## 4 Results  
### Environmental Impact of Aggregates  
Table 5 shows the six environmental impacts associated with each aggregate released by the ezEPD of South Korea [42] and the German OKOBAUDAT DB [34]. Figure 1 shows the scale of the difference between the environmental impact of each aggregate and that of gravel, which is a natural aggregate. As can be seen in Table 6 and Figure 1, the environmental impact of recycled aggregate in all of the six environmental impact categories varied from 2.31 (GWP) to 157.71 (ODP) times higher than that of gravel. This appeared to be due to the energy consumption (e.g., electricity and diesel) and the water resource consumption (e.g., industrial water) associated with the process of extracting and processing recycled aggregate, a process that involves crushing waste concrete with equipment such as jaw crushers [24]. This was despite the fact that the environmental impact of waste concrete, which is the raw material of recycled aggregate, is close to zero. However, an environmental impact of zero was associated with slag and bottom ash aggregates. This was because they were classified as simple industrial by-products which did not require separate processing. The environmental impact of waste glass aggregate was smaller than that of gravel in terms of ADP and ODP. However, it was 42.41 (GWP) to 98.10 (EP) times higher in terms of GWP, AP, POCP, and EP. It appears that waste glass aggregate exhibited this environmental impact due to the energy consumed in the selection and processing of the raw materials, even though the environmental impact of the raw materials was close to zero, as with recycled aggregate.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Classification** & **Unit** &
\begin{tabular}{c} **Environmental Cost** \\ **Factor (USD/Unit)** \\ \end{tabular} \\ \hline ADP & kg-Sbeq & \(1.78\times 10^{-2}\) \\ GWP & kg-CO2 eq & \(5.16\times 10^{-3}\) \\ ODP & kg-CFC11 eq & \(4.43\times 10^{1}\) \\ AP & kg-SO2 eq & \(1.09\times 10^{1}\) \\ POCP & kg-C2H4 eq & \(2.52\times 10^{0}\) \\ EP & kg-PO4\({}^{3}\)-eq & \(1.93\times 10^{0}\) \\ \hline \hline \end{tabular}  
* ADP: abiotic depletion potential, GWP: global warming potential, ODP: ozone depletion potential, AP: acidification potential, POCP: photochemical ozone creation potential, EP: eutrophication potential, United States Dollar (USD) = 1200 Korean Won.  
\end{table}
Table 5: Environmental Cost Factor.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Classification** & **ADP (log-Sbeq/kg)** & **GWP (log-CO2 eq/kg)** & **ODP (log-CC11 eq/kg)** & **AP (log-SO2 eq/kg)** & **POCP** & **EP (log-PO4\({}^{+}\)eq/kg)** \\ \hline Sand & \(4.98\times 10^{-6}\) & \(2.21\times 10^{-3}\) & \(1.26\times 10^{-10}\) & \(6.29\times 10^{-6}\) & \(1.17\times 10^{-6}\) & \(1.10\times 10^{-6}\) \\ Gravel & \(1.04\times 10^{-5}\) & \(6.46\times 10^{-3}\) & \(1.75\times 10^{-11}\) & \(1.13\times 10^{-5}\) & \(2.25\times 10^{-7}\) & \(2.10\times 10^{-6}\) \\ Recycled Aggregate & \(1.00\times 10^{-4}\) & \(1.49\times 10^{-2}\) & \(2.76\times 10^{-9}\) & \(8.54\times 10^{-5}\) & \(1.89\times 10^{-5}\) & \(1.53\times 10^{-5}\) \\ Slag Aggregate & 0 & 0 & 0 & 0 & 0 & 0 \\ Bottom Ash & 0 & 0 & 0 & 0 & 0 \\ Aggregate & \(5.08\times 10^{-8}\) & \(2.74\times 10^{-1}\) & \(2.62\times 10^{-15}\) & \(5.93\times 10^{-4}\) & \(1.35\times 10^{-5}\) & \(2.06\times 10^{-4}\) \\ \hline \hline \end{tabular}  
* ADP: abiotic depletion potential, GWP: global warming potential, OOP: ozone depletion potential, AP: acidification potential, POCP: photochemical ozone creation potential, EP: eutrophication potential.  
\end{table}
Table 6: Six Environmental Impacts Associated with Each Aggregate.