Effect of hybrid fibre reinforcement and rubber aggregates on the flexural performance of reinforced concrete beams.

This research examines the effect of incorporating hybrid fibres and rubber aggregates on the flexural behaviour of reinforced concrete beams. Rubber shreds, prepared from waste conveyor belts and coated with sand to enhance bonding, were used as partial replacements for coarse aggregates at levels of 2.5%, 5%, and 7.5%. Additionally, glass fibre and polypropylene fibres were introduced into the concrete mix at dosages of 0.3% at different combinations, including PP 70% + Glass 30%, PP 60% + Glass 40%, PP 50% + Glass 50%, PP 40% + Glass 60%, and PP 30% + Glass 70%. A total of eighteen reinforced concrete beams were cast for this investigation, each with dimensions of 250 mm × 150 mm × 3000 mm. The beams were subjected to four-point bending tests over a clear span of 2800 mm to evaluate their flexural response. Values such as first crack load, deflection at first crack, yield load, deflection at yield, ultimate load, and deflection at ultimate were recorded. Load-deflection curves were plotted for all beam types. The results revealed that beams incorporating both sand-coated rubber shreds and hybrid fibres generally exhibited improved flexural performance compared to conventional concrete beams and those containing only rubber aggregates. Specifically, the beam containing 7.5% sand coated rubber and hybrid fibres (40% polypropylene + 60%glass fibres) showed notable improvement, with the first crack load increasing by 29.77%, deflection at first crack load by 21.47%, yield load by 52.86%, deflection at yield load by 28.73%, ultimate load by 14.32% and deflection at load by 53.84 relative to the control specimens.