## 4 Results and Discussion
### Adhesion Work  
Adhesion work is an indicator to characterize the adhesion properties of asphalt and aggregate in a dry state. The greater the adhesion work of the asphalt-aggregate, the better the adhesion performance of the asphalt and the aggregate, and the stronger the water damage resistance [34].  
Figure 5: Influence of aging on cohesion work of aged asphalt.  
The water damage of the asphalt mixture mainly includes two aspects: the cohesive failure of the asphalt cracking and the adhesion failure of the asphalt from the surface of the aggregate [35; 36]. Adhesion work is used to characterize the adhesion performance of asphalt and aggregate in the dry state. The larger the value, the better the adhesion performance of asphalt and aggregate, and the stronger the resistance to water damage [37].  
To make horizontal comparisons of different asphalts, the same aggregate was selected, and the adhesion work between it and different asphalts was calculated. Previous research and engineering practice have shown that alkaline limestone tends to adhere well to asphalt compared with acidic aggregates such as granite. Therefore, to decrease the adverse effects caused by the surface energy characteristics of the aggregate, limestone was selected as the aggregate, and its SFE and components were obtained according to a previous study [34], as shown in Table 5.  
According to the calculation method for surface energy and its component, by substituting the SFE parameters of different asphalts and aggregates into Equation (5), the adhesion work of different asphalt and limestone aggregate systems can be obtained. The results are shown in Figure 6.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type** & \(\gamma\) & \(\gamma^{d}\) & \(\gamma^{p}\) & \(\gamma^{+}\) & \(\gamma^{-}\) \\ \hline Limestone & 219.9 & 51.9 & 168.0 & 13.0 & 540.7 \\ \hline \end{tabular}
\end{table}
Table 5: SFE and its component of limestone (mJ/m\({}^{2}\)).  
Figure 6: _Cont._  
On the whole, among the three kinds of asphalts (matrix asphalt, Sasobit warm asphalt, and Evotherm M1 warm asphalt), the adhesion work of Evotherm M1 warm asphalt and limestone is the largest, while the adhesion work of Sasobit warm asphalt and limestone is the least. The adhesion work of Sasobit warm asphalt and limestone is 22.57% lower than that of the neat asphalt and limestone. Compared with the neat asphalt, the adhesion work of Evotherm M1 warm asphalt and limestone increases by 23.63%. After aging, the adhesion of matrix asphalt, Evotherm M1 warm asphalt, and limestone gradually decreased. The adhesion of Sasobit warm asphalt-limestone decreased and then increased. The adhesion work of the matrix asphalt and Evotherm M1 WMA tended to be stable after 150 h of UV aging.  
Related studies have shown that aging causes the light components in the asphalt to be converted to heavy components through volatilization; then the asphaltene content is greatly improved, the relative colloid/asphalt content is continuously reduced, and the asphaltene content is continuously increased, resulting in the attenuation of asphalt adhesion [38]. When UV aging of 150 h is reached, the light component and the asphaltene content in the asphalt reach a relatively stable state, so that the asphalt adhesion performance tends to be stable. The adhesion work of Sasobit warm asphalt and limestone shows an inflection point at 100 h of UV aging--that is, the adhesion performance decreases first and then increases. Combined with the change of SFE parameters of Sasobit WMA shown in Figure 4, the polar component of Sasobit WMA also showed a trend of decreasing first and then increasing with the extension of UV aging time, and the inflection point also appeared at 100 h of UV aging. According to the data, the increase of the polar component of Sasobit warm asphalt after aging is beneficial to the increase of the adhesion work of the asphalt-aggregate system, combined with the high-quality aggregates, and the adhesion of Sasobit warm asphalt after aging is improved.