## 3 Results and Discussion
### Rutting Resistance  
Due to the fact that the rutting factor is influenced by many factors, such as tire pressure, tire size, vehicle speed, road surface temperature, etc., which cannot be completely consistent in actual road use, in order to accurately evaluate the performance of asphalt pavement at high temperatures, it is more appropriate to use the non-recoverable creep \(J_{\rm nr}\), because it can provide more objective and stable evaluation results. In addition, the measurement method of \(J_{\rm nr}\) is relatively simple and easy to operate, and it is currently widely used to evaluate the high-temperature performance of asphalt pavement.  
Figure 19 illustrates that adding fibers to asphalt mastics improves the material's stability at higher temperatures by comparing the time-strain curves derived from the MSCR test. It has been discovered that bamboo fibers have a better modification effect than basalt fibers, and the high-temperature stability of fiber-modified asphalt mastics steadily increases with increasing fiber percentage. When assessing the ability of asphalt materials to resist rutting at high temperatures, a lower \(J_{\rm nr}\) value is indicative of superior performance. \(J_{\rm nr}\) is a widely used standard index that quantifies the extent of irreversible deformation or creep in a material subjected to a sustained load over a period of time.  
Figure 17: Diagram showing two-phase crack growth in an LAS test.  
Figure 18: Crack length summary of fiber modified asphalt mastic.  
According to Figure 20, the \(J_{\rm nr}\) value falls as the fiber content rises, suggesting that fibers can improve asphalt mastic's resistance to rutting at high temperatures. The main reason is likely due to the formation of a network structure by fibers in the asphalt mastic, which increases its cohesion and shear strength. Under high-temperature conditions, the fibers effectively disperse and bear the stress of the asphalt, preventing deformation and damage of the mastic, thereby improving its structural stability. Additionally, the addition of fibers can enhance the shear resistance of the asphalt mastic, reducing deformation and flow under high temperature conditions. Fibers can absorb and disperse shear forces, increasing the viscoelasticity of the mastic and preventing shear failure.  
The results of the \(J_{\rm nr}\)-diff-index-based sensitivity analysis of asphalt mastics to high-temperature creep stress are shown in Figure 21. The investigation demonstrates that the modified asphalt mastics' stress sensitivity rises when basalt fiber content rises. Bamboo-fiber-modified asphalt mixtures exhibit irregular changes in stress sensitivity, unlike basalt-fiber-modified asphalt mastics, which show a monotonic increase with increasing fiber content. According to AASHTO MP 19 [40], the \(J_{\rm nr}\)-diff index has a threshold value of 75%. Both the asphalt mastics modified with basalt fibers and those modified with bamboo fibers satisfy this technical standard, indicating that the modified asphalt mastics are resistant to stress sensitivity.  
Figure 19: Time–strain curves of different types of fiber-modified asphalt mastics.  
Figure 20: Effect of fiber modification on asphalt mastic \(J_{\rm nr}\) values.