# Storage Stability of Bimodal Emulsions vs. Monomodal Emulsions
## 4 Conclusions  
The sedimentation of an emulsion is directly related to the concentration of residual bitumen and the viscosity of the emulsion. As shown in equation 1, there is a lower average drop size, lower settling velocity, and, at higher residual bitumen concentration, lower settling velocity. [PERSON] law refers to the frictional force experienced by spherical objects moving within a viscous fluid in a lamellar regime of low Reynolds numbers. This equation is fulfilled as long as the spherical particles moving through the sine of the viscous fluid are not configured to form a bimodal distribution.  
Bimodal emulsions are characterized by having two different and controlled droplet size and distribution. The optimal formulation contains a first small size of about 1 \(\upmu\)m and a second size of about 5 \(\upmu\)m with a proportion of 1/2, respectively. The decrease in viscosity that can be observed in bimodal emulsions when compared to their equivalent monomodal emulsions can be a consecution of the distribution of the different droplets in the matrix of the emulsion. Small particle size droplets could occupy the gaps between the large droplets and promote the decrease of viscosity [24].  
The viscosity of the bimodal emulsion of 60 wt. % with a B35/50 penetration grade bitumen was 262 mPa.s, while when we use B15/25, the viscosity obtained was 24.75 for the same bitumen concentration of 60 wt. %. It seems that the penetration grade bitumen has greater influence on the viscosity value of bimodal emulsions than the final bitumen concentration, since, when we measured the viscosity of the bimodal emulsion 60 wt. % with B35/50 penetration grade bitumen was 262, while when the concentration is 70 wt. % the viscosity is almost the same, 253. It seems that the bitumen concentration does not influence the final viscosity. The bitumen penetration grade is more important.  
Storage stability is a very important parameter that has to be considered in the formulation of asphalt emulsions. The stability of the emulsion determines its appropriate use. The main factors that influence the storage stability of an emulsion are viscosity and average droplet size. Focusing on [PERSON] law, the lower the average droplet size of the emulsion, the lower the sedimentation rate; and the more viscosity the emulsion has, the lower the sedimentation rate. In the present paper, we have observed that this rule is fulfilled as long as bimodal emulsions are not considered. The storage stability of bimodal emulsions is much higher than their monomodal counterparts, even though they have a lower viscosity than these.  
The authors would like to thank the Catalan Government for the quality accreditation given to their research group GREA (2014 SGR 123). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. [PERSON] would like to thank Ministerio de Economia y Competitividad de Espana for [PERSON], FJCI-2014-22886 and [PERSON] would like to specially thank Sorgique Company for giving her the opportunity to develop this study using its manufacture production plant equipped with the most advanced technology to develop this kind of emulsions.  
[PERSON] conceived, designed and performed the experiments; [PERSON] and [PERSON] analyzed the data.  
The authors declare no conflict of interest.