Steel slag is a by-product of steel manufacturing. Approximately 160 kg of steel slag is generated per ton of steel produced. The common chemical compounds in steel slag are SiO2, CaO, Fe2O3, Al2O3, and MnO. The major mineral components of steel slag are C3S, C2S, C4AF, RO phase, and free-CaO. Many studies have shown that steel slag can be applied in ceramics, road pavement materials, and other materials. However, in some countries, a large amount of steel slag is still stockpiled without full utilization.
The application of steel slag powder as a mineral admixture in concrete has been investigated in many studies. Steel slag powder has hydraulic properties, and its hydration process is similar to that of cement. Studies have shown that concrete that contains steel slag powder performs better in terms of workability than plain cement concrete does. The early autogenous shrinkage and adiabatic temperature rise of the concrete containing steel slag powder are also lower than those of concrete without steel slag powder. Additionally, the nonevaporable water content of the hardened paste containing fine steel slag powder is close to that of hardened plain cement paste at late ages. Due to the negative influence of steel slag powder on the compressive strength, the chloride-ion penetration resistance, carbonation resistance, and sulfate-attack resistance of concrete, the cement replacement ratio should not be very high.
Research has also shown that steel slag could be used as either a coarse or fine aggregate for concrete. The physical properties of steel slag aggregate are better than those of crushed limestone aggregate. Due to the high density of steel slag, concrete containing steel slag aggregate has a higher density than plain cement concrete does. In addition, concrete containing steel slag aggregate displays satisfactory compressive strengths and flexural strengths.
Ultra-high performance concrete (UHPC) is a new type of cement-based material. In general, UHPC consists of cement, silica fume, quartz sand, fiber, superplasticizer, and other constituents and exhibits very high compressive strength, high ductility, and outstanding durability. High-temperature curing is usually used for UHPC, which is beneficial for the early hydration of cement and mineral admixtures. The applications of many kinds of industrial by-products, such as ground-granulated blast furnace slag, phosphorus slag, fly ash, and copper slag, in UHPC have been reported.