An Innovative High-Content Steel Slag Alkali-Sulfate Composite Activated Binder: Hydration Behavior and Application

The low activity and expansion risk of steel slag limit its large-scale utilization in cementitious systems. This study developed an alkali-sulfate synergistic activation method to prepare binder with steel slag content exceeding 50 wt%. The effects of alkali activator dosage, modulus, steel slag and flue gas desulfurization gypsum content on the mechanical properties and workability were systematically investigated. With a mix of 60% steel slag, 30% fly ash, 10% desulfurization gypsum and activated by additional 20% alkali activator with modulus 1.0, the 28-day compressive strength reached 12.85 MPa, along with excellent volume stability. Microstructural characterization revealed that the main hydration products are C-A-S-H and ettringite, which jointly form a dense microstructure. When used to solidify lead-zinc tailings for backfill, the binder yielded satisfactory strength and effectively immobilized heavy metals (Pb, As, Cd, Zn), with leaching concentrations meeting environmental standards and immobilization efficiencies > 80%. Heavy metals were primarily immobilized through physical encapsulation, ion exchange, and co-precipitation. This study elucidates the hydration and mechanisms of high-content steel slag systems under alkali-sulfate synergistic activation, providing a sustainable technical framework for large-scale utilization of steel slag and tailings management.