Flexural Behaviour of Reinforced Concrete Beams Cast with Hybrid Fiber Reinforced High-Strength Concrete Incorporating Steel, Coir and Palm Fibers

Abstract

The brittle nature of high-strength concrete often limits its structural performance under flexural loading despite its superior compressive strength. The incorporation of hybrid fibers has emerged as an effective approach to enhance ductility, crack resistance, and energy absorption capacity of reinforced concrete members. This study investigates the flexural behaviour of reinforced concrete beams cast with hybrid fiber reinforced high-strength concrete incorporating steel, coir, and palm fibers. Eight concrete mixes, including one control mix and seven fiber-reinforced mixes, were developed using M50 grade high-strength concrete. Reinforced concrete beam specimens were cast and tested under two-point loading to evaluate ultimate load capacity, load-deflection behaviour, flexural toughness, ductility, and crack propagation characteristics. The experimental results demonstrated that the incorporation of hybrid fibers significantly enhanced the structural behaviour of reinforced concrete beams. Among all the investigated mixes, the beam cast with Mix M4 containing 0.5% steel fiber, 0.25% coir fiber, and 0.25% palm fiber exhibited the best performance. The ultimate load carrying capacity increased from 70 kN for the control beam to 90 kN, representing an improvement of approximately 28.6%. The hybrid fiber reinforced beams also exhibited higher deflection capacity, improved ductility, greater energy absorption, and reduced crack widths compared to conventional concrete beams. The presence of steel fibers effectively bridged macro-cracks, while coir and palm fibers contributed to micro-crack control and post-cracking toughness. The study concludes that the combined use of steel, coir, and palm fibers provides an effective and sustainable hybrid reinforcement system capable of significantly improving the flexural performance and structural behaviour of reinforced concrete beams.