# Preparation and Properties of Waterborne Polyurethane and SBS Composite-Modified Emulsified Asphalt
## 3 Results and Discussion
### Surface Free Energy Analysis  
#### 3.6.1 Experimental Data and Cohesive Energy Analysis  
The contact angle data between asphalt and reagents obtained from the experiment are shown in Table 4.  
The surface energy parameters of the aggregates used in the experiment are shown in Table 5. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Temperature**(\(\lx@math@degree\)**C**)} & \multirow{2}{*}{**Asphalt**} & \multicolumn{3}{c}{**Reagent**} \\ \cline{3-5}  & & **Formamide** & **Glycerol** & **Distilled Water** \\ \hline \multirow{3}{*}{20} & SEA & 83.86 & 89.01 & 88.35 \\  & PU+3 & 82.39 & 88.60 & 83.97 \\ \cline{1-1}  & PU+6 & 83.32 & 89.46 & 83.54 \\ \cline{1-1}  & PU+9 & 83.53 & 89.76 & 88.79 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Advance contact angles (\(\lx@math@degree\)) of four types of asphalt with various reagents. Figure 16: Unrecoverable creep compliance of four types of asphalt under 0.1 kPa and 3.2 kPa loads. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Aggregate**} & \multicolumn{5}{c}{**Surface Energy Parameter (m/m\({}^{2}\))**} \\ \cline{2-5}  & \(\gamma^{LW}\) & \(\gamma^{AB}\) & \(\gamma^{\star}\) & \(\gamma^{-}\) & \(\gamma\) \\ \hline \multirow{2}{*}{diabase limestone} & 63.82 & 51.06 & 3.02 & 216.88 & 114.88 \\  & 143.22 & 1.903 & 0.0023 & 393.68 & 145.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Aggregate surface energy parameters. The surface energy parameters of the evaporated residue of composite-modified emulsified asphalt were calculated and are shown in Table 6.  
From Table 6, it can be seen that the surface energy parameters of modified emulsified asphalt are mainly non-polar components (\(\gamma^{LW}\)), with \(\gamma^{LW}\) much larger than \(\gamma^{AB}\), indicating that modified emulsified asphalt is a substance dominated by non-polar intermolecular forces, which is consistent with the basic chemical properties of asphalt. From Table 5, it can be seen that the surface energy components of the aggregate are mainly polar alkali components (\(\gamma^{-}\)), which is different from asphalt with non-polar components (\(\gamma^{LW}\)). At the same time, the total surface energy of the aggregate is above 100 mJ/m\({}^{2}\), which is consistent with the test results obtained from relevant literature, indicating that the aggregate is a material with high surface energy. The cohesive energies of four types of composite-modified emulsified asphalt were calculated and shown in Figure 17.  
From the graph, it can be seen that at 20 \({}^{\circ}\)C, the cohesive energy of the three dosages of PU+ was increased compared to that of SEA. Among them, PU+6 had the highest cohesive energy, with a value of 40.903 mJ/m\({}^{2}\), which is 13.15% higher than that of SEA. The SBS polymer crosslinked in a network form in SEA exhibited the worst anti-fracture ability. With the addition of PU+, the anti-fracture ability of asphalt gradually increased. However, the large-particle polymer formed by the crosslinking of SBS and PU+ in PU+9 did not show better cohesive energy than the small-particle SBS and PU+ polymer, indicating its weaker anti-fracture ability. PU+6 exhibited the best fracture resistance. The cohesive energy results are consistent with the previously discussed performance metrics. The small-particle SBS and PU+ polymer structure in PU+6 not only enhanced its shear and deformation resistance but also significantly improved its fracture resistance. This highlights the effectiveness of the small particle distribution in optimizing the mechanical properties of the asphalt mixture.