Effect of step‑wise mixing strategy with CO2‑MEA solution on carbonation curing of steel slag‑cement paste

This study introduces a step-wise mixing strategy utilizing CO 2 -loaded monoethanolamine (CO 2 -MEA) solution as both a slag modifier and mixing water, followed by carbonation curing. The performance influence mechanisms of cement-based materials incorporating modified steel slag and CO 2 -MEA solution as mixing water were investigated using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TGA). Results indicate that during the initial mixing stage, carbonation reactions between the CO 2 -MEA solution and free calcium oxide/silicate phases in steel slag generate calcium carbonate deposits on particle surfaces. These deposits increase surface roughness and specific surface area, enhance the CO 2 capture capacity of steel slag, and modify its surface chemical properties. Additionally, the strategy improves the volumetric stability of cement pastes, demonstrating its potential to mitigate expansion-related issues in practical applications. Despite the retardation of early hydration caused by the amine-rich mixing water, the compressive strength of the paste is increased by 1.8%, 10.4%, and 4.9% after carbonation curing for 2 h, 4 h, and 8 h, respectively, compared with the untreated group. This performance correlates with a 24.8% reduction in total porosity (from 34.7% to 26.1%) and improved thermal stability over prolonged curing. Ultimately, this combined modification and solvent replacement strategy achieves a maximum 9.5% enhancement in CO 2 uptake within the steel slag-cement pastes. These findings lay a mechanistic foundation for advancing CO 2 sequestration technologies while valorizing industrial by-products, establishing a scalable solution for developing low-carbon cementitious materials through synergistic resource recycling.