# Comparative \"from Cradle to Gate\" Life Cycle Assessments of Hot Mix Asphalt (HMA) Materials
## 2 Data and Methods  
The authors calculated the environmental impact of two HMA produced by two different Italian asphalt mix companies (Company 1 and Company 2) that are located near Rome. The declared unit for the analysis is 1 Mg of bituminous concrete for binder layer used in flexible pavements. To compute the product declaration of this declared unit of material, which is a necessary step in the LCA analyses, the authors considered the methodological requirements stated in the ISO 14025:2006 standard [40], as well as those stipulated in the \"General Programme Instructions of the International EPD System 2.5\" [41], and in the Product Category Rules in the European standard 15804:2012+A1:2013 [42]. The standard EN 15804 \"Sustainability of construction works, environmental product declarations, core rules for the product category of construction products\" [42] provides guidelines to elaborate an unbiased set of data useful to examine and improve the environmental performance of a building material. For conducting the LCA of the two HMA considered in the study, some pre-specified minimum requirements are stated by the Product Category Rules (PCR)--which were developed and proposed by the Norwegian Environmental Product Declaration (EPD) Foundation [43]--for preparing an environmental declaration (EPD) for a product group consisting of asphalt and crushed stone. Indeed, the cited documents can be used to develop a type III label EPD of these materials [35]. This methodological approach was selected to conduct the environmental impact assessment of these mixtures because several experts consider that it offers the most comprehensive strategy currently available to perform these types of analyzes.  
The bituminous mixes evaluated, which volumetric properties are summarized in Table 1, satisfy the Italian standards for road materials [44; 45]. As observed in this Table, the composition of both mixes is identical. In fact, their only difference is the source or origin of the materials, as explained in a later section.  
The selected boundary of the system is a \"from cradle to gate\", which means that the life cycle analysis requires data for the raw materials and fuel sources, as well as for transport and manufacturing processes. This means that the LCA study considered A1, A2 and A3 stages (upstream and core processes), as explained in Figure 1. Modules from A4 to D (i.e., construction process, use, end-of-life stages and benefits and loads beyond the system boundary) were considered to be beyond the scope of this work and, therefore, they were not included as part of the analysis (Figure 1).  
The EPD(r) system defines three data categories for the inventory analysis phase [41]:  
* primary data, obtained through on-site surveys and carried out by the producers;
* secondary data, available in the literature;
* tertiary data (also defined as other generic data), obtained through statistical averages.  
In this study, primary data include:  
* the composition of the mix;
* the performance of the vehicles used for aggregates and bitumen transport;
* the annual fuel consumption of the asphalt mix plants; and
* the distance of the asphalt plant from the quarries and the refinery.  
Secondary data are related to the environmental impact of raw materials, fuels and transport, and they were obtained from existing environmental databases available in the literature [46; 47; 48]. Finally, tertiary data were not used in this study.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Component** & **Volume (\%)** & **Density (kg/m\({}^{3}\))** & **Weight \({}^{*}\) (kg)** \\ \hline Bitumen & 10 & 1020 & 44.1 \\ Aggregates (limestone) & 85 & 2600 & 955.9 \\ Air void content & 5 & - & - \\ \hline \end{tabular} \({}^{*}\) These values refer to the declared unit.  
\end{table}
Table 1: Mixes composition.  
Figure 1: System boundaries.