As the highway community implements the Strategic Highway Research Program (SHRP) Superpave technology, they are finding it has tremendous potential to reduce asphalt pavement rutting and thermal cracking. The use of the Superpave process and technology is rapidly growing with many projects planned for the 1997 construction season and beyond. Virtually all States are in some phase of designing and/or constructing Superpave projects. While some States are still experimenting with one or two projects, others have completed many projects and the Superpave technology is set to become their standard asphalt paving method.
As with any new technology during the implementation phase, fine-tuning the technical elements and results demands constant attention and technical evaluation. During this phase it is critical to be technically informed. As such, we are finding that misinformation and resultant misunderstandings are occurring in the Superpave program. Three current Superpave implementation areas that fit this category are constructability issues, the performance prediction models and Westrack.
Concerning constructability, some typical asphalt paving construction troubleshooting areas are being used by some as an opportunity to question the Superpave technology. Experience has shown that once the construction processes are properly analyzed, successful operations and products have resulted. Just one example is the type and size of compaction equipment. Some States are finding that pneumatic rollers tend to pick up some Superpave mixes and steel-wheeled rollers work better. Also, a heavier initial breakdown roller needs to be right behind the paver in order to assist in achieving compaction.
The fact that compaction was not achieved on some projects using standard rolling operations and equipment used for Marshall designed mixes does not justify questioning the Superpave technology. As with any asphalt paving project, proper operations will have to be determined for a quality product - many times on a project-by-project basis depending on local materials and conditions.
Concerning the performance prediction models, the Federal Highway Administration (FHWA) made a significant decision recently related to this Superpave process element. The "Superpave Models Update," March 27, 1997, memorandum from the FHWA Superpave Technology Delivery Team Leader provides a detailed overview of the decisions related to the performance prediction models' contract and development. Basically, more research is necessary to perfect this prediction process.
The decision that further research is needed on the performance prediction models has caused some confusion about the validity of the other elements of the Superpave process, i.e., the performance-graded binder specifications and the volumetric mix design using the gyratory compactor. The models decision does not impede the use or technology advancement of the binder specifications nor the volumetric mix design procedure using the gyratory compactor. When the prediction models are developed, they will give designers information to optimize binder and mix design characteristics for addressing rutting and thermal cracking. The FHWA and the Asphalt Technical Working Group remain committed to the implementation of performance-graded binder specifications in 1997 and the volumetric mix design procedure using the gyratory compactor by 2000. All of these items may be individual elements of the Superpave process; however, maximum benefits can be achieved when all three elements are used together.
Concerning Westrack, some people have been alarmed in that some test sections are failing. Actually, several test sections were designed to fail or to confirm known under designed strategies. The mixes at Westrack were specifically designed to duplicate construction errors such as high asphalt content and wide variations in gradation. The evaluation of these mix characteristics have proven that their detrimental effect on performance is significant. Some people also think that Westrack is strictly a Superpave facility. In reality, Westrack is a facility whose primary objective is to test and evaluate performance-related specifications. Some mixes using Superpave technology were used in this research effort.The FHWA is committed to achieving the Superpave implementation goals and perfecting each element in concert with our partners. As we proceed, the need for each of us to properly understand and disseminate accurate information is crucial. To accomplish this, we urge FHWA engineers and representatives, along with our highway community partners, to participate in activities such as asphalt user-producer groups, the Superpave regional centers, the Lead States program, technical and expert task groups and other Superpave-related activities. One such activity is to review actual Superpave construction projects to understand and accurately share local successes and issues. Through these mechanisms we all can address the technical aspects on a level playing field to advance and modify, where necessary, the Superpave process. By keeping the implementation phase in this context, we can realize the full potential of the SHRP Superpave technology.
For more information, Mr. Steinke can be reached at 202-366-0392.
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