An emerging upcycling strategy for sustainable building materials: Unveiling the unique self-hydration mechanism of hot-stuffed steel slag

Upcycling industrial by-products into high-value construction materials is a pivotal strategy for establishing a circular economy within the built environment. The hot-stuffing process is an emerging technology for steel slag treatment, yet the intrinsic cementitious properties of hot-stuffed steel slag (HS) remain underexplored. This study investigates the self-hydration mechanisms of HS by comparing it to ordinary slag (OS). Results reveal that the hot-stuffing consumes the C₁₂A₇, f -CaO, and MgO phases, forming new stable hydrates like Al(OH)₃, Ca(OH)₂, and C₃AH₆. This chemical alteration is coupled with a physical transformation, where the particle size distribution is refined from a multi-modal curve to a more uniform uni-modal curve. This alteration creates a unique kinetic behavior characterized by a prolonged induction period of approximately 30 h, attributed to the delayed precipitation of calcium-bearing hydrates as evidenced by pore solution analysis. Despite this initial period, the sustained hydration of β-C₂S in HS drives continuous pore structure refinement. Consequently, HS achieves a superior 90-day compressive strength of 15.1 MPa, overtaking the 13.9 MPa of OS. Furthermore, life cycle assessment confirms its environmental superiority, with a Global Warming Potential of 20.23 kg CO₂-eq/t, less than half that of OS. This work elucidates the scientific principles of HS hydration, validating it as a volume-stable, low-carbon functional binder component for sustainable construction. © 2026 The Authors.