VAA, VDOT, NCAT bring balanced mix design to Virginia

Virginia continues to be a leader in the implementation of Balanced Mix Design. Recently VAA and VDOT held companion workshops on the topic of Balanced Mix Design (BMD). These workshops provided an opportunity for both decision-makers and practitioners to become more knowledgeable and engaged in this new method for designing and accepting asphalt mixtures. The first workshop was held on October 29 and was sponsored by VDOT. Titled the “Regional Balanced Mix Design Workshop” and tailored to be somewhat Virginia specific, Dr. Randy West, P.E. and Dr. Fan Yin, P.E. from the National Center for Asphalt Technology (NCAT) facilitated the one-day event. The primary objective was to share current information on Balanced Mix Design that will help stakeholders move forward with implementation. Areas discussed included the limitations of the present Superpave™ mix design method and why volumetric based mix design alone does not necessarily tell us anything about the quality of the binder or the interactions of the different binder components and additives (such as rejuvenators).

Immediately following this event, VAA sponsored two, one-day, Balanced Mix Design Demonstration Workshops. This workshop was designed to provide asphalt quality control practitioners direct exposure to the specific tests Virginia is piloting for Balanced Mix Design. Adam Taylor and Nathan Moore, both Assistant Research Engineers for NCAT, provided a very informative overview and discussion about the evolution and development of the various performance tests being evaluated for BMD. They also discussed the benefits and drawbacks of each test and why Virginia has focused on three specific tests for its pilot/research effort. One participant summed it up well: “Both Adam and Nathan knew what they were talking about… Not from a book sense, but real hands-on information.” Equipment suppliers from Pavement Technology, Inc., Troxler Electronic Laboratories, Inc., Humboldt Mfg. Co., and Gordon Technical Sales & Service provided the equipment for the demonstration portion of the workshop. This allowed participants the opportunity to see each piece of equipment in action.

For 2020, the pilot/research effort continues. Now that they have the background knowledge and exposure, many producers and contractors are expressing the desire to get more involved in the pilot effort. Another workshop participant said, “I think that it is a good idea but needs more time to understand the small things that can change the way mixes react to this kind of testing.” This is a critical step to the success of the evolutionary process toward performance-based asphalt mix design.

The journey towards performance-based mix design was summed up well in this statement, “I’m biased, but think it will provide a way to have better-performing mixes by allowing different approaches and materials that current specs can’t handle. I think it will allow each producer to optimize its materials for efficiencies that can’t be done under current specs. It may not be for every job, but for important routes, the effort involved should be well spent.”