## 2 Methodology
### Labeling Scheme  
Once all the data were collected, each property was classified into its category (see Table 1). The characterization methods of these properties were chosen to match existing European standards and practices as well as possible. In the cases where no harmonized European methods were available, the Spanish technical standard was used (see Table 1). Figure 3: Tiresonic Mk4-LA2 IC for acoustics characterization of road surfaces and detail of the microphone positions. Figure 2: Splash and spray trailer and measuring details. Even though characteristics of asphalt mixtures for thin overlays may differ widely between different applications (e.g., motorway vs. low-volume rural road), the designed labeling scheme was deliberately kept as simple as possible, and the same number of label classes was chosen for all the properties. This study proposes a set of performance classes from A to D on the label according to the reduced sample size of collected data, but the developed tool is flexible enough to scale-up the range of characterization as data arise. The proposed boundaries of the label classes are chosen such that A is excellent, B represents a current good practice, C represents an acceptable performance, and D does not meet the standards (see Figure 4). In order to define the limits of each label class, a statistical treatment of the results was carried out to detect outliers, and to establish the working range of the reliable results and their statistical distribution. All indicators were statistically tested to determine if the dataset was well modeled by a normal or log-normal distribution. In order to verify this assumption, normality tests were applied; in particular, graphical methods were used: the histogram was compared to the normal probability curve, the normal probability plot was analyzed, and the boxplot symmetry was checked (see Figure 5). \begin{table}
\begin{tabular}{c c c c} \hline
**Category** & **Property** & **Indicator** & **Standard** \\ \hline \multirow{4}{*}{\begin{tabular}{c} Mechanical \\ performance \\ \end{tabular} } & Stability & \begin{tabular}{c} Marshall stability Marshall \\ deformation \\ \end{tabular} & EN 12697-34 [26] \\  & Disaggregation & Dry Cantabro Loses (\%) & EN 12697-17 [27] \\  & Water sensibility & Indirect tensile strength ratio & EN 12697-12 [28] \\  & Cracking resistance & Tensile strength displacement at 50\% post-peak load & F\(\ddot{\text{e}}\)rix test [23] \\ \hline \multirow{3}{*}{\begin{tabular}{c} Functional \\ performance \\ \end{tabular} } & Macrotexture & Surface mean texture depth (mm) & EN 13036-1 [29] \\  & Skid resistance & Sideway force coefficient & UNE 41201 IN [30] \\  & Splash and spray & Number of drops & - \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} Environmental \\ performance \\ \end{tabular} } &
\begin{tabular}{c} Tire–pavement noise \\ \end{tabular} & Sound absorption coefficient & EN 10534-1 [31] \\  & Production temperature & Production temperature (\({}^{\circ}\)C) & EN 13108-21 [32] \\  & Recycled asphalt & Percentage of RAP out of the total & - \\  & pavement (RAP) & mass of the mixture (\%) & - \\  & Reuse of by-products & Yes/no & - \\ \hline \end{tabular}
\end{table} 
Table 1: List of considered properties for each category. Figure 4: Label classes for the properties. Based on the requirements established by the Spanish technical standard [20], the boundary between acceptable and non-acceptable label classes was defined, but it could be easily applied to any other international standard.