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

## TL;DR

This study develops a new binder using steel slag and alkali-sulfate activation, achieving good strength and heavy metal immobilization for sustainable construction.

## Contribution

A novel alkali-sulfate activation method enables high steel slag content (>50%) in a binder with good performance and environmental benefits.

## Key findings

- A binder with 60% steel slag achieved 12.85 MPa compressive strength after 28 days.
- The binder effectively immobilized heavy metals in lead–zinc tailings with >80% efficiency.
- Hydration products like C-A-S-H and ettringite formed a dense structure, ensuring volume stability.

## Abstract

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.