Concrete materials in structures are prone to fire and deteriorate under elevated temperatures, and their retained properties are critical to the soundness and serviceability demands of the structure. The effort to improve concrete toughness and ductility necessitates fibres in concrete. Adding biofibers to concrete has been considered promising due to their eco-sustainability, relatively high stiffness, and CO2 neutrality compared to conventional fibres. Based on previous research, Jute, Hemp, and Sisal in the concrete composite have benefited pore pressure and crack reduction of heated concrete. However, lately, the fire performance of Kenaf Fiber Reinforced Concrete (KFRC) is yet to be examined despite increasing structural usage. Therefore, this research presents an experimental report on a 28-day cured KFRC, and Plain Concrete (PC) as reference mixtures, heated for 100°C, 200°C, 300°C, 400°C, 600°C and 800°C, sustained for 2 h and tested after cooling. The fibres were treated and examined through SEM and TGA to ascertain their interfacial and thermal properties, using an optimum volume (0.75%) and length (25 mm) in the grade 40 mix. The KFRC’s residual physical and mechanical properties, weight, ultrasonic pulse velocity, and morphology were determined and compared with the control samples. The test results revealed that KFRC peaked its compressive strength at 300°C with a 4% strength gain and was thermally stable up to 400°C, compared with PC, which gained 3% at 400°C with superior performance. KFRC split tensile and flexural strength up to 300°C improved by 2% and 1% compared with the PC, which had 1% and 0% gain, respectively. Kenaf fibre improved concrete ductility and crack reduction under 400°C. The research would provide a database for KFRC standards development, fire-resistant design, and application strategy.
