Majority of States Building Superpave Pavements This Year

The Superpave system is increasingly being put into practice across the country, with two-thirds of States reporting that they are using or planning to use the Superpave volumetric mix design process this construction season. The projects include overlays, large-scale reconstruction, and new construction.

The Asphalt Technical Working Group (TWG) has set 1997 as the target date for implementation of the performance-graded (PG) binder specification-a goal to which two-thirds of the States have already committed. The TWG has set 2000 as the date for implementation of the Superpave volumetric mix design procedures.

All States now have the equipment required to test binders for conformance with the Superpave PG binder specification and to fabricate test specimens that can be used to determine how well a mix will perform in real-world conditions.

At least two States-Arizona and Indiana-are already using the Superpave mix analysis and performance prediction procedures to determine how well a mix will perform under high traffic volumes and loads or other demanding conditions. While neither State highway agency has the requisite equipment yet, they were able to contract out the performance analysis work.

"We're making terrific headway," says Doug Forstie of the Arizona Department of Transportation (DOT). "We have at least eight projects in place that were built using the Superpave volumetric mix design procedures, and we've done some performance testing using the Superpave shear tester. We've formed a Superpave implementation team, involving cities, counties, suppliers, universities, contractors, and FHWA. This team has been the driving force for building Superpave pavements."

Highway contractors and suppliers are working closely with State highway agencies to implement the Superpave system. In many States, industry-agency groups have been formed to foster interest in and awareness of Superpave among contractors and suppliers. Pat Strong of North Carolina DOT says, "There seems to be growing interest in Superpave among the highway industry in the State." In Florida, contractors have volunteered to design and deliver Superpave mixes for several big jobs.

FHWA's Don Steinke, the new chairman of the Asphalt TWG, applauds this public-private effort to implement the Superpave system. "When I went to the North Central Asphalt User/Producer Group meeting this spring, I was amazed by the enthusiasm of States and industry on Superpave. I saw a real partnership between highway agencies, suppliers, contractors, and academia on the implementation process. I'm very pleased that this partnership has taken place."

Some States are already sold on the Superpave system. The highway agencies in Indiana and New York, for example, plan to use the Superpave volumetric mix design procedures in all construction jobs starting in 1999. Mississippi is buying Superpave gyratory compactors for all of its highway districts to make implementation of the Superpave mix design procedures possible before 2000. In Georgia, says Ronald Collins of the State's highway agency, "We're pretty encouraged by the Superpave mixes-we're getting good results. We're doing a Superpave project in every district to give people Statewide experience with the Superpave mix. We plan to supplement the Superpave design procedure by proof-testing mixtures using the Georgia loaded wheel tester."

In Maryland, the State highway agency will begin a project this year to widen part of Interstate 695, the highway around Baltimore that carries an average of 150,000 vehicles per day. The project involves 175,000 tons of Superpave mix, including some reclaimed asphalt pavement, as well as 75,000 tons of stone matrix asphalt that will be tested with the Superpave gyratory compactor.

The partnerships forged by the regional asphalt user-producer groups are valuable, according to the States. Mark Felag of Rhode Island DOT says belonging to the same user-producer group as New York State gives his State access to New York's expertise and experience. "When we got our binder test equipment and the Superpave gyratory compactor, New York helped us design our laboratory," he says. "It's like having a big brother."

Lon Ingram of Kansas DOT speaks for many States when he says, "We know Superpave is going to improve our process."

The matrix below indicates which States are constructing or plan to construct Superpave pavements this year and the expected dates for adoption of the PG binder specification. The matrix is based on a telephone survey conducted in May 1996. All 50 States, Washington, D.C., Puerto Rico, and five Canadian Provinces and Territories responded.

A Level by Any Other Name�

The Asphalt Technical Working Group has recommended that Superpave mixes no longer be referred to by the terms level 1, level 2, and level 3. The terms were a source of confusion, as they were often misinterpreted as representing three discrete mix design procedures rather than a series of procedures that built on one another. Here's a brief rundown on the Superpave terminology.

• The Superpave volumetric mix design procedures are used for all Superpave mixes. The procedures include selecting aggregates and binders that meet the Superpave criteria and using the Superpave gyratory compactor to fabricate test specimens for determining volumetric properties of the mix.
• For pavements that are to be used in critical locations, additional mix testing and analysis are performed using the Superpave shear tester and the indirect tensile tester. The test results are then entered into computer models that predict pavement performance.

For a brief overview of the Superpave system, request a copy of FHWA's new brochure, The Superpave System: New Tools for Designing and Building More Durable Pavements (Publication Number FHWA-SA-96-010); telephone: 301-577-0818; fax: 301-577-1421.

For a step-by-step look at the Superpave mix design process, order a copy of the new 12-minute videotape, Understanding Superpave Mix Design, produced jointly by FHWA and the National Asphalt Pavement Association (NAPA). The videotape covers materials selection, aggregate blending, specimen preparation, the Superpave gyratory compactor, and mix analysis. Available from NAPA (telephone: 301-731-4748; fax: 301-731-4621).

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