Post-fire strengths and morphological properties of high-strength concrete reinforced with kenaf fibres

The high manufacturing cost of conventional fibres and the need for greener and more sustainable constructions necessitate the adoption of plant-based fibres in concrete. Previous research has shown that fibres remarkably influence the post-fire behaviour of concrete. Post-fire concrete strengths and micro-imageries are vital to the serviceability requirements of concrete. Therefore, this paper presents an experimental report on a 28-day cured kenaf fibrous high-strength concrete (KFHSC), heated from ambient temperature to 800 ºC at 100 ºC intervals, sustained for 1, 2, and 3 h, and tested after being cooled naturally to ambient temperature. The fibres were treated and examined through SEM to ascertain their interfacial properties. Test samples of concrete grade 60 were prepared using an optimum volume (0,75 %) and length (25 mm). The KFHSC's residual strength characteristics, weight, ultrasonic pulse velocity, and morphology were determined and compared with plain (unreinforced) high-strength concrete. The findings show that samples of both mixes degraded with an increase in temperature and exposure durations. However, kenaf fibre retrained crack extension at a lower temperature phase and through networks of channels within the matrices, reduced pore pressure build-up at a higher temperature phase and consequently lessened the explosive spalling of the heated concrete.