# Research on Mechanical Performance of Porous Asphalt Mixture with High-Viscosity Modified Asphalt
## 2 Preparation and Performance Analysis of High-Viscoelastic Modified Asphalt
### Research on the Optimum Type of High-Viscosity Modifier  
To determine whether both A and B high-viscosity modified asphalts meet the performance requirements for porous asphalt courses, this study investigated the rheological performance of two types of high-viscosity modified asphalt and normal SBS-modified  
Figure 7: 60 \({}^{\circ}\)C dynamic viscosity test results.  
asphalt using BBR. The test results were used to identify a high-viscosity modified asphalt suitable for actual project needs, aiding in engineering selection. BBR can measure the mechanical performance of asphalt materials at low temperatures. The test flowchart is shown in Figure 8.  
The asphalt was first subjected to RTFOT short-term aging, followed by PAV long-term aging. The aged asphalt was then placed into test molds with dimensions of 101.6 mm \(\times\) 12.7 mm \(\times\) 6.4 mm. After the asphalt was completely cooled, the creep strength (s) and creep rate (m) were measured at \(-6\,^{\circ}\mathrm{C}\), \(-12\,^{\circ}\mathrm{C}\), and \(-18\,^{\circ}\mathrm{C}\) to characterize the low-temperature cracking resistance of the asphalt [39]. The test results are shown in Figures 9 and 10.  
Figure 8: The operation flow chart of the bending beam rheometer.  
Figure 9: The change in creep strength S with temperature for high-viscosity modified asphalt.  
From the test results in Figures 9 and 10, the S values of the three asphalts showed an increasing trend, while the m values showed a decreasing trend as the temperature decreased. At temperatures ranging from \(-6\)\({}^{\circ}\)C to \(-18\)\({}^{\circ}\)C, the asphalt creep strength (S) and low-temperature fracture resistance were inversely proportional. At \(-6\)\({}^{\circ}\)C and \(-12\)\({}^{\circ}\)C, all three asphalt specimens had m \(\geq\) 0.3, meeting the specifications. However, the creep rate of the three asphalt specimens was below 0.3 at \(-18\)\({}^{\circ}\)C, indicating that the fracture-resistant properties of asphalt gradually weakened with decreasing temperature. When the test temperature was \(-12\)\({}^{\circ}\)C, the S values were ordered as follows: A-modified asphalt < B-modified asphalt < SBS-modified asphalt. The m values were ordered as follows: SBS-modified asphalt > A-modified asphalt > B-modified asphalt. These results show that the incorporation of high-viscosity modifiers increased the strength of asphalt [40]. To provide a more intuitive analysis of the low-temperature performance of different asphalt materials, the creep rate and creep strength ratio (m/S) were introduced to evaluate the low-temperature performance of asphalt. A larger ratio indicates better low-temperature cracking performance [41]. At \(-12\)\({}^{\circ}\)C, the m/S ratios were ordered as follows: A-modified asphalt > B-modified asphalt > SBS-modified asphalt. This indicates that the incorporation of the two high-viscosity modifiers enhanced the resistance of asphalt materials to temperature shrinkage cracking at low temperatures, with modifier A being more effective. Therefore, in this research, high-viscosity modifier A was used to prepare high-viscosity modified asphalt, and porous asphalt mixtures were designed using A-modified asphalt for mechanical performance research.