# Application of Foundry Wastes in Eco-Efficient Construction Materials: A Review
## 5 Valorization of Foundry Waste in Construction Materials
### Foundry Waste Mixtures  
The incorporation of different foundry wastes into construction materials allows for the utilization of the diverse characteristics of each type of waste, consequently improving the overall performance of the materials. It is common to find in the literature the mixing of waste foundry sand (WFS) with slags, as well as ternary mixtures with other industrial wastes. Next, studies on the valorization of foundry waste mixtures in construction materials will be presented. In an attempt to maximize waste utilization, reduce processing costs, and increase recycling rates, [PERSON] et al. [19] investigated the use of general foundry waste in Portland cement concrete as a partial substitute for natural aggregates. It was determined that the mechanical properties were not significantly affected by the replacement of up to 30% of the aggregate mass, which included fine or coarse foundry waste. However, when combined fine and coarse waste materials were added to the concrete, there was a negative impact on the mechanical properties, especially whenever the replacement exceeded 20% of the natural aggregates. In another study, [PERSON] et al. [108] used WFS and GGBFS as the main components to produce sustainable concrete. The aim of the study was to use these waste materials to create concrete while simultaneously promoting more eco-friendly construction methods. The main conclusions indicated that alkali-activated GGBFS can replace conventional Portland cement in concrete production. Using the waste materials, the study was able to create concrete samples that met the minimum requirements for strength and water absorption for various construction applications. The microstructural analysis revealed that the increase in concrete strength was aided by hydration products, such as calcium silicate hydroxide. The metal leaching tests showed that heavy metals were immobilized in the samples, complying with regulations and making the concrete suitable for use in construction without compromising the environment. [PERSON] et al. [109] examined the impact of adding different percentages of calcined WFS on the performance of alkali-activated lightweight concrete (AALC). GGBFS was also used in the mixture. The WFS was calcined at 900 \({}^{\circ}\)C, and the study suggested that it may act as an auxiliary activator for the AALC mixture. Moreover, after 3 and 7 days, the AALC with calcined WFS showed a considerable increase in compressive strength, although, after 28 days, there was a slight loss of strength. This indicated that the incorporation of calcined WFS positively influenced the compressive strength in an initial phase, despite a slight reduction in strength in a later phase. [PERSON] et al. [110] evaluated the application of FA, GGBFS, WFS, and recycled fine aggregates (RFA) in the production of waste-based concrete, replacing 100% of natural sand. This work investigated the physical, mechanical, and durability properties of concrete produced with a new combination of FA, GGBFS, and WFS, which had not been previously studied in the literature. The study found that the concrete with WFS exhibits better workability compared to the concrete using RFA at the same sand replacement level. Moreover, the compressive strength of concrete with 50% RFA and 35% GGBFS surpasses that of conventional concrete. The results also suggest that replacing sand with WFS and RFA, up to a maximum of 25%, allows for obtaining an elastic modulus similar to that of traditional concrete. The replacement of sand with WFS in concrete, up to 50%, results in water absorption levels like those of traditional concrete. [PERSON] et al. [111] studied the use of GGBFS as a substitute for cement to determine the maximum amount that can be replaced without compromising the strength of the concrete. They established the upper limit for GGBFS replacement and subsequently replaced natural sand with WFS to investigate the impact on the mechanical properties of concrete.