# Micromechanism of the Dispersion Behavior of Polymer-Modified Rejuvenators in Aged Asphalt Material
## 4 Discussion  
The dispersion behavior of rejuvenators directly affects their rejuvenating effectiveness in aged asphalt binder. There are many factors that can promote or obstruct this dispersion behavior, such as the effective diffusivity, viscosity, interfacial tension, molecular group structure, etc. In this study, we have proposed a multi-component rejuvenator with polymer modifiers to improve the performance of rejuvenated binders. In general, the dispersive ability of CRs is considered to be enough for the process of pavement recycling. However, the dispersive ability of the MR-1 rejuvenator, which directly compounded the SBS modifier with extracted oil, was observed to decrease significantly compared with CR. The GPC analysis showed that, as the dispersing agent was added to MR-1, the dispersive ability of the polymer-modified rejuvenator was improved to the level of CR. Based on the results of the analysis, there are two reasons for this phenomenon: (1) The dispersing agent reduced the viscosity of the rejuvenator from 5.36 Pa-s to 2.21 Pa-s at a temperature of 135 \({}^{\circ}\)C, and increased its dispersion rate in the aged asphalt binder; (2) As other studies have shown, the asphaltene micelles which bonded in the asphalt colloid structure provided the main dispersion resistance against the rejuvenator [33]. In asphalt structures, the asphaltene associated by hydroxyl hydrogen bond and agglomerate to form asphaltene micelles. The polar groups in the methacrylate quaternary copolymer (the principal constituent of the dispersing agent) can form carboxyl hydrogen bonds with asphaltene,  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**CR**} & \multicolumn{3}{c}{**MR-2**} & \multirow{2}{*}{**Aged**} & \multirow{2}{*}{**Virgin (AH-70)**} & \multirow{2}{*}{**1-D**} \\ \cline{2-2} \cline{5-8}  & **3\%** & & & & & & & & & \\ \hline Ductility/cm & \textless{}1.0 & \textless{}1.0 & \textless{}1.0 & \textless{}1.0 & 10.5 & 22.5 & \textless{}1.0 & \textless{}1.0 & 26.3 \\ Maximum tension force/N & 101.2 & 102.5 & 139.8 & 134.1 & 135.1 & 142.6 & 98.8 & 116.5 & 156.6 \\ Fracture tension force/N & 101.2 & 102.5 & 139.8 & 134.1 & 7.6 & 37.3 & 98.8 & 116.5 & 85.2 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Force–ductility analysis results for the aged, virgin, and rejuvenated asphalt binders.  
Figure 11: Force–ductility curves for the aged asphalt, virgin asphalts, and rejuvenated asphalts at a temperature of 5 \({}^{\circ}\)C: (**a**) The enlarged image of the beginning stretch section of the force–ductility curves; (**b**) The complete force–ductility curves image of the 1-D, MR-2-6%, and MR-2-9% samples at a temperature of 5 \({}^{\circ}\)C.  
and the binding force of carboxyl hydrogen bonds is stronger than that of hydroxyl bonds [34]. Thus, the agglomerate structure of asphaltene is partly broken, which is evidenced by the smaller asphaltene micelles observed in the AFM analysis (see Figure 7d,e), and the dispersing resistance from the molecular group structure is reduced.  
Based on the results of the DSR, toughness and tenacity, and force-ductility analyses, the asphalt with polymer-modified rejuvenator exhibits the performance features of modified asphalt material, indicating that asphalt binder which is rejuvenated by polymer-modified rejuvenator could improve the performance of recycled pavement material at high and low in-service temperatures. In summary, the polymer-modified rejuvenator not only dispersed the light components into the aged asphalt binder, but also formed a polymer network which reinforced the aged asphalt binder.