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Federal Highway Administration > Publications > Focus > October 1996 > Superpave 2000: Focusing on the Pavements of the Future
October 1996Publication Number: FHWA-SA-96-021

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Superpave 2000: Focusing on the Pavements of the Future

"We've called this meeting for one reason: to focus on the future," said Art Fendrick, Federal Highway Administration (FHWA) division administrator in Indiana, in welcoming the more than 300 highway designers, contractors, and others from the United States, Canada, Japan, and Poland to the Superpave 2000 conference held in Indianapolis in August. Over the 1.5-day conference, participants heard from highway contractors, agencies, and others with experience designing and constructing Superpave pavements. To get a better understanding of the Superpave system, the participants also spent an afternoon touring nearby Superpave project sites and laboratories.

Indiana Governor Evan Bayh, in a welcoming letter to the conference participants, stressed the need to adopt the Superpave system: "Motorists will benefit from Superpave, which will result in less maintenance, fewer travel restrictions, better road service, and less inconvenience."

The conference was sponsored by the Indiana Department of Transportation (DOT), Asphalt Pavement Association of Indiana, Indiana Mineral Aggregates Association, North Central Superpave Center, American Association of State Highway and Transportation Officials (AASHTO), and FHWA.

Key issues discussed at the conference included the use of reclaimed asphalt pavements (RAP) in Superpave mixes, Superpave software, aggregate quality, the WesTrack project, and warranty projects.

RAP: A Valuable Resource

John D'Angelo, asphalt team leader in FHWA's Office of Technology Applications, discussed the use of RAP in Superpave mixes. Many roadway projects require that an existing asphalt wearing course be removed before a new overlay is placed, making the supply of RAP plentiful.

"RAP is a valuable resource we cannot waste," said D'Angelo. "The Superpave system should improve our ability to use RAP effectively."

D'Angelo outlined the four steps involved in incorporating RAP into an asphalt mix:

  • Determine the Superpave performance-graded asphalt binder required for the project.
  • Separate the asphalt binder from the aggregate in the RAP and test the binder to determine its Superpave grade.
  • Estimate the percentage of recycled asphalt to be used in the trial mix.
  • Determine how much new asphalt will need to be added to the asphalt from the RAP. The Superpave mix design procedures will then allow the mix designer to test how well the trial mix will perform in the field.

D'Angelo pointed out that there are still some questions to be answered, such as whether a modified asphalt binder will blend with an asphalt binder recovered from RAP. The Asphalt Technical Working Group and its expert task groups, composed of asphalt specialists from academia, industry, and highway agencies, are studying this issue.

Restricted Zone

Tom Kennedy, professor at the University of Texas at Austin and technical director of the Superpave Center at Austin, discussed the restricted zone included in the Superpave aggregate gradation guidelines. "The purpose of the restricted zone is to avoid tender mixes," said Kennedy. "It essentially eliminates rounded, dirty, fine-graded aggregates."

Kennedy cautioned mix designers to heed the restricted zone. "Lots of people report good-performing mixes that violate the Superpave gradation guidelines," he said. "Although many of those mixes initially perform well, we as a community have accepted mixes that do not last as long as they should. We need to design pavements for a 20-year life, not a 4- or 5-year life."

Industry Perspective

Panelists David Jahn, vice-chairman of the Technical Committee of the National Stone Association; John Yzenas, technical services manager for the Levy Company; and Tony Kriech, director of research for Heritage Research Group; voiced several key concerns of the aggregate industry:

  • Some high-performance aggregate sources cannot meet the voids in mineral aggregate requirements of the Superpave volumetric design procedures.
  • The restricted zone, which was incorporated into the design process for combined gradations that contain round natural materials, has little relevance for 100 percent manufactured materials.
  • The fine aggregate angularity test procedure erroneously identifies cubical manufactured materials as being spherical. As a result, highly cubical manufactured sands may not meet Superpave's fine aggregate angularity requirements and would be restricted from use. The Mix Expert Task Group is developing a guideline for analyzing the possible conflicts.

Dale Decker, vice-president for research and technology at the National Asphalt Pavement Association, emphasized the need for training in the Superpave system. "It will be a Herculean effort to train the 300,000 people in the hot-mix industry to understand the Superpave system so that they can do their job well."

Decker also pointed out the need to work out the details of a quality control/quality assurance plan for the Superpave system. "Field management is very important, and the contractor is now being made responsible for mix design. We need guidelines, not requirements."

Superpave Validation and Software

Jon Epps, faculty member at the University of Nevada, Reno, and WesTrack team member, gave a status report on the WesTrack accelerated pavement testing project. One of the project's two primary objectives is to validate the Superpave mix design and analysis procedures.

WesTrack is a 2.9-km (1.8-mi) oval test track in the Nevada desert. Over a 2-year period, four driverless trucks will apply 10 million equivalent single-axle loads to the pavement, simulating at least 10 years of Interstate-level traffic loads on the pavement's test sections.

Sensors in the test track monitor the pavement temperatures and loads. Each test section is periodically evaluated for visual distress, rutting, deflection, roughness, and friction. (For more information on WesTrack, see the September 1996 and October 1995 issues of Focus.)

Matt Witczak, faculty member at the University of Maryland at College Park and principal investigator for FHWA's Superpave software and models contract, provided an update on the status of the Superpave software. In May 1996, a prototype of the software, based on the original DOS software developed under SHRP, was distributed by AASHTO to materials engineers in State highway departments. It provides the Superpave volumetric mix design procedures.

