Phase II of the Superpave Models Project Under Way

The second phase of the Federal Highway Administration's (FHWA) Superpave models project is now under way. The project, which is being conducted by the University of Maryland (UM) and a team of subcontractors, is part of FHWA's multiyear plan for developing a system for predicting the performance of asphalt mixes designed using the Superpave system.

During the first phase of the models project, the UM team conducted a comprehensive review of the theory, application, implementation, feasibility, results, and conclusions of the Superpave performance prediction models system initially developed under the Strategic Highway Research Program (SHRP). The review, which was completed in fall 1996, concluded that the models system required technical corrections and field calibration before it would be ready for implementation by highway agencies and industry.

As a result, FHWA's Superpave Technology Delivery Team modified the work plan for the second phase of the models project. Because Phase I found several errors or limitations in the way asphalt concrete materials were characterized in the models, Phase II will emphasize materials characterization—that is, the structure and behavior of materials in asphalt mixes.

The UM team will develop the framework for the Superpave performance prediction models and the materials characterization procedures for use with that framework. The framework will cover the four major types of distress found in new and rehabilitated pavements—thermal cracking, fatigue cracking, permanent deformation, and reflection cracking. The Superpave performance prediction models will be completed, calibrated, and validated under a series of future contracts.

In addition, the UM team will address the need among highway agencies and industry for a simple performance test for use with the Superpave mix design procedures. By providing additional information on the predicted performance of a mix, this test could be useful in mix design and quality control procedures. The UM team will evaluate the performance test equipment that is now available, then guide the development of any new test equipment and develop related test procedures. The test should be available by early next year.

Phase II also calls for the UM team to develop a new educational software program. The program, which will analyze rutting, fatigue fracture, and thermal fracture in asphalt pavements, is intended for use in research and education. It will help engineers, students, and others get ready to use the American Association of State Highway and Transportation Officials' (AASHTO) 2002 Design Guide, now under development, and it will help them understand the computer models that will form the basis of the Superpave performance prediction procedures. The program is scheduled to be available late summer 1998.

For more information, contact Katherine Petros at FHWA (phone: 202-366-1340; fax: 202-366-9981; email: katherine.petros@fhwa.dot.gov) or visit the UM team's Web site (www.ence.umd.edu/superpave).

The Superpave Models Expert Task Group (ETG) provides FHWA with technical advice and support on the Superpave models project. The ETG will hold its first Phase II meeting this month.