Let’s Get Technical: A Literature Review

Update submitted by Stormy Brewster, Marathon Petroleum, Research Sub-Committee Chair

Fabrication of Solvent-free Asphalt Emulsion Prime with High Penetrative Ability

Prime coats are typically applied to base, requiring penetration, before a layer of hot mix asphalt is applied on top. Current prime coats, cutback asphalt and solvent emulsions, contain high levels of fuels. VOC’s (Volatile Organic Compounds) from these fuels are released into atmosphere when used in the field. In addition, if not formulated correctly, the asphalt emulsion can break on the surface and not reach the penetration depth needed. This paper looks at formulating solvent free emulsions by varying emulsifier contents and adding JFC  (fatty alcohol-polyoxymethylene ether) to produce an emulsion capable of penetrating the surface. Penetration depth on cement treated base was measured along with particle size, contact angle and shear strength.

The authors found that increasing JFC increased penetration depth of the emulsion when used up to 0.5%. Emulsifier contents were varied from 1.5-4.5. A large jump in penetration depth was seen from 1.5-3.5%, but only an additional 0.5mm from 3.5-4.5%. When looking at asphalt content, it was shown that producing high asphalt contents on the mill and then lowering through dilution could lead to higher penetration depths, but did not look good in shear strength. Contact angle decreased with the use of JFC. Particle size decreased with increasing emulsifier contents. It should be noted that the authors used 1.5% as the starting point for this emulsifier and it was producing poor particle size.  

ζ Potential as a Measure of Asphalt Emulsion Stability

Current asphalt emulsion specifications date back to the 1920s, therefore, new and innovative specifications should be developed to improve emulsion performance. This article, titled “ζ Potential as a Measure of Asphalt Emulsion Stability” aims to study how ζ potential measurements can enhance our understanding of emulsion properties and performance. More specifically, the authors are exploring how ζ potential influences quick set emulsions. In this context, ζ potential can be understood as the electrical charge around asphalt droplets suspended in the continuous water phase. Factors that influence the zeta potential of an asphalt emulsion include the emulsifier chemistry, and the pH of the emulsifier solution wherein droplets will adopt a positive charge at low pH (cationic) and a negative charge at high pH (anionic).

The authors explore how pH, emulsifier dosage, and temperature influence the ζ potential of an amine based quick set asphalt emulsion. Of these three parameters, pH demonstrated to have the largest effect on ζ potential for the asphalt emulsions evaluated. Furthermore, the authors also investigated how zeta potentials changes as a function of titrating aggregate into the asphalt emulsion. This interaction had the largest influence on changes in zeta potential of all parameters evaluated and demonstrates the mechanism by which aggregates destabilize emulsions and cause irreversible emulsion breakage. In summary, this work suggests that ζ potential values can indicate the level of stability of an emulsion and may play an important role in asphalt emulsion formulation.

Storage Stability of Bimodal Emulsions vs. Monomodal Emulsions

Storage stability and viscosity continue to represent key parameters in asphalt emulsion handling and use and some of the primary methods by which the products are tested and specified for use. Emulsions are dispersions of the asphalt in a water medium by way of mechanical energy and then stabilized by way of chemical energy through surfactants. The type and amount of asphalt and surfactant used are key indicators towards this performance, but it does not tell the entire story. It’s generally assumed that asphalt emulsions will follow Stoke’s Law, which relates to fluid flow within a low Reynolds number medium and should theoretically apply to asphalt emulsions. Put simply it should mean that as particle size goes down and viscosity goes up the sedimentation rate of an asphalt emulsion should slow down. This means both viscosity and particle size are key indicators towards overall emulsion stability, and this is indicated by the results in the article where they manufactured emulsions with difficult to emulsify asphalts intentionally.

The article also explores the concept of bimodal asphalt emulsions and finds that they behave contrary to expectations. The bimodal nature can lead to a lower viscosity and a slower sedimentation rate at the same time. The article theorizes this is due to the complex packing of the bimodal particles giving them high storage stability with low viscosity. The article verified this by testing several asphalt emulsions and showing that with bimodal systems you can have both a low viscosity and a high storage stability due to the arrangement of the particles. These multi modal systems with low viscosity and high stability could offer unique opportunities within asphalt emulsion applications that require lower viscosities.

Ouyang, J., Sun, Y., & Zarei, S. (2019b, September 24). Fabrication of solvent-free asphalt emulsion prime with high penetrative ability. Construction and Building Materials. 

https://www.sciencedirect.com/science/article/pii/S0950061819324626 
Pinto, I., Buss, A. (2020) ζ Potential as a Measure of Asphalt Emulsion Stability. Energy & Fuels 34 (2), 2143-2151. 10.1021/acs.energyfuels.9b03565.

https://doi.org/10.3390/app7121267
Querol, N., Barreneche, C., & Cabeza, L. (2017). Storage stability of bimodal emulsions vs. monomodal emulsions. Applied Sciences, 7(12), 1267.