Several years ago, a national group of representatives from industry, highway agencies and academia set forth two goals: implementation of the Superpave binder specification by 1997 and of the Superpave volumetric mix design procedures by 2000. Today, the first goal has been largely met: More than two-thirds of the states are already using the Superpave binder specification, and most of the remaining states will make the switch this year. States and industry are well on their way to meeting the second goal: The Superpave volumetric mix design procedures, which employ the Superpave gyratory compactor to prepare trial mixes, were used on highway projects in two-thirds of the states in the 1996 construction season. Highway agencies at the local level are following suit.
Of age, but still growing
The improved binder specifications and mix design procedures, which are the key components of the Superpave system, are clearly ready to be used now. The system will, however, continue to evolve and expand over the next decade. Here's a preview of what's ahead.
A beta release of Version 2.0 of the Windows 95-based Superpave software will be available in June. It will include step-by-step procedures for the Superpave volumetric mix design process. The final release of Version 2.0, available this fall, will include both a field management module, which can be used to verify that the asphalt mix delivered to a job site matches the job mix specifications, and a module for analyzing reclaimed asphalt pavement.
A prototype (Version 1.0) of the Superpave software, which was originally conceived under the Strategic Highway Research Program by researchers from the Texas Transportation Institute, University of California-Berkeley, Pennsylvania State University, and University of Florida, had been released in 1996. Since then, under an FHWA contract, a team headed by Matt Witczak at the University of Maryland (UM) has refined, enhanced, and improved the software to make it easier to use and to take advantage of the computer processing power and operating systems now readily available.
The UM team will concentrate on developing methods for accurately characterizing the materials properties of asphalt concrete and building the framework for the performance models, which predict how different mixes will perform under various environmental and traffic conditions. The models will primarily be used to design asphalt pavements that carry very heavy traffic loads and large volumes, such as interstate highways. Once the models have been completed and rigorously field validated under a follow-on contract, they will be incorporated into the Superpave software.
At a recent meeting between FHWA top management and representatives from the National Asphalt Pavement Association (NAPA), Asphalt Institute, American Association of State Highway & Transportation Officials, and Transportation Research Board, Dick Morgan, NAPA vice-president said, "When the performance models are ready for implementation, industry will be ready to use them. In the meanwhile, the Superpave mix design procedures give us a mix design system that should be much more reliable than anything we've had before."
The UM team and the University of California-Berkeley also will work on development of a fundamental strength test to be used in conjunction with the Superpave volumetric mix design procedures. The test, which can determine a mix's susceptibility to rutting, is on a fast track and should be available for widespread use by early 1999.
Useful developments on the horizon
Several projects now in the pipeline will allow us to complete the Superpave system (the expected completion dates are shown in parentheses):
-- Development of an integrated environmental effects and aging model (2000),
-- Completion and verification of an integrated performance prediction model for both new and rehabilitated pavements (2005), and
-- Validation and calibration of the asphalt performance prediction model (2006).
If you haven't yet had any training in the Superpave system, there's no shortage of places to turn. Various levels of training are offered by numerous organizations, including the National Highway Institute, the Superpave regional centers, and others. The upcoming Fifth Annual U.S. Hot-Mix Asphalt Conference and National Superpave Workshop (to be held Oct. 29-31 in Phoenix) will feature a full day of presentations and discussions on the Superpave system.
For more information,contact Gary Henderson at (202) 366-1549 or fax: (202) 366-9981; e-mail: [email protected].