## 2 Methodology  
### Materials  
For this study, the same type of asphalt mixture was used as that used in the production of both the HMA (used as a reference) and the various WMAs with different chemical additives (applied during manufacturing in order to reduce the temperature of mixing). Such a mixture has a dense-graded mix type AC 22 35/50 S (EN 13108-1) whose mineral skeleton is composed of limestone aggregates (which allows for sufficient contact with the bitumen to achieve a bond between binder and aggregates) [18] for the different fractions (0/6, 6/12, 12/18, and 18/25 mm) with a maximum particle size equal to 22 mm. The main properties of these aggregates are displayed in Table 1, where it is clear that this material presents appropriate characteristics for its application in the manufacturing of asphalt mixtures. Filler was recovered from the crushing of limestone rocks, which provides fine particles with alkaline properties that facilitate the adhesion with bitumen. This material was less than 0.063 mm in size for more than 96% of the particles, with a density equal to 0.6 Mg/m\({}^{3}\) (EN 1097-3). The binder employed was type B35/50 whose penetration was equal to 44 dmm (EN 1426) with a softening point of approximately 52 \({}^{\circ}\)C (EN 1427). With all of these materials, the asphalt mixture was manufactured using a bitumen dosage equal to 4% over the total mass. The mixture used as a reference to evaluate the influence of the different additives was manufactured at 165 \({}^{\circ}\)C, which is a common temperature for this type of mixture. Table 2 lists the main physical and mechanical properties for this material, where it is possible to see that the mixture presents appropriate properties for its application in asphalt pavements for roads. In order to be able to decrease the manufacturing temperature for the WMA, three types of surfactant additives were used, which are referred to in this study as A1 (a traditional surfactant additive with amine composition), A2 (a nano-additive that modifies the alkalinity of the aggregate surface) and A3 (a vegetable additive with active surface properties). Before the manufacturing of the various WMA, the additives were blended with the bitumen by using a rotational blender at 300 revolutions per minute for 10 min. The temperature of blending was around 160 \({}^{\circ}\)C, and after this process the bitumen was incorporated directly into the mixer over the aggregates at various temperatures (145 \({}^{\circ}\)C or 120 \({}^{\circ}\)C, depending on the case studied). The mixing time was similar to that used for the HMA, and the compaction temperature was almost 10 \({}^{\circ}\)C lower than the mixing temperature (as was the case for the conventional hot mix asphalt). \begin{table}
\begin{tabular}{c c c c c} \hline
**Properties** & & **18/25** & **12/18** & **6/12** & **0/6** \\ \hline \multirow{6}{*}{Particle size (UNE-EN 933-1)} & Sieves (mm) & \% passing & \% passing & \% passing & \% passing \\ \cline{2-5}  & 25 & 100 & 100 & 100 & 100 \\  & 22 & 90 & 100 & 100 & 100 \\  & 16 & 4 & 38 & 100 & 100 \\  & 8 & 0 & 0 & 23 & 100 \\  & 2 & 0 & 0 & 0 & 62 \\  & 0.5 & 0 & 0 & 0 & 28 \\  & 0.25 & 0 & 0 & 0 & 16 \\  & 0.063 & 0.1 & 0.2 & 0.1 & 3.0 \\ \hline \multirow{6}{*}{Coarse aggregate shape. Flakiness index (UNE-EN 933-3)} & 5.25 & 5.82 & 12.01 & - \\  & Percentage of fractured face (UNE-EN 933-5) & 95.8 & 95.2 & 97.1 & - \\ \cline{1-1}  & Resistance to fragmentation (UNE-EN 1097-2) & 24.7 & 24.7 & 24.7 & - \\ \cline{1-1}  & Cleaning (organic impurity content) (UNE-EN 146130) & 0.26 & 0.99 & 2.27 & - \\ \cline{1-1}  & Sand equivalent (UNE-EN 933-8) & - & - & - & 83.02 \\ \hline \multirow{6}{*}{Relative density and absorption (UNE-EN 1097-6)} & \multirow{2}{*}{Apparent density (Mg/m\({}^{3}\))} & 2.73 & 2.75 & 2.71 & 2.80 \\  & ADS (Mg/m\({}^{3}\)) & 2.68 & 2.69 & 2.64 & 2.72 \\ \cline{1-1}  & Density after drying (Mg/m\({}^{3}\)) & 2.70 & 2.71 & 2.66 & 2.75 \\ \cline{1-1}  & Water absorption (\%) & 0.64 & 0.81 & 0.93 & 1.03 \\ \hline \end{tabular}
\end{table}