The two activating ingredients come from very different corners of heavy industry. Kanbara reactor desulfurization slag, or KRDS, is the residue left when molten iron is desulfurized in a Kanbara reactor vessel before steelmaking. It is rich in calcium and carries a strongly alkaline character, along with a meaningful chloride content inherited from the desulfurization process. Soda residue, or SR, is the waste stream from soda ash production, and it too is alkaline. Rather than treating these two materials as liabilities, the researchers paired them deliberately to create what they describe as a dual-alkaline solid waste synergistic activation system. Each waste contributes calcium, alkalinity and, in the case of KRDS, chloride ions, and the combination turns out to accelerate the hydration of the reactive components far more effectively than either activator alone.

The reactive backbone of the system is supplied by ground granulated blast-furnace slag, a well-established supplementary cementitious material from iron production, and fly ash, the fine powder captured from coal combustion flue gases. Both are alumino-silicate rich, and both respond to alkaline activation by dissolving and reprecipitating as binding phases. The team systematically adjusted the mix proportions of the four components and evaluated the resulting pastes and mortars with compressive strength and fluidity tests, mapping how the ratios of KRDS, SR, GGBS and FA governed early and later-age performance. The abbreviation KSGF denotes the full four-part system, while comparison blends such as KG, SG, KSG and KSF allowed the authors to isolate the contribution of each ingredient.

What makes the study more than a mix-design exercise is the depth of the microstructural investigation. The researchers characterized their materials using X-ray diffraction, thermogravimetric analysis with derivative thermogravimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy coupled with energy-dispersive spectroscopy. Together these techniques reveal which crystalline and amorphous phases form, how much bound water each phase holds, how the silicate network polymerizes, and how the solid microstructure develops in three dimensions over time. The results converge on a coherent picture of why the dual-alkaline system outperforms simpler formulations.

The first key finding concerns tricalcium aluminate, or C3A, one of the most reactive phases in calcium-rich binders. According to the study, C3A hydration is significantly accelerated by the KR desulfurization slag and alkali-slag system through the combined action of calcium, alkalinity and chloride ions. In conventional all-solid-waste binders, hydration is often sluggish, and one reason is that an early hydration film forms on particle surfaces, acting as a barrier that inhibits further reaction. The KSGF system attacks this problem directly. As Friedel’s salt, a calcium chloroaluminate phase, grows within the hydrating matrix, the crystallization pressure it exerts disrupts the hydration film, allowing slag hydration to continue rather than stall.

This mechanism has cascading benefits. With the diffusion barrier broken, hydration proceeds deeper into the slag and fly ash particles, producing more calcium aluminosilicate hydrate gel, the glue-like C-(A)-S-H phase that gives the material its strength. The study further reports that the calcium-chloride synergy enhances the incorporation of aluminum into the C-(A)-S-H structure. Aluminum substitution in the silicate chain is known to cross-link and strengthen the gel network, and the resulting microstructure is measurably denser: the researchers observed reduced porosity across the system. A finer, less connected pore network generally translates into better mechanical performance and improved resistance to the transport of aggressive species.

Perhaps the most consequential result, however, involves chloride. In cementitious materials, free chloride ions are notorious for depassivating reinforcing steel and triggering corrosion, which is why chloride-bearing wastes have historically been restricted in construction applications. The KSGF system flips this liability into an asset through the formation of layered hydrocalumite, a layered double hydroxide belonging to the AFm family of phases. Hydrocalumite’s positively charged layers and exchangeable interlayer anions provide an ideal host for chloride: the study shows that the activation system promotes layered hydrocalumite formation, which effectively immobilizes chloride ions and reduces the fraction of free chlorides in the pore solution. In effect, the binder locks up the very ion that would otherwise disqualify it from service.

The thermal behavior of this chloride-bearing phase matters too, because AFm phases can destabilize and release their bound anions at elevated temperatures. The authors report that hydrocalumite thermal stability is improved through enhanced Al-O and Ca-O bond energies via chloride-aluminum coordination. In other words, when chloride and aluminum coordinate within the hydrocalumite structure, the chemical bonds anchoring the framework become stronger, raising the temperature at which the phase degrades. This improves the overall thermal stability of the material and gives added confidence that the immobilized chloride will stay put under realistic exposure conditions, including fire scenarios that concern building designers.

Taken together, the findings address the three obstacles the authors set out to solve: low hydration efficiency, inhibition by early hydration films, and the restricted application of all-solid-waste cementitious materials due to chloride ions. The dual-alkaline system accelerates hydration, the calcium-chloride synergistic effect breaks the hydration film, reduces porosity and improves thermal stability, and layered hydrocalumite enables solidification of chloride while decreasing free chloride ions. The practical implication is a pathway toward construction binders in which the cement, the activator and even part of the chemistry that would normally be a contaminant all come from waste streams that would otherwise be landfilled.

The environmental arithmetic is compelling. Ordinary Portland cement production accounts for a substantial share of global carbon dioxide emissions, driven both by the calcination of limestone and by the fossil fuels burned to reach clinkering temperatures. All-solid-waste binders of the KSGF type sidestep clinker entirely, repurposing desulfurization slag, soda residue, blast-furnace slag and fly ash into a material whose hydration chemistry is not merely tolerated but actively engineered. The work was supported by the Key Project of the National Natural Science Foundation of China and several Liaoning provincial programs, reflecting the strategic weight that Chinese institutions place on industrial waste valorization. If the dual-alkaline activation strategy proves scalable, steel plants and soda ash factories could find themselves supplying not waste, but the raw materials of a lower-carbon construction industry, one hydration reaction at a time.

Subject of Research: A dual-alkaline all-solid-waste cementitious system combining Kanbara reactor desulfurization slag, soda residue, blast-furnace slag and fly ash with enhanced hydration and chloride solidification.

Article Title: Preparation and Mechanical Properties of KSGF All-Solid-Waste Cementitious Materials

Article References: Zhang, Y., Chen, W., Tan, Y., Wang, Q., Nehdi, M. L., & Meng, W. (2026). Preparation and Mechanical Properties of KSGF All-Solid-Waste Cementitious Materials. Waste and Biomass Valorization. https://doi.org/10.1007/s12649-026-03785-8

Image Credits: AI Generated

DOI: 10.1007/s12649-026-03785-8

Keywords: all-solid-waste cementitious materials, Kanbara reactor desulfurization slag, soda residue, ground granulated blast-furnace slag, fly ash, chloride solidification, hydrocalumite, Friedel's salt, alkali activation, C-(A)-S-H, compressive strength, sustainable construction