## 4 The Role of Metallurgy Slags in Sustainable Construction
### Innovative Uses in Bricks and Ceramics  
Beyond conventional uses, metallurgy slags are being explored as primary materials in the manufacture of bricks and ceramics. The high silica and alumina content in these slags make them suitable for the production of heavy clay products. Incorporating slag into brick manufacturing can reduce the firing temperature needed, thus saving energy and reducing emissions. Furthermore, bricks made with slag exhibit enhanced durability and better thermal insulation properties compared to traditional clay bricks [265]. Several types of slag are currently utilized in brick. [PERSON] et al. [266] explored the performance and reaction mechanisms of alkali-activated clay bricks incorporating steel slag and fly ash. Steel slag enhanced early compressive strength, while clay brick provided silicon and aluminum, aiding the reaction process. Fly ash dissolved quickly at higher temperatures, supplying additional silicon and aluminum, and together with clay brick, promoted calcium dissolution from steel slag. The optimal mix, with 30% steel slag, formed calcium-alumino-silicate-hydrate (C-A-S-H) and sodium-alumino-silicate-hydrate (N-A-S-H) gels that strengthenedthe system by wrapping partially hydrated clay brick. In another study, [PERSON] et al. [267] conducted a comprehensive evaluation of aluminum ash and calcium carbide slag for brick manufacturing under ultra-high pressure conditions. The optimal conditions were a 1:9 ratio of aluminum ash to calcium carbide slag, 300 MPa pressure, 5-day curing time, and natural curing. The resulting bricks showed high compressive (75 MPa) and flexural strength (3.6 MPa), excellent waterproof properties, and met environmental standards for leaching toxicity, demonstrating a viable approach to recycling these industrial wastes into high-performance building materials. [PERSON] et al. [268] examined the microstructure and mechanical properties of CO\({}_{2}\)-cured steel slag bricks at a pilot scale, while [PERSON] et al. [97] investigated how moisture content affects bio-carbonated steel slag bricks. Both investigations demonstrated innovative uses of CO\({}_{2}\) and microbial carbonation in steel slag brick production. [PERSON] et al. [268] found that bricks with 25% steel slag achieved the highest CO\({}_{2}\) uptake (7.5%) and a compressive strength of 27.7 MPa, meeting standards for load-bearing bricks, with excellent volume stability and freeze-thaw resistance. [PERSON] et al. [97] showed that moisture content significantly influences the carbonation process, with optimal water levels enhancing CO\({}_{2}\) diffusion and bacterial activity, improving carbonation efficiency, while too much moisture reduced these effects, impacting the final carbonation depth. [PERSON] et al. [269] studied the impact of electric arc furnace slag on enhancing the quality and environmental safety of fired bricks that include municipal solid waste incineration fly ash. The slag increased density and reduced porosity and water absorption by over 50%, enhanced compressive strength by 50%, and lowered thermal conductivity. It also promoted chemical reactions and significantly reduced heavy metal leaching, making the bricks safer and more durable, addressing the drawbacks of using fly ash in brick manufacturing. [PERSON] et al. [270] focused on recycling waste river sludge into unfired green bricks stabilized with phosphogypsum, slag, and cement. The study used hemihydrate phosphogypsum to dehydrate the sludge, and combined it with cement, sodium metasilicate, and slag. The optimal mix achieved a compressive strength of 31 MPa, meeting quality standards, with 96% waste utilization. The microstructural analysis confirmed the formation of calcium silicate hydrate and ettringite, enhancing brick strength. [PERSON] et al. [271] developed CO\({}_{2}\)-cured, carbon-reducing slag-based masonry bricks at a pre-industrial scale, replacing conventional hydraulic binders with steel industry slags.