cost, hybrid systems offered substantial post-fire repair savings (up to 58%) over CM, making them economically favorable despite higher upfront investment.