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

2.2.7 Polymer Blends
Select polymer additives may be blended together to achieve desired composite
properties that cannot be obtained from a single polymer modifier alone. Moreover,
blending may prove a viable option when the availability and cost of a particular polymer
modifier make it attractive for its use, but where the resulting rheological and
performance characteristics that it produces may not fully satisfy design requirements.
In such cases, the addition of complementary modifiers may provide the means through
which design specifications may be satisfied, while permitting the use of the desired
primary modifier. Additionally, supplemental modifiers are frequently added to improve
the overall compatibility between the polymer and bitumen phases and to improve longterm
mixture stability. While practical considerations preclude the exhaustive
documentation of the numerous potential polymer combinations, examples of some of
the most common blends found within the literature are presented for illustrative
purposes.
Applications which utilize polyethylene as the primary modifier are frequently
augmented via the addition of elastomers such as PB, in order to achieve better mixture
stability (29). Morrison et al (1994) report that polyethylene-modified asphalt emulsions
can be effectively stabilized with either virgin PB or lower-cost de-vulcanized CRM (29).
In such instances, the mechanism for attaining this increase in stability lies in the
attachment of steric stabilizer molecules at the polyethylene-asphalt interface.
Ait-Kadi et al (1996) report that blends of HDPE and EPDM produce improved
performance with respect to penetration, the loss of aromatics (aging), and viscosity,
when compared to neat asphalt (27). Comparisons of HDPE/EPDM blends to straight
HDPE-modified asphalt in this study indicate little performance difference, although
microscopic evaluation suggests that the former generally yields a better distribution of
the polymer phase than does the latter. This characteristic has important cost and
handling implications, since modifiers which are difficult to disperse translate into
significantly higher energy requirements and longer mixing times (34). In addition, more
thorough and homogeneous dispersal of the polymer phase within the bitumen
generally leads to improved mixture stability, which increases potential storage life.
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