Experimental Investigation of Combined Recycled Fine and Coarse Aggregate Replacement in Concrete

Abstract

This study experimentally investigates the feasibility of replacing natural fine and coarse aggregates with recycled concrete aggregates (RCA) in M25 concrete. A control mixture and four recycled aggregate mixtures containing 10%, 20%, 30% and 40% combined replacement were produced using a design procedure based on IS 10262:2019. Fresh-state performance was evaluated by slump, while hardened-concrete performance was assessed using 7- and 28-day compressive strength, 28-day split tensile strength, and 28-day flexural strength. The control mixture exhibited a slump of 75 mm and a 28-day compressive strength of 32.8 MPa. At 10% and 20% RCA replacement, the compressive strengths remained close to the control value, at 32.5 and 31.8 MPa, respectively. Beyond 20%, the reduction became pronounced, reaching 28.1 MPa at 30% and 24.4 MPa at 40% replacement. Similar trends were obtained for split tensile and flexural strengths. The 20% mixture maintained a slump of 75 mm and achieved split tensile strength of 3.05 MPa and flexural strength of 3.70 MPa at 28 days. Although the 10% mixture produced marginally higher mechanical properties, 20% was identified as the optimum replacement level investigated because it enabled greater utilization of recycled aggregate without a loss of control-level slump and with satisfactory mechanical performance. The findings indicate that controlled combined replacement of natural fine and coarse aggregates can provide a technically viable route for incorporating processed C&D concrete waste into M25 concrete.