# Anti-Aging Performance and Action Mechanism of Asphalt Modified by Composite Modification
## 3 Results and Discussion
### Dynamic Shear Rheological Test Results  
(1) PG grade  
The high-temperature grading results for OMA, LMA, and ULMA are shown in Table 4. An analysis of Table 4 indicates that as aging time increases, the PG grade of all three types of asphalt gradually improves, showing significant enhancement in high-temperature stability. Compared to unaged asphalt, after 184 h of aging, both OMA and ULMA saw their PG grades rise by one level from PG-64 to PG-70; LMA's PG grade increased by two levels, from PG-64 to PG-76. However, at most aging stages, the PG grades of modified asphalt are generally consistent with those of the base asphalt, making it difficult to deeply assess the differences in high-temperature rheological performance between base asphalt and modified asphalt. Therefore, according to AASHTO M320-15, the failure temperature (temperature at which G/sin\(\delta\) 1.0 kPa) is used for further evaluation of the high-temperature stability of the three types of asphalt.  
(2) Failure temperature  
Figure 7 shows the failure temperatures of different types of asphalt during ultraviolet aging. As illustrated, the failure temperatures of all three asphalts increase with prolonged aging time. Compared to unaged asphalt, the failure temperatures of all aged asphalts have risen to varying degrees. Specifically, after 184 h of aging, the failure temperatures of OMA, ULMA, and LMA have increased by 15.46%, 15.78%, and 23.11%, respectively. The ranking of failure temperatures is LMA > ULMA > OMA, indicating that both hydrotalcite and composite modifiers can significantly improve the high-temperature stability of asphalt. Under the same conditions, LMA has a higher failure temperature than ULMA, further demonstrating the superior performance of composite modifiers. For example, after 138 h of aging, the failure temperature of OMA is 73.17 C. After adding modifiers, the failure  
Figure 6: Ductility, differential ductility, and ductility ratio of matrix asphalt and modified asphalt.  
_Appl. Sci._**2024**, _14_, 10250 By analyzing the rutting factors before and after aging, it is evident that the rutting factor of aged asphalt is greater, indicating that ultraviolet aging can enhance the rutting resistance of asphalt. Moreover, the rutting factors of modified asphalts are significantly higher than those of the base asphalt, showing that hydrotalcite and composite modifiers can improve the high-temperature rutting resistance of asphalt. This is because the modifiers swell and decompose within the light components of the asphalt, forming a stable network structure that significantly improves the high-temperature performance of the asphalt. The ranking of rutting factors for the three types of asphalt is LMA > ULMA > OMA, indicating that LMA has better high-temperature rutting resistance than ULMA, meaning that the addition of hydrotalcite alone is more effective in improving the high-temperature rutting resistance of asphalt.  
To more clearly describe the deformation behavior of OMA, LMA, and ULMA under different aging conditions, the cumulative deformation of these asphalt types under 0.1 kPa and 3.2 kPa stress states was calculated, as shown in Figures 10 and 11. With increasing  
Figure 9: Strain–stress relationship of 70# asphalt and modified asphalt under different UV aging times.  
aging, the cumulative strain of the different asphalt types gradually decreases, with the order of cumulative strain being OMA > ULMA > LMA. Compared to the base asphalt, the modified asphalts exhibit smaller cumulative deformation, with LMA showing less cumulative deformation than ULMA. For example, at the 138 h aging point, the cumulative deformation of OMA is 8532.53%. After adding modifiers, the cumulative deformation of ULMA and LMA decreased by 5.60% and 22.22%, respectively. The decrease in cumulative strain for LMA is significantly greater than for ULMA, indicating that hydrotalcite improves the high-temperature deformation resistance of asphalt more effectively.