Introduction
Steel slag, a by-product generated during steel manufacturing, poses significant environmental challenges due to its disposal issues. However, it also presents an opportunity for carbon utilization through carbonation curing. By exposing steel slag to carbon dioxide, its properties can be enhanced while simultaneously reducing CO2 emissions. This study explores how varying CO2 concentrations influence the curing process, focusing on the carbon uptake, mechanical strength, and microstructural transformations of compact steel slag. The investigation aims to optimize the use of industrial flue gas as a sustainable means of CO2 sequestration and material strengthening.
Experimental Design and CO2 Concentration Range
The research examined a broad spectrum of CO2 concentrations, ranging from 0.04% (representing ambient atmospheric levels) to 27% (simulating industrial flue gas conditions). Compact steel slag samples were subjected to these environments for carbonation curing. The experimental setup allowed observation of how differing CO2 levels influence carbonation kinetics and hydration processes. Through controlled exposure and precise measurement, the study assessed both chemical and physical responses within the material. This range provided a realistic perspective on the potential use of actual industrial emissions for efficient steel slag treatment and carbon capture.
CO2 Uptake and Carbon Sequestration Efficiency
Results revealed that even at a relatively low CO2 concentration of 4%, steel slag demonstrated substantial carbon absorption, achieving a CO2 uptake of 7.3%. This outcome highlights the material’s inherent ability to act as an effective carbon sink. As CO2 concentration increased, the rate and extent of carbon sequestration also improved proportionally. The study confirms that carbonation curing is not only an environmentally beneficial process but also a practical approach for industrial-scale carbon capture, utilizing waste by-products from steel production to mitigate greenhouse gas emissions effectively.
Mechanical Strength Development
Mechanical testing showed a significant improvement in the compressive strength of compact steel slag following carbonation curing. Under 4% CO2 concentration, the material achieved a strength of 42.03 MPa after 72 hours of curing. Higher CO2 concentrations further enhanced this strength, suggesting a direct relationship between carbon uptake and material densification. The increased formation of calcium carbonate compounds within the matrix contributed to pore refinement and improved bonding between particles. This enhancement demonstrates that carbonation not only supports environmental sustainability but also leads to the production of durable and high-performance construction materials.
Microstructural Transformations
Microstructure analysis revealed distinct crystal morphology changes as CO2 concentration increased. Initially, the calcium carbonate formed primarily as aragonite, but at higher CO2 levels, it transitioned into the thermodynamically stable calcite form. This transformation indicated improved material stability and densification due to enhanced carbonation. The change from aragonite to calcite crystal structures provided evidence of effective CO2 interaction with steel slag components. These microstructural modifications directly influenced mechanical performance and durability, proving that higher CO2 environments facilitate the development of stronger and more compact materials.
Role of Carbonation and Hydration Mechanisms
Both carbonation and hydration reactions contributed to the overall consolidation of steel slag during curing. At lower CO2 concentrations, hydration dominated, leading to the formation of calcium silicate hydrates that bind particles together. As CO2 levels increased, carbonation became the primary mechanism, forming dense calcium carbonate matrices that improved strength and stability. This interaction between hydration and carbonation created a synergistic effect, optimizing the material’s performance. Understanding the balance between these two processes is essential for tailoring curing conditions to maximize both carbon capture and mechanical enhancement.
Conclusion
The study demonstrates that carbonation curing of steel slag under varying CO2 concentrations offers a dual advantage—effective carbon sequestration and improved material properties. Even low CO2 environments significantly enhance performance, while higher concentrations promote greater strength and structural stability. The transition from aragonite to calcite and the balance between hydration and carbonation highlight the process’s scientific and industrial potential. Utilizing industrial flue gas directly for curing opens promising avenues for sustainable construction materials and carbon management, transforming steelmaking waste into a valuable resource for environmental and engineering applications.
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