## 4 Results and Discussion
### TGA Test Results  
TGA test was employed to evaluate the effect of NHSS on the thermal properties of asphalt under the F-T aging process. Figure 18 presents the thermal properties of modified and unmodified asphalt binder without F-T aging process. As observed, TGA thermographs relate to particular phases of degradation with distinct initial and final degradation temperatures and the addition of modifiers changes the distinct initial and final degradation temperatures, which are the result of pyrolysis of the specimen. The TGA curves of CBMA and NHSSMA are more gradual than that of BA, indicating that the addition of modifiers effectively improves the thermal properties of asphalt.  
From TGA curves of all the asphalt samples, the following parameters were calculated for further comprehension of the effect of NHSS on the thermal properties of asphalt under the F-T aging process: (1) Start of thermal degradation (T\({}_{s}\), \({}^{\circ}\)C); (2) Temperature at 20% weight loss (T\({}_{20\%}\), \({}^{\circ}\)C); (3) Peak temperature (temperature at 50% weight loss) (T\({}_{p}\), \({}^{\circ}\)C); (4) End of thermal degradation (T\({}_{e}\), \({}^{\circ}\)C); (5) Residual mass (M\({}_{e}\), %). Table 8 and Figure 19 present a summary of TGA test parameters of BA, CBMA and NHSSMA at different F-T cycles.  
As shown in Table 8, the T\({}_{\rm s}\) value of CBMA and NHSSMA increased by 49 \({}^{\circ}\)C and 46 \({}^{\circ}\)C, respectively, compared to BA, and the T\({}_{\rm p}\) value of CBMA and NHSSMA were 13 \({}^{\circ}\)C and 8 \({}^{\circ}\)C higher than BA. This indicates that the addition of modifiers effectively improved the thermal properties of asphalt. The M\({}_{\rm e}\) value of BA, CBMA and NHSSMA was 11.8%, 14.62% and 13.86%, respectively. The M\({}_{\rm e}\) value of modified asphalt materials was generally 2% to 3% higher than that of unmodified asphalt, which was roughly equal to the amount of the modifiers. This also indirectly indicates the modified asphalt prepared by the high-speed shearing method has good uniformity, and the modifier materials can be well dispersed in the asphalt, which can improve the storage stability of the modified asphalt.  
It can be seen from Figure 19b that the T\({}_{\rm s}\), T\({}_{\rm 20\%}\), T\({}_{\rm p}\), and M\({}_{\rm e}\) index of NHSSMA decreased with the increase of F-T cycles. After 30 F-T cycles, the T\({}_{\rm s}\) value of BA, CBMA and NHSSMA decreased by 1.9%, 15.2% and 20.4%, the T\({}_{\rm 20\%}\) value of BA, CBMA and NHSSMA decreased by 1.5%, 7% and 12.7%, and the T\({}_{\rm p}\) value of BA, CBMA and NHSSMA decreased by 1%, 4% and 2.7%. This indicates that the TGA parameter variation of the modified asphalt was larger than that of BA. This may be because carbon black and NHSS are inorganic materials, and its connection with asphalt is more likely to be destroyed under the F-T aging process. The decomposition temperature of saturated fraction, aromatic fraction, colloid and asphaltene of asphalt was 300 \({}^{\circ}\)C, 412 \({}^{\circ}\)C, 438 \({}^{\circ}\)C, 472 \({}^{\circ}\)C, respectively. When the temperature reached the thermogravimetric termination temperature (T\({}_{\rm e}\)), the other three components, except the asphaltenes, were basically burnt out. Moreover, the base asphalt used in the test was the same asphalt, and the proportion of the four components of each asphalt sample was basically the same. Therefore, the F-T aging process and the modified material do not affect the T\({}_{\rm e}\) parameter.