# High-Temperature Rheological Properties of Asphalt Mortar Modified with Spent FCC Catalysts
## 3 Results and Discussion  
### Temperature Scan Test Results  
The phase angle (\(\delta\)) obtained from the temperature scan test conducted using the dynamic shear rheometer is an effective indicator for characterizing the rheological properties of asphalt slurry [36]. Figure 4 illustrates the trend of the phase angle of the asphalt slurry with increasing S-FCC-C replacement admixture under different high-temperature conditions. The results indicate a general decrease in the phase angle as a result of FCC spent catalyst doping at the temperatures of 58 \({}^{\circ}\)C, 64 \({}^{\circ}\)C, 70 \({}^{\circ}\)C, and 76 \({}^{\circ}\)C employed in the experiment. This decrease suggests that the addition of S-FCC-Cs enhances the elastic component of the asphalt mastic while reducing the viscous component. The filler's  
Figure 3: Schematic of the testing process. The rotation direction of the spin axis of DSR is A-B-A-C-A. abundant specific surface area enables greater asphalt adsorption, resulting in a larger surface area interacting with the asphalt, a thinner asphalt film, a higher percentage of structural asphalt, and a lower percentage of free asphalt. Consequently, the phase angle tends to decrease with an increasing S-FCC-C replacement admixture, leading to an overall improved stability of the asphalt mastic [37,38]. However, certain test groups exhibited an increase in the phase angle at 20% and 60% replacement doping. For instance, at 64 \({}^{\circ}\)C, the phase angle of the asphalt mastic increased with 20% HC replacement doping, and at 76 \({}^{\circ}\)C, it increased with 60% SL replacement doping. This phenomenon can be attributed to the fact that the asphalt slurry material itself is a multi-phase material with inherent heterogeneity, resulting in a more intricate phase angle-change curve [39]. In specific cases, such as JX at 76 \({}^{\circ}\)C with 80% alternative doping and ZH at 58 \({}^{\circ}\)C with 80% alternative doping, a substantial increase in the phase angle was observed. Apart from potential test errors associated with the asphalt slurry itself, this increase can be attributed to the excessively large surface area of the filler relative to the amount of asphalt. In such cases, the surface of the filler particles may not be sufficiently conducive to forming a strong asphalt film, leading to reduced cohesion of the asphalt mastic, decreased overall strength, and an increase in the phase angle [40]. To investigate the influence of high temperature on the rheological properties of asphalt mortar with different S-FCC-C substitution doses, the phase angle variation trend of S-FCC-C-modified asphalt slurry with temperatures at various doping levels was analyzed, as presented in Figure 5. From the figure, it can be observed that except for JX at 80% substitution dose and HC at 100% substitution dose, the phase angles consistently increased as the temperature rose from 58 \({}^{\circ}\)C to 76 \({}^{\circ}\)C. This shift indicates that the asphalt mastic gradually transitioned into a more viscous state, and the elevated temperatures adversely affected the internal structure of the modified asphalt mastic, leading to reduced stability. Notably,  
Figure 4: Change diagram of the phase angle of S-FCC catalyst-modified asphalt slurry at different temperatures. the rising phase angles of the two aforementioned samples indicate a deviation from the overall trend, potentially attributed to specific characteristics of their compositions [41]. In general, the phase angles of the five S-FCC-C modified asphalt slurries were smaller when compared to those of the pure mineral powder asphalt slurry, with a more pronounced effect observed at higher S-FCC-C admixture levels. This phenomenon suggests that the inclusion of S-FCC-Cs resulted in a thinner asphalt film on the powder's surface within the asphalt mastic, particularly with increased doping amounts. Consequently, the structural asphalt content was higher, resulting in enhanced overall strength of the mastic.