In the quest for sustainable construction materials and reduced carbon emissions, a groundbreaking study led by An Tai from the College of Materials Science and Engineering at Nanjing Tech University has unveiled a promising technique: supercritical carbonation of steel slag. This innovative process not only enhances the utilization of steel slag but also contributes to CO2 sequestration, offering a dual benefit for the construction and energy sectors.
Steel slag, a byproduct of steel production, has long been underutilized due to its unpredictable volume stability and potential for expansion. However, Tai and his team have demonstrated that supercritical carbonation can significantly improve the material’s properties. By treating steel slag in an industrial autoclave device, they observed the formation of nano-CaCO3 and amorphous SiO2, both on the surface and interior of the carbonated steel slag. “The high diffusivity and reactivity of supercritical CO2 play a crucial role in this transformation,” Tai explains.
The study, published in *Case Studies in Construction Materials* (translated from Chinese as “典型建筑材料研究”), identified two distinct carbonation mechanisms. In gas-solid carbonation, where moisture is less than 0.02, a direct reaction model was established. In contrast, aqueous carbonation, with moisture levels above 0.02, follows a surface coverage and interior generation model. These findings provide a deeper understanding of the carbonation process and its impact on steel slag.
One of the most significant outcomes of this research is the improvement in the early compressive strength and soundness of steel slag. The activity indexes of the carbonated steel slag were found to be more than 80% and even above 90% at just three days. This rapid strength development is attributed to the involvement of nano-CaCO3 and -SiO2 in cement hydration, leading to the production of Mc and Fe-bearing C-S-H gel. The result is a material with lower porosity and enhanced strength.
The commercial implications of this research are substantial. For the construction industry, the enhanced properties of carbonated steel slag open up new possibilities for its use in various applications, reducing the reliance on traditional cement and lowering carbon emissions. For the energy sector, the potential for CO2 sequestration through supercritical carbonation offers a viable pathway to mitigate the environmental impact of industrial processes.
As the world grapples with the challenges of climate change and sustainable development, innovations like supercritical carbonation of steel slag provide a glimmer of hope. By transforming industrial byproducts into valuable construction materials and sequestering CO2 in the process, this research paves the way for a more sustainable future. The findings of Tai and his team not only advance our understanding of carbonation mechanisms but also highlight the potential for synergy between the construction and energy sectors in the pursuit of a greener tomorrow.