Activation methods and performance of steel slag–granulated blast furnace slag cementitious materials: A review

Given the substantial CO₂ emissions and the intensive depletion of non-renewable resources associated with Portland cement-based binders, the development of cost-effective, low-carbon cementitious materials has become increasingly critical. Steel slag (SS) and granulated blast furnace slag (GBFS) represent the primary solid by-products of the iron and steel industry; and their efficient valorization is essential for reducing the carbon footprint of construction materials and alleviating the pressure of solid waste disposal. However, challenges such as the low reactivity and poor volume stability of SS, coupled with the dependency of GBFS on activators and the growing scarcity of high-quality slag resources, have significantly restricted their widespread application. While studies on SS–GBFS composite powders have flourished, a comprehensive consolidation of their activation strategies is still lacking. This paper systematically reviews the primary activation strategies for SS–GBFS cementitious materials, with a specific focus on mechanical grinding activation, alkali excitation, sulfate/chloride activation, carbonation treatment, and emerging techniques involving acid/acid phosphates, organic additives, and bio-physical field assistance. The impacts of these methods on hydration mechanisms, microstructural evolution, and macroscopic performance are comprehensively summarized. Analysis reveals that an optimal synergistic hydration effect is achieved within an SS/GBFS mass ratio of 2:3 to 3:2. Among chemical methods, alkali activation exhibits the most pronounced effect by inducing a dense C–(A)–S–H gel network. In contrast, mechanical grinding and sulfate/chloride activation offer a more cost-effective way by enhancing mineral dissolution and regulating the precipitation of ettringite, monosulfoaluminate, and Friedel’s salt, though risks of delayed ettringite expansion and chloride-induced corrosion warrant caution. Emerging sustainable approaches—leveraging industrial by-products (gypsum and alkaline residues), trace organic alkanolamines, or biomass ash—demonstrate superior potential for developing eco-friendly binders. Furthermore, the research progress concerning the workability, compressive strength, durability, and environmental performance of SS–GBFS binders is evaluated. A comparative analysis of different activation strategies is also conducted from the perspectives of energy intensity, economic viability, and environmental load. Finally, this review addresses critical challenges, including feedstock variability, activator dependency, and engineering applicability, and proposes future research directions to provide a theoretical foundation and technical reference for the design and industrial application of high-performance, low-carbon SS–GBFS cementitious materials. • Synergistic hydration of SS and GBFS is triggered in alkaline environments. • Alkali activation yields high strength but incurs excessive energy/emissions. • Sulfate and chloride activations entail potential long-term durability risks. • Industrial wastes, organic alkanolamines and biomass ash offer sustainable alternatives. • Minimizing reliance on commercial activators is a key future priority.