Performance of reinforced manhole cover slabs with treated coconut shell coarse aggregate and GGBFS

The increasing demand for sustainable construction materials has encouraged the use of agricultural and industrial by-products in concrete. However, despite the demonstrated potential of Coconut Shell Aggregate (CSA) as a lightweight aggregate, its application in precast reinforced concrete elements remains limited. This study investigates the feasibility of producing precast reinforced concrete slabs incorporating treated-CSA and Ground Granulated Blast Furnace Slag (GGBFS), and evaluates their structural performance in accordance with IS 12592:2002. Two concrete mixes conventional concrete (CC) and treated-CSA GGBFS-based concrete (TCSAC) were used to cast and test light-duty (LD-2.5) manhole cover slabs of 600 × 600 × 100 mm according to IS 12592:2002. Key parameters including compressive strength, permanent set, crack development, ultimate load capacity and settlement were assessed. TCSAC and CC mixes attained 28-day compressive strengths of 41.55 N/mm 2 and 40.89 N/mm 2 , respectively, both of which are higher than the minimum required strength for manhole cover slabs. The permanent set value of TCSAC was comparable to CC and were within standard limits. Both TCSAC and CC slabs successfully resisted the applied 25 kN seating load with no observable cracking. Ultimate load of TCSAC was 2.95% lower than CC but well above the test load requirement. The results confirm that lightweight and LD-2.5 grade manhole cover slabs can be effectively produced using treated-CSA, manufactured sand, and GGBFS.