Influential role of alkaline earth activators on durability and deterioration of GGBS binder in saline environments

Alkaline-earth-activated ground granulated blast-furnace slag (GGBS) offers a cost-effective and eco-friendly binding material. However, the interactions between activators and salt ions significantly influence their durability. In this work, the contrasting roles of magnesium oxide (MgO) and calcium oxide (CaO) activators in GGBS binders were investigated, providing insights into durability, microstructural performance and deterioration mechanisms over a year in different salt solutions. The results indicated that GGBS activated with magnesium oxide (MO-GGBS) remained intact in sodium sulfate solution, whereas GGBS activated with calcium oxide (CO-GGBS) suffered expansion damage and strength loss, with ettringite, cracks and voids adversely affecting the microstructure. MO-GGBS inhibited ettringite formation because of its inherent hydrotalcite production, reducing aluminium interactions with external sulfates. However, MO-GGBS showed greater deterioration than CO-GGBS in magnesium sulfate solution, exhibiting surface cracks, strength loss and a porous microstructure with gypsum formation. CO-GGBS hydration resulted in hydrate gels with higher calcium content and pH buffering capacity, which counteracted magnesium-induced decalcification. Both binders demonstrated minimal deterioration in sodium chloride solution, forming chloride-binding phases including Friedel’s salt and hydrocalumite. MO-GGBS exhibited higher seawater resistance than CO-GGBS, with less physical damage, strength loss and microstructure deterioration. These insights highlight the potential of MO-GGBS as a sustainable material for applications in seawater, sulfate and chloride-rich conditions.