## 3 Results and Discussion
### CE-SCB Test  
(a) The gradation of the asphalt mixture influenced both the \(G_{f}\) and \(FI\) (as shown in Figure 16). A good linear correlation between these two parameters was observed, with R\({}^{2}\) = 0.843 \(p\)-value \(<\) 0.01 (as shown in Figure 17). These results indicated that the \(G_{f}\) and \(FI\) of the asphalt mixture change in the same way with the gradation variation. Therefore, \(G_{f}\) and \(FI\) were recommended as evaluation indicators. (b) The \(G_{f}\) and \(FI\) varied among different gradations of the asphalt mixture, with the gradation of 10C having the highest values of these parameters. The \(G_{f}\) reflected the energy required for the asphalt mixture to develop and propagate cracks until failure, while the \(FI\) represented an intrinsic property of the material that characterizes the crack growth rate and the resistance to fatigue damage. As shown in Figure 16, the maximum difference in \(G_{f}\) between gradations was 2085 \(\mathrm{J/m^{2}}\), and the maximum difference in \(FI\) was 13.1, with a relative difference exceeding 30%. The gradation of 10A had the lowest \(G_{f}\) and \(FI\), while all the 10C gradations had higher values of these parameters, indicating better resistance to load-induced damage. (c) There were differences in the correlation between the grading parameters and the \(G_{f}\) and \(FI\). As shown in Figure 18, the \(P_{4.75\mathrm{mm}}\) and \(P_{2.36\mathrm{mm}}\), \(PCSI\), and \(D_{c}\) had the best correlation with \(G_{f}\) and \(FI\), with R\({}^{2}\) values greater than 0.7. These values indicated a strong linear relationship. Therefore, these four parameters were selected to further analyze the effect of gradation changes on the performance of the asphalt mixture. Figure 16: CE-SCB results of AR-SAMI. Figure 17: Correlation between \(G_{f}\) and \(FI\). (d) The \(G_{f}\) and \(FI\) of the asphalt mixture decreased with the increase of \(P_{4.75\text{mm}}\), \(P_{2.36\text{mm}}\), \(PCSI\), and \(D_{c}\), as shown in Figure 19. These parameters indicated that the gradation became finer, the fine aggregate content in the mixture increased, and the coarse aggregate was suspended in asphalt mortar. This reduced the resistance to crack expansion and accelerated the failure of the specimen. The increase of \(D_{c}\) also disrupted the coarse aggregate skeleton, which provided deformation resistance for the mixture. Therefore, the \(D_{c}\) value should be minimized in the gradation design. Figure 19: Correlation of gradation parameters with \(G_{f}\) and \(FI\). (**a**) Passing rate of key sieve with \(G_{f}\). (**b**) Passing rate of key sieve with \(FI\). (**c**) \(PCSI\) with \(G_{f}\) and \(FI\). (**d**) \(Dc\) with \(G_{f}\) and \(FI\). Figure 18: R\({}^{2}\) of gradation parameters fitting curve. (**a**) \(G_{f}\). (**b**) \(FI\). (e) The coarse aggregate content has an effect on the crack resistance and crack expansion resistance. As shown in Figure 20, it can be seen that with the increase of coarse aggregate content, the peak load shows a trend of increasing and then decreasing, while the amount of deformation experienced to reach the peak load continues to increase. This indicates that an increase in the coarse aggregate content improves the aggregate skeleton strength and crack resistance. Excessive coarse aggregate content reduces the peak load of the asphalt mixture, but the amount of deformation experienced at the peak load continues to increase and the \(G_{f}\) does not show a significant decrease. After the peak load, the load decay of asphalt mixture with lower coarse aggregate content is faster, indicating that their resistance to crack expansion is poor. Combined with Figure 21, it can be found that the specimens with less crack expansion in the same gradation contain more and denser coarse aggregates, which indicates that the presence of coarse aggregates can effectively cause crack expansion resistance.