# Preparation and Properties of Waterborne Polyurethane and SBS Composite-Modified Emulsified Asphalt
## 3 Results and Discussion  
### Conventional Performance Analysis  
The softening point is a critical indicator for evaluating the high-temperature performance of asphalt. Figure 2 illustrates the softening points of four types of asphalt. The softening point of PU+3 was the highest at 73 \({}^{\circ}\)C, and the softening point of PU+9 was 71.6 \({}^{\circ}\)C. Both of these values were higher than that of standard emulsified asphalt (SEA). The softening point of PU+3 was increased by 5.49% compared to that of SEA, and the softening point of PU+9 was increased by 3.47% compared to that of SEA. The softening point of PU+6 was the lowest at 66 \({}^{\circ}\)C, which is 4.62% lower than that of SEA. Based on the softening point data, PU+3 and PU+9 exhibited better high-temperature performance, while PU+6 showed slightly weaker high-temperature performance compared to SEA. However, the difference in softening point values was not significant. Considering that the softening point alone is not a comprehensive indicator of the high-temperature performance of composite-modified emulsified asphalt evaporation residue, a more detailed comparison of high-temperature performance will be conducted in conjunction with further analysis. Ductility at 5 \({}^{\circ}\)C is commonly used to evaluate the low-temperature performance of modified asphalt. Figure 2 also displays the ductility of the four types of asphalt. PU+3 had the highest elongation at 66 cm, which is 8.55% higher than that of SEA. PU+6 had the lowest elongation at 48.2 cm, which is 20.72% lower than that of SEA. PU+9 had an elongation of 52.5 cm, which is 13.65% lower than that of SEA. These results indicated that the ductility of PU+6 and PU+9 was significantly reduced, reflecting their weaker low  
Figure 2: Softening points and ductility of four types of asphalt (5 \({}^{\circ}\)C). In the low-temperature range of 10-30 \({}^{\circ}\)C, the complex shear modulus and rutting factor of the three dosages of PU+ were significantly higher than those of SEA. Among the three dosages, PU+9 exhibited the highest values. The effect of dosage variation was minimal, and the impact of dosage diminished as the temperature increased. For instance, at 10 \({}^{\circ}\)C, the complex shear modulus of PU+6 was increased by 115.16% compared to that of SEA, while that of PU+9 increased was by 130.14%, showing a difference of 14.98% between the two. The rutting factor of PU+6 was increased by 171.88% compared to SEA, and that of PU+9 was increased by 184.34%, with a difference of 12.46% between them. In this temperature range, PU+6 showed the smallest phase angle, while SEA and PU+3 exhibited larger phase angles than the other two. Figure 8: Phase angles of four types of asphalt at 50–70 \({}^{\circ}\)C.  
Figure 6: Rutting factors of four types of asphalt at 50–70 \({}^{\circ}\)C.  
Figure 7: Phase angles of four types of asphalt at 10–30 \({}^{\circ}\)C.  
In the high-temperature range of 50-70 \({}^{\circ}\)C, PU+9 exhibited the highest complex shear modulus and rutting factor among the four types of asphalt, although the improvement effect was much less pronounced than at lower temperatures. For example, at 50 \({}^{\circ}\)C, the complex shear modulus of PU+9 was increased by 15.33% compared to that of SEA, and the rutting factor was increased by 15.34%. At 70 \({}^{\circ}\)C, the complex shear modulus of PU+9 was increased by 13.04% compared to that of SEA, and the rutting factor was increased by 13.21%. PU+6 consistently showed the smallest phase angle in the high-temperature range, while SEA and PU+9 had larger phase angles than the others. At lower temperatures, the addition of PU+ significantly enhances the shear and deformation resistance of modified emulsified asphalt. The specific content of PU+ does not significantly affect this improvement, and as the temperature increases, the improvement effect gradually weakens.