Temperature-dependent behaviour and microstructure of fungus-treated carbonate sand

This study investigates a bio-mediated reinforcement technique for carbonate sand using fungal mycelium, emphasising its temperature-dependent mechanical performance under elevated temperature conditions. Specimens composed of Pleurotus ostreatus, wheat bran, and carbonate sand are subjected to undrained triaxial shear tests at 20, 35, and 50 °C. The microstructural mechanisms underlying the thermal response are also analysed to support the interpretation of the strength behaviour. The results indicate that fungal treatment significantly enhances shear strength, reduces pore pressure accumulation, and raises dilative behaviour during shear. As the temperature increases, the mechanical response transitions from strain hardening to strain softening, with peak strength and stiffness increasing by approximately 20%. With rising temperature, the strength parameters exhibit a reduction in cohesion and an increase in internal friction angle, indicating a shift from bonding-dominated to friction-dominated behaviour. Thermal exposure induced hyphal shrinkage and fusion, enhancing interparticle bonding through the formation of adhesive bridges. These changes reduce surface porosity and pore circularity by over 50%, contributing to matrix densification and enhanced stability. These findings demonstrate that fungal mycelium enables thermally resilient, low-carbon ground improvement, particularly in tropical, coastal, and carbonate-rich environments.