## 4 The Role of Metallurgy Slags in Sustainable Construction
### Slags in Cement Production
Additionally, using modified magnesium slag reduced carbon emissions by 7.95% and production costs by over 10% per ton of cement, demonstrating significant environmental and economic benefits. Mechanical and Durability Performance of Construction Materials Incorporating Secondary Raw Materials  
Beyond the environmental and economic advantages discussed in earlier sections, the incorporation of secondary resources, namely cellulose fibers, mining tailings, and metallurgical slags, also leads to measurable changes in key technical properties of construction materials. While previous parts of this manuscript have addressed material types, usage contexts, and sustainability benefits, this section focuses specifically on their influence on mechanical strength, dimensional stability, and long-term durability. The studies already cited demonstrate that cellulose fibers, particularly those derived from waste paper or industrial by-products, enhance tensile strength and crack resistance when added in appropriate dosages to cementitious materials. For example, reinforced concrete prepared with 0.9 kg/m\({}^{3}\) of cellulose fiber has shown notable improvements in compressive, tensile, and flexural strength under demanding structural conditions [42]. Similar benefits have been observed at lower incorporation levels (5-10%), where compressive strength increased without compromising workability [96]. However, higher dosages may induce durability issues due to increased water absorption and potential fiber degradation, especially under humid conditions [98]. Strategies such as fiber pre-treatment or combining with pozzolanic additives have been proposed to mitigate these effects and maintain matrix integrity [14]. In the case of mining tailings, several applications reflect a positive impact on the mechanical behavior of concrete, especially when using iron tailings as aggregate substitutes. As previously presented, replacing up to 30% of natural aggregate with iron tailings in hydraulic concrete led to increased compressive strength and abrasion resistance, as well as extended service life under abrasive and wet environments [154]. Optimal results were obtained when substitution ratios remained within 10-40% for fine aggregates and 5-20% for cement, providing improvements in permeability and freeze-thaw resistance due to the filler effect of finely ground tailings [157]. Nonetheless, the type of tailing remains a determining factor: materials from copper or zinc mines tend to be limited to non-structural uses due to risks of leaching or chemical instability [150; 156]. Reactivity and durability can be optimized by selecting tailings with appropriate mineralogical compositions, particularly those with a combined content of silica, alumina, and iron oxides above 75% [157]. Similarly, metallurgical slags, such as blast furnace slag, steel slag, and copper slag, play a significant role in improving the mechanical and durability properties of cementitious materials. Ground granulated blast furnace slag, when used as a cement substitute in proportions between 20% and 30%, has been shown to increase both early and long-term compressive and tensile strengths while enhancing resistance to sulfate and chloride attacks [242, 243]. Steel slags from electric arc furnaces serve effectively as aggregates, increasing density and strength in concrete structural elements [247], while copper slag, typically used as a partial fine aggregate replacement (50-60%), improves abrasion resistance and bulk density [251]. In asphalt applications, steel slag has demonstrated exceptional performance in enhancing moisture resistance, fatigue life, and rutting resistance in road surfaces [257, 261]. Moreover, slags, such as phosphorus and nickel slag, also contribute positively to sulfate resistance, thermal stability, and impermeability, though their use requires careful control to prevent the leaching of heavy metals or volumetric instability [253, 256].