Version 2.0 of the Superpave software, which will be a completely new, Windows-based version of the Superpave volumetric mix design procedures, is scheduled for release in April 1997. To ensure the software will meet the needs of users, a group of 20 mix designers from State highway agencies and industry have been providing the project team with suggestions on the concepts and functionality of Version 2.0.

"Industry and agency input is the key to the success of Version 2.0 of the software,"said Witczak.

Version 3.0 of the software, which will include enhanced performance models and material characterization, is scheduled for release in spring 2000.

States' Perspectives

Gale Page, materials engineer with the Florida Department of Transportation (DOT), reported that, beginning in 1997, all Interstate highway projects in Florida will be designed using the Superpave specifications and mix design procedures. Florida DOT is currently allowing contractors to use the Superpave system on existing jobs. Seven Superpave projects (totaling 246,000 metric tons {270,000 tons}) are completed or under way, and each project contains about 20 percent RAP.

"Is there a risk to adopting Superpave?" said Page. "The risk is in not adopting Superpave. The Superpave pavements certainly can't perform worse than our existing mix."

Larry Michael, regional engineer with Maryland DOT, said that Maryland is also committed to implementing the Superpave system. The State adopted the Superpave binder specification in July 1996-ahead of schedule-and plans to implement the Superpave mix design procedures by 2000.

"The leadership of the State Highway Administration asked, 'If it's good, why wait?'" said Michael. "As a result, Maryland is actively pursuing a very aggressive implementation plan for Superpave."

Don Corum, pavement materials testing engineer with Arizona DOT, described how Arizona had a major problem with cold-temperature cracking in its asphalt pavements at high elevations. Finding that the pavement temperature was warmer than the air temperature, the DOT developed an algorithm for adjusting the low air temperature to represent low pavement temperature.

The varied climate in Arizona necessitates that 22 different binder grades be available for use. "The temperature algorithm allows us to more accurately determine which binder grade we need, which we predict will save us $2 million a year," said Corum. "The Superpave binder specification works-and it is practical for our use. It is definitely an improvement."

All paving projects bid in 1997 in Arizona will specify use of Superpave binders. Some pilot Superpave mix design projects will also be built in 1997. "If all goes well, we'll fully implement the Superpave mix design procedures in 1998," said Corum.

Indiana DOT's Dave Andrewski recalled his State's first Superpave project, on Interstate 65 in 1993. "Rumors were spreading only a couple of years later that the project was experiencing severe rutting," said Andrewski. "But we went out and measured it and found only 1 to 2 millimeters of rutting. And it is still holding up well."

Andrewski cautioned contractors to "do their homework before jumping in" on Superpave projects. "The more progressive contractors are bidding on the Superpave projects."

Indiana will implement the Superpave binder specifications and the Superpave mix design procedures with field quality control/quality assurance on 40 to 50 projects in 1997 and on all projects statewide by 2000.

"We plan to work closely with the North Central Regional Superpave Center, which is located in Indiana," said Andrewski. "They can help us move forward with Superpave performance analysis."

Warranty Specifications

Gerry Huber, from Heritage Research Group, described how the highway agencies and contractors in Wisconsin and Indiana are developing innovative ways of delivering contracting services.

"The desire is to make performance part of the contract," said Huber. "We want to achieve quality and encourage innovation. Our existing contracting procedures do not factor in performance, with the result that a contract can be termed successful, even if the pavement performs poorly."

Bids on several paving projects let in Indiana and Wisconsin included the contractors' estimates of the number of days traffic would be disrupted by construction. The State assessed a cost to each peak-hour lane closure and non-peak-hour lane closure. The cost of the delays was then added to the construction costs, and the contract was awarded to the low bidder. The contractor had to also provide a 5-year warranty on the project: any repairs needed during the warranty period would be made by the contractor and at the contractor's expense. The warranty is based on customer expectations-namely, the smoothness of the ride, and the safety of travel on the pavement (as evidenced by rutting, skid resistance, ride quality, and longitudinal cracking).

Milestone Contractors was awarded a warranty project on Interstate 70 in Indiana. "We all had a lot of concerns about the warranty, which was a potential liability," said Milestone's John Spangler. "The State's pavement management system provided good records of the performance of overlays on portland cement concrete. We toured the sites and reviewed the data, and this information, coupled with our belief in the Superpave mix design system, gave us the confidence to bid the project."

Spangler says that warranties will cause contractors "to become much more intelligent about what we're doing." For example, as part of its quality control/quality assurance program, Spangler met with the drivers of the trucks carrying the hot-mix asphalt to the paving site to discuss their role in delivering a quality pavement.

Spangler calls the I-70 warranty project "a true example of partnering"

and says that the project "was probably the best job our company ever built."

North Central Superpave Center

Becky McDaniel, technical director of the North Central Superpave Center, described the center's operations and roles. The center, one of five such regional Superpave centers, serves 12 States and 2 Canadian provinces, providing training, conducting research, and "doing whatever else the region needs." The center will also provide laboratory support for the Superpave performance models contract.

Pavements for the 21st Century

Lee Gallivan, FHWA's coordinator for the Superpave 2000 conference, says that "States are being asked to consider changing existing practices to address the needs of the 21st century, while continuing to build pavements using existing materials and test equipment. Judging by the comments I've received, the conference was a success in explaining the do's and don'ts of the Superpave system."

For more information about the Superpave 2000 conference, contact Lee Gallivan, FHWA, 317-226-7493 (fax: 317-226-7341; email: victor.gallivan@fhwa.dot.gov).

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Updated: 04/07/2011

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