About the research
Pavement preservation treatments that utilize asphalt emulsions are growing in popularity due to the overwhelming need for infrastructure preservation and treatment cost effectiveness, as well as because of the versatility of asphalt emulsion applications. Emulsions are not well understood by many practitioners in the civil engineering community. The integration of new technologies into asphalt emulsion specifications and quality assurance programs has lagged compared to rheological specifications adopted in the hot-mix asphalt industry.
Part of the challenge is due to the complexity of asphalt emulsion systems and the need to tailor asphalt emulsion formulation to each treatment and, sometimes, each project. Microsurfacing and slurry seal treatments use quick-setting emulsions. The emulsion formulations and mixture designs may be engineered to work together to maintain adequate consistency during mixing and then rapidly set and break once placed on the roadway surface. This rapid break allows for rapid curing of the new pavement surface, allowing the road to be opened to traffic in as little as one hour after treatment application. The formulation of microsurfacing and slurry seal emulsions is crucial to achieving this rapid break.
The primary objective of this study was to investigate if zeta potential could be useful as a measure of emulsion stability and set time in slurry seal and microsurfacing emulsions and mixtures. An experimental design was developed to study zeta potential as a function of important asphalt emulsion formulation parameters: the pH of the emulsifier solution, emulsifier dosage in the continuous phase, and temperature of the asphalt emulsion while measuring zeta potential. Fine aggregates of various reactivity (limestone and bentonite) were suspended in the solution and titrated into the emulsion while changes in zeta potential were measured. The point of zero zeta potential, or the isoelectric point, at which the emulsion flocculates was also observed.
Finally, an experiment was designed to observe cohesion measurements at various levels of water content and asphalt emulsion content, while using specially formulated emulsions for which pH and zeta potential were known. Findings demonstrate proof-of-concept for using zeta potential as a scientific measurement that could help engineer and measure the reactivity of asphalt emulsions and provide better understanding of aggregate-emulsion interactions. Study limitations and opportunities for future research are also presented.