| To mitigate its environmental impact, this study investigated the effects of ground steel slag powder used as a cementitious admixture on the compressive strength, frost resistance, and shrinkage behavior of concrete, and further examined its microscopic mechanism of action in concrete. The results indicate that the incorporation of steel slag powder improves the compressive strength (7–90 d), drying shrinkage performance, and frost resistance of concrete, with the optimum replacement level being 15%. Concrete containing 15% steel slag powder exhibited a 90 d compressive strength of 56.4 MPa, a 180 d shrinkage strain of 604.4 × 10?6, and a mass loss of 4.0% after 150 freeze–thaw cycles, at which point its compressive strength remained 28.9 MPa. Compared with concrete without steel slag powder, the concrete containing 15% steel slag powder showed a 16.0% increase in 90 d compressive strength, a 16.1% reduction in 180 d shrinkage strain, and a 1.2% decrease in mass loss after 150 freeze–thaw cycles. Steel slag powder can participate in the hydration reaction of cement-based materials and generate C–S–H gel, which helps fill the internal micropores of concrete. As a result, concrete incorporating steel slag powder contains fewer voids and exhibits a denser microstructure. |