Mechanical performance of EPS-self compacting concrete reinforced with waste plastic fibers under elevated temperatures

Purpose This study aims to investigate the effects of recycled polyethylene terephthalate (PET) fibers and expanded polystyrene (EPS) beads on the mechanical behavior of self-compacting concrete (SCC) exposed to elevated temperatures up to 600°C. Design/methodology/approach Five SCC mixtures were prepared: a reference mix, an EPS-modified mix (10% replacement of coarse aggregate by volume), and three mixes incorporating PET fibers at volume fractions of 0.35%, 0.5% and 0.75%. Fresh properties were evaluated using slump flow, T50, V-funnel, L-box and sieve segregation tests. Based on fresh performance, 0.5% PET fibers were selected as the best content. Three mixtures (R, E 10% and 0.5% f) were exposed to temperatures of 25°C, 100°C, 200°C, 400°C and 600°C. Residual compressive and flexural strengths were determined. Findings EPS improved workability but reduced mechanical strength due to weak interfacial bonding and low stiffness. PET fibers slightly reduced flowability while enhancing compressive and flexural strength through crack-bridging and improved stress distribution. Strength increased at 200°C due to continued hydration and microstructural densification, followed by significant degradation at ≥ 400°C due to dehydration, microcracks and decomposition of hydration products. Severe deterioration occurred at 600°C. Practical implications The developed mixtures are suitable for lightweight structural applications exposed to moderate temperatures (≤200°C), while their use at higher temperatures (>400°C) requires caution due to rapid strength loss. Originality/value This study provides insight into combined EPS–PET effects under thermal exposure. While individual effects of PET or EPS on concrete performance have been reported, this study examines their integrated contribution to heat resistance and post-fire mechanical behavior. The research also promotes sustainable construction practices and offers potential pathways for enhanced fire safety in structural applications.