Performance analysis of fiber reinforced recycled aggregate concrete at elevated temperatures using response surface methodology

The increasing risk of fire hazards and the environmental burden of construction and demolition (C&D) waste necessitate sustainable, fire-resistant building materials. This study investigates the potential of recycled aggregate concrete (RAC) reinforced with fibers to enhance high-temperature performance while promoting waste utilization. In the first phase, concrete mixtures with 0%, 25%, and 50% recycled aggregate (labeled RAC00, RAC25, and RAC50) were evaluated at 23 °C, 300 °C, and 600 °C. RAC00 exhibited a 16% reduction in compressive strength at 300 °C and over 50% at 600 °C. While RAC25 initially showed a 10-30% decrease compared to conventional concrete at room temperature, it exhibited only a 1% strength decline at 300 °C and a 28% reduction at 600 °C, making it the most effective composition for further study. In the second phase, steel fibers (SF) and polypropylene fibers (PPF) were incorporated into RAC25, yielding substantial tensile strength improvements: RAC25-SF increased by 5.6% at 23 °C, 24.8% at 300 °C, and 28.3% at 600 °C. RAC25-PPF showed a 12.5% increase at 23 °C but declined at higher temperatures, with a 9.9% decrease at 300 °C and 32.9% at 600 °C. SF enhanced strength across all temperatures, while PPF reduced performance above 200 °C. Fiber additions improved ductility, toughness, and moisture retention, mitigating crack propagation under heat. Statistical modeling using ANOVA and response surface methodology (RSM) confirmed high model validity (R² > 0.80). The study concludes that RAC25 with steel fibers offers a sustainable, heat-resistant construction material, addressing both fire resilience and C&D waste challenges.