Behavior of calcined clay based geopolymers under sulfuric acid attack: Meta-illite and metakaolin

[Display omitted] •Four different calcined clay geopolymers were studied under sulfuric acid attack.•Meta-illite (MI) and metakaolin (MK) were activated by Na or K-silicate solutions.•SEM/EDS, XRD, FT-IR and MAS NMR analyses were performed before and after attack.•All geopolymer pastes were affected by low leaching of alkali cations. This paper studies the behavior of four different calcined clay-based geopolymers under sulfuric acid attack and gives insights into their degradation mechanisms. Pastes were cast using metakaolin and meta-illite and were activated by two different alkaline solutions. Mineralogical and microscopic characterizations were performed on pastes before and after attack. Results indicated that all pastes were affected by low leaching of alkali cations, and thus by a linkage disequilibrium of the geopolymer network. Meta-illite based geopolymers, which had not been addressed in the literature until now, hold promise for improving the durability of materials in aggressive environments.