# Comparative \"from Cradle to Gate\" Life Cycle Assessments of Hot Mix Asphalt (HMA) Materials
## 2 Data and Methods
### Life Cycle Impact Assessment  
Data collected in the LCI phase are used for the LCIA through the characterization factors defined by EN 15804. These are factors derived from an environmental model that are applied to convert the assigned LCI results to a common unit of a category indicator. Therefore, this procedure reduces the scores of the environmental impact of each category to the same measurement units, expressed as equivalent (eq.) after the \"conversion\" process. For a given set of substances, the equivalence describes the amount of the reference substance that would have the same environmental effect. Consequently, they allow quantifying the extent to which each pollutant contributes to different environmental impacts.  
As an example of the result of this process, Table 10 lists the environmental impact of 1 Mg of limestone, which was obtained using the information presented in Tables 7-9.  
The resulting data containing information about emissions, use of resources and wastes for each one of the six categories evaluated describe the upstream process and allow calculating the A1-A2 modules of the EPD.  
The allocation rules used in the LCIA comply with the EN 15804 regulation [42]. All materials and energy flows were included in the calculation, therefore, energy and mass contributions considered  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Environmental Impact** & **Quantity** & **Unit** \\ \hline Global warming potential, _GWP_ & \(2.57\times 10^{0}\) & kg CO\({}_{2}\) eq. \\ Depletion potential of the stratospheric ozone layer, _ODP_ & \(2.71\times 10^{-7}\) & kg CFC-11 eq. \\ Acidification potential of soil and water, _AP_ & \(6.15\times 10^{-2}\) & kg SO\({}_{2}\) eq. \\ Eutrophication potential, _EP_ & \(1.18\times 10^{-2}\) & kg (PO\({}_{4}\))\({}^{3-}\) eq. \\ Formation potential of tropospheric ozone, _POCP_ & \(4.07\times 10^{-3}\) & kg C\({}_{2}\)H\({}_{4}\) eq. \\ Abiotic depletion potential for fossil resources, _ADP-fossil fuels_ & \(6.02\times 10^{1}\) & MJ \\ Human Toxicity Potential (_HTP_) & \(8.53\times 10^{-1}\) & kg 1/4-DCB eq. \\ \hline \hline \end{tabular}
\end{table}
Table 10: Environmental impacts of 1 Mg limestone.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Resource Use** & **Quantity** & **Unit** \\ \hline Use of natural energy resources & 0.95 & kg \\ Use of natural resources, non-energy & 1040 & kg \\ Total primary energy & 60.9 & MJ \\ Renewable energy & 0.7 & MJ \\ Non-renewable energy & 60.2 & MJ \\ Electricity consumption & 2.54 & kWh \\ Use of fresh water & 27.6 & L \\ \hline \hline \end{tabular}
\end{table}
Table 8: Use of resources in the process of obtaining limestone at the quarry.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Waste to Disposal** & **Quantity (kg)** \\ \hline Hazardous waste & \(8.82\times 10^{-3}\) \\ Non-hazardous waste & \(2.39\times 10^{-1}\) \\ \hline \hline \end{tabular}
\end{table}
Table 9: Limestone’s waste to disposal.  
in the analysis were fully allocated into the system. Nevertheless, energy and material contributions related to asphalt production but different from the main object of the present analysis were excluded (e.g., bitumen-bound aggregate mixtures). Finally, the wastes generated directly from the asphalt production, if carried out within the plant, were allocated to the production of asphalt.  
The authors obtained the EPD of 1 Mg of asphalt concrete to be used in the construction of binder courses collecting data during the inventory analysis phase and selecting the characterization factors provided by EN 15804 and by [PERSON] [55] for \"Human Toxicity Potential\" (_HTP_). Although it is not defined by the EN 15804 specification, the additional parameter _HTP_ was considered as part of the analysis due to the interest of the European Community on this aspect.  
In summary, the product declaration considers parameters describing the environmental impact, the use of resources, the waste categories, the output flow materials, and the potential of human toxicity.