# Effect of Micro-Silica Addition into Electric Arc Furnace Steel Slag Eco-Efficient Concrete
## 1 Introduction  
With the growth of population and the expansion of construction and industry activities, the demand for the use of materials such as steel and concrete is increasing. This has led to an increase in the generation of greenhouse gases and wastes from these two sectors. Therefore, the reduction of emissions and the use of recycled materials are very important. Helping to conserve irreplaceable natural resources, reducing environmental pollution and reducing the energy spent during the production of new materials, are among the goals for the future engineering. One of the materials that can have a huge impact on this is slag. Slag is an artificial and lateral product, which occurs when iron isolates in iron melting furnaces from impurities in iron ore. Slag is a combination of silicate and metallic oxides that remain after the cooler of the gross material. This combination is applied after a solid form in a variety of uses, which are the ceremonies of refractory and fertilizer and railway wool materials and road subgroup materials, asphalt and concrete materials [1]. Steel furnace slag (SFS) is a type of slag that is a product of iron production. This material is produced in both forms, basic oxygen furnace (DOF) that is the product of converting iron to steel, which is also known as Linz-Donawitz (LD), or LD-converter slag and electric arc furnace (EAF) that is melting scrap steel product [2]. With regard to the possibility of valorising slag as aggregate, EAFS aggregates or slags from metal furnaces have an important role because in recent decades, the steel industry in Europe has advanced in the technology of making steel [2, 3]. EAF technology is used in about 30% of European carbon and low alloy steel production. In Spain alone, approximately 70% of all steel is produced in arc furnaces (10 t/year of EAF steel), which represents about 15% of all European EAF steel (67 t/year) [4, 5, 6]. Slags are generally classified into two categories: Blast furnace (BF) slag and steelmaking (SM) slag. EAF slag, one of the SM slags which is extracted from the recycling of electric arc furnace waste. There are a large number of studies that propose to use this waste as recycled aggregates for concrete; avoiding this makes use of natural resources to produce aggregate for structural purposes [7; 8]. EAFS has the appearance of black stone, which is very dense compared to other natural aggregates, usually with rough texture and angular shape [9]. Iron, calcium and silicon oxide are the main components of electric furnace slag, while the concentration of other compounds (magnesium, aluminium, manganese) is lower [10]. Since EAFS, such as limestone aggregate, have good resistance to compressive strength, researchers have tried to use and replace the ordinary aggregate using them [11]. Some studies show that this aggregate has been successful against penetration sulfites and Chlorides as well as gaining compressive strength [12; 13]. Moreover, research is made on its properties, including cases such as production of concrete sleepers, use in ballast, use in foundations and substrates, as well as aggregates in concrete to improve the mechanical properties of concrete [14; 15; 16; 17], use in concrete as aggregate [18] and slag bricks and slag ceramic tiles [16]. However, at high temperatures, concrete with natural aggregates performs better than concrete with EAFS aggregates, which may be due to the presence of iron compounds in EAFS aggregates. [19; 20]. To improve this, EAFS aggregates can be washed by the method of grating, which causes damage due to the intense use of water resources and the entry of pollutants into the environment, which itself could violate the aim of its preservation [17]. In Europe, the EAF industry uses radioactivity detection arcs but EAFS and fly ash can show concentrations of natural radionuclides.