Optimizing CO2 mineralization parameters of steel slag to improve carbonation resistance of concrete: chemical and microstructure effects

To enhance the carbonation resistance of concrete, this study optimized CO2 mineralization parameters of steel slag using the Taguchi method, revealing a nonlinear relationship between carbon content and mineralized parameters. The optimal conditions (150 min, 2.1 MPa, 78.5 degrees C and 36.4% humidity) achieved a carbon fixation rate of 7.82%. A amount of carbonation products covering the surface of steel slag, significantly improving steel slag's microstructure and chemical properties. Incorporating 10% CO2 mineralized steel slag reduced the carbonation depth of concrete to 7 mm, a 30% improvement compared to pure cement concrete (10 mm). The micro-nano mineralization products fill the pores and enhance the bonding between steel slag and hydration products, thereby reducing CO2 ingress into the concrete and maintaining a high pH level. These findings show an extensible way to recycle steel slag and improve the durability and sustainability of concrete.