Characterizing Chronologically Aged Basic Oxygen Furnace Slags as Aggregates and Their Use in Asphalt Concrete Mix as Filler  
[PERSON]  
1 Department of Civil and Environmental Engineering, Nazarbayev University, Astana 010000, Kazakhstan; [EMAIL_ADDRESS]  
2 Department of Chemistry, University of Calabria, 87036 Rende, Italy; [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Civil and Environmental Engineering, Nazarbayev University, Astana 010000, Kazakhstan; [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Civil and Environmental Engineering, Nazarbayev University, Astana 010000, Kazakhstan; [EMAIL_ADDRESS]  
[PERSON]  
2 Department of Chemistry, University of Calabria, 87036 Rende, Italy; [EMAIL_ADDRESS]  
Footnote 1: [[https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci)]([https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci))  
Footnote 2: [[https://www.mdpi.com/journals/pdf/pdf/13/](https://www.mdpi.com/journals/pdf/pdf/13/)]([https://www.mdpi.com/journals/pdf/pdf/13/](https://www.mdpi.com/journals/pdf/pdf/13/))  
electric arc furnace (EAF) slags are beneficially used in asphalt mixtures due to having a \"rough surface texture, high angular shape, high specific gravity\" [3]. Moreover, due to the \"rich content of Fe\({}_{2}\)O\({}_{3}\), CaO, SiO\({}_{2}\) and MgO\" in slags, these are quite good for cement, fertilizer production, and soil refining purposes [4]. The use of steel slags is energy efficient and can reduce carbon dioxide emissions by almost 40% compared to commonly used cement [5]. BOF slags are non-metallic solid wastes consisting of silicates, alumina silicates, calcium aluminum silicates, and iron oxides [6]. It was found that highly oxidized elemental iron is commonly detected in BOF slags, as some portion of molten iron cannot be recovered into the steel [7; 8]. Despite the presence of harmful metals in BOF slags, a high phosphorus content must also be dealt with, as it minimizes steel quality [9]. Thus, special attention must be paid to these issues when using slags. However, slag components may vary from batch to batch, depending on the cooling, treatment, and storage conditions [10]. In addition, calcium silicates in BOF slags, such as \"dicalcium silicate (Ca\({}_{2}\)SiO\({}_{4}\)), tricalcium silicate (Ca\({}_{3}\)SiO\({}_{5}\)), and wollastonite (CaSiO\({}_{3}\))\" make these slags acquire cementitious characteristics [10]. BOF slags contain around 25-55 wt.% of lime, which is problematic [11]. Namely, BOF and EAF slags are often stockpiled outside, where they are subjected to the hydration of lime (CaO) and magnesium (MgO) oxides [7]. This results in \"free lime volume instability\", which restricts the usage of BOF and EAF in conditions where moisture is present. There are examples of road surfaces with slags that are hydrated and then become fractured due to the aforementioned free lime expansion [9]. A 10% volume increase in BOF slag in such conditions and the generation of hydroxides (Ca(OH)\({}_{2}\) and Mg(OH)\({}_{2}\)) at ambient temperatures were detected [12]. The iron content in BOF slags is equal to a 14-30 wt.%, which restricts BOF slag use in cement production [13]. However, in order to avoid volume instability of BOF, it is recommended that slags undergo aging or weathering processes before their application; these processes may take some time [14]. Moreover, BOF slags with limited applicability also impose a problem regarding storage and management, as more land spaces are required to accommodate yearly increasing amounts of BOF slags and high management expenses to deal with BOF's environmental issues. In 2000, in Australia and New Zealand, 64% of BOF slags (510,000 tons) were utilized in \"sealing aggregate, asphalt aggregate, base, subbase, construction fill, subsoil drains and grit blasting\" [13]. In some other countries, BOF slags are used as fertilizer for agricultural purposes by increasing the phosphorus amount in the slags [15]. BOF slags are also used as soil conditioners [16] and in glass production [15].