Using Polymer Modified Asphalt Emulsions in Surface Treatments A ...

Figure 1: Examples of Copolymers
2.1.2 Asphalt Emulsions
Asphalt emulsions are formed by the milling of raw asphalt into microscopic particles
which are dispersed in water with the aid of a chemical emulsifying agent called a
“surfactant” (sometimes referred to as “soap”). In such cases, the dispersed asphalt
forms discrete droplets which are intrinsically insoluble in water. The emulsion is said to
be “stabilized” if the asphalt droplets remain well-dispersed such that phase separation
does not occur. Stabilization is achieved through the use of surfactants, which consist
of polar molecules comprised of a hydrophilic (water loving) “head” and hydrophobic
(water avoiding) “tail.” The tail of the surfactant molecule is attracted to the asphalt
particles, forming a coating around each particle which consists of the hydrophilic heads
of the emulsifying agent. The hydrophilic portions of these surfactants are very reactive
with water, and aid in keeping the droplets dispersed and in suspension.
Surfactants are classified as anionic, cationic, or non-ionic based upon the nature of the
charge of the hydrophilic portion of the molecule. Anionic and cationic emulsifiers are
the most commonly used in pavement surface treatment applications. The electrical
potential that exists between the surface of the surfactant-coated asphalt particles and
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