# Life Cycle Assessment for the Production Phase of Nano-Silica-Modified Asphalt Mixtures
## 4 Results and Discussion  
### CASE 1A: Impact Assessment of Nano-Silica-Modified Asphalt Mixtures Analysis  
OpenLCA version 1.7.4 was used to model and analyzed the environmental impacts of nano-modified asphalt materials and the analysis results are shown in Table 4.  
Increase in the production of the raw materials and/or the FU results in an increase in fuel and energy usage and will cause a significant increase in the impact scores in each category. The environmental performance of 7.44563 \(\times\) 10\({}^{3}\) kg CO\({}_{2}\)-Eq/FU global warming of nano-silica-modified asphalt mixture is better than the results of ([PERSON] et al.) who found the modification of asphalt materials with a polymer to be 44.9 \(\times\) 10\({}^{3}\) kg CO\({}_{2}\)-Eq per FU of 1 km by 3.5 km wide asphalt pavement.  
\begin{table}
\begin{tabular}{c c c} \hline
**Impact Category** & **Reference Unit** & **Impact Result** \\ \hline Environmental impact \(|\) global warming & kg CO\({}_{2}\)-Eq & 7.44563 \(\times\) 10\({}^{3}\) \\ Human health \(|\) respiratory effects, average & kg PM2.5-Eq & 8.86935 \(\times\) 10\({}^{2}\) \\ Environmental impact \(|\) ozone depletion & kg CFC-11-Eq & 3.71600 \(\times\) 10\({}^{-2}\) \\ Environmental impact \(|\) eutrophication & kg N-Eq & 1.49156 \(\times\) 10\({}^{1}\) \\ Human health \(|\) carcinogenic & kg benzene-Eq & 2.18467 \(\times\) 10\({}^{3}\) \\ Environmental impact \(|\) photochemical oxidation & kg NOx-Eq & 3.03420 \(\times\) 10\({}^{1}\) \\ Human health \(|\) non-carcinogenics & kg toluene-Eq & 6.07040 \(\times\) 10\({}^{6}\) \\ Environmental impact \(|\) ecotoxicity & kg 2,4-D-Eq & 1.08917 \(\times\) 10\({}^{4}\) \\ Environmental impact \(|\) acidification & moles of H+–Eq & 1.87879 \(\times\) 10\({}^{5}\) \\ \hline \end{tabular}
\end{table}
Table 4: LCIA results of nano-silica-modified asphalt mixtures per FU.  
\begin{table}
\begin{tabular}{c c c c c} \hline  & \multicolumn{4}{c}{**Normalization Factors and Reference Year**} \\ \cline{2-5}
**Impact Category** & \multicolumn{2}{c}{**US 2008**} & \multicolumn{2}{c}{**US-CA 2005/2008**} \\ \cline{2-5}  & **Impact per Year** & **Impact per Person Year** & **Impact per Year** & **Impact per Person Year** \\ \hline Ecotoxicity-metals (CTUe) & 3.30 \(\times\) 10\({}^{12}\) & 1.10 \(\times\) 10\({}^{3}\) & 3.70 \(\times\) 10\({}^{12}\) & 1.10 \(\times\) 10\({}^{4}\) \\ Ecotoxicity-non-metals (CTUe) & 2.30 \(\times\) 10\({}^{10}\) & 7.60 \(\times\) 10\({}^{1}\) & 2.50 \(\times\) 10\({}^{4}\) & 7.40 \(\times\) 10\({}^{1}\) \\ Carcinogens-metals (CTUcanc) & 1.40 \(\times\) 10\({}^{16}\) & 4.50 \(\times\) 10\({}^{-5}\) & 1.50 \(\times\) 10\({}^{4}\) & 4.30 \(\times\) 10\({}^{-5}\) \\ Non-carcinogens-metals (CTUcanc) & 3.10 \(\times\) 10\({}^{3}\) & 1.00 \(\times\) 10\({}^{-3}\) & 3.40 \(\times\) 10\({}^{2}\) & 1.00 \(\times\) 10\({}^{-3}\) \\ Global warming (kg CO\({}_{2}\),eq) & 7.40 \(\times\) 10\({}^{12}\) & 2.40 \(\times\) 10\({}^{4}\) & 8.00 \(\times\) 10\({}^{12}\) & 2.40 \(\times\) 10\({}^{4}\) \\ Ozone depletion (kg CFC-11 e) & 4.90 \(\times\) 10\({}^{7}\) & 1.60 \(\times\) 10\({}^{-1}\) & 4.90 \(\times\) 10\({}^{7}\) & 1.50 \(\times\) 10\({}^{-1}\) \\ Acidification (kg CO\({}_{2}\) or SG) & 2.80 \(\times\) 10\({}^{10}\) & 9.10 \(\times\) 10\({}^{1}\) & 3.20 \(\times\) 10\({}^{10}\) & 9.50 \(\times\) 10\({}^{1}\) \\ Eutrophication (kg Ne) & 6.60 \(\times\) 10\({}^{9}\) & 2.20 \(\times\) 10\({}^{1}\) & 7.00 \(\times\) 10\({}^{9}\) & 2.10 \(\times\) 10\({}^{10}\) \\ Photoelectrochemical ozone formation (kg CO\({}_{2}\),eq) & 4.20 \(\times\) 10\({}^{11}\) & 1.40 \(\times\) 10\({}^{3}\) & 4.90 \(\times\) 10\({}^{11}\) & 1.50 \(\times\) 10\({}^{3}\) \\ Respiratory effects (kg PM2.5 eq) & 7.40 \(\times\) 10\({}^{9}\) & 2.40 \(\times\) 10\({}^{9}\) & 1.00 \(\times\) 10\({}^{10}\) & 3.00 \(\times\) 10\({}^{1}\) \\ \hline \end{tabular}
\end{table}
Table 3: Normalization factors for impact categories based on inventories from the US (2008) and US-Canada [45].