Utilization of Common Shell Wastes as a Limestone Alternative in Cementitious Materials

Efforts to decarbonize the concrete industry have motivated the use of alternative sustainable materials. While limestone fillers are promising, reducing reliance on virgin materials and natural resources remains essential. Shell waste from seafood and egg production are available in large quantities and their disposal poses several environmental challenges. Utilizing these CaCO ₃ -containing waste shells as an alternative to conventional limestone can divert shell waste from landfills while lessening cement demand. To test this hypothesis, five types of waste shells were ground into powder, including oyster shells, mussel shells, crab shells, shrimp shells, and eggshells. The raw shell powders were first characterized, followed by testing of hydration kinetics and mechanical properties. Results indicated that shell powders were analogous to limestone filler, consisting primarily of calcite, with the exception of shrimp shells. Small amounts of organics were also present in the shell materials. Incorporation of eggshell or oyster shell at a 20% cement replacement yielded compressive strengths similar to limestone after 28 days of curing, but other materials reduced strength. The mortar flow and compressive strength were likely influenced by morphology, size, chemical composition, and organics of the shell powders. The findings of this study indicate that substituting limestone filler in cementitious materials with recycled shell materials is feasible.