## 4 Results  
### Aggregate Characterization  
The bulk chemical analyses of the fresh and stockpiled BOF slags are reported in Table 1. Variation in the chemical composition of both the fresh and stockpiled BOFS over a 3-month period is evident. Lower SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), and SO\({}_{3}\) and higher CaO and MgO generally characterize the fresh BOFS compared to those in the stockpiled BOFS. From the X-ray powder diffraction (XRD) analysis, the mineralogy of the fresh and stockpiled BOF slags was determined, and the results are presented in Figure 12. The main difference between the fresh and stockpiled BOFS was in the abundance of free lime (CaO) and calcite (CaCO\({}_{3}\)) and a small amount of portlandite (CaOH)\({}_{2}\)) in the fresh BOFS, whereas the stockpiled BOFS contained a high amount of portlandite instead of free lime. Both the fresh and stockpiled BOFS contained relatively high amounts of quartz (SiO\({}_{2}\)), wustite (FeO), magnetite (Fe\({}_{3}\)O\({}_{4}\)), free lime, and portlandite, and minor amounts of calcium silicate (Ca\({}_{2}\)SiO\({}_{4}\)) and srebrodolskite (Ca\({}_{2}\)Fe\({}_{2}\)O\({}_{5}\)). Amorphous content existed in both the fresh and stockpiled BOFS. A higher amount of portlandite and calcite in both types of BOFS can be explained by the following chemical reaction. \[\mathrm{CaO}_{\mathrm{(S)}}+\mathrm{CO}_{\mathrm{2(g)}}-\mathrm{CaCO}_{\mathrm{ 3(S)}}\ \mathrm{\Delta H}=-178.3\ \mathrm{kJ/mol\ CO_{2}} \tag{1}\]  
\[\mathrm{Ca(OH)_{2(S)}}+\mathrm{CO}_{\mathrm{2(g)}}-\mathrm{CaCO}_{\mathrm{3(S) }}+\mathrm{H}_{2}\mathrm{O}_{\mathrm{(I)}}\ \mathrm{\Delta H}_{\mathrm{r}}=-113.1\ \mathrm{kJ/mol\ CO_{2}} \tag{2}\]  
Figure 13 displays various particle sizes (with mesh sizes) of stockpiled BOF slags that were sifted following the ASTM C 136 guidelines. Regardless of the specific layer within the pile or the age of the BOF slags, these materials exhibited an angular shape and possessed a rough texture. Consequently, when BOF slags are employed as aggregates in \begin{table}
\begin{tabular}{c c c} \hline \hline
**Composition** & **Fresh BOF** & **Stockpiled BOF** \\ \hline MgO & 1.75 & 1.31 \\ Al\({}_{2}\)O\({}_{3}\) & 0.51 & 1.69 \\ SiO\({}_{2}\) & 5.88 & 7.72 \\ P\({}_{2}\)O\({}_{5}\) & 1.31 & 1.73 \\ SO\({}_{3}\) & 0.21 & 0.3 \\ K\({}_{2}\)O & 0.09 & 0.05 \\ Na\({}_{2}\)O & - & - \\ CaO & 47.40 & 47.76 \\ TiO\({}_{2}\) & 0.75 & 0.69 \\ MnO & 4.59 & 2.82 \\ Fe\({}_{2}\)O\({}_{3}\) & 35.46 & 34.44 \\ CuO & 0.05 & 0.04 \\ ZnO & 0.47 & 0.19 \\ SrO & 0.02 & 0.02 \\ BaO & 0.03 & - \\ PbO & 0.03 & 0.02 \\ Au\({}_{2}\)O\({}_{3}\) & - & 0.08 \\ Bi\({}_{2}\)O\({}_{3}\) & - & - \\ ClO\({}_{2}\) & 0.11 & 0.09 \\ Cr\({}_{2}\)O\({}_{3}\) & 0.33 & 0.31 \\ Nb\({}_{2}\)O\({}_{5}\) & 0.01 & 0.01 \\ V\({}_{2}\)O\({}_{5}\) & 0.97 & 0.65 \\ PrO\({}_{2}\) & 0.02 & - \\ NiO & 0.02 \\ CoO & - & 0.04 \\ MoO\({}_{3}\) & - & - \\ ZrO\({}_{2}\) & - & 0.01 \\ Ga\({}_{2}\)O\({}_{3}\) & - & 0.01 \\ Sum & 100.00 & 100.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Bulk chemical composition of fresh and stockpiled BOF slags. applications such as Portland cement concrete, hot mix asphalt concrete, or base courses, they have the potential to enhance their stability and strength through aggregate interlocking. However, it is important to note that their angular and rough-textured nature may result in reduced workability compared to rounded and smooth-textured aggregates, making it more challenging for them to move smoothly past each other. Figure 14 illustrates BOF slags that have undergone an extended aging process, resulting in weathered and aged products with a distinctive light brown coloration. As previously mentioned, the principal crystalline phases found in pure BOF slags include wustite, magnetite, free lime, larnite, and brownmillerite.