U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
|Accelerating Infrastructure Innovations|
Publication Number: FHWA-SA-97-026
Date: August 1997
Testing asphalt binders for conformance to the Superpave specifications is time-consuming and can tie up a supplier's storage space and delay construction. Now, however, a new procedure for pre-qualifying suppliers of asphalt binders streamlines the quality control process, while assuring highway agencies and contractors that the binder they are getting meets their specifications.
The procedure, "Standard Practice for Certifying Suppliers of Performance Graded Asphalt" (PP26), provides a framework highway agencies can use to grant Approved Supplier Certification (ASC) to suppliers of Superpave binders. As outlined in PP26, a supplier would submit a written request to a highway agency for status as an approved supplier of asphalt binders that meet the Superpave specifications. To be eligible for consideration, the supplier would have to submit a detailed quality control plan, and to retain its certification its laboratory would have to be accredited by the American Association of State Highway and Transportation Officials (AASHTO) before August 29, 2000.
The supplier must also provide the highway agency with the results from the complete set of Superpave binder tests. If the supplier's tests show that the binders meet the Superpave specifications and the quality control plan meets the agency's criteria and the requirements set forth in PP26, the supplier can be placed on the agency's ASC list, which gives the supplier a green light to begin shipping materials once a project gets under way.
The supplier must then periodically run the entire battery of Superpave tests on the binders being shipped; the minimum frequency and number of tests is set by the highway agency. As long as the binders continue to meet the Superpave specifications, the supplier can continue to ship the material. To verify the supplier's test results, the highway agency will conduct its own tests of the asphalt binders.
If the supplier's or the agency's tests show the binder to be in noncompliance with the specifications, the supplier must halt all shipments of the material until the problem is resolved. Because materials that fail to measure up to the Superpave specifications are promptly identified, the result is a strong focus on quality.
The overall goal of the certification procedure is to prevent delays in asphalt paving projects. "If you have a contractor on board and the job is ready to go, but you don't have an approved source of asphalt binders, construction can be delayed," says Haleem Tahir of AASHTO. "If the supplier has earned Approved Supplier Certification, you know the supplier has good quality control procedures and you can have confidence in the quality of their products. As a result, you don't have to delay the project while you perform the full set of Superpave binder tests."
The procedure is flexible enough to suit virtually all highway agencies. "In Indiana, we have always sampled the binder from contractors' tanks, but most other States sample at the refinery," says Dave Andrewski of the Indiana Department of Transportation (DOT), who helped develop the specification. "Under PP26, States can sample the binder where they prefer, and they can choose the frequency of tests."
The procedure is welcomed by the companies that refine and supply asphalt binders. "We were worried because the Superpave tests would take 2 days to complete, which would tie up our tanks while we performed them," says April Swanson of Amoco Oil. "PP26 solves the problem." According to Tahir, an added advantage is that once a supplier has a proven track record, the agency can opt to reduce the frequency and number of tests.
Suppliers that do business in more than one State will particularly benefit from the certification procedure and the Superpave binder specification, Swanson notes. Even if each State stipulates different requirements for suppliers' quality control plans, the basic plan will be the same.
The AASHTO certification procedure is based closely on a certification procedure developed for the North Central Asphalt User-Producer Group (NCUPG). "The main objective of the North Central User-Producer Group's plan was to give suppliers the responsibility to develop a quality control plan that would fit with their manufacturing process," says Swanson, who helped develop the plan.
The draft plan was circulated to State highway agencies and contractors for comments. Once the NCUPG procedure was final, it was made available to States in the region. Realizing that the plan could serve as a model for a nationwide certification program, AASHTO's Subcommittee on Materials then began the process of converting the NCUPG plan into a national framework for certification.
"PP26 is a good starting point for the development of a certification plan that will be fairly uniform across the United States," says Jack Telford of Oklahoma DOT and a member of the Subcommittee on Materials. "It allows everybody the flexibility they need to develop something that will work."
The procedure appears in the 1997 supplement to the AASHTO Provisional Standards (Publication Code PS-97I). To order, contact AASHTO at 800-231-3475 (fax: 800-525-5562).
Highway agencies and contractors with questions or comments on the specification should write to Jack Telford, Division Engineer, Materials, Oklahoma Department of Transportation, 200 NE 21st Street, Oklahoma City, Oklahoma, 73105 (fax: 405-522-0552).
A "supplier" is defined in PP26 as any company that alters the binder, including the refinery or the hot-mix asphalt plant (if, for example, it adds modifiers to the asphalt). The last company to alter the binder prior to its use in construction is responsible for ensuring that the material meets the Superpave specifications.