|Abstract or Summary
- This study investigated the laboratory performance of crumb rubber modified
mixtures compared to a standard bituminous mixture using performance based test
procedures. This study was part of an asphalt resurfacing program for the Seattle
Washington area. Laboratory analyses were used to estimate the long term pavement
performance of these mixtures in the field. Six mixtures were tested: The standard
Class 'A' surface mixture for the Seattle area, Plus Ride II® base course gradation (dry
process) using AC 5 and AR 4000W binder types, Plus Ride II® surface course
gradation (dry process) using AC 5 and AR 4000W binder types, and ARHM-GG
surface course gradation using crumb rubber modified (CRM) AR 2000 (wet process).
The performance based tests used on each mixture evaluated the different failure
modes a pavement may encounter in the field: fatigue cracking, permanent
deformation (rutting), thermal cracking, age hardening, and water sensitivity. Many of
the tests used were developed by the Strategic Highway Research Program (SHRP) to
test for a mixtures susceptibility in these failure modes.
Test results indicate the CRM mixtures performed better than the Class 'A'
surface mixture, with respect to fatigue cracking. All of the Plus Ride II® mixtures
performed inadequately when tested for permanent deformation. On the other hand,
the ARHM-GG surface mixture performed well, even better than the Class 'A' surface
mixture with respect to permanent deformation. The ARHM-GG surface mixture
showed better low temperature characteristics when compared to the Class 'A' surface
and Plus Ride II® mixtures. The CRM mixtures were less susceptible to aging than the
Class 'A' surface mixture. Finally, all of the mixtures demonstrated low moisture
The final conclusions were made relative to the Class 'A' surface mixture. The
ARHM-GG surface mixture performed as well as, and in some cases better than, the
Class 'A' surface mixture. The ARHM-GG surface mixture may be used where the
Class 'A' surface mixture was specified. The Plus Ride II® base and surface (AC 5
and AR 4000W) mixtures did perform better than the Class 'A' surface mixture in
some tests, however it performed worse in others. Therefore, it was recommended
that the Plus Ride II® mixture designs be re-evaluated to provide adequate performance
in the failed tests.