## 3 Results and Discussion
### Life-Cycle Assessment Results  
Figures 2-9 illustrate the results of the life-cycle impact assessment (LCIA). The normal scenario involves comparing conventional river-sand-based subbase layers and alternative-material-based subbase layers, without considering the avoidance of using alternative materials. In this comparison, EAF slag had a higher global warming potential (GWP) impact than the other materials. All other alternative materials, in general, had a lower GWP contribution than the river sand layer. Overall, GBF slag had approximately seven \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Parameter** & **Unit** & \begin{tabular}{c} **Benchmark** \\ **IC 2** \\ \end{tabular} & \begin{tabular}{c} **CDW** \\ **Mix** \\ \end{tabular} & \begin{tabular}{c} **CDW** \\ **CC** \\ \end{tabular} & \begin{tabular}{c} **CDW** \\ **CB** \\ \end{tabular} & \begin{tabular}{c} **GBF** \\ \end{tabular} & \
\begin{tabular}{c} **EAF** \\ \end{tabular} &
\begin{tabular}{c} **FA** \\ \end{tabular} \\ \hline Polycyclic aromatic hydrocarbons (PAHs) & mg/kg & 30 & \textless{}0.01 & 0.96 & 5.22 & \textless{}0.01 & \textless{}0.01 & \textless{}0.01 \\ Hydrocarbons (C10-C40) & mg/kg & 1000 & 22 & 140 & 79 & \textless{}10 & 32 & \textless{}10 \\ Extractable organically bound halogens (EOX) & mg/kg & 10 & \textless{}1 & \textless{}1 & \textless{}1 & \textless{}1 & \textless{}1 & \textless{}1 & \textless{}1 \\ Zinc & mg/kg DM & 1500 & 189 & 81 & 156 & 6.1 & 253 & 40 \\ Mercury & mg/kg DM & 5 & \textless{}0.1 & 0.18 & \textless{}0.1 & \textless{}0.1 & \textless{}0.1 & \textless{}0.1 \\ Nickel & mg/kg DM & 500 & 22 & 15 & 11 & 2.8 & 40 & 11 \\ Copper & mg/kg DM & 400 & 100 & 28 & 26 & 6.7 & 224 & 19 \\ Chromium & mg/kg DM & 600 & 24 & 30 & 19 & 21 & 2900 & 24 \\ Cadmium & mg/kg DM & 10 & 0.75 & 0.67 & 0.26 & \textless{}0.1 & 2.8 & 0.26 \\ Lead & mg/kg DM & 700 & 33 & 42 & 37 & \textless{}5 & \textless{}5 & 7.6 \\ Arsenic & mg/kg DM & 150 & 12 & 5.4 & 5.9 & 5.5 & 7.4 & 19 \\ pH value & & 5.5–12 & 8.4 & 10.9 & 11 & 9.2 & 10.4 & 10.7 \\ Electric conductivity & \textless{}5/cm & 2000 & 117 & 501 & 1.040 & 486 & 239 & 427 \\ Chloride & mg/L & 100 & 2.3 & 3.3 & 14 & 1.6 & 2.2 & 2.0 \\ Sulfate & mg/L & 200 & 8.3 & 85 & 330 & 230 & 5.0 & 77 \\ Arsenic & \textless{}9/L & 60 & 7.2 & \textless{}5 & \textless{}5 & \textless{}5 & \textless{}5 & 72 \\ Lead & \textless{}9/L & 200 & 14 & 23 & 17 & 7.6 & 22 & 4.7 \\ Cadmium & \textless{}9/L & 6 & 0.11 & \textless{}0.1 & 1.3 & \textless{}0.1 & \textless{}0.1 & \textless{}0.1 \\ Chromium & \textless{}9/L & 60 & 5.2 & 11 & 16 & 6.1 & 9.7 & 148 \\ Copper & \textless{}9/L & 100 & 8.4 & 9.0 & 13 & 9.1 & 12 & 14 \\ Nickel & \textless{}9/L & 70 & 3.8 & \textless{}0.5 & 3.5 & 4.6 & 5.0 & 48 \\ Mercury & \textless{}9/L & 2 & \textless{}0.2 & 0.22 & \textless{}0.2 & \textless{}0.2 & \textless{}0.2 & \textless{}0.2 \\ Zinc & \textless{}9/L & 600 & 39 & 2.8 & 5.6 & 20 & 30 & 21 \\ Phenol index & mg/L & 100 & 0.008 & \textless{}0.005 & \textless{}0.05 & 0.02 & 0.007 & 0.02 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the chemical investigation program. times higher impact than all other materials. Therefore, the comparison of GBF slag and conventional river sand was kept separate so as to better understand the other alternatives. The GWP contribution analysis of the different material-based layers in a normal scenario indicated that more than 52% of the CO\({}_{2}\) footprint was associated with the transportation process rather than the material processing stage for all materials except GBF slag, the footprint of which was about 91.5% from material processing. The entire GWP impact for fly ash arises from the transportation process, as the material production carries a zero allocation. The contribution of GWP from transportation remains very low when compared to material processing in the use of GBF slag. Compared with EAF slag, the CDW layer and fly ash layers had 61% and 70.7% lower GWP impact contributions, respectively, among the alternative materials.