## 3 Effects of Freeze-Thaw Cycles on Degradation of Performance
### Static and Dynamic Compression Creep  
Considering the creep test was greatly affected by the preparation of the specimen, the influence of preparation would mask the actual influence of freeze-thaw cycles on high-temperature creep characteristics when the interval between freeze-thaw cycles was short. Therefore, asphalt mixture specimens after 0 and 15 freeze-thaw cycles were used for comparative analysis. The creep curves of asphalt mixtures before and after freeze-thaw cycles were shown in Figures 11 and 12.  
Figures 11a and 12a indicate that the creep curve could be clearly divided into two stages: (1) Migration period: creep deformation increased rapidly at the moment of loading and the creep rate decreased rapidly as time went on. (2) Stable period: the creep deformation increased linearly and the creep rate remained constant. In Figure 11a, the curve entered stable period after 1000 s, so \(t_{1}\) and \(t_{2}\) could be taken as 1000 s and 3600 s to calculate the creep rate in the stable period. In Figure 12a, the curve entered stable period after 500 cycles (1000 s), so it was possible to calculate the creep rate by taking \(t_{1}\) = 1000 s and \(t_{2}\) = 1800 s. Comparing the creep curves before and after freeze-thaw cycles, it could be concluded that the total strain of two types of asphalt mixtures increased under freeze-thaw cycles, after 15 freeze-thaw cycles, the curve of creep time and strain moved up significantly, which fully demonstrated that the freeze-thaw cycles occurred damage of specimens. The creep strain of NBAM group was smaller than that of AM group and the strain difference b  
Figure 11: Static creep: (**a**) relationship between static creep time and strain; (**b**) the change of creep rate.  
Figure 12: Dynamic creep: (**a**) relationship between dynamic creep time and strain; (**b**) the change of creep rate.  
freeze-thaw cycles was smaller, which indicated that the deformation resistance at high temperature was enhanced and the modifiers reduced the sensitivity of high-temperature performance to the freeze-thaw cycles. Comparing the creep rate change before and after freeze-thaw cycles, the static creep rate of each type of asphalt mixture increased significantly. The AM group increased 3-fold, while the NBAM group doubled. The dynamic creep rate also increased after freeze-thaw cycles. The creep rate was negatively correlated with the dynamic stability. Therefore, it could be concluded that the anti-rutting ability of asphalt mixture was significantly reduced after freeze-thaw cycles. The degradation trend was obviously weakened when the modified materials were added. In summary, the freeze-thaw cycles reduced the high-temperature stability of asphalt mixture, and at the same time, the addition of nano-TiO\({}_{2}\)/CaCO\({}_{3}\) and basalt fiber reduced the sensitivity of high-temperature stability to the freeze-thaw cycles.  
The stability, stiffness modulus, and splitting tensile strength of the NBAM group were 17%, 20%, and 16% higher than those of the AM group before the freeze-thaw cycle. After 20 freeze-thaw cycles, these indexes were 67%, 41%, and 48% higher than AM group, respectively. It can be seen that the basalt fiber and nano-TiO\({}_{2}\)/CaCO\({}_{3}\) can effectively improve the performance of asphalt mixture under freeze-thaw cycles. From the performance of NBAM and AM after 15 F-T cycles, we can conclude that the DBFAM pavement can present longer service life in seasonal frozen regions. This is important for reducing road maintenance and traffic disruption, and the costs expected for AM and NBAM are 0.330 CNY/Kg and 0.403 CNY/Kg. It is still important in seasonal frozen regions of China, although the cost of the modified asphalt mixture has increased.