Balanced Mix Design for Surface Asphalt Mixtures: Phase I: Initial Roadmap Development and Specification Verification

About the report:

The Virginia Department of Transportation (VDOT), as with many owner agencies, is interested in ways to facilitate the increased durability of asphalt mixtures in an effort to make its roadway network more sustainable, longer lasting, and more economical.  The balanced mix design (BMD) method addresses this through the incorporation of performance criteria into mix design and acceptance.  VDOT has committed to the implementation of the BMD method in an effort to improve asphalt mixture performance. 

The purpose of this study was to continue advancing efforts toward VDOT’s implementation of BMD by developing a performance-based mix design roadmap for application in Virginia.  The proposed roadmap was developed to provide guidance on the specific needs and activities necessary for VDOT to adopt the BMD concept.  A specific need outlined in the roadmap was to validate and/or refine the selected initial performance tests and associated test threshold criteria. To accomplish this, 13 asphalt mixtures were evaluated using performance-measuring laboratory tests. The results of these tests were used to assess the initial performance tests and test threshold criteria selected for BMD use.

The proposed roadmap is intended to be an evolving resource for outlining the agenda of activities necessary for implementation of BMD.  The roadmap identified specific needs addressed in this study.  Based on the results for the mixtures evaluated as part of those needs, the Asphalt Pavement Analyzer (APA) rut test(hereinafter “APA test”); indirect tensile cracking test (IDT-CT) (hereinafter “IDT-CT test”); and Cantabro mass loss test (hereinafter “Cantabro test”) are suitable for continued use in BMD.  The current threshold criteria for all three tests were reasonable, based on additional testing and analysis. 

The study recommends that the roadmap for BMD continue to be refined to provide a clear direction of the activities necessary for implementation and serve as a resource to evaluate progress.  VDOT should continue to use the APA, IDT-CT, and Cantabro tests for BMD.  The APA and IDT-CT test results should be compared and correlated with those of fundamental rutting and cracking tests, respectively, and with performance predictions obtained from mechanistic-empirical pavement design simulