## 3 Results and Discussion
### Blending Degree of the Virgin and RAP Binders in RAM  
The addition of large proportions of CTBN to virgin bitumen could affect the performance of RAM, while the lack of CTBN could result in a large CV of I\({}_{\text{CTBN}}\); consequently, the chosen CTBN content of the virgin bitumen used in the RAM was 5 wt. %. Since the virgin aggregate particles were smaller than 13.2 mm, aggregate particles exceeding 13.2 mm in size were selected as RAP, and three RAP specimens were selected randomly. Three locations were selected randomly from each specimen, and three RAP FTIR samples were taken from different depths at each location; subsequently, the spectra of the samples were measured by FTIR microscopy. The areas of the absorption peaks associated with nitrile stretching vibrations and the antisymmetric vibrations of -CH\({}_{3}\) groups were analyzed with the Peakfit software, and the I\({}_{\text{CTBN}}\) values were calculated by Equation (1). Meanwhile, according to the standard curve (Figure 6), the CTBN contents at different RAP depths were obtained, and the results are shown in Figure 7.  
Figure 6: The standard curve. Figure 7: _Cont._Figure 7 shows that CTBN was present at different depths within the RAP films in the RAM, but the CTBN content decreased with an increase in the depth. This finding indicates that the virgin bitumen blended with the RAP binder in the RAM, but the percentage of virgin bitumen decreased gradually with an increase in the depth. Since the CTBN content in the virgin bitumen was 5 wt. %, the percentages of virgin bitumen at different RAP depths in the RAM were quantitatively acquired by comparing the CTBN contents of RAP specimens with 5 wt. %, as shown in Figure 8. Because the proportion of RAP in the RAM was 45 wt. %, the optimum bitumen content was 5.1 wt. %; in addition, the RAP contained 5.0 wt. % bitumen. Hence, the virgin bitumen ratio at any point in the RAM was 55.88% when the virgin bitumen and RAP binder were completely blended. Figure 8: _Cont._  
Figure 7: CTBN contents at different RAP depths: (**a**) RAP specimen 1; (**b**) RAP specimen 2; and (**c**) RAP specimen 3. Figure 8 shows that the virgin bitumen percentage in the outer RAP layer was higher than that found in the case of complete blending (55.88%), indicating that the RAP film was wrapped by the virgin bitumen and that the RAP binder was completely blended with the virgin bitumen. With an increase in the RAP film depth, the percentage of virgin bitumen in the RAP decreased. The virgin bitumen percentage in the middle RAP layer was slightly lower than that in the case of complete blending, which indicates that the virgin and RAP binders were not completely blended, but were still blended relatively well. Meanwhile, although some virgin bitumen contributed to the blending of the virgin and RAP binders within the inner layer of the RAP film, the percentage of virgin bitumen was only approximately half of that in the case of complete blending. This means that the blending degree of virgin and RAP binders was very low, and the inner layer of the RAP film was mainly composed of the RAP binder. These results suggest that the blending of virgin and RAP binders occurs in RAM with high percentages of RAP, but this blending is incomplete. Although the virgin and RAP binders did completely blend together within the outer layer of the RAP film, the blending degree decreased with an increase in the depth of the RAP film. In summary, the virgin and RAP binders did not effectively blend, and the blending degree was relatively low within the inner layer of the RAP film, which may significantly affect the pavement performance of the RAM. This study proposes a method for quantitatively analyzing the effective bitumen content of RAP and the blending degree of virgin and RAP binders in RAM. By quantitatively evaluating the blending degree of virgin and RAP binders in RAM, the influences of the recycling agent, mixing temperature, mixing time, and other parameters on the performance of RAM can be evaluated more directly and effectively.