Empirical Study of the Effect of Recycled Concrete Aggregate on Structural Performance of Reinforced Concrete Beams in Hot-Humid Climatic Conditions

The reuse of recycled concrete aggregate from demolished structures offers a pathway toward reducing the demand on virgin natural aggregates and diverting construction demolition waste from landfill, but the structural implications of its use in reinforced concrete beams under Nigeria's hot-humid coastal climate remain insufficiently empirically characterised. This study investigates the effect of recycled concrete aggregate substitution on the structural performance of reinforced concrete beams in hot-humid conditions representative of the South South geopolitical zone. Reinforced concrete beams were fabricated with recycled aggregate replacement levels of 25, 50, 75, and 100 percent of coarse aggregate, alongside a natural aggregate control mix. Specimens underwent an accelerated tropical weathering conditioning regime over 60 days before structural testing under four-point bending. Mechanical properties including flexural capacity, stiffness, crack width at service load, and ductility were measured and analysed. Additionally, carbonation depth and chloride diffusion coefficient were determined from companion specimens. Results indicate that flexural capacity decreased by 6, 12, 21, and 31 percent for the respective substitution levels relative to the control, with the 25 percent substitution showing performance within the structural Eurocode 2 serviceability tolerance range. Accelerated carbonation was significantly elevated at replacement levels above 50 percent, corresponding to increased interfacial transition zone porosity as confirmed by scanning electron microscopy. The study fills a gap in tropical performance data for recycled aggregate concrete and recommends a 25 percent maximum substitution limit for structural applications in Zone I coastal exposure conditions in Nigeria. Keywords: recycled concrete aggregate, reinforced concrete beams, hot-humid climate, structural performance, sustainability.