Flexural strength and toughness of steel fiber reinforced concrete beams

Abstract

This study has proposed to evaluate the flexural response of reinforced concrete (RC) beam elements of size 150 mm × 200 mm × 1000 mm (with conventional steel rebars of reinforcement ratio of 0.6%) with and without steel fibers of varying reinforcement index (RI) (product of fiber aspect ratio, AR and volume fraction, Vf%). The mechanical strength (compressive, split tensile and prismatic flexural strength) of concrete are ascertained with hooked steel fibers (HSF) and crimped steel fibers (CSF) in RI of 0.25–1.50 in comparison to controlled concrete (CC) with no fibers. RC beams (with and without HSF and CSF of RI = 0.5–1.0) have been tested under flexure and the loads and deflection at first cracking, yielding, peak and ultimate failure points show that the performance of fibrous beams are higher than non-fibrous beams, and CSF is effective than HSF in RC beams. The RC beams with CSF has higher residual strength and toughness (at deflection point, L/150, L being the span), and total absorbed energy than the specimens with HSF. The residual strength and toughness (at L/150) and the total absorbed energy (TAE) of RC beams with HSF and CSF are higher than the control beams (without fibers). The experimental reserve flexural capacity (ERFC) of RC beams ≥ 1.30. The stiffness of the fibrous RC beams at initial pre-cracking, post-cracking and pre-peak stages are higher than the non-fibrous beams. The deflection ductility indices (yield and peak) have shown an increase when RI is increased from 0.5 to 1.0. The flexural test results have shown that addition of HSF and CSF has improved the first cracking, yielding and peak loads of RC beams (at RI = 0.5, 0.6 and 1.0). The crack spacing and width of flexural cracks in the RC beams have reduced due to the addition of steel fibers, and CSF has shown better cracking behavior than HSF in the beams. The equivalent flexural strength (toughness factor) and strength ratio of RC beams (with conventional reinforcement) with CSF are higher than the beams with HSF, and, therefore, crimped fibers are recommended for effective use in construction.