## 1 Introduction  
With the acceleration of urbanization and infrastructure development, many RAP materials have accumulated [1, 2, 3]. These materials not only cover a lot of land but can also cause serious environmental pollution [4]. As the costs of pavement materials rise, research into RAP recycling technology is receiving increased attention [5]. Typically, 15-30% material cost reductions can be achieved, with RAP utilization rates between 5% and 15% [6, 7]. Factors hindering the application of high-content RAP materials in recycled asphalt pavement include the phenomenon of its pseudo-granularity and the complexity of quality control in the construction process [8, 9, 10, 11]. Promoting higher content percentages of RAP used in pavement engineering has drawn the attention of researchers [12, 13]. However, one problem relating to the use of a higher RAP content is the agglomeration effect. The agglomeration of RAP aggregates is attributed to the viscoelastic effect of old asphalt, where the fine RAP aggregates agglomerate into coarse RAP aggregates, leading to the creation of RAP clusters. RAP clusterscannot be completely separated during asphalt pavement milling [14]. The RAP cluster phenomenon during the cold milling of asphalt pavements has been investigated, and the cold milling method was determined to inevitably cause RAP clusters [15]. Currently, the mix design of reclaimed hot mix asphalt mixtures (RHMAs) does not take into account the effect of RAP clusters [16; 17]. [PERSON] et al. have argued that, even if a rejuvenator is added, RAP aggregates are difficult to disperse completely during the mixing process [18]. [PERSON] et al. concluded that when the RAP content exceeded 30%, the actual and design grade difference would be enlarged due to the agglomeration effect of RAPs [19]. Therefore, the agglomeration effect is considered a phenomenon that negatively affects recycled asphalt mixtures [20]. Currently, there are two main categories of RAP aggregate separation methods: physical separation methods and chemical separation methods [7; 21]. [PERSON] et al. used a centrifugal device to crush, shear, and grind the coarse RAP in order to achieve a purely physical action [22]. [PERSON] et al. chiefly used special wire brushes to impact, scrap, and grind the RAP material to separate the aged asphalt-rich mortar from the pseudo-size particles [23]. [PERSON] et al. proposed a biological separation process for asphalt aggregate, using microorganisms to alter the adhesion between the asphalt and aggregate to achieve oil-rock separation [7]. To further verify that the biological separation process could effectively solve the phenomenon of RAP clusters, [PERSON] et al. proposed a method for asphalt aggregate separation using bio-oil as a solvent; the results indicated that the separation of old asphalt and aggregate could effectively remove agglomerates and solve the pseudo-granularity problem in recycled mixtures [3]. However, none of these methods can be widely used. The mechanical stripping method uses friction and collision to peel asphalt from the aggregate surface [24]. It damages the edges and surface characteristics of the aggregate, and separating the asphalt and aggregates in RAP with small particle sizes is difficult [22]. The stripped asphalt still adheres to some mineral aggregates, and the aging interface persists [25]. The chemical separation method mainly uses solvents, such as trichloroethylene, carbon tetrachloride, gasoline, diesel, kerosene, etc., to extract the asphalt [26]. Although it can effectively ensure the integrity of the aggregate, the use of expensive or highly toxic solvents can pose a threat to the environment. When using these methods, the raw material and equipment loss is significant, the chemical reagents can easily pollute the environment, and the recycling effect is poor. Surfactants--with their hydrophilic heads and hydrophobic tails--are widely used in oily sludge (OS) treatment to remove crude oil adsorbed onto solid particles.