# Siderurgical Aggregate Cement-Treated Bases and Concrete Using Foundry Sand
## 1 Introduction  
Cement-treated bases (CTB) consists of native soils, gravels, or manufactured aggregates blended with prescribed quantities of cement and water [1]. CTB are also known as cement-treated aggregate base, cement-stabilized base or soil cement, depending on the materials used [2]. The more adequate cements for CTB are those whose hardening time is long enough to assure the workability of the mixture, moderate heat of hydration to limit the effects of cracking by retraction, low development of resistance and stiffness module. According to \"Centro de Estudios Experimentales--Ministerios de Obras Publicas\" (CEDEX), the amount of cement recommended is 4% or higher [3]. In other cases, depending of the type of soil, it is determined by the soil group type [4, 5]. The water content starts the hydration process and facilitates the compaction process. It is recommended to use 5-7% by mass of the aggregate [3]. The use of CTB is due to the shortage of conventional aggregates and energy demands [6]. In addition, the use of CTB improves workability of road materials, increases the strength of the mixture, enhance durability and increases load spreading capacity [7]. The procedure to manufacture laboratory test specimens of CTB involves using the Proctor test procedure [8]. The aggregates are mixed with selected water and cement contents and confined in a mold where confining pressure of the proctor mass compacts the aggregates to obtain maximum dry density and optimal water content. CTB properties like California bearing ratio (CBR), tensile strength and unconfined compressive strength (UCS) depend on the density, water content and confining pressure,which depend on the conditions to be simulated. There is a linear relationship between the UCS and the cement content [9; 10; 11]. The moisture content also affects the development of the UCS [10]. The natural aggregates (NA) of the CTB have to fulfill an adequate grading curve [3], Los Angeles abrasion value, plastic index, flakiness index, sand equivalent and crushing value [10]. The milestone aggregates are the most common NA used for CTB but in recent years there has been an increasing number of studies of CTB with recycled aggregates (RA) as a replacement for the NA. An RA is a recycled aggregate material that comes from different sources like brick stone [12], burnt rocks [13], concrete [14], reclaimed pavement [15], reclaimed asphalt [16], masonry [17], foundry sand [18] and precast elements [19; 20]. The use of these RAs as filler materials has shown they produce an increase of mechanical and durability properties of concrete [21; 22]. Their use as recycled aggregate concrete (RAC) and CTB [17; 23; 24; 25] has also been studied, demonstrating their viability in cement and CTB as they present behaviors similar to those made with NA. According to World Steel [26], the total global production of crude steel in 2018 was 1808.4 Mt, where 28.8% of the production was from electric furnaces [27]. Electric Arc Furnace Slags (EAFS) are by-products of the steel-making process, where the electric-arc furnaces (EAF) use high-power electric arcs to produce the heat necessary to melt recycled steel scrap and to convert it into high quality steel [28]. The slag has a lower density than steel and in a liquid state floats on top of the molten steel. It is extracted from the furnace and is air-cooled in order to form crystalline structures [29]. Once the steel has passed the valorization process it can be called a siderurgical aggregate (SA), which has been shown to have characteristics that can be useful for the civil engineering and has led to its use in concrete [29; 30]. Multiple studies [31; 32; 33] have demonstrated the potential use of EAFS as SA for concrete, showing that compressive strength increases or is very similar to that in traditional concrete. In self-compacted concrete, SA has a similar mechanical performance to concrete manufactured with other additions [34; 35]. Studies with asphalt mix showed that SAs are an alternative to a coarse fraction [36; 37; 38].