Durability behavior of concrete incorporating varying replacement ratios of recycled coarse and fine aggregates sourced from high-strength concrete under harsh environmental conditions

The growing global demand for construction materials and the depletion of natural aggregates (NA) have intensified the need for sustainable alternatives. Recycled aggregates (RA) offer a promising pathway to support circular economy principles. In this study, 135 concrete cubes casted and classified into three groups: a control group with no replacement, a second group incorporating only recycled coarse aggregate (RCA), and a third group incorporating both RCA and recycled fine aggregate (RFA) at replacement levels of 25%, 50%, 75%, and 100%. Ultrasonic pulse velocity (UPV) and compressive strength were evaluated under normal curing, chloride immersion, sulfate attack, and 100–200 freeze–thaw cycles. Results showed the most pronounced losses occurring under sulfate attack and prolonged freeze–thaw cycling. Compressive strength followed a different pattern, remaining relatively stable after 100 freeze–thaw cycles but declining significantly under sulfate exposure and after 200 cycles. Mixtures containing RCA consistently outperformed those containing both RCA and RFA. Notably, a 50% replacement ratio emerged as the optimum level, achieving compressive strength ratios of 1.12–1.22 while maintaining acceptable UPV values across exposure conditions, attributed to the high quality of the parent concrete (≈55 MPa). Future research should investigate long-term microstructural characterization, alongside environmental and economic assessments.