The study of the mechanisms affecting the preparation parameters of carbonated steel slag is of great significance for the development of carbon sequestration materials. In order to elucidate the mechanism of the influence of moisture on CO₂ diffusion and particle cementation in steel slag, the effects of different water–solid ratios and water contents on the mechanical properties, carbonation products, and pore structure of steel slag after carbonation were investigated. The results show that increasing the water–solid ratio of steel slag can control the larger initial porosity and improve the carbon sequestration capacity of steel slag, but it will reduce the mechanical properties. The carbonation process relies on pores for CO₂ diffusion and also requires a certain level of moisture for Ca²⁺ dissolution and diffusion. Increasing the water content enhances particle cementation and carbonation capacity in steel slag specimens; however, excessive water hinders CO₂ diffusion. Reducing the water content can increase the carbonation depth but may compromise gelling and carbon sequestration ability. Therefore, achieving a balance is crucial in controlling the water content. The compressive strength of the steel slag with suitable moisture and initial porosity can reach 118.7 MPa, and 217.2 kg CO₂ eq./t steel slag can be sequestered.

To prepare lightweight ultra high performance concretes used in the large-span and super-tall structure engineering fields, the effects of water-binder ratio on the mechanical performances, hydration products, and microstructure of the arched shell interface transition zone between the prewetting spherical lightweight aggregates and cement matrix were studied. The experimental results showed that adding prewetting spherical lightweight aggregates promoted the formation of an arched shell interface transition zone. And the hydration degree, microhardness, and elastic modulus values of the arched shell interface transition zone were still higher than the cement matrix. With the reduction of the water-binder ratio, the microhardness, elastic modulus, thickness, and compactness of the interface transition zone had an increase, and the internal curing action of the prewetting spherical lightweight aggregates was more obvious. Especially when the water-binder ratio was 0.18, the hydration degree of the arch shell interface transition zone increased by 18.27% compared with the cement matrix after 28 days curing time. It was concluded that the prewetting spherical lightweight aggregates could have better internal curing and arched shell effects in cement-based materials with a low water-binder ratio. Therefore, adding prewetting spherical lightweight aggregates was regarded as a potential measure to fabricate the lightweight ultra high performance concretes.

The aim of this study is to enhance the value and utilization of red mud generated in the Bayer process by preparing composite cement mortars. The effects of two different types of Bayer red mud with varying physical and chemical characteristics on the fluidity, mechanical strength, mineral composition, and microstructure of the composite cement mortar were systematically evaluated. The results showed that the optimal addition of red mud A was 10 wt%, while it was 20 wt% for red mud B. The mechanical properties of the composite cement mortar met the standards for P·O42.5 cement. Furthermore, the composite mortar with the addition of red mud B showed higher flexural and compressive strengths compared to the composite mortar with red mud A. This improvement is attributed to the smaller particle size of red mud B, which filled the micro-pores and increased the compactness of the cement stone, as well as its higher content of Na₂O, K₂O, and other free alkalis, which resulted in more obvious alkali activation, accelerating the hydration of the active minerals in the slurry.

Utilizing supplementary cementitious materials is an effective way to fabricate low-carbon cement-based materials. In this paper, the composite mortars with good properties were prepared by mixing them with basic oxygen furnace slag (BOFS), Bayer red mud (BRM), and phosphogypsum (PG). The influences of the replacement amounts of BRM and PG on the mechanical properties, hydration characteristic, chloride corrosion resistance, and microstructure of the materials were investigated. The results showed that simply adding 10 wt% BRM slightly modified the properties of the composite mortars. With the increase in PG, the mechanical strength and corrosion resistance coefficient K_C of the mortars first increased and then decreased, in contrast to the chloride migration coefficient D_RCM and electric flux Q. Among the samples, sample S3, with 6 wt% BRM and 4 wt% PG, had the best properties, a flexural strength of 6.6 MPa, and a compressive strength of 43.5 MPa at a curing age of 28 d. And the values of D_RCM and Q of the sample, respectively, decreased by 44.06% and 22.83% compared with the control sample, along with the value of K_C corroded after 120 d increasing by 16.33%. The microstructure analysis indicated that the alkali activation of BRM promoted the generation of lamellar portlandite and reticular and granular C-S-H gel. The free aluminum in BRM could dissolve into C-S-H gel to induce the generation of C-A-S-H gel. Furthermore, the generated amount of ettringite increased by adding PG. The aforementioned improvement in mechanical properties is primarily attributed to BRM promoting the hydration of the composite mortars and inducing the transformation of the C-S-H gel into C-A-S-H gel, and PG promoting the generation of ettringite. Moreover, the filling effects of BRM and PG decreased the porosity and number of harmful pores. It increased the compactness of the microstructure to endow the composite mortars with excellent chloride corrosion resistance.

Ladle refining slag (LFS), classified as solid waste, presents an imminent need for comprehensive utilization. Notably, LFS contains a substantial amount of γ-Ca₂SiO₄ (γ-C₂S) with remarkable carbonation potential, making it an ideal candidate for the production of carbonated cement through Carbon Capture and Storage (CCS) technology. This study delves into the carbonation reaction of the cast and molded lump LFS within a CO₂ pressure vessel. It systematically examines the influence of water-solid ratio and water content on the initial properties of specimens. Furthermore, the investigation encompasses the impact of temperature, reaction time, and CO₂ pressure on carbonation processes and resultant products, contributing to the formulation of a carbonation reaction and mass-transfer mechanism. The research reveals pivotal findings: lower water-solid ratios lead to denser specimens with higher strength, and an optimal 7% water content facilitates effective cementation and reactant dissolution. The controlled growth of densely layered calcite at 20°C yields impressive strengths of up to 120.5MPa, while elevated temperatures, such as 60°C, encourage the growth of smaller calcium carbonate crystals, resulting in a favorable carbon sequestration rate of 19.72%. Extending the carbonation time enhances the conversion rate of γ-C₂S to calcium carbonate. Intriguingly, CO₂ pressure exerts minimal influence on the specimens. The research elucidates the five-step carbonation process and its underlying diffusion mechanism. In essence, this study harnesses CCS technology to offer a high-value solution for addressing LFS disposal challenges.