The new mix consists of a coarse graded Superpave gradation made from quarried stone. The mix met all Superpave requirements for aggregate properties and volumetrics. Sections were placed as in the original sections with low, optimum, and high asphalt content and low, medium, and high in place air voids. Quality control testing was conducted behind the paver during construction and the data indicates the mixes had the required volumetric properties and reasonable gradation and asphalt content. The binder was checked and met Superpave requirements. Most of these new sections exhibited some deformation within two days of trafficking. There is something about these coarse graded mixes that needs to be more fully understood.
Coarse graded mixes, similar to the mix place at WesTrack, have been placed on many pavements around the country. These mixes have performed well. From Baltimore to Saint Louis to Phoenix, these mixes have been placed on pavements with high traffic and in hot climates and have not had the failures we see at WesTrack. There are many questions about what has happened with the new sections placed at WesTrack.
The FHWA understands the need to quickly address the questions the arise from the performance at WesTrack. To quickly look into questions FHWA is pulling together an independent team of experts, from FHWA, States, industry, and academia, to evaluate the new test sections. The team will look into each aspect of the design and construction of the new test sections to determine what might be the cause of the early distress. A report will be produced to put forward the findings of the team to the industry.
We will continue to work on answering the many questions on the performance of Superpave. There will be more refinements and corrections as we gain experience. Several sections at WesTrack have not performed as expected. Similar mixes are performing in the real world under real conditions. Only by continuing to building pavements and evaluating their performance will we improve our ability to design and build asphalt pavements for the 21st century.
For more information email Terry Mitchell (Phone: 202-366-0121) or John D'Angelo (Phone: 703-285-2434).
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