Structural Performance of Steel–Concrete Composite Slabs Incorporating Recycled Concrete Aggregates

The transition toward circular construction requires structural solutions capable of integrating recycled materials without compromising mechanical reliability. In this context, recycled concrete aggregates (RCA) derived from construction and demolition waste represent a promising alternative to natural aggregates. This study investigates the structural performance of steel–concrete composite slabs incorporating RCA through an extensive experimental program carried out within the SARCOS research framework. A total of 48 full-scale composite slabs were produced with RCA replacement ratios ranging from 0% to 100% and tested under four-point bending with span lengths of 2.40 m, 2.80 m, and 3.20 m. The results highlight a consistent three-stage structural response characterized by an initial elastic phase, followed by interface debonding and a post-peak flexural stage with stable residual capacity. Composite slabs with moderate RCA contents exhibited collapse loads comparable to, or slightly higher than, those of conventional slabs, indicating that enhanced aggregate roughness improves mechanical interlock and friction at the steel–concrete interface. Conversely, full RCA replacement produced reductions in stiffness and peak resistance in the most recent test series, although a more ductile post-peak response was observed. Overall, the findings demonstrate that recycled aggregate concrete can be effectively employed in composite floor systems, particularly for short- and medium-span applications where longitudinal shear transfer governs structural behavior. The experimental evidence contributes to the understanding of bond mechanisms in sustainable composite structures and provides useful insights for the refinement of Eurocode-based design approaches.