Assessment of sulfate resistance in cementitious systems incorporating low-grade calcined kaolinite clay and limestone

This study investigated the sulfate resistance and expansive behavior of binary binders incorporating low-grade calcined kaolinite clay (CC) and ternary binders as limestone calcined clay cement (LC3), considering both external and internal sulfate attack. Hydration products and microstructural changes were analyzed and compared with conventional binders using fly ash and slag. The optimal sulfate resistance was observed in binders with 40% CC, which outperformed ordinary Portland cement (OPC), fly ash, and slag mixtures under drying-wetting cycles, achieving a sulfate resistance coefficient 30% higher than OPC. While LC3 displayed higher mechanical strengths, CC binders showed greater sulfate resistance due to the absence of limestone and a higher proportion of pozzolanic reactants. Ettringite formation during hydration in the CC system contributed to beneficial micro-expansion without compromising strength, even with internal gypsum addition. Notably, both CC and LC3 binders exhibited improved internal sulfate tolerance when evaluating the potential sulfate resistance performance.