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

high temperature performance, but were shown to significantly improve low temperature
susceptibility (26).
Hesp and Woodhams (1991) note that polyolefin modifiers impart a wide range of
beneficial characteristics to applied asphalt emulsions, including decreases in thermal
cracking and high temperature rutting, greater fatigue resistance, improved skidresistance,
and increased stone retention (30). However, Hesp also observes that the
primary obstacles which inhibit the widespread adoption of polyolefin compounds in
PME, are problems related to gross phase separation at elevated storage temperatures.
Indeed, the authors note that without the use of a stabilizer, polyolefin-modified asphalt
emulsions commonly have stable life-spans of only one hour or less. The findings of
Hesp and Woodhams are in general agreement with those of Perez-Lepe, and indicate
that the primary mechanism of instability in polyolefin-modified asphalt emulsions is the
coalescence of the polymer phase which eventually leads to creaming (28, 30). The
most promising and cost-effective method for achieving mixture stability in such cases,
is regarded to be the addition of steric stabilizers which are thought to secure emulsion
stability by being preferentially absorbed at the polyolefin-asphalt interface (28, 30).
EVA is a commonly used plastomeric modifier which represents a copolymer of
ethylene and vinyl acetate. By co-polymerizing ethylene and vinyl acetate, the latter
serves to reduce the crystallinity of the former, resulting in increased elasticity and
better compatibility with the base asphalt (3). In EMA and ethylene acrylate modifiers,
the crystalline structure of polyethylene is similarly reduced via the introduction of acrylic
acid (3). Panda and Mazumdar (1999) report decreased penetration and ductility, and
improved temperature susceptibility in EVA-modified versus unmodified binders (31).
Additionally, EVA modified asphalts have been shown to retain their desirable physical
properties even after prolonged periods of storage, and do not appear to be adversely
affected by minor variations in mixing methods or temperatures (31).
The use of reclaimed waste plastics such as HDPE and LDPE as modifiers, have been
shown to be somewhat effective in improving fatigue resistance, and in reducing
penetration (24, 32). However, it is noteworthy that some stability problems with these
mixes have also been reported, particularly at higher additive concentrations (24).
24