Fresh, physical, and mechanical performance of concrete incorporating pre-soaked recycled coarse aggregate derived from construction and demolition waste: Experimental evaluation and linear regression analysis

Construction and demolition waste can partially substitute natural aggregate when processed as recycled coarse aggregate (RCA), although adhered mortar is associated with higher porosity and may reduce concrete performance. This study evaluates RCA produced from demolition waste collected in Tikrit, Iraq, at 0%, 20%, 40%, 60%, and 80% replacement of natural coarse aggregate by mass. All RCA mixtures used the same 48 h water-conditioning protocol to obtain a saturated surface-dry state. At a constant w/c ratio of 0.48, slump, 28-day water absorption and density, and compressive, flexural, and splitting tensile strengths at 7 and 28 days were measured. Slump decreased from 83 to 53 mm, water absorption increased from 3.97 ± 0.45% to 7.53 ± 0.49%, and density decreased from 2.394 ± 0.070 to 2.268 ± 0.020 g/cm³. At 28 days, compressive strength decreased from 31.13 ± 0.35 to 22.80 ± 0.40 MPa; RCA20 and RCA40 retained 96.5% and 91.3% of control strength, respectively. At 7 days, compressive strength decreased from 22.40 ± 0.56 to 13.93 ± 2.05 MPa as RCA replacement increased from 0% to 80%, with the 7-day/28-day strength ratio declining from 72.0% to 61.1%. Inferential analysis confirmed significant replacement-level effects for water absorption and several strength responses, while regressions incorporating within-mixture variability remained statistically significant. Within the investigated mixtures, 20–40% RCA provided the most favorable measured balance between reducing natural coarse-aggregate use and retaining 91–97% of the control 28-day compressive strength; however, structural and durability applications require additional verification.