## 1 Introduction  
Polyester polymer concretes (PPCs) are composite materials made up of organic resins as a binder, and aggregates or fillers as the target materials. These composite materials develop, by means of exothermic chemical reactions with hardeners and accelerators, a continuous resistant polymer matrix around the target particles. PPCs have been receiving increasing interest in recent years because of their good characteristics compared with traditional concrete, namely: improved mechanical strength, superior durability, good resistance to water, lower permeability, high chemical and corrosion resistances, excellent adhesion and a fast curing process, among others [1, 2]. However, PPCs also show some disadvantages, like a lower workability, fresh resin odor, lower resistance to high temperatures, and higher cost compared with conventional concrete [3]. An effective way to decrease these shortcomings, in agreement with the actual environmentally friendly thinking trends, consists of using recycled targets instead of raw materials for PPC manufacturing. PPCs show a high potential for the incorporation of recycled materials because of the nature of their polymer matrix and their lack of bonds with the target particles [4]. In addition, the use of recycled targets for PPC manufacturing could suppose an effective method of valorization for large quantities of different wastes. This could not only improve the sustainability of the resulting PPC products, but also the natural resources preservation, in accordance with the circular economy principles [5]. Different applications could benefit from the use of PPC-containing recycled target materials, mainly those that are not subject to strict structural concrete regulations. Nevertheless, not all wastes have the same potential for PPC manufacturing, as their own characteristics can modify the fresh or final product properties. Extensive research works have been conducted for determining the properties of PPCs made up of different recycled targets, like aggregates, sand, clay, fillers, fly ash, fuel ashes, plastics, or recycled fiber reinforced polymers, among others [1; 3; 4; 6; 7; 8; 9; 10; 11; 12; 13]. However, nowadays, huge amounts of different wastes, with potential as PPC targets, continue to be disposed in landfills around the world and pollute the environment. Based on their good properties as aggregates for conventional concrete manufacturing, one of the most promising is metallurgical wastes [14; 15; 16; 17]. Nonetheless, there is a lack of knowledge about the ability of these materials as PPC components. Thus, this study analyzes the aptitude of two metallurgical wastes as target materials for PPC manufacturing--alumina filler (AF) and ladle slags (LS). Large quantities of both wastes are continuously generated, and because of the lack of effective valorization methods, high volumes are available around the world. Their use for PPC manufacturing would have important environmental and economic advantages for waste producers and PPC manufacturing companies. Under these environmental and economic considerations, an experimental laboratory investigation was carried out. Its aim was to develop the knowledge--which is currently not available--between these non-conventional target materials and the fresh and mechanical properties of polyester polymer concrete.