## 4 Results and Discussion  
### Contact Angle  
The contact angle refers to the tangent of the gas-liquid interface at the intersection of the gas, liquid, and solid phases. The angle \(\theta\) between the tangent and the solid-liquid boundary of the liquid is a measure of the degree of wetting. If \(\theta<90^{\circ}\), the solid surface is hydrophilic, that is, the liquid relatively easily wets the solid, and the smaller the angle, the better the wettability. If \(\theta>90^{\circ}\), the solid surface is hydrophobic, that is, the liquid does not easily wet the solid and easily moves on the surface. The final contact angle test results are the average of five parallel tests. The contact angle data are shown in Table 4.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Type of Asphal**} & \multirow{2}{*}{**Reagent**} & \multicolumn{6}{c}{**Contact Angle/(\({}^{\circ}\))**} \\ \cline{3-8}  & & **Base** & **RTFOT** & **50 h** & **100 h** & **150 h** & **200 h** & **PAV** \\  & & **Sample** & **UV** & **UV** & **UV** & **UV** & **UV** & **PAV** \\ \hline \multirow{3}{*}{Base Asphal} & Distilled water & 100.81 & 101.04 & 102.23 & 103.15 & 104.90 & 100.27 & 104.52 \\  & Glycerol & 103.46 & 103.14 & 100.68 & 94.36 & 96.35 & 95.82 & 101.72 \\  & Formamide & 84.86 & 88.57 & 88.84 & 84.93 & 88.26 & 90.60 & 93.25 \\ \hline \multirow{3}{*}{Evotherm M1 WMA} & Distilled water & 99.42 & 97.72 & 99.97 & 98.11 & 99.68 & 101.18 & 104.96 \\  & Glycerol & 103.46 & 100.29 & 97.03 & 97.32 & 94.53 & 95.11 & 101.04 \\  & Formamide & 80.87 & 79.85 & 81.50 & 85.68 & 84.75 & 85.31 & 85.53 \\ \hline \multirow{3}{*}{Sasobit WMA} & Distilled water & 99.49 & 101.99 & 103.48 & 106.41 & 105.92 & 101.99 & 108.54 \\  & Glycerol & 96.94 & 94.87 & 90.70 & 95.85 & 92.87 & 94.87 & 95.47 \\ \cline{1-1}  & Formamide & 81.07 & 83.24 & 88.62 & 87.67 & 86.57 & 83.24 & 87.76 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Contact angle data of asphalt at 25 \({}^{\circ}\)C.  
Figure 3: Contact angle preparation and measurement.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Probe Liquids** & \(\gamma_{L}\) & \(\gamma_{L}^{d}\) & \(\gamma_{L}^{p}\) & \(\gamma_{L}^{+}\) & \(\gamma_{L}^{-}\) \\ \hline Distilled water & 72.8 & 21.8 & 51.0 & 25.50 & 25.5 \\ Glycerol & 64.0 & 34.0 & 30.0 & 3.92 & 57.4 \\ Formamide & 58.0 & 38.0 & 19.0 & 2.28 & 39.6 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Surface free energy (SFE) characteristics of three probe liquids at 25 \({}^{\circ}\)C (mJ/m\({}^{2}\)).  
As shown in Table 4, with the degree of aging strengthened, the contact angle of base asphalt and WMA with water gradually increased, indicating that aging improves the hydrophobicity of the asphalt [24; 25]. In addition, for unaged asphalt, the contact angle of asphalt with water was: asphalt > Sasobit warm asphalt > Evotherm M1 warm asphalt. After RTFOT, UV, and PAV aging, the contact angle of asphalt with water was: Sasobit WMA > base asphalt > Evotherm M1 WMA. The change of the contact angle of Sasobit warm asphalt with water after aging presented as larger than that of Evotherm M1 warm asphalt.  
According to the analysis, Sasobit is an organic synthetic hard wax that has strong hydrophobicity. Therefore, the hydrophobicity of Sasobit warm asphalt will increase accordingly. Evotherm M1 is a surface-active additive for Evotherm M1 WMA, of which the hydrophilic group may be one of the direct causes of the increase in the hydrophilicity of asphalt. The antistripping agent added to the Evotherm M1 warming agent can also increase the hydrophilicity of asphalt to some extent, leading to the minimum contact angle of Evotherm M1 warm asphalt after aging.