Huihui Du

Semi-dry desulfurization ash (SDA) is generated in rapidly increasing quantities and remains underutilised, despite its high CaO content, which makes it a promising candidate for CO₂ storage via carbonation curing. However, the carbonation behaviour and consolidation mechanism of standalone SDA compacts are not yet well understood. In this study, SDA compacts were prepared at water-to-solid (w/s) ratios of 1.5:10 and 1.83:10 and subjected to carbonation curing for 0–24 h under controlled CO₂ conditions. Compressive strength, CO₂ uptake, and microstructural evolution were assessed using XRD, TG–DTG, FTIR, and SEM. CO₂ uptake increased with curing time and reached approximately 20% after 24 h, whereas compressive strength exhibited a non-linear response, peaking at 8.67 MPa after 6 h at w/s = 1.5:10 and declining thereafter. Phase and microstructural analyses indicate that strength development is governed by the transformation of Ca(OH)₂ to CaCO₃ polymorphs, with early densification followed by increased porosity as calcite coarsens. Sulphur-bearing phases (e.g., CaSO₃·0.5H₂O) remain largely inert under the tested conditions. These findings demonstrate that carbonation curing can significantly enhance CO₂ fixation in SDA and generate low-strength construction materials while also highlighting the need to optimise mix design and curing parameters to mitigate strength loss at extended curing times.

In order to solve the problems of the large-scale resource utilization of iron ore waste rock, waste rock is used to prepare green building materials, but it needs to be further promoted for use in high-strength concrete. In this study, high-strength concrete was prepared using iron ore waste rock as coarse and fine aggregates combined with solid waste-based cementitious materials. The mechanical and durability properties of washed and unwashed concrete with two types of aggregates were compared, including compressive strength, freeze resistance, chloride ion resistance, carbonation resistance, pore distribution, microstructural characteristics, and environmental and economic benefits. The results indicated that water-washing pretreatment significantly reduced the stone powder content of waste stone aggregate from 14.6% to 4.5%, which had a significant effect on the basic properties of concrete. The compressive strength of concrete with water-washed waste rock aggregate was 61 MPa, 64.9 MPa, and 68.8 MPa at 28, 56, and 360 days, respectively, with long-term stability. The washed aggregate concrete had a porosity of less than 4%, freeze-resistant grade of F200, 28 d electrical flux <500 C, and a carbonation depth of less than 10 mm. The improved performance of the washed aggregate concrete was attributed to the fact that after washing pretreatment, the water absorption of the aggregate was reduced, the cementitious materials were fully hydrated, and the internal microstructure was denser. The high-strength concrete prepared in this study effectively used iron ore waste rock and solid waste-based cementitious materials, which not only reduces environmental burden but also provides basic data references for future engineering applications using iron ore waste rock aggregate concrete.

This paper presents a novel low-carbon binder formulated from fly ash (FA), ground granulated blast furnace slag, steel slag, and desulfurization gypsum as a quaternary solid waste-based material. It specifically examines the influence of FA content on the mechanical properties and hydration reactions of the quaternary solid waste-based binder. The mortar test results indicate that the optimal FA content is 10%, which yields a 28-day compressive strength 11.28% higher than that of the control group without FA. The spherical particles of fly ash reduce the overall water demand and provide a “lubricating” effect to the paste due to their continuous gradation, improving the fluidity of the slag-steel slag-gypsum cementitious materials. The micro test results indicate that fly ash has minimal effect on the early hydration products and process of the solid waste-based cementitious materials, but after 7 days, it continuously dissolves silicon-oxygen tetrahedrons or aluminum-oxygen tetrahedrons, consuming Ca²⁺ and OH⁻ in the system. After 28 days, the amount of ettringite and C-(A)-S-H gel generated increases significantly. The pozzolanic activity of fly ash is mainly stimulated by the Ca(OH)₂ from steel slag in the later hydration stage. Additionally, spherical fly ash particles can fill the voids in the hardened paste, reducing the formation of cracks and weak zones, and thereby contributing to a denser overall structure of the hydrated binder. The findings of this paper provide data support for the development of low-carbon cement-free binders using fly ash in conjunction with metallurgical slags, thereby contributing to the low-carbon advancement of the construction materials industry.