# Performance of Warm-Mixed Flame Retardant Modified Asphalt Binder
## 5 Results and Analysis of Superpave Evaluation Index Test of Asphalt Binder
### Repeated Creep Recovery Test  
For a long time, anti-rutting factor G*/sin\(\delta\) has been considered an acclaimed index for the evaluation of the high temperature performance of asphalt binders, but there are some limitations in representing the high-temperature performance of modified asphalt binder [22; 23]. Therefore, it is proposed in the NCHRP9-10 report of the U.S. to evaluate the high temperature performance of modified asphalt binder with repeated creep recovery tests [24]. This test method simulates the effect of load on pavement surfaces in the driving process by constantly loading and unloading the samples, which can effectively make up for the deficiency of only considering the elasticity and viscosity of asphalt binder in dynamic shear rheological tests, and more accurately reflect the creep and recovery ability of asphalt binder [25; 26]. In view of the above reasons, in order to better evaluate the high-temperature performance of asphalt binder and the changes to the elasticity and viscosity of asphalt binder under long-term repeated loading, a dynamic shear rheometer (DSR) was employed in this paper to make a repeated creep recovery test on SBS modified asphalt binder, Sasobit modified asphalt binder, and warm-mixed flame retardant asphalt binder, and the accumulated strain \(\gamma\) was adopted as a high-temperature performance evaluation index. In this test, stress control mode was adopted, the stress level was 120 Pa, and a plate of 25 mm was used with a gap of 1 mm. Three different test temperatures: 30 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, and 50 \({}^{\circ}\)C were adopted, the loading duration for each cycle of creep was 1 s, unloading duration was 9 s, and the total cyclic loading was 100 times. The test loading pattern is shown in Figure 5.  
In order to evaluate the high-temperature performance of the three kinds of modified asphalt binder, the cumulative strain development curves at three different temperatures from the 51 st to 60 th creep recovery cycles were selected to make analysis; see Figures 6-8. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Types of** & & & **+1\% Sasobit** & **+1\% Sasobit** & **+1\% Sasobit** & **+1\% Sasobit** & **+1\% Sasobit** \\
**Asphal Binder** & & & **+5\% FR** & **+6\% FR** & **+7\% FR** & **+8\% FR** \\ \hline PG Grading & 76 & 82 & 82 & 82 & 82 & 82 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Summary of performance graded (PG) grading results. Figure 5: Loading pattern of repeated creep recovery test. Figure 6: Strain response of asphalt binder at 30 \({}^{\circ}\)C.  
Figure 7: Strain response of asphalt binder at 40 \({}^{\circ}\)C.  
It can be seen from Figures 6-8 that 1 during the 51 th and 60 th loading cycles, the accumulated strain value of asphalt binder tested at 50 \({}^{\circ}\)C is significantly greater than those tested at 40 \({}^{\circ}\)C and 30 \({}^{\circ}\)C, which shows that with the increase of the test temperature, the accumulated strain value of asphalt binder increased accordingly. 2 At three different temperatures, the accumulated strain values of Sasobit modified asphalt binder and warm-mixed flame retardant asphalt binder are significantly lower than that of SBS modified asphalt binder, which indicates that both Sasobit and flame retardant can markedly enhance the deformation recovery ability of asphalt binder. In addition, in order to better analyze the accumulated strain of asphalt binder, the accumulated strain values of asphalt binders under a stress level of 120 Pa, at three different temperatures of 30 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, and 50 \({}^{\circ}\)C in the 1 st, 10  
It can be seen in Figures 9-11 that 1 at different temperatures, the accumulated strain values of modified asphalt binder increased with the increase of loading numbers, showing a curvilinear growth trend and viscoelastic rheological characteristics.