# Micromechanism of the Dispersion Behavior of Polymer-Modified Rejuvenators in Aged Asphalt Material
## 1 Introduction  
Rejuvenators, due to their rich maltene constituents and high permeation ability, can re-balance the composition of aged asphalt binders and have become the key material in pavement-recycling technology [1; 2; 3]. In recent years, many pavement materials have reached the end of their service life and have been abandoned in the city (Figure 1). Therefore, developing more effective and durable recycling technologies to rejuvenate this waste asphalt concrete is important for sustainable urban construction [4; 5; 6].  
At present, the basic composition of the rejuvenator that is commonly used in asphalt pavement recycling is single component, being comprised of materials such as petroleum by-products, industrial oils, living waste, plant extract oils, etc., [7; 8; 9; 10; 11; 12], the common feature of which is a high content of aromatics. Laboratory research and different engineering application results show that rejuvenators can restore the rheological and physical properties of binders [13; 14; 15; 16]. [PERSON] et al. studied theeffect of two generic rejuvenators effect on asphalt binders through rheological property analyses. The result of this study showed that the two complex modulus master curves of virgin binder and rejuvenated binder almost overlapped at 12% rejuvenator content [17]. Additionally, [PERSON] et al. conducted a comprehensive study to evaluate the use of different recycling agents on the properties of rejuvenated binders. The results of this research revealed that all six different agents selected in the study were able to reduce the kinematic viscosity of the aged binder at an intermediate temperature [18]. Many previous studies have indicated that rejuvenators merely soften aged asphalt binder and recover the rheological and physical properties to the level of the ordinary virgin asphalt, though do not significantly improve its performance [19; 20]. Therefore, the function of rejuvenator for the improvement of the viscoelasticity and toughness of asphalt binder would be of significance for the durability of recycled pavement, especially given the present trend of using more reclaimed asphalt pavement in recycled mixtures, and the need for higher performance requirements of recycled pavement due to a likely increase in traffic volume in the future [21; 22].  
Studies on the modification of aged asphalt binder using a rejuvenating process have recently been receiving research attention. For example, [PERSON] et al. [23] demonstrated the feasibility of modifying aged asphalt binder by analyzing its features, as well as those of the rejuvenator and modifier. However, this study did not offer specific technical measures. Additionally, a United States patent [24] proposed a method in which a modifier, such as SBS, SBR, or rubber powder, is mixed with a rejuvenator directly during mixing of the asphalt binder in a plant, to achieve the modifying goals. However, in this patent the authors failed to list the technological means by which to ensure the effectiveness of the modifiers on aged asphalt binder. Modifiers require an extended period to disperse and swell in aged asphalt binder at high temperatures, and thus with a short mixing process it was difficult to obtain an anticipative modification effect. To date there are no effective methods to complete the rejuvenating and modifying process simultaneously.  
The primary objective of this study is to investigate the effectiveness of polymer-modified rejuvenators on aged asphalt binder, including the two critical aspects of dispersion and performance. The dispersion behavior between the rejuvenator and aged asphalt binder was studied by measuring changes in the molecular weight distribution and micro-colloidal structure along the vertical axis. The effect of rejuvenation and modification on aged asphalt binder was also studied.