# Application of Foundry Wastes in Eco-Efficient Construction Materials: A Review
## 3 Overview of the Foundry Industry
### Foundry Processes  
Among the most common metal casting methods, sand casting, investment casting (lost wax casting or precision casting), and die casting stand out. Casting molds can be classified into two types: disposable molds, used in processes such as sand casting and investment casting, which are destroyed after each use to extract the piece, and permanent molds, like those used in die casting, which are not disposable. Disposable molds are created from a permanent matrix, as in sand casting, or from a disposable matrix, as in investment casting, while permanent molds naturally do not require a matrix [24]. In die casting, which is a fast method of metal molding, molten metal is injected into a reusable steel mold under pressure and at high speeds. The rapid filling of the cavity, usually in less than 0.1 s, allows economical production of castings, with advantages such as high productivity, detailed shapes, thin walls, aesthetically pleasing surfaces, and precise dimensions. The reusable steel mold has great durability, lasting from 100,000 cycles for aluminum alloys to over a million cycles for zinc castings [25]. However, die casting also has disadvantages, such as the high initial costs of the machines and the creation of new molds. Moreover, its applicability is limited to low melting point alloys and smaller parts in terms of weight [22]. Sand casting is a versatile method for shaping metals, providing flexibility in the characteristics of products of various sizes, shapes, and quality. Typically, the sand is shaped around a mold and compacted to achieve the desired hardness, either by compression for clay-bonded sands or by chemical hardening in the case of molds with chemical binders. The production of molds involves the creation of two halves to facilitate the removal of the matrix and, once reassembled, they form a cavity that corresponds to the shape of the matrix. The casting process begins with the melting of the metal, followed by its pouring into the mold cavity, allowing it to solidify in the space defined by the sand mold and the cores. After solidification, the casting is removed from the mold, usually through a vibration that releases the sand, followed by the removal of the filling and feeding channels [26]. Investment casting, also known as \"lost-wax casting\" or \"precision casting\", is a manufacturing technique with centuries of existence, famous for creating parts with excellent surface quality, precise dimensions, and complex shapes. This technique is especially useful for making almost perfect castings [27]. Ancient writings, molds, and metal objects suggest that investment casting was widely used in ancient civilizations as copper metallurgy evolved. The method has progressed from the creation of complex shapes to the production of parts with curved surfaces [28]. A significant advancement in ancient civilizations was the discovery that metals could be melted and shaped using molds, which probably occurred independently in various regions before 4000 B.C. Historical records indicate that the origin of the lost-wax casting technique involved the use of a bee wax model, covered with clay, which was then heated to harden the clay and melt the wax. The transition from a manual process, performed once, to a mechanized system began in the early 20 th century, initially seen in dental practices [29]. Although the lost-wax technique was common in antiquity, its contemporary form, known as investment casting, only began to be widely used in the industry more recently. Its development in jewelry and engineering progressed independently, gaining popularity in engineering during World War II [30]. The investment casting process involves several stages. First, wax molds are created by injecting molten wax into a mold, with the option to incorporate cores for internal surfaces by injecting wax around preformed cores [31]. After the wax injection, the wax mold is removed from the die with the help of an ejector pin and immersed in water until it solidifies.