Publication Number: FHWA-SA-98-028
Date: December 1998

A Simple Test for Superpave Mix Performance

You've put together an asphalt mix that uses the best materials and follows the Superpave mix design guidelines to the letter. But how will the mix really hold up to traffic and climate conditions at the project site? What you need is a simple performance test. "States and contractors are looking for a test that will tell us what will work in the field in terms of rutting and other distress," says Larry Michael of the Maryland State Highway Administration. "Even with the Marshall mix design procedures, we never had anything that would predict performance."

Under a Federal Highway Administration (FHWA) contract, a University of Maryland (UM) team of researchers is now working on finding a simple performance test procedure that will give highway agency and industry staff a quick, effective, and economical way to assess the performance of Superpave mixes. The UM team is evaluating existing tests of asphalt mixture engineering properties to determine if any can be adapted to be a simple performance test. The test will be pass/fail-it will indicate whether you have an acceptable or inferior mix for project conditions. This determination would be based on some fundamental engineering property of the mix.

If none of the existing tests is suitable, the team will recommend how these tests can be modified and then assemble the required protocols, standards, and procedures. The test protocols are expected to be available by December 1999.

When completed, the simple performance test will replace the assortment of test procedures highway agencies and industry now use to assess the performance of asphalt mixes. Although some of these test procedures are relatively quick and easy to use, the accuracy of these tests has not been thoroughly evaluated.

The simple performance test will have another advantage over existing test procedures-it will work in different climates and with various materials. "Unlike the loaded wheel test and other empirical procedures, which must be calibrated for local aggregates and other factors, the simple performance test would be equally applicable in different parts of the country," says FHWA's Katherine Petros.

Researchers developing the simple performance test hope to have a final product that, once commercialized, will cost about $50,000, a price Dale Decker of the National Asphalt Pavement Association says most contractors will find acceptable, as long as the test is required for all Superpave projects.

The simple performance test will supplement, not replace, the still evolving Superpave performance prediction models and related test procedures, which will provide comprehensive information about the performance of a mix, particularly for projects in extreme climates or with very heavy traffic loads. The Superpave models may require more costly, sophisticated laboratory equipment, and the related test procedures could take days to complete. The Superpave models and test procedures are intended to be mix design and evaluation tools. The simple performance test, in contrast, should be reasonably portable and should take less than 8 hours to conduct, making it better suited for routine mix design and quality control/quality assurance procedures.

Highway agencies and industry are eager to see the simple performance test developed. "If we had a way to simply, accurately, and economically evaluate the performance of a mix, we'd be better off," says Decker.

For more information, contact Katherine Petros at FHWA (phone: 202-366-1340; fax: 202-366-9981; email: katherine.petros@fhwa.dot.gov).

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