A Green Sintering-Free Binder Material with High-Volumetric Steel Slag Dosage for Mine Backfill

Abstract

Cemented paste backfill (CPB) is a sustainable mining method that has been increasingly utilized. Demand for high-performance and low-cost binder material is one of the limitations in CPB utilization. This work aims to examine a new, green, and economical steel-slag-based binder for CPB and to explore valorization techniques of steel slag (SS). Proportioning experiments were performed to obtain the best binder recipes for various steel slag dosages. The hydration heat, hydration products, and pore structure of a high-volumetric steel slag binder (H-SSB) were further inspected. Results show that the H-SSB, which contains 50 wt.% of SS, has a competitive strength performance superior to ordinary Portland cement (OPC) regardless of its 30–50% lower cost than OPC. The 7-day and 28-day strengths of H-SSB CPB are 1.24 and 0.74 MPa, respectively, which meets the meets of most free-standing backfill applications. The H-SSB generates less hydration heat and a larger amount of gel and ettringite hydrates than OPC in its early hydration, which can reduce the thermal expansion risks and strengthen the mechanical properties of CPB. Though the H-SSB CPB has a larger porosity than OPC-CPB at 28-day curing (45% vs. 37%), most pores are small and uniform in diameter (500–2000 nm), which is less harmful to CPB strength development. The H-SSB has secondary hydration effects in the long-term age, which can fill and refine the pore structure. The proposed H-SSB has benefits in reducing backfill costs, minimizing green gas emissions, and extending steel slag valorization techniques that can promote sustainable development of the mining and steel industries.