Elevated Temperature Behavior of Bagasse and Human Hair Fiber‐Reinforced Fly Ash Geopolymer Composites

ABSTRACT This study investigates the thermo‐mechanical performance of fly ash‐based geopolymer composites reinforced with bagasse and human hair fibers at varying fiber contents (1%, 1.5%, and 2% by weight). Composites were exposed to elevated temperatures (200°C, 400°C, 600°C, and 800°C) and fabricated using sodium hydroxide and sodium silicate as alkali activators. Compressive strength (CS) and flexural strength (FS) were evaluated across all compositions and thermal conditions. Results indicate a significant reduction in mechanical performance with increasing temperature. For 2% fiber content, the CS of bagasse fiber composites decreased from 25.87 MPa at 200°C to 7.12 MPa at 800°C, while human hair composites showed a decrease from 24.45 MPa to 13.62 MPa. Flexural strength followed a similar trend, with human hair composites exhibiting superior retention of strength across the temperature range. SEM analysis revealed stronger fiber–matrix bonding and reduced porosity in human hair composites, contributing to enhanced thermal stability. Despite thermal degradation effects, composites with up to 1.5% fiber content demonstrated sufficient mechanical integrity for moderate‐temperature applications. The findings highlight the potential of utilizing sustainable, low‐cost fiber reinforcements in geopolymer systems, offering viable alternatives to synthetic composites in thermally demanding environments between 200°C and 600°C.