## 3 Results and Analysis
### SCB Test and Analysis
#### 3.1.4 Analysis of Influence of Moisture on Cracking Resistance of the CR Mixture  
The cracking of the asphalt mixture was mainly characterized by low-temperature fracture and medium-temperature fatigue cracking. Based on DIC technology, the strain energy density (\(D_{E}\)) and interfacial damage factor (\(D_{I}\)) of the CR mixture before and after immersion with different failure forms were analyzed, as shown in Figures 9-12. Figure 8: Variation curve of horizontal strain with loading time/times of repeated load. Figure 9: \(D_{E}\) of CR mixture before and after immersion under medium temperature fatigue failure. It can be seen from Figures 9-12 that the \(D_{E}\) of CR decreases after immersion, and the \(D_{I}\) occurs earlier than that of the dry environment. In addition, it can be seen that the \(D_{I}\) increases faster in the environment with water, indicating that the interface is easier to be destroyed in the environment with water. As a kind of viscoelastic-plastic composite material, the temperature and loading mode have great significance to the performance of the asphalt mixture. By comparing Figures 9 and 11, the strain energy density of the asphalt mixture at low temperature  
Figure 11: \(D_{E}\) of CR mixture before and after immersion under low temperature fracture. Figure 12: \(D_{I}\) of CR mixture before and after immersion under low-temperature fracture. Figure 10: \(D_{I}\) of CR mixture before and after immersion under medium temperature fatigue failure. is significantly reduced by three orders of magnitude compared to that under repeated medium-temperature load. This indicates that when the temperature is lower, the loading time is shorter, the force is larger and the accumulated microstrain of the asphalt mixture before fracture is smaller; that is, the specimen fracture occurs when there is no obvious deformation. Although the strain energy density of the specimen decreases due to both failure modes, it can be found that the strain energy density of the specimen after immersion is 15.5% lower than that of the dry specimen under low-temperature fracture failure, and the strain energy density of the specimen after immersion is 4.1% lower than that of the dry specimen under medium temperature repeated load. Obviously, the damage from water is more serious under the low-temperature fracture. This is due to the decrease in asphalt adhesion caused by water immersion in the asphalt mixture, which makes the asphalt peel off from the aggregate surface. Under the low-temperature condition, the temperature stress generated in the asphalt layer exceeds the tensile strength of the asphalt mixture, and cracks occur at the adhesion interface between the asphalt and the aggregate. Therefore, the low-temperature condition intensifies the damage effect from water on the interface between the asphalt and the aggregate. Comparing Figures 10 and 12, it can be seen that the curve in Figure 10 shows that the damage factor of repeated medium-temperature load increases gradually with time, which can be divided into three stages. The first stage is the rapid growth stage, in which \(Exx\) increases rapidly, but the duration is short. The specimen as a whole resists the applied repeated load, but there is no cracking, and the strain increases rapidly, indicating that the crumb rubber-asphalt mixture has a certain deformation resistance. The second stage is the accelerated growth stage, in which \(Exx\) and the growth rate gradually increase until reaching the peak value, which is caused by the gradual generation and full development of cracks until they are penetrated. The third stage is the abrupt fluctuation decline stage. In this stage, \(Exx\) drops suddenly after the peak value. Then, the fluctuation drops to the lowest value because the specimen is completely cracked, and the horizontal strain gradually decreases with the release of horizontal stress. However, in Figure 12, the peak in the damage factor value of low-temperature fracture failure occurs suddenly.