Effect of kenaf fiber on the mechanical properties of reinforced concrete structures

Abstract

There is currently a great deal of interest in developing technology using natural organic fiber materials in cement composites. Kenaf is one of the organic fiber that has potential to be used in concrete. Kenaf fiber has many advantages such as affordability, renewability, recyclability, and biodegradability. Its tensile properties are comparable to those of other natural fibers, such as jute, flax and bamboo. Fiber reinforced concrete (FRC) was introduced to the industry to improve concrete properties and to prevent the cracking of reinforced concrete members. Nevertheless, the limited use of FRC in load-bearing structures seems to be due to a lack of accepted design mixes and guidelines. This study investigates the physical and mechanical properties of Kenaf fiber reinforced concrete (KFRC) and its structural behaviour as concrete beam under static loads. This study was carried out mainly by experiment. The experiments were conducted according to relevant American Standards (ASTM) and British Standards (BS), as well as recommended methods from past researchers. A number of parameters were observed from the experiment, such as physical properties (colour, fiber distribution in concrete, surface morphology, density, aspect ratio, weight loss and water absorption), properties of fresh KFRC (slump, compacting factor and vebe time), properties of hardened KFRC (ultrasonic pulse velocity, rebound hammer, density, compressive strength, splitting tensile strength, flexural strength, static modulus of elasticity and equivalent compressive strength) and performance of KFRC when used as beams under flexural loadings (ultimate load, deflection, cracking, steel strain, concrete strain, bonding between concrete and steel reinforcement and neutral axis). A total of 1300 concrete specimens (cube, cylinder and prism) and 7 beam specimens were casted and tested in this study. A theoretical model for the analysis and design of Kenaf fiber reinforced concrete materials and structural beam elements was proposed and evaluated. Results show that the presence of Kenaf fiber in concrete improved the properties such as splitting tensile strength, flexural strength and ultimate load of beam. However, it reduced the concrete properties if the fiber used was over the limit, the properties such as density, slump, compacting factor, vebe time, ultrasonic pulse velocity, rebound hammer, compressive strength, static modulus of elasticity and equivalent compressive strength. KFRC only can perform well under the suitable fiber to cement volume fractions of up to 0.75%. Fiber length did not affect concrete performance. The performance of KFRC was greatly influenced by the distribution and orientation of Kenaf fibers in concrete. Control and handling during the mixing process of KFRC was a major factor in producing quality concrete. Finally the use of Kenaf fiber as reinforcement in concrete is highly recommended based on improvements in material strength and structural performance.