Combined effect of hybrid PE-PBO fiber reinforcement on the mechanical properties of lightweight fly ash-slag-based engineered geopolymer composites at ambient temperature and after exposure to elevated temperatures

This study introduces a novel lightweight engineered geopolymer composite (EGC) that exhibits high ductility at ambient temperature and enhanced residual performance after exposure to elevated temperatures. To simultaneously achieve high ductility, thermal stability, and weight reduction, this composite utilizes a hybrid reinforcement comprising polyethylene (PE) and poly(p-phenylene benzobisoxazole) (PBO) fibers at a low total volume fraction of 1.0%, alongside expanded polystyrene beads. While the inclusion of PBO fibers moderated the strain capacity, the hybrid PE-PBO EGC still achieved a strain capacity significantly surpassing that of previously reported PBO-reinforced composites. Regarding thermal resistance, the strain-hardening behavior of mono-PE EGCs deteriorated significantly above 100 °C. In contrast, the PBO- and hybrid PE-PBO systems retained enhanced strain-hardening capabilities at moderate exposure (100 °C), before transitioning to a strain-softening response at 300 °C. The typical morphologies of the fibers and matrix of the EGCs after exposure to elevated temperatures were observed using SEM. • Lightweight EGCs incorporating hybrid PE-PBO fibers and EPS beads were developed. • The hybrid EGC exhibited a density of 1.50 g/cm 3 and a tensile strain capacity of 4.14%. • Timing of thermal exposure significantly affected compressive strength depending on fiber types. • PBO fibers in the hybrid system prevented catastrophic failure at elevated temperatures. • Moderate heating at early age improved the mechanical properties of PBO-reinforced composites.