# Performance Evaluation of Asphalt and Asphalt Mixtures Modified by Fuel-Resistant Admixture
## 3 Results and Discussion
### Performance of FRMA
#### 3.1.3 BBR Test  
The S-value and m-value from the BBR test are depicted in Figure 7. The experimental results satisfy the error tolerance criteria stipulated for repetitive tests outlined in AASHTO T 313 [21]. The S-value and m-value reflect the flexibility and stress relaxation ability of asphalt at low temperatures, respectively. Generally, higher S-values and lower m-values indicate poorer crack resistance performance of asphalt at low temperatures.  
As shown in Figure 7a, the S-value of asphalt at \(-6\)\({}^{\circ}\)C exhibits an upward trend with increasing FRM dosage, albeit a relatively minor overall increase. The S-value at \(-6\)\({}^{\circ}\)C fluctuates with increasing FRM, which may be attributed to uneven distribution  
Figure 6: DSR test results of modified asphalt at different test temperatures: (**a**) complex modulus; (**b**) phase angle; (**c**) rutting factor.  
of FRM in the asphalt caused by excessive dosage. The S-value at \(-12\)\({}^{\circ}\)C demonstrates a V-shaped variation. In comparison to the base asphalt, the S-value of FRMA with 1% and 3% FRM decreases by 52.9% and 43.2%, respectively, indicating a significant reduction in stiffness and a shift toward elastic behavior. However, when the FRM dosage exceeds 3%, the S-value increases, resulting in a notable decrease in low-temperature flexibility. Additionally, as the test temperature decreases, the S-value of the same asphalt increases, indicating a reduction in low-temperature flexibility.  
As observed in Figure 7b, the m-value at different temperatures exhibits a parabolic variation with increasing FRM dosage. In comparison to the other dosages, 1% FRMA has the highest m-value, and when the dosage exceeds 1%, the m-value significantly decreases. These results suggest that an appropriate amount of FRM is beneficial for the temperature stress dissipation of asphalt, but as the dosage increases, the stress relaxation performance diminishes.  
In summary, the judicious use of FRM can effectively enhance the low-temperature flexibility and stress dissipation ability of asphalt, thereby strengthening its resistance to low-temperature cracking. The emergence of this outcome is hypothesized to be linked to the establishment of an elastic network structure within the asphalt facilitated by the modifier, thereby enhancing the asphalt's elasticity and flexibility [24]. This phenomenon contributes to the attenuation of asphalt deformation at lower temperatures, consequently bolstering its resistance to low-temperature creep. However, when the dosage of FRM is excessively high, interactions among polymers may intensify, resulting in a structure that is relatively deficient in elasticity [25; 26]. This rigid configuration at lower temperatures could render the modified asphalt mixture more brittle, consequently diminishing its susceptibility to low-temperature creep. Furthermore, heightened concentrations of the modifier may lead to a decline in compatibility between the modifier and asphalt, resulting in an uneven dispersion of polymers within the asphalt. Under such circumstances, the formed structure could adversely affect the low-temperature performance.  
According to SHRP specifications, the low-temperature performance at \(-12\)\({}^{\circ}\)C for 1% and 3% FRMA meets the usage requirements of S \(\leq\) 300 MPa and m \(\geq\) 0.3.