Shear and Flexural Performance of Recycled Plastic Aggregate Concrete

Rapidly growing plastic waste and limited recycling pathways have heightened concerns about landfilling and environmental pollution. At the same time, accelerated urban development has increased demand for natural aggregates, hastening resource depletion. Using recycled plastic as aggregate in concrete offers a circular solution that addresses both challenges, diverting plastic from waste streams while reducing reliance on virgin aggregates. This study evaluates the structural response of reinforced concrete beams incorporating recycled plastic aggregates (RPA) at 25% and 50% replacement of natural coarse aggregate, with specimens tested under shear and flexural loading. Relative to the control, ultimate strength decreased by 12–20% in shear and 19–24% in flexure as RPA content increased from 25% to 50%. Failure modes shifted from brittle, abrupt post-peak drops in control beams to more gradual softening with RPA, indicating enhanced toughness and energy dissipation. Among the mixes, 25% RPA provides a practical balance, moderate strength loss with improved post-peak stability, whereas 50% RPA maximizes toughness at a higher capacity penalty. Overall, the results support RPA as a viable, sustainability-aligned aggregate alternative for applications where energy dissipation and crack tolerance are design priorities.