U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
|Accelerating Infrastructure Innovations|
Publication Number: FHWA-SA-96-023
Date: December 1996
WesTrack, FHWA's hot-mix asphalt test track in Nevada, is less than 1 year old, but already the day-in, day-out heavy truck traffic is beginning to take its toll. Five of the 26 test sections had such significant permanent deformations (ruts 25 to 35 mm [1 to 1.4 in] deep or more) that they had to be rehabilitated in November.
Surprised? Don't be. The WesTrack project was designed to evaluate how variations in construction quality-namely asphalt content, aggregate gradation, and compaction-affect pavement performance. Many of the test sections were intentionally built with less-than-optimum construction properties. The rutting was expected-and confirms the importance of proper materials and construction practices.
The other 21 test sections at WesTrack also show some rutting, but to a lesser degree. This rutting is also not unexpected in light of the very concentrated, heavy loading the track receives and the high temperatures during the Nevada summer. In the first 5 months of loading, more than 1 million equivalent single-axle loads (ESALs) were applied to the pavement-roughly equal to the loads many Interstate highways carry in a year or more.
What Does It Mean?
Although data are still being collected and analyzed, the team has made several initial observations:
A second objective of the WesTrack project is verification of the Superpave performance prediction models and the Superpave mix analysis system. Only 4 of the 26 WesTrack sections were designed to be true Superpave pavements-that is, with optimum asphalt contents, air voids, and aggregate gradations. The other 22 sections have significant variations in one or more of these three properties (representing variations often encountered in the field) and would not be expected to perform nearly as well as the optimum sections. The laboratory and field performance data do indicate inadequate coarse aggregate angularity may be contributing to the early rutting in even the optimum sections.