# Phase Separation Study on the Storage of Technically Specification Natural Rubber Modified Bitumen
## 3 Results and Discussion
### Phase Separation Simulation of TSNR-Modified Asphalt
The simulation results will be used to assess the ability of the combined Navier-Stokes model for laminar and phase field flow to predict the storage stability of TSNR-modified bitumen, as well as the effects of bitumen density and viscosity on gravity-induced phase separation at 160 \({}^{\circ}\)C. Evaluation of the phase separation simulation in Figure 12 shows that modified bitumen has poor compatibility at 160 \({}^{\circ}\)C storage temperature. TSNR was initially evenly distributed in the asphalt, but during storage, phase separation was caused by differences in molecular weight, density, and viscosity between components. Thermodynamically, the mixture of asphalt and TSNR cannot mix due to the two materials' incompatible characteristics and properties, also known as an immiscible blend. Figure 11: Geometry and mesh used in the simulation. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**No**} & \multirow{2}{*}{**TSNR Content (\%)**} & \multirow{2}{*}{**Temperature (\({}^{\circ}\)C)**} & \multicolumn{2}{c}{**Density, \(\rho\) (kg/m\({}^{3}\))**} & \multicolumn{2}{c}{**Viscosity, \(\mu\) (Pa.s)**} & \multirow{2}{*}{**Phase Separation**} & \multirow{2}{*}{\(\chi\) **(10\({}^{-5}\)**} \\  & & & **Asphalt** & & & & **Rate, v (10\({}^{-6}\) m/s)** & \\ \hline
1 & 8 & 160 & 1034.670 & 868.560 & 0.151 & 0.517 & 3.3206 & 9.633 \\
2 & 10 & 130 & 1034.670 & 868.560 & 0.640 & 0.871 & 0.6756 & 1.960 \\
3 & 10 & 160 & 1034.670 & 868.560 & 0.151 & 0.517 & 2.8639 & 8.308 \\
4 & 12 & 160 & 1034.670 & 868.560 & 0.151 & 0.517 & 2.4693 & 7.163 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Component parameters used in simulation. Figure 12 shows the difference in volume fraction of the asphalt component with storage time at steady state. At the beginning of storage (t = 0), the asphalt phase was evenly distributed in the mixture. However, after a few minutes of storage, the asphalt component showed incompatibility with the TSNR component. Carefully observable in Figure 12, the initially green surface area at t = 0 h, which indicates that the asphalt and TSNR components are evenly mixed, changes to a blue color in a very short period of less than 1 min (t = 0.05 h). At t = 0.05 h, the phenomena of coalescence and flocculation are visible, confirming that the phase separation of modified asphalt must have started with the coalescence and flocculation of TSNR components in the mixture. The speed of coalescence and flocculation determines the speed of formation of density and viscosity differences between the two phases. At t = 0.1 h, it can be seen that a small part of the asphalt component moves vertically downward due to the influence of gravity. This process continued until 1 h of storage and reached equilibrium at 12 h of storage. Based on the simulation results shown in Figures 13 and 14, there is no significant difference in density and viscosity in the first 12 h. Based on this, it can be confirmed that the separation movement shown in Figure 12 at t = 0.1 h to t = 6 h is the movement of asphalt phases that do not interact with TSNR components. This possibility can occur because some asphalt phases that do not interact with TSNR components have higher density and lower viscosity. The mixture reached equilibrium in the first 12 h (t = 12 h). Although the TSNR-modified bitumen reached equilibrium at 12 h of storage, the phase separation process continued for 72 h (t = 72 h). This is confirmed by the simulation results in Figures 13 and 14, which show that the density and viscosity differences between the top and bottom fractions increase with storage time and settling velocity. By comparing all the surface area images of the volume fractions, the asphalt has a noticeable color difference with the addition of  
Figure 12: Simulation results of TSNR-modified asphalt phase separation by volume fraction. 10% TSNR. This color difference can be interpreted as a higher concentration of asphalt components in this domain than modified asphalt with 8 and 12% TSNR.