Performance of kenaf fibre reinforced concrete under static and dynamic loadings

Abstract

Concrete is considered as a brittle material, its enrichment with distributed short kenaf fibres is believed to increase the toughness of matrices. This is achieved by prohibiting the concrete from being cracked and propagated. Kenaf is a natural fibre has typically some benefits such as being renewable, eco-friendly, biodegradable and locally accessible as compared to other types of fibres used for concrete reinforcement. This study was conducted experimentally to investigate the characteristics of kenaf fibre reinforced concrete (KFRC) materials and to determine the performance of kenaf fibre reinforced concrete beams under static and dynamic loadings. The basic concrete materials used in the study are 10 mm aggregate, ordinary portland cement and clean water. Mixing procedures were evaluated to produce KFRC materials with different chopped fibre lengths (10 mm, 15 mm, 20 mm, 25 mm and 30 mm) and fibre volume fractions (0.5%, 1%, 1.5% and 2%). At the preliminary stage, the alkaline treatment test was carried out on the kenaf fibres. Then, the raw materials and concrete properties were investigated by a series of physical and mechanical property tests on fresh and hardened concrete to identify the optimum characteristics of fibre length and content to be used in the concrete mixture. The study also investigated the structural behaviour of KFRC beams, in which the samples were undertaken by monotonic bending load and repeated bending load tests under four points loading system until failure. The load-deformation behaviour of the beams was observed and monitored during testing. Results from the study of alkaline treatment on kenaf fibres found that the best condition was 5% NaOH in three hour emerging time. The study also found that the optimum length of kenaf fibres was 20 mm and the optimum volume fraction yields the value of 1%. From the KFRC beam tests, it was found that the KFRC beams exhibited better performance as compared to normal concrete beams. The best static and dynamic behaviour was observed for the beam using KFRC in tension zone and plain concrete in compression zone, with the ultimate bending load of 5.9% higher than normal concrete beam after the flexural test and 15.6% higher than normal concrete beam after the repeated load test. By observation, the number of crack formation in tension zone increased by 40% and crack spacing was less by 15% as compared to normal concrete beams. The total energy absorption from the load-deflection behaviour of KFRC beams until ultimate failure was 77% higher than normal concrete beams. The relationships between KFRC material and structural performance against fibre lengths and volume fractions have been developed based on the non-linear numerical models and proposed for the analysis and design of KFRC. Conclusively, KFRC material and structure exhibit appreciable tensile, flexural, and impact strength under static and dynamic loadings compared to normal concrete.