## 4 Results and Discussion
### FTIR Test Results  
The FTIR spectra of the BA, CBMA and NHSSMA are given in Figures 14-16. From the FTIR spectrum of BA, it can be seen that the strong absorption peak at 2918 cm\({}^{-1}\) and 2851 cm\({}^{-1}\) is the asymmetric and symmetric stretching vibration absorption band of C-H in aliphatic (mainly alkanes and naphitenes), and the peak at 1600 cm\({}^{-1}\) is the C-C stretching vibration in aromatics, peaks at 1458 cm\({}^{-1}\) and 1375 cm\({}^{-1}\) is the in-plane bending vibration absorption peak of C-H in aliphatic, peak at 1032 cm\({}^{-1}\) is the sulfoxide group (S=O) stretching vibration, four small absorption peaks in the range of 863 cm\({}^{-1}\)-724 cm\({}^{-1}\) are the out-of-plane bending vibration of C-H on aromatic benzene rings. Thus, asphalt is mainly composed of saturated hydrocarbons, aromatics, aliphatics and heteroatom derivatives. From Figure 15, the positions and intensity of each peak in the FTIR spectra of CBMA is basically the same as that of BA, which indicates that the incorporation of carbon black does not change the properties of the asphalt, but pure physical blending. It can be seen from Figure 16, two peaks emerged at 3675 cm\({}^{-1}\) and 1300 cm\({}^{-1}\), which indicates that there is a certain chemical reaction between NHSS modifier and the asphalt except for physical blending. The strong absorption peak at 3675 cm\({}^{-1}\) is the vibration absorption band of O-H in carboxyl group, which is formed by the graft reaction of nano hydrophobic silane silica with asphalt. The peak at 1300 cm\({}^{-1}\) is caused by the infiltration of CO\({}_{2}\) during the mixing process. After different F-T cycles, damaged specimens were collected for Fourier Transform Infrared Spectroscopy test to identify the utility of NHSS. From the FTIR spectrum of the three kinds of asphalt after different F-T cycles, it can be found that the F-T aging process does not change the peak position but changes the peak area and peak height in the FTIR spectrum. Generally, the change of the aliphatic compounds is characterized by the aliphatic functional groups (1377 cm\({}^{-1}\) and 1462 cm\({}^{-1}\)). The larger the aromatic functional group content, and the higher the saturated fraction content, the greater the penetration and the lower the viscosity of asphalt. The aromatic functional group (1600 cm\({}^{-1}\)) corresponds to the aromatic ring component (aromatic, colloidal and asphaltene) in the asphalt. The higher the aromatic functional group content, the higher the ductility of asphalt. Moreover, the content of carboxyl and sulfoxide functional groups is generally used as evaluation indexes to evaluate the aging degree of asphalt. The main peak area and peak height of BA, CBMA and NHSSMA under the F-T aging procedure are summarized by Origin 9.0 software in Tables 6 and 7 and Figure 17.  
It can be clearly seen from Figure 17 that the peak area and peak height of the main functional groups for BA, CBMA and NHSSMA generally increase as the number of F-T cycles increase. Furthermore, the sulfoxide functional groups content index of BA, CBMA, and NHSSMA changes significantly under the F-T aging process. This is mainly because the polar molecules easily react with the organic sulfides of asphalt to form sulfoxide functional groups (S=O, 1032 cm\({}^{-1}\)) under the F-T aging process. Since the chemical activity of sulfur is higher than that of carbon, sulfur can participate in the reaction more rapidly under the F-T aging process. Moreover, the formation reaction of carbonyl (C=O, 1700 cm\({}^{-1}\)) and the formation reaction of sulfoxide group have a competitive relationship, so when the change in the amount of the sulfoxide group is large, the amount of change in the carbonyl group is relatively small. In addition, the sulfur content of Panjing AH-90# asphalt is relatively low compared with other asphalt, but a large number of sulfoxide groups were formed, and the carbonyl content changed very little under the F-T aging process. This may be attributed to the F-T aging process.