## 4 The Role of Metallurgy Slags in Sustainable Construction
### Slags in Cement Production  
The use of slag in cement production is well-established, with its ability to substitute a portion of the clinker in Portland cement, known as slag cement. This substitution not only conserves limestone and reduces the energy required for clinker production but significantly diminishes CO\({}_{2}\) emissions. The resulting slag cement generally shows improved performance characteristics, such as lower heat of hydration, better workability, and increased resistance to aggressive environments, making it highly desirable for marine and hydraulic constructions [275]. Several examples illustrate how different types of slag, with varying compositions and processing techniques, contribute to the performance and sustainability of eco-cements. [PERSON] et al. [24] investigated the use of steel slag, ferroickel slag, and copper mining waste in cement production, highlighting their potential to partially replace traditional cement materials and enhance sustainability. Steel slag, with its high calcium oxide content and chemical properties similar to Portland cement, replaced up to 30% of traditional cement, significantly reducing CO\({}_{2}\) emissions and enhancing mechanical properties, such as compressive strength and durability. Ferronickel slag, rich in silicon dioxide (up to 40%), exhibited pozzolanic activity, contributing to the formation of secondary calcium silicate hydrates and improving long-term strength in blended cements. Copper slag, characterized by high iron oxide (around 40%) and low calcium content, also showed promise as a pozzolanic material, particularly when rapidly cooled to maintain an amorphous silica state, allowing effective participation in the hydration process. When used at replacement levels of about 15-20%, copper slag contributed similar compressive strength gains as traditional pozzolans, demonstrating its value in cement formulations. [PERSON] et al. [276] successfully demonstrated that steelmaking slag, enriched with noncarbonated CaO from the decarbonization of limestone during steel production, can effectively replace a portion of natural limestone in cement clinker production. Their findings revealed that this substitution not only contributes to a significant reduction in CO\({}_{2}\) emissions but enhances the overall material properties of the cement. The slag's rich calcium content proved beneficial in maintaining the necessary lime saturation factor for optimal clinker formation. Through their detailed analysis, the authors also confirmed that the adjusted slag, when processed with targeted grinding and chemical stabilization, integrates well into cement mixtures, providing improved performance characteristics, such as increased durability and strength of the final cement product. [PERSON] et al. [277] investigated eco-sustainable cements made from iron-making slag and gypsum waste, with formulations containing 80-90% blast furnace slag, 10-20% gypsum, and 10-15% basic oxygen furnace slag. The best-performing eco-cement achieved compressive strengthsgreater than 50 MPa at 28 days and over 80 MPa at 180 days. This high performance was attributed to its composition, which included basic oxygen furnace slag with high basicity (3.1), a significant content of brownmillerite (19%), and dicalcium silicate (21%), along with blast furnace slag rich in aluminum (15%). These factors contributed to enhanced hydration, the formation of ettrinigite, and consistent strength growth throughout the curing process. [PERSON] et al. [278] explored a large-scale industrial method for using modified magnesium slag in cement production to address the disposal challenges of magnesium slag waste. The study found that cement produced with modified magnesium slag met the standards for general Portland cement. The hydration process revealed a unique interaction between magnesium slag and clinker, enhancing early hydration and contributing to the cement's performance.