Synergistic utilization of high-volume magnesium slag and blast furnace slag in sustainable ternary binders: From macro-performance to environmental benefits

The high-volume valorization of magnesium slag (MS) offers a promising route for developing low-carbon cementitious materials for construction applications. However, its practical use in cement-based materials is hindered by a limited understanding of technical barriers regarding dimensional stability and resistance to aggressive environments. To address this issue, this study establishes a cross-scale mechanism-performance-durability framework integrating phase assemblage evolution and microstructural characterization to design a sustainable binder system incorporating high volumes of MS (40 wt%-60 wt%) and granulated blast furnace slag (GBFS) with a replacement level of up to 80%. The synergistic evolution of phase assemblages and pore structures reveals a unique stabilization mechanism where the in-situ reaction of reactive periclase in MS effectively compensates for matrix shrinkage while GBFS induces a fundamental transformation of the pore structure through the pozzolanic effect, reconstructing harmful macro-pores into dense pores. Consequently, despite an 80% clinker reduction, the ternary system achieves a 28-day compressive strength of 26–32 MPa. While MS expansion neutralizes early-age shrinkage to near-zero, GBFS-induced pore refinement increases the stabilized long-term shrinkage by ∼25% relative to plain cement. Furthermore, differentiated defense strategies are elucidated for resistance to aggressive environments. In Na₂SO₄ environments, the system chemically suppresses gypsum crystallization by establishing a low-calcium environment. In more aggressive MgSO₄ environments, a dual physical barrier and chemical tolerance mechanism is identified where the intrinsic chemical stability of magnesium silicate hydrate gel and hydrotalcite prevents magnesium induced decalcification. A normalized performance-sustainability analysis confirms that the ternary system not only substantially reduces embodied carbon and energy but also achieves optimal eco-efficiency per unit of mechanical strength. This research elucidates the stabilization mechanisms of high-volume MS-based binders, providing a scientific basis for designing durable, low-carbon cementitious materials using high-volume industrial by-products. © 2026 Elsevier Ltd.