Asphalt Emulsion Technology
ituminous emulsions are complex fluids. Their stability is governed by intermolecular
forces—a result of a balance of repulsive and attractive forces. The formulator skillfully
must understand and balance these forces such that the emulsion can be produced consistently,
stored, pumped, transported, and applied by the practitioner in the field without experiencing any downtime in the operation.
Bituminous emulsions form the basis for many paving applications in our asphalt
industry, including driveway sealants, cold-pour crack sealants, and roofing emulsions. Their
rheological (i.e., flow) properties often dictate the uses for which they are suitable. For example,
the viscoelastic properties of a slow setting versus a rapid-setting emulsion are different. We
expect one day to be able to use rheological properties of bituminous emulsions to predict their
success or failure in their respective applications. Even when rheological properties are not
critical in the final product, they influence the workability of the emulsion as it is applied in the
field. This is true for fog or chip sealing emulsions.
Significant improvement has occurred over the years to make quality bituminous
emulsion products and their subsequent application in the field. However there remains
considerable work to be done in the sense that further improvement can only occur when the
principles of chemistry and physics are fully incorporated into the practical engineering
component of road building. The study of bituminous emulsion in our industry can only become
less of an intellectual backwater when we begin to incorporate the new advances in experiment
and theory of colloid science to create a renaissance in bituminous emulsions in our paving
Bituminous emulsions were discussed in a technical session at the 84th Annual Meeting
of the Transportation Research Board (TRB). The papers in this document were written
following the session and are based on the presentations; the papers in this circular have not
undergone a formal peer review.
The four papers serve as an overview of the chemistry, production, quality assurance
testing, and application of bituminous emulsions. They offer the beginner a start in this exciting
and challenging field of bituminous emulsions.
Appreciation is expressed to the authors for their contributions; to Robert McGennis, who
facilitated the first TRB bituminous emulsion technology session; and to Rebecca McDaniel,
who provided valuable editorial input to the text.