# Preparation and Properties of Waterborne Polyurethane and SBS Composite-Modified Emulsified Asphalt
## 3 Results and Discussion
### Multi-Stress Creep Recovery Analysis  
As shown in Figure 14, the shear strain of the four types of asphalt was relatively small at a load level of 0.1 kPa, while the shear strain significantly increased at a load level of 3.2 kPa. This indicates that the size of the vehicle load would have a significant impact on  
Figure 12: DCC curves of four types of asphalt.  
Figure 13: Fatigue life curves of four types of asphalt.  
road deformation, with heavier vehicles potentially causing deeper deformation. Under a load of 0.1 kPa, the strain of the evaporated residue was relatively small and recovers quickly, exhibiting a high recovery percentage. However, under a load of 3.2 kPa, the strain of the evaporated residue increased sharply, and the recovery rate and percentage decreased rapidly.  
At both 0.1 kPa and 3.2 kPa load levels, PU+6 exhibited the lowest strain, indicating its optimal deformation resistance. PU+3 and PU+9 exhibited the highest strain, indicating weaker deformation resistance than SEA. This contradicts the conclusion from the temperature sweep analysis, necessitating further examination from the perspectives of recovery percentage and unrecoverable creep compliance.  
Figure 15 shows the recovery percentage (\(R\)) values of the four modified emulsified asphalts at load levels of 0.1 kPa and 3.2 kPa. Generally, a higher \(R\) indicates a greater proportion of recoverable strain in asphalt, reflecting better elasticity. At a load level of 0.1 kPa, SEA had the highest \(R\), reaching 79.5%, while PU+3 had the lowest \(R\), at 54%. At a load level of 3.2 kPa, SEA's \(R\) was 37.9%, and PU+6's \(R\) was 37.7%. The \(R\) values of SEA and PU+6 were similar, with a difference of only 0.53%. PU+3 had the lowest \(R\), at 20%, while PU+9 had a slightly higher \(R\), at 21.9%.  
Despite SEA's weaker deformation resistance, its high elasticity resulted in a larger proportion of recoverable deformation, reflecting a lower strain value in the creep recovery curve than PU+3 and PU+9. Fluorescence microscopy experiments indicated that SBS polymers crosslinked in a network form in SEA had a better ability to recover from deformation and exhibited better elasticity. PU+6 also showed good elasticity and deformation recovery ability, consistent with previous findings where PU+6 exhibited the smallest phase angle.  
Figure 14: Strain curves of four types of asphalt.  
Figure 15: Recovery percentages of four types of asphalt under 0.1 kPa and 3.2 kPa loads.  
Figure 16 shows the unrecoverable creep compliance (\(J_{nr}\)) of the four types of asphalt under load levels of 0.1 kPa and 3.2 kPa. \(J_{nr}\) reflects the magnitude of irreversible deformation under a certain load, indicating the material's resistance to permanent deformation. Asphalt with lower \(J_{nr}\) values have stronger resistance to permanent deformation. At both load levels of 0.1 kPa and 3.2 kPa, PU+3 exhibited the highest \(J_{nr}\), while PU+6 exhibited the lowest \(J_{nr}\).  
The results showed that PU+6 had the best deformation resistance among the tested asphalts, as it demonstrated the lowest strain and \(J_{nr}\) values, along with a relatively high recovery percentage. PU+3 and PU+9, while showing good performance in some areas, generally had higher strain and \(J_{nr}\) values, indicating weaker deformation resistance than PU+6 and SEA. This was further confirmed by fluorescence microscopy experiments, which showed that SBS and PU+ polymers in PU+6 were densely distributed in small-particle form, enhancing both shear resistance and deformation recovery abilities, leading to superior deformation resistance and rutting resistance.