Modified binder composition for improved carbonation resistance of activated low-kaolinite clay-blended cementitious materials

Other conference contribution, 2026

Low-kaolinite calcined clays are promising supplementary cementitious materials owing to their wide availability. However, compared with high-kaolinite systems, their lower reactive alumina content results in a different hydrate assemblage, which may influence carbonation resistance. In this study, a hydrate assemblage engineering approach is proposed as a strategy to improve carbonation resistance of low-kaolinite clay-blended binders. A reference binder containing 30 wt.% activated low-kaolinite clay was first characterized using thermogravimetric analysis and 29Si MAS NMR. The results showed that the binder contained lower portlandite and limited AFm buffering compared with OPC, leading to earlier carbonation of the C-A-S-H phase. Thermodynamic modelling (GEMS) was then used to redesign the binder composition through the addition of calcium hydroxide and limestone to promote the formation of carbonate-bearing AFm phases. The sulfate content was subsequently optimized using isothermal calorimetry. The proposed methodology provides a rational framework for hydrate assemblage engineering of low-kaolinite clay-blended binders as a strategy towards improving carbonation resistance.