## 3 Test Results, Analyses, and Discussion
### Rheological Properties
#### 3.1.2 MSCR Analysis  
Percentage recovery (\(R\)), which reflects the recovery deformation for a period of ten creep and recovery cycles at each stress level, represents the elastic recovery performance of an asphalt-binder [34]. The larger percent recovery (\(R\)) indicates better rutting resistance of asphalt-binders [35]. Figure 7a shows the recovery response of the rejuvenated SBSMA with different rejuvenators at different rejuvenation cycles measured at 0.1 kPa and 3.2 kPa stress levels, respectively. From Figure 7, it is evident that as the rejuvenation cycles increased, the percentage recovery of the asphalt-binder decreased under the same stress level. This meant a decline in the percentage recovery ability of the asphalt-binders after rejuvenation and the conversion promotion of the rejuvenators to the viscous component of the asphalt-binder. The percentage recovery of the third rejuvenated asphalt-binder with the Type III rejuvenator was 25.62% (3.2 kPa), which compared to the RTFO residue and the third rejuvenated asphalt-binder with Type II, represents a reduction factor of three. At the same stress level, the superiority ranking of the percentage recovery of SBSMA after similar rejuvenation cycles was Type II > Type I > Type III. Figure 6: Failure temperature of SBS asphalt-binders at different aging and rejuvenation cycles: (**a**) High-temperature continuous grade; (**b**) intermediate-temperature continuous grade. The non-recoverable creep compliance (\(J_{\rm nr}\)) reflects the residual strain level of asphalt-binders after the loading-recovery cycle, which represents the rutting resistance of asphalt-binder. With an increased number of rejuvenation cycles, the rejuvenated asphalt-binders with Type I and Type III rejuvenators exhibited an increasing trend in the \(J_{\rm nr}\) value and the non-recoverable strain at the same stress level (see Figure 7b). This implies a continuous drop in the rutting resistance. Particularly, the \(J_{\rm nr0,1}\) and \(J_{\rm nr3,2}\) values of the third rejuvenated asphalt-binder with Type III reached 0.684 kPa\({}^{-1}\) and 0.959 kPa\({}^{-1}\), over 3 times the corresponding values of the RTFO residue. On the contrary, the rejuvenated asphalt-binder with Type II exhibited a continuously decreasing trend, indicating an improvement in the rutting resistance of the asphalt-binder. These findings are consistent with the results from temperature sweep tests and further illustrate that the Type II rejuvenator had a poor repeated rejuvenation effect. When comparing the differences of the MSCR evaluation indices (\(R\) and \(J_{\rm nr}\)) under the two stress levels shown in Figure 7, the results showed that the differences in \(J_{\rm nr0.1}\) and \(J_{\rm nr3,2}\) of the rejuvenated asphalt-binders with the Type I and III rejuvenators increased with an increase in the rejuvenation cycles. The discrepancy between \(J_{\rm nr0.1}\) and \(J_{\rm nr3,2}\) revealed that the stress sensitivity of the asphalt-binder, namely an increasing sensitivity of the rejuvenated SBSMA to the variation of stress loading as the rejuvenation cycles increased. The trend was mainly attributed to the degradation of the SBS polymer in the SBSMA asphalt-binder during the repeated rejuvenation, which weakened the modification effects of the asphalt-binder. Comparing Figures 7a and 8a, the percentage recovery of the asphalt-binder slightly increased after aging, pointing to improved resistance to permanent deformation. This increase in percentage recovery indicates a potential increase in elasticity of the asphalt-binders due to aging. Figure 7a also shows that under the same stress level, the creep recovery of the asphalt-binder decreased when the rejuvenation cycles increased. This indicates that the addition of the rejuvenators could supplement the viscous component of the asphalt-binder to effectively compensate and delay the aging of the asphalt-binder [36].