## 1 Introduction  
Due to the mature production process, cost-effectiveness, and the outstanding performance in terms of rutting, cracking, and moisture resistance, styrene-butadiene-styrene-modified asphalt-binder (SBSMA) is one of the most commonly used asphalt-binders for pavement construction, particularly as a surfacing layer [1]. The principle idea is to take advantage of the good binding and hardening properties of the SBS polymer to achieve effective modification of the bituminous material [2]. Thus, SBSMA has broad market prospects and accounts for more than 50% of the modified asphalt-binder around the world [3]. Nevertheless, SBSMA is inevitably prone to aging during the service life of the pavement as a result of the negative effects of oxygen, heat, and ultraviolet (UV) light, which ultimately lead to the hardening and embrittlement of the asphalt-binder [4; 5]. These effects usually result in the degradation of the SBS polymer and oxidation along with the volatilization of light components and the polycondensation of the asphalt-binder, consequently causing a decay in the physico-rheological properties [6; 7; 8]. Many researchers have observed an increase in the complex modulus (\(G^{\star}\)), elastic modulus (\(G^{\prime\prime}\)) and creep recovery (\(R\)), but a reduction in phase angle (\(\delta\)) and non-recoverable creep compliance (\(I_{\text{nr}}\)) with the deepening of the aging by DSR, which means that the viscous behavior of the asphalt-binder has partly moved to elastic behavior [9; 10; 11]. SBSMA's performance decay accelerates pavement distresses and shortens its service life under traffic loading and fluctuating environmental conditions. It is essential to make a proper decision to restore the physico-rheological properties of the asphalt-binder at an appropriate time during the life cycle of the pavement [12]. Therefore, rejuvenators are often added to aged asphalt-binders to soften them and make the rejuvenated asphalt-binders more fluid. Specifically, the effects of the rejuvenators on the asphalt-binders include an increase in the penetration grade, ductility, phase angle, m-value, and a corresponding decrease in the softening point, viscosity, shear complex modulus, rutting factor, and stiffness, respectively [13; 14]. During the aging and rejuvenation processes, the change in the physico-rheological properties of the SBSMA can be attributed to the chemical composition and microstructures. Fourier transform infrared (FTIR), atomic force microscopy (AFM), environmental scanning electron microscope (ESEM), and other new technologies have been successfully applied to analyze the aging mechanism and rejuvenating process of SBSMA at a micro scale [11; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. FTIR was used to investigate the aging and rejuvenation mechanism of SBSMA as well as the relationship between the chemical and rheological characteristics by identifying the differences between the absorption peaks which represent the functional groups and contents in the asphalt-binder based on Lambert-Beer's Law [15; 16; 17; 18]. [PERSON] et al. [20] found that the oxygen content of the asphalt-binder increased greatly after thermal aging, leading to an increase in the polar functional groups such as carbonyl and sulfoxide groups in the asphalt-binder. In terms of rejuvenation, rejuvenators regularly decreased the carbonyl and sulfoxide indices [21]. The AFM can obtain the microscopic morphology of the asphalt-binder surface [10]. [PERSON] et al. [22] observed that the bee structures slightly increased after PAV aging, and rejuvenator made the microstructures larger. [PERSON] et al. [23] studied aging effects of varying processing parameters on the phase structure of SBSMA. [PERSON] et al. [24] observed a decrease in the surface roughness with aging. [PERSON] et al. [25] observed that tiny bee structures appeared with the addition of the rejuvenator.