Characterization of continuous kenaf-glass fiber hybrid composites for structural application

Abstract

Kenaf fibers generally has some advantages such as eco-friendly, biodegradability, renewable nature and lighter than synthetic fibers. However, their mechanical properties are lower than synthetic fibers. Hybridization of bio-fiber with a synthetic fiber could improve the mechanical properties of composites. The aims of the study are to characterize and evaluate the properties of kenaf fiber composites and its hybridizations with glass fiber and also to investigate the performance of biocomposite as the strengthening plate for structural applications. The study was conducted in three stages. Firstly, the raw materials and composites were developed by conducting laboratory tests on physical and mechanical properties. The properties and the effects of different conditions of alkaline treatment on the properties of kenaf fibers were studied due to the various alkaline treatment conditions. Besides, the scanning electron microscopy was employed to observe the specimens appearance, fracture area and fiber diameter. The tensile properties of glass fiber composites, kenaf fiber composites and hybrid kenaf/glass fiber composites were determined with various fiber volume contents. The second stage was the application of composite materials as strengthening plate in reinforced concrete beams and subjected to flexural test under the four points loading system until failure. Fifteen beam specimens were prepared and tested for the study. The third stage was analytical investigations and theoretical development of the properties of composites and performance of strengthened reinforced concrete (RC) beams. According to the results of this study, the average diameter, the density and tensile strength of kenaf fiber were 67.6 μm, 1.2 g/cm3 and 780 MPa, respectively. Meanwhile, the tensile strength of hybrid kenaf/glass bio-composites exhibited almost equivalence to the glass fiber composites and also the highest strain energy density among the composites in the same value of fiber content. It was observed that increasing the glass fiber fraction more than 10% in hybrid composite caused the reduction in the ultimate tensile strain. For the hybrid bio-composites, debonding between the kenaf and glass layers caused the failure of composites. The flexural tests of RC beams showed the equivalent performance of the hybrid kenaf/glass bio-composite and the glass fiber composite strengthening plates. An analytical investigation has validated that the rule of mixture (ROM) could predict reasonably the elastic modulus of composites. The analytical model of this study based on the nonlinear stress–strain curve of concrete predicted well the moment capacity of RC beams as compared to the ACI 440.2R guideline. Therefore, this model was proposed in order to establish the analytical formulations for RC beams strengthened with the composites plates.