Sodium sulfate and magnesium sulfate resistances of mortar with multi-binder systems of calcined kaolinite clay, fly ash, and limestone powder

This study aimed to assess the durability of mortars subjected to sulfate solutions (specifically Na2SO4 and MgSO4). The effectiveness of cement replacement materials (CRMs) such as calcined kaolinite clay (C), high CaO fly ash (F), and limestone powder (L) in multi-binder systems was studied. The pastes' microstructure, phase assemblage, and elemental profiles were examined. The results showed that mortars containing calcined kaolinite clay and high CaO fly ash (C30F15) had the lowest expansion when exposed to Na2SO4 and MgSO4. This was caused by the decreased portlandite and expansive products, improved mortar's compressive strength, and refined pore structure (smallest pore size and lowest pore volume). However, the use of the CRMs, especially when calcined kaolinite clay was combined with fly ash or limestone powder, raised the weight loss and surface deterioration of mortars in a MgSO4 solution because of the lowered pH in the pore solution and formation of MSH.