The impact of combined recycled coarse aggregates from non-hazardous construction and demolition waste on self-compacting concrete performance for sustainable construction

The use of recycled gravel in self-compacting concrete (SCC) has been widely studied to reduce natural aggregate consumption and construction waste. However, most studies focus on single or dual recycled gravel and use conservative replacement levels. The combined use of multiple recycled gravel from non-hazardous construction and demolition waste (NHCDW), including recycled concrete (Rc), clay brick (Rb), ceramic tiles (Rb2), bituminous materials (Ra), and PVC (Rx), remains largely unexplored, particularly at moderate to high replacement ratios. This study investigates the assessment of producing SCC using combined recycled coarse aggregates (RCA) from NHCDW as full replacements for natural gravel (NG). Twelve SCC mixtures were designed incorporating Rc, Rb, Rb2, Ra, and Rx and NG. Fresh properties were evaluated using slump flow, t500, V-funnel, J-ring, and L -box tests, while hardened properties included density, porosity, mechanical strength, electrical resistivity, and microstructural analysis using SEM/EDX. Results show that SCC with RCAs maintains satisfactory flowability (SF2-VF2 classes) even at 100% replacement. Compressive strength decreased by 9–21%, tensile strength by 5–17%, and modulus of elasticity by 6–32%. Brick-rich mixtures exhibited greater porosity and lower resistivity, whereas concrete-based RCAs provided better mechanical stability and density. The findings demonstrate that combined NHCDW gravel can fully replace natural gravel in SCC, promoting circular and sustainable construction practices. The study also proposes limit values for the incorporation of combined recycled coarse aggregates in SCC. This research was conducted within the EU Horizon MOBICCON-PRO project, which aims to reduce landfill waste and enhance the reuse of construction materials.