# Comparative \"from Cradle to Gate\" Life Cycle Assessments of Hot Mix Asphalt (HMA) Materials
## 3 Results  
Data collected in the LCI were modeled using the characterization factors listed in [42] and proposed by [PERSON] et al. [56]. As explained previously, the concept of characterization factors permits to compare the ability of different substances to cause the same environmental consequence. These factors convert the assigned LCI results into a common unit of a category indicator as explained by Equation (4).  
\[IC=\sum_{x}CF_{ic}(x)\cdot INV(x) \tag{4}\]  
where _IC_ is the Impact Category, obtained from the inventory _INV(x)_ of the substance \(x\) and _CF\({}_{ic}(x)\)_ the characterization factor assigned to the substance \(x\) for the calculation of _IC_.  
For environmental impacts which have a chemical unit of measure, the unit is expressed as equivalent (eq.) due to the applied \"conversion\" process.  
Table 11 presents the resulting impact categories of 1 Mg of the asphalt concrete produced by both companies.  
As observed, the main differences between the impacts of the two mix materials summarized in Table 11 are related to the fuels and transport and manufacturing modules, while quality and quantity of raw materials are the same for both companies. Except for ADP-fossil fuels, Company 1 has an overall lower environmental impact. The results are compliant with the fact that this company uses methane gas as a fuel source. Out of all fossil fuels, natural gas--which is used by Company 1--has the highest ratio between energy produced by combustion and emitted CO\({}_{2}\) and, therefore, it has a  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Impact Categories** & **Company 1** & **Company 2** & **Unit** \\ \hline Global Warming Potential, _GWP_ & 34.48 & 38.04 & kg CO\({}_{2}\) eq. \\ Acidification Potential, _AP_ & 0.16 & 0.16 & kg SO\({}_{2}\) eq. \\ Ozone layer Depletion Potential, _ODP_ & \(2.55\times 10^{-7}\) & \(2.55\times 10^{-7}\) & kg CFC-11 eq. \\ Eutrophication Potential, _EP_ & 0.78 & 0.78 & kg (PO\({}_{4}\)\({}^{3-}\)) eq. \\ Formation potential of tropospheric ozone, _POCP_ & 0.01 & 0.01 & kg C\({}_{2}\)H\({}_{4}\) eq. \\ Abiotic Depletion Potential for fossil resources, _ADP-fossil fuels_ & 441.58 & 438.05 & MJ \\ Use of natural energy resources & 9.34 & 10.25 & kg \\ Use of natural resources, non-energy & 1054.75 & 1054.76 & kg \\ Total primary energy & 422.78 & 419.41 & MJ \\ Renewable energy & 0.68 & 0.68 & MJ \\ Non-renewable energy & 422.10 & 418.73 & MJ \\ Electricity consumption & 4.92 & 4.77 & MJ \\ Net use of fresh water & 0.03 & 0.03 & m\({}^{3}\) \\ Components for reuse & 0 & 0 & kg \\ Materials for recycling & 0.30 & 0.30 & kg \\ Materials for energy recovery & 0 & 0 & kg \\ Human Toxicity Potential (_HTP_) & 2.97 & 2.54 & kg 1,4-DCB eq. \\ \hline \hline \end{tabular}
\end{table}
Table 11: Impact categories of 1 Mg of asphalt concrete for the two companies.  
low contribution to global warming. Besides, it was found that Company 1 requires more electricity than Company 2 to produce the declared unit of bituminous concrete, and Company 2 has a lower HTP in comparison to Company 1.  
The interpretation phase of the results included the analysis of the average percentage contribution of fuels and raw materials (A1 phase), internal and external transport (A2 phase) and manufacturing processes (A3 phase) of the two companies [39]. Table 12 summarizes the results obtained for the analysis conducted for both mix plants.  
The values in this table refer to the percentage of contribution of each phase (i.e., A1 to A3), to the total LCA of the environmental impact under evaluation. Consequently, the values in every column always sum up to 100%. The advantage of presenting the LCA results in this way is that it permits to easily identify and analyze the stages that contribute the most to each environmental hazard or impact, as done by [PERSON] et al. [57].