Influence of recycled concrete aggregate source and size fraction on concrete strength and pore structure

This study investigated the influence of recycled concrete aggregate (RCA) source and aggregate fraction on the mechanical and transport performance of concrete. RCA was obtained from three local sources, denoted S1, S2, and S3, with a maximum aggregate size of 19 mm and separated into fine and coarse fractions. Concrete mixtures were produced by replacing natural fine aggregate with 100% fine RCA, natural coarse aggregate with 100% coarse RCA, or both fine and coarse aggregates with RCA from the same source. The fine RCA fractions were coarser than the natural fine aggregate, with fineness modulus values of 3.10, 2.99, and 3.20 for S1, S2, and S3, respectively, compared with 2.70 for the natural sand. RCA water absorption was substantially higher than that of natural aggregates, ranging from 7.8% to 19.9% for fine RCA and 8.1% to 10.2% for coarse RCA. The control concrete achieved 46.8 MPa compressive strength and 3.98 MPa splitting tensile strength, while RCA mixtures ranged from 28.1 to 41.5 MPa and 1.93 to 2.99 MPa, respectively. Total RCA replacement caused the largest strength reductions, with S2-T and S3-T reaching 29.3 and 28.1 MPa. Concrete water absorption increased from 2.1% for the control to 7.8–11.9% for RCA mixtures, while permeable voids increased from 8.42% to 17.7% to 25.1%. SEM and EDS analyses confirmed that old adhered mortar, interfacial defects, cracks, and chemically heterogeneous phases governed the source-dependent performance of RCA concrete.