Concrete is a widely used construction material, but the production of traditional aggregates, such as gravel and granite, are depleting natural resources and causing environmental damage. Coconut shells are a promising alternative aggregate, as they are strong, durable, and have a low environmental impact. The aim of this research is to find out the viability to replace part of the traditional coarse aggregates in concrete with leftover coconut shells as an alternative. This study involved designing the mix for M25 grade control concrete (concrete without coconut shells), Subsequently, coarse aggregate (CA) was replaced with coconut shell (CS) in varying proportions: 5%, 10%, 15%, 20%, 25%, & 30% by volume. Tests for split tensile strength, compressive strength, flexure strength, and fast chloride penetration are all included in this investigation. The results of this study indicate that waste coconut shells can be effectively utilized as a partial replacement for coarse aggregate in M25 grade concrete. Replacement of course aggregate up to 10% with coconut shells resulted in workable concrete with satisfactory strength characteristics.