U.S. Department of Transportation
Federal Highway Administration
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Focus
| Accelerating Infrastructure Innovations |
Publication Number: FHWA-SA-97-023
Date: May 1997
Several years ago, the Asphalt Technical Working Group (TWG) challenged States and industry to implement the Superpave binder specification by 1997 and the volumetric mix design procedures by 2000. It was an aggressive schedule; after all, the Superpave specifications and procedures necessitated massive changes in the way States and industry did business. Asphalt suppliers would have to modify the way they tested and graded binders, highway agencies would have to rewrite their purchase specifications, engineers and technicians would have to become proficient in new devices and test methods, and contractors would have to learn how to deal with this unconventional mix design.
But through a carefully charted, broadly supported course of training, information dissemination, and pooled-fund purchases, these hurdles were overcome. Today, the first goal has been largely met: More than two-thirds of the States are already using the Superpave binder specification, and most of the remaining States will make the switch this year. And States and industry are well on their way to meeting the second goal: The Superpave volumetric mix design procedures, which employ the Superpave gyratory compactor to prepare trial mixes, were used on highway projects in two-thirds of the States in the 1996 construction season.
County and other local highway agencies across the United States are also making the transition to the Superpave system. With responsibility for most of the roads in this country, these agencies are eager to reap the benefits of more durable, longer-lasting asphalt pavements.
The foundation of the Superpave system-namely, the improved binder specifications and mix design procedures-is already well established, but the system will continue to evolve and expand over the next decade (see timeline). To bring leaders in the highway industry up to date on the planned evolution of the Superpave system, FHWA Executive Director Tony Kane and members of the agency's Superpave Technology Delivery Team recently met with representatives from the Asphalt Institute, National Asphalt Pavement Association (NAPA), Transportation Research Board, American Association of State Highway and Transportation Officials, and Superpave Lead States team. This article summarizes the items covered in that meeting.
A preliminary release of Version 2.0 of the Windows 95-based Superpave software will be available next month. It will include step-by-step procedures for the Superpave volumetric mix design process. The final release of Version 2.0, to be available in fall 1997, will include a module for analyzing reclaimed asphalt pavement and a field management module, which can be used to ensure that the asphalt mix delivered to a job site matches the job mix specifications.
The Superpave software was originally conceived under the Strategic Highway Research Program (SHRP), by teams of researchers from the Texas Transportation Institute, University of California-Berkeley, Pennsylvania State University, and University of Florida. Version 1.0 was released as a prototype in 1996. Since then, under an FHWA contract, a team headed by Matt Witczak at the University of Maryland (UM) has refined, enhanced, and improved the software to make it easier to use and to take advantage of the computer processing power and operating systems now readily available.
The UM team will also develop the framework for the Superpave models, which can be used to predict how different mixes will perform under various environmental and traffic conditions. Once the models have undergone rigorous field validation, they will be incorporated into the Superpave software. The performance prediction models will primarily be used to design asphalt pavements that carry very heavy loads and large traffic volumes, such as Interstate highways.
"Version 2.0 of the Superpave software is the next step in the evolution toward a computer program that will eventually integrate mix design, structural design, and models for predicting pavement performance," says Gary Henderson, leader of FHWA's Superpave Technology Delivery Team. "The software builds on the excellent foundation laid by the SHRP team of researchers."
The UM team will concentrate on developing methods for accurately characterizing the materials properties of asphalt concrete. These properties will form the basis for the performance models.
The UM team and the University of California-Berkeley will also work on development of a fundamental strength test for use in conjunction with the Superpave volumetric mix design procedures. The test is on a fast track and should be available for widespread use by early 1999.
"The fundamental strength test will give you a quick and easy way to look at the engineering properties of materials and thus provide an indication of how well the mix will withstand rutting and cracking," says FHWA's John D'Angelo. "Existing tests, such as loaded wheel testers, work strictly on empirical relationships, which have some limitations; the new test will overcome those limitations."
Several additional projects are in the pipeline (expected completion dates are shown in parentheses):
To keep all these projects in sync with one another, FHWA is establishing a Models Coordination Team.
"Many states and contractors are already using the Superpave mix design procedures-well in advance of the target date of 2000," says Dick Morgan, vice president of NAPA. "When the performance models are ready for implementation, industry will be ready to use them. In the meanwhile, the Superpave mix design procedures give us a mix design system that should be much more reliable than anything we've had before."
For more information, contact Gary Henderson at 202-366-1549 (fax: 202-366-9981; email: gary.henderson@fhwa.dot.gov).
The Fifth Annual U.S. Hot Mix Asphalt Conference and National Superpave Workshop will feature a full day of presentations and discussions on the Superpave system. State and local highway agencies and contractors will talk about what they've learned from experience with the Superpave system. Other topics on the agenda include updates on WesTrack, the Superpave specifications, and aggregate issues.
The conference is typically cosponsored by the National Asphalt Pavement Association (NAPA), State asphalt pavement associations, and the Asphalt Institute. This year, the Arizona Department of Transportation, FHWA, the American Association of State Highway and Transportation Officials, and the National Association of County Engineers have joined hands with the traditional sponsors to showcase progress and activities in Superpave implementation.
The conference and workshop will be held October 29-31 in Phoenix, Arizona. For more information, contact Jennifer Thornberry at NAPA, 301-731-4748 (fax: 301-731-4621).
"Key Dates in the Evolution of the Superpave System"
Superpave Models, published several times each year by the University of Maryland and FHWA, contains technical information on materials characterization and performance models, as well as tips on using the Superpave software.
To be added to the mailing list, send your name, address, phone and fax numbers, and email address to Harrington-Hughes & Associates, 733 15th St., N.W., Suite 700, Washington, DC 20005; fax: 202-347-6938 . The publication is also available through the Internet: www.ence.umd.edu/research.d/superpave.d/superpave.html.
