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Federal Highway Administration / Publications / Focus / February 1997

Accelerating Infrastructure Innovations

Publication Number: FHWA-SA-97-020
Date: February 1997

NCHRP Projects Investigate Enhancements to the Superpave System

A number of National Cooperative Highway Research Program (NCHRP) projects are investigating further enhancements to the Superpave system.

NCHRP project 9-7, "Field Procedures and Equipment to Implement SHRP Asphalt Specifications," conducted by Brent Rauhut Engineering, Inc., focused on developing quality control/quality assurance (QC/QA) testing procedures for Superpave mixes. By allowing highway agencies to determine if the mix delivered to the job site matches the mix designed in the laboratory, the QC/QA procedures will ensure that Superpave pavements perform as expected. The project team developed guidelines to train technicians in QC/QA procedures. It also developed a prototype field version of the Superpave shear tester. Publication of the final report is planned for summer 1997.

NCHRP project 9-9, "Refinement of the Superpave Gyratory Compaction Procedure," is designed to improve and expand the Superpave mix design procedures. The project is being conducted by the National Center for Asphalt Technology (NCAT) at Auburn University. The project team is investigating if changes are needed to the American Association of State Highway and Transportation Officials (AASHTO) provisional standard, "Method for Preparing and Determining the Density of Hot Mix Asphalt (HMA) Specimens by Means of the SHRP Gyratory Compactor" (TP4). The project team will also develop procedures for using the Superpave gyratory compactor to design stone matrix asphalt (SMA) and open-graded, gap-graded, and large stone mixes. Publication of a final report is planned for late 1998.

Two other NCHRP projects not explicitly associated with the Superpave system address the use of the Superpave equipment to design non-Superpave mixes. Under NCHRP project 9-8, "Designing Stone Matrix Asphalt Mixtures," NCAT is developing procedures for using the Superpave gyratory compactor and the direct tension tester to design and analyze SMA mixes. The project is scheduled to end in June 1998. Under NCHRP project 4-18, "Design and Evaluation of Large Stone Mixtures," the Texas Transportation Institute studied using the Superpave shear tester and the Superpave performance models to design and evaluate mixes with large aggregates (25 to 64 mm [1 to 2.5 in]). The final report on the project is scheduled for publication early this year.

Under NCHRP project 9-10, "Superpave Protocols for Modified Asphalt Binders," the Asphalt Institute is investigating whether changes are needed to the AASHTO provisional standard "Specification for Performance Graded Asphalt Binders" (MP-1) and related tests when evaluating modified binders. The project will also identify any problems with the mix analysis tests related to modified binders. Work is scheduled to wrap up in September 1998.

Two new Superpave research projects will be awarded early this year. NCHRP project 9-1, "Incorporation of Reclaimed Asphalt Pavement in the Superpave System," will examine the use of reclaimed asphalt pavement in Superpave mixes, an increasingly important issue as the Superpave system becomes the mix design system of choice. NCHRP project 9-13, "Evaluation of Moisture Sensitivity Tests," will evaluate the AASHTO standard "Resistance of Compacted Bituminous Mixtures to Moisture-Induced Damage" (T-283) and recommend any changes necessary to make it compatible with the Superpave system.

For more information on the NCHRP projects, contact Ed Harrigan at the Transportation Research Board (TRB), which manages NCHRP research (telephone: 202-334-3232; fax: 202-334-2006; email: eharriga@nas.edu), or visit the NCHRP section of TRB's Web site at http://www2.nas.edu/trbcrp/nchrp5.html.

The National Cooperative Highway Research Program is a program of the American Association of State Highway and Transportation Officials (AASHTO). Program funding comes solely from State highway agencies. The Transportation Research Board (TRB) administers the program, under contract to AASHTO.

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