<p>Rapid urbanization and increasing infrastructure needs have driven the demand for concrete, leading to the depletion of natural coarse aggregates and raising environmental concerns. As a sustainable alternative, coconut shell aggregate (CSA), derived from agricultural waste, offers the potential for producing lightweight concrete that reduces dead load and environmental impact. This study investigates the performance of reinforced concrete slab panels incorporating treated CSA as coarse aggregate and partial cement replacement with ground granulated blast furnace slag (GGBFS). Reinforced CSA concrete panels (600 × 600 × 100&#xa0;mm) were cast and tested under two distinct loading conditions: central concentrated load with four-sided support and central line load with two-sided support. For comparison, conventional concrete (CC) panels of the same dimensions were also cast and tested under similar conditions. The experimental results revealed that CSA concrete panels exhibited first crack loads, ultimate loads, and deflection behaviour comparable to CC panels, with CSA slabs demonstrating greater ductility. Under central concentrated loading, the peak load capacities of both materials were similar, while CSA slabs showed slightly higher deflection. Under central line loading, CSA panels showed a more significant reduction in load-carrying capacity, indicating lower stiffness but greater flexibility. These findings underscore the potential of CSA and GGBFS as sustainable materials in precast concrete applications, offering comparable structural performance to conventional concrete while promoting environmental benefits.</p>