Influence of Recycled Coarse Aggregate Replacement on the Mechanical Performance of Concrete at Different Curing Ages

Abstract

The increasing demand for sustainable construction materials has intensified interest in recycled coarse aggregate (RCA) as a substitute for natural aggregates in concrete. RCA offers environmental benefits by reducing landfill waste and conserving natural resources, yet concerns remain regarding its mechanical performance due to adhered mortar, higher porosity, and variability in quality. This study experimentally evaluated the influence of RCA replacement levels (0%, 5%, 10%, 15%, and 20%) on the mechanical properties of concrete at curing ages of 7, 14, and 28 days. Mechanical properties assessed included compressive strength, flexural strength, split tensile strength, and Young’s modulus. Results revealed a consistent decline in performance with increasing RCA content, particularly at 28 days, where compressive strength and Young’s modulus showed the largest reductions. Flexural and split tensile strengths also decreased but more gradually. Interestingly, the 15% RCA mix consistently outperformed the 5% and 10% mixes, indicating non linear behaviour and suggesting that moderate RCA replacement may improve aggregate packing and internal curing. Overall, the findings confirm that RCA can be incorporated into concrete at low to moderate replacement levels without compromising structural reliability. RCA replacement up to 15% is recommended for structural applications, while 15–20% may be suitable for non structural uses. The study contributes to sustainable construction practices by demonstrating that RCA concrete remains viable when its reduced mechanical properties are properly accounted for in design.