Valorization of mussel and oyster shells toward metakaolin-based alkaline activated material

Abstract The valorization of oyster or mussel shells toward metakaolin-based geomaterials was investigated. The aim is to better understand the feasibility and the reaction involved during the incorporation of shells (natural or calcined) into a metakaolin-based alkaline solution for potential building or contaminants sorbents applications. Mixtures are realized by (i) the substitution of metakaolin (MK) source by shells raw material (from 0 to 100% mass) or (ii) addition up to 50% mass. Substitution of MK by shells was conducted without material structure loss up to 40% and 30% addition, whether the type and treatment of shells used. In each addition or substitution, the results highlight the duality between both reactions i.e. polycondensation versus hydration. (i) using natural shells, only polycondensation reaction occurs due to the unreactivity of shells (interaction of shells with matrix by surface binding: role of aggregates or fillers); (ii) using calcined shells, coexistence of polycondensation in first followed (or stopped) by hydration reaction: presence of portlandite and C(A)SH. Then the results traduce the role of MK (Al and Si source) reactivity and calcium form (carbonate versus lime; reactivity) in MK-based alkali activated materials. The geochemical leaching approach can be used as a sensitive probe of the structural network.