# Storage Stability of Bimodal Emulsions vs. Monomodal Emulsions
## 3 Results
### Emulsion Sedimentation  
Three different groups of emulsions were manufactured combining concentration of 60 wt. % and 70 wt. % residual bitumen and B35/50 and B15/25 penetration grade bitumen, following the manufacturing protocol established in Section 2.2. In three cases, one momonodal emulsion of small controlled particle size, one monomodal emulsion of large particle controlled size, and a third bimodal emulsion mixing the previous two in a controlled rate of 1/2 small/large particle size were manufactured. The first emulsion manufactured is a 60 wt. % bitumen emulsion formulated with a B35/50 penetration grade bitumen. Results obtained are shown in Figure 8. It can be seen that after one month since its manufacture the small-sized monomodal emulsion (d(0.5)s) settled slightly with supernatant starting from day 14. In contrast, the monomodal emulsion of large size (d(0.5)l) has a supernatant of 0.8 mL after one month from its manufacture. The viscosity results obtained are summarized in Table 3.  
Figure 7: Particle size distribution for a 70 wt. % B15/25 for (**a**) d(0.5)s, (**b**) d(0.5)l, and (**c**) bimodal emulsion. Although the bimodal emulsion has a viscosity lower than the emulsion of large size, 262 mPa-s in front of 376 mPa-s, it does not present supernatant after one month from its manufacture, which is more similar to the emulsion of small sizes [20; 25]. Three new emulsions were made where the residual bitumen concentration was increased to 70% residual bitumen. The bitumen used was the same as in the previous case, a B35/50. The first emulsion was a monomodal emulsion, d(0.5)\({}_{\mathrm{s}}\), and the second emulsion a monomodal, d(0.5)\({}_{\mathrm{t}}\), resulting in a bimodal emulsion from the mixture of 1/2 of the above two. Ten mL of emulsion was introduced into  
Figure 8: Emulsions of 60 wt. % B35/50: (**a**) global vision; (**b**) sedimentation curve; (**c**) monomodal d(0.5)\({}_{\mathrm{t}}\); (**d**) monomodal d(0.5)\({}_{\mathrm{s}}\); (**e**) bimodal emulsion. \begin{table}
\begin{tabular}{c c c c c c} \hline
**60 \({}^{\circ}\)C** & **Emulsion** & **Bitumen** & **d(0.5)\({}_{\mathrm{l}}\)** & **d(0.5)\({}_{\mathrm{s}}\)** & **d(0.5)\({}_{\mathrm{bimodal}}\)** \\
**50 rpm** & **Concentration** & **Bitumen** & **d(0.5)\({}_{\mathrm{l}}\)** & **d(0.5)\({}_{\mathrm{s}}\)** & **d(0.5)\({}_{\mathrm{bimodal}}\)** \\ \hline
1 & 60 & 35/50 & 376 & 878 & 262 \\
2 & 70 & 35/50 & 878 & 1805 & 253 \\
3 & 60 & 15/25 & 37.25 & 253 & 24.75 \\ \hline \end{tabular}
\end{table} 
Table 3: Viscosity measurement for the different prepared samples. three closed sedimentation tubes and left to stand at room temperature. The supernatant was read as the volume fraction, f\({}_{v}\), at different times. Results are shown in Figure 9.  
In the monomodal emulsion of large size, d(0.5)\({}_{h}\), there was a slight sedimentation, 0.5 mL, after a month of storage; while the monomodal emulsion of small size, d(0.5)\({}_{s}\), practically had no sedimentation and only a light supernatant was observed from day 14; and finally, the bimodal emulsion corresponding to the mixture of the two above at ratio 1/2, did not have a supernatant after a month of its manufacture. Therefore, the bimodal emulsion was more stable for storage than the monomodal emulsion of large size, although it had lower viscosity (at 60 \({}^{\circ}\)C and 50 rpm the bimodal emulsion had a viscosity of 253 mPa-s, while the monomodal emulsion of large size had a viscosity of 878 mPa-s). In view of the excellent results obtained, it was decided to test the behavior of these emulsions by varying the starting bitumen, using harder penetrating bitumen, that is more unfavorable for its manufacture. The 60 wt. % emulsions were made again but using a harder bitumen, B15/25. The emulsions of this hard residue are of great interest in the world of paving, although both their  
Figure 9: Emulsions of 70 wt.