Longitudinal Shear Behaviour in Recycled Aggregate Concrete Composite Slabs: A State-of-the-Art Review

The environmental challenges posed by concrete production, particularly high carbon dioxide emissions and the extensive use of natural resources, necessitate more sustainable construction practices. Recycled Aggregate Concrete (RAC) offers a promising alternative by reducing waste from construction and demolition activities while conserving natural aggregates. This review investigates RAC integration within composite steel-concrete slabs, emphasizing longitudinal shear behaviour—a crucial factor in structural integrity and load distribution. Through a comprehensive analysis of experimental results and theoretical advancements, this study examines the effects of recycled concrete aggregate replacement ratio, water-to-cement ratio, and steel deck geometry on shear bond strength and overall performance. Advanced analytical methods, such as the m-k method and its adaptations, are reviewed to assess their predictive capabilities and applicability in Recycled Aggregate Concrete Composite Slabs (RACCS). The study identifies critical gaps in the current literature, particularly regarding the combined influence of geometric and material variables on longitudinal shear resistance. The results highlight increased performance variability in RAC systems, primarily due to interfacial degradation and reduced aggregate quality, which compromise the mechanical interlock and friction-based shear transfer mechanism. The review critically evaluates the m–k method and its extensions, showing that while the framework remains applicable, the coefficients m and k are strongly influenced by Recycled Concrete Aggregates (RCA)-related parameters and require physical reinterpretation. Overall, the review concludes that RAC-based composite slabs can achieve satisfactory performance when appropriately designed but require tailored analytical approaches to ensure safety and reliability in structural applications.