## 4 Results and Discussion  
### Effect of freeze-soak-scour Cycles on Properties of NHISS-AC  
As it is shown in Figures 6 and 7, the voids content of the two mixtures gradually increases as the number of freeze-soak-scour cycles increases. After 20 freeze-soak-scour cycles, the void content of AC is already in line with the Chinese specification (the voids content of AC \(<\) 5%), and NHISS-AC is still within the standard range. This is because the adhesion of NHISS modified asphalt and aggregate is greater than that of base asphalt and aggregate. Therefore, the voids content change ratio of NHISS-AC is significantly lower than that of AC after multiple cycles, so NHISS-AC has better durability. It can be seen from Figure 7 that as the number of cycles increases, the weight loss ratio of the two mixtures gradually increases, indicating that the loose fine aggregate of pavement is taken away by the wheel with the increase of freeze-soak-scour cycle in the spring-thawing season, which leads to the reduction of quality of mixtures and the increase of the weight loss ratio of mixtures. Moreover, the NHSS modified asphalt has a better bond strength with the aggregate than the base asphalt so that the weight loss ratio of NHSS-AC is always smaller than the AC after different freeze-soak-scour cycles. As it is shown in Figure 8, Marshall stability of mixtures decreases with increasing freeze-soak-scour cycles, and the Marshall stability of the AC has been lower than Chinese specification after 15 cycles (Marshall stability of AC \(\geq\) 8.0 KN). However, the Marshall stability of the NHSS-AC remained within the scope of the Chinese specification after 20 cycles. The Marshall stability loss ratio of NHSS-AC is far less than that of AC under the same cycles. It can be seen that NHSS has  
Figure 6: Void content changes of mixtures under freeze-soak-scour cycles. Figure 7: Weight loss ratio changes of mixtures under freeze-soak-scour cycles. certain advantages in improving the high temperature mechanical properties of asphalt mixtures in spring-thawing season. The data of \(-10\)\({}^{\circ}\)C splitting test is shown in Table 5. The splitting tensile strength and destruction tensile strain are continuously reduced with the increase of the number of cycles. After 20 cycles, the splitting tensile strength of AC decreased by 9.7% and destruction tensile strain decreased by 10.3%. By contrast, the splitting tensile strength of NHSS-AC decreased by 8.3% and destruction tensile strain decreased by 10.7%. Thus, the low temperature mechanical property of NHSS-AC is better than that of AC in freeze-thawing season. The change of destruction stiffness modulus is disordered, because the attenuation curve of splitting tensile strength and destruction tensile strain is not consistent. The result of freeze-soak-scour splitting test is shown in Figure 9. It illustrates that the \(\mathrm{R_{FTn}}\) of the mixtures continuously reduced with the increase of the number of cycles, and the \(\mathrm{R_{FTn}}\) of the AC drastically attenuated during the first five cycles, and the decay rate tends to be slow after that. The \(\mathrm{TSR_{n}}\) of NHSS-AC is lower than that of AC at various points in the freeze-soak-scour cycles, and the \(\mathrm{TSR_{n}}\) of NHSS-AC is 5% higher than the AC. Thus, the water stability of NHSS-AC is better than that of AC in freeze-thawing season. Figure 8: Marshall stability changes of mixtures under freeze-soak-scour cycles.