Experimental Investigations on the Flexural Responses of Reinforced Rubberized Concrete Beams with High Rubber Contents and Longitudinal Reinforcement Ratios

The accumulation of end-of-life tyres represents a growing environmental burden, motivating the incorporation of tyre rubber as a partial aggregate replacement in concrete. However, the flexural performance of reinforced rubberized concrete (RuC) beams at high rubber contents and elevated longitudinal reinforcement ratios remains insufficiently investigated. This study experimentally examined the flexural behaviour of RC beams cast with conventional concrete and RuC incorporating 40% and 60% replacement of small coarse aggregate by volume, at longitudinal reinforcement ratios of 1.5% and 2.0%, approaching the over-reinforced range. Eighteen beams were tested under four-point bending until failure by concrete crushing, with deflection, crack development, and material properties monitored throughout. Rubber incorporation reduced the modulus of elasticity and compressive strength, corresponding to a Eurocode 2 class downgrade from C45/55 to C35/40, while increasing peak axial strain. At 1.5% reinforcement, increasing rubber content progressively enhanced deflection capacity and ductility, with RuC60 beams reaching a ductility coefficient of 2.52 versus 2.43 for conventional beams. At 2.0% reinforcement, this benefit was suppressed, with ductility converging to 1.40–1.47 across all mixes as compression zone crushing increasingly governed failure. These findings indicate that the structural benefits of high-rubber-content RuC are most pronounced in moderately reinforced beams and diminish as sections approach the over-reinforced regime, informing the applicability envelope of RuC for load-bearing flexural elements.