Effects of acid-leached manganese slag on supersulfated cement hydration

In this study, the effects of two types of acid-leached manganese slag, MS(X) and MS(Y), on the hydration behaviour, microstructure evolution and mechanical performance of supersulfated cement (SSC) were investigated. The hydration kinetics, strength development, pore structure and hydration products were systematically analysed. The results showed that the incorporation of manganese slag significantly influences the hydration and structural development of SSC, with distinct effects depending on the type and dosage of manganese slag. Low manganese slag contents promoted strength development, whereas excessive incorporation delayed hydration, reduced the formation of ettringite (AFt) and calcium silicate hydrate (C–S–H) gel and caused the mechanical properties to deteriorate. Compared with MS(X), MS(Y) exhibited a more pronounced retardation effect because of its higher phosphorus impurity content and lower effective gypsum availability. The soluble phosphate released from MS(Y) consumed Ca2+ ions and suppressed the formation of hydration products, leading to a relatively looser microstructure and lower compressive strength. Microstructural and pore structure analyses revealed that high manganese slag contents lead to a coarser pore network and reduced gel continuity, consistent with the observed strength reduction. Overall, the appropriate incorporation of manganese slag enables the preparation of SSC with acceptable performance while promoting the sustainable utilisation of manganese slag in low-carbon cementitious materials.