Sustainable Textile Waste in Recycled-Aggregate Concrete: Mechanical Performance, Microstructure, and Cradle-to-Gate Environmental Screening

Abstract Textile waste can provide a secondary reinforcement resource while recycled coarse aggregate (RCA) reduces demand for virgin aggregate, but their combined effects in concrete remain uncertain. This study evaluates nine mixtures combining 0%, 50%, and 100% RCA replacement with 0%, 1%, and 2% apparent-volume fractions of uncoated 95% polyester–5% elastane knitted waste. Slump, fresh density, 28-day compressive strength, and splitting-tensile strength were examined, with selected powders characterized by SEM, XRD, and EDX. At matched RCA levels, 1% textile increased reported mean compressive strength by 5.7–11.8% and splitting-tensile strength by 3.1–4.9%. Nevertheless, strength in the 1% series fell from 33.5 to 27.5 MPa as RCA increased. A descriptive decomposition assigned 85.5% of compressive-strength variation to RCA, 9.7% to textile, and 4.8% to non-additivity. Screening impacts were 506.7–541.7 kg CO₂-eq/m³, with cement contributing 88.1–94.2%. The 1% textile level was the best tested condition, but validation is required before structural or whole-life claims.