Finite element simulation of composite slabs with recycled concrete aggregates: collapse mechanisms and interface behaviour

The growing use of recycled aggregates in concrete represents a sustainable strategy to reduce the environmental impact of construction, but their influence on structural behaviour remains insufficiently understood. This study presents a numerical investigation of steel–concrete composite slabs incorporating recycled aggregate concrete (RAC), aimed at reproducing the experimental results obtained on twelve full-scale specimens with different aggregate replacement ratios (0–100%) and span lengths (2.4–3.2 m). Advanced non-linear finite element models were developed in ABAQUS to simulate the load–deflection response and interface debonding between the concrete and steel sheeting. A cohesive interaction law was implemented to capture progressive bond degradation and shear transfer. The comparison between numerical and experimental data demonstrates that the models accurately predict the load-bearing capacity and stiffness trends, while highlighting the beneficial effect of recycled aggregates on interface adhesion due to their increased surface roughness. The study confirms the potential of cohesive modelling as a reliable and cost-effective tool for analysing and designing composite slabs made with recycled concrete.