This study examines the structural performance of reinforced concrete beams incorporating crumb rubber (CR) as a sustainable partial replacement for sand, aiming to advance environmentally friendly construction while maintaining mechanical integrity. A novel hybrid reinforcement bar (HRB) consisting of a steel core encased in glass fiber-reinforced polymer (GFRP) layers is proposed to enhance ductility, corrosion resistance, and bond behavior. Unlike conventional hybrid systems, the HRB integrates both materials into a monolithic unit, enabling superior composite action. Nine full-scale beams were tested under four-point bending, with variables including CR replacement levels (0 %, 10 %, 20 %) and three reinforcement types: conventional steel, HRB, and a steel-GFRP hybrid configuration. Key performance indicators, such as crack propagation, load–deflection behavior, stiffness, energy absorption, ductility, and strain distribution, were systematically analyzed. Increasing CR content led to moderate compressive and tensile strength reductions. However, beams with 10 % CR and HRB achieved a 25 % higher flexural capacity than steel-reinforced controls. Bond-slip behavior was found to be sensitive to both CR dosage and reinforcement type. Nonlinear finite element analysis (NLFEA) accurately captured experimental trends, including load-deflection response and crack development. Flexural strength predictions using ACI 318–19 provisions closely matched experimental outcomes. These findings demonstrate the structural viability of CR-modified concrete reinforced with HRBs and support its application in sustainable, high-performance concrete systems.
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