Effect of Carbonation on the Water Resistance of Steel Slag—Magnesium Oxysulfate (MOS) Cement Blends

Magnesium oxysulfate (MOS) cement has the advantages of lightweightedness, high strength, and low thermal conductivity, but the utilization of MOS cement is limited due to low water resistance. This paper studied the influence of steel slag and CO2 treatment on the compressive strength and water resistance of MOS cement. The hydration products and microstructures were characterized by X-ray diffraction (XRD), thermogravimetric analysis-differential scanning calorimetry (TG-DSC), scanning electron spectroscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results showed that the strength of MOS cement reached 89.7 MPa with steel slag and CO2 treatment; the water-resistance coefficients of the control and samples containing 10%, 20%, and 30% reached 0.91, 0.81, 1.01, and 1.08 MPa, respectively. The improvement in the strength and water resistance coefficients was because of carbonation that accelerated the hydration of C2S in the steel slag and formed a Ca-Mg-C amorphous substance. The carbonation products contributed to better water stability and denser matrix denser while inhibiting the hydration of MgO, which led to improving the water resistance of the sample.