PERIWINKLE SHELL

The intelligent partial replacement of fine aggregate with periwinkle shell in sandcrete blocks have emerged as a sustainable approach to address the environmental and economic challenges associated with conventional sanderete block production. Periwinkle shells, a marine waste abundant in coastal regions like Nigeria, are primarily composed of calcium carbonate (-95%) and have a low specific gravity (1.3-1.4 g/em'), making them a viable lightweight substitute for river sand. Studies, such as those by Ichetaonge et al.(2023) and Osarenmwinda and Aigbogun (2017), demonstrate that replacing fine aggregate with crushed periwinkle shell (CPWS) at levels up to 15% achieves compressive strengths of 2.0-3.0 MPa, meeting the Nigeria Industrial Standard (NIS 87:2000) for non-load bearing walls. The well-graded particle size distribution of CPWS (coefficient of uniformity = 6.58) enhances its suitability, but its high water absorption (10-20%) and reduced workability necessitate optimized mix designs, often incorporating admixtures like superplasticizers or pozzolanie materials such as fly ash to improve performance. The mechanical and durability properties of CPWS-based sandcrete blocks are influenced by replacement levels, mix proportions, and curing methods, Research indicates that compressive strength decreases with higher CPWS content, with significant reductions beyond 20% replacement (c.g., 18.00 N/mm? at 50% replacement, Osarenmwinda and Aigbogun, 2017). The use of CPWS promotes environmental sustainability by reducing reliance on river sand. mitigating the ecological damage caused by dredging, and repurposing marine waste, thus supporting circular economy principles (Ede et al., 2016). Also CPWS-based blocks reduce
construction costs by 15 -20% and create local jobs through shell processing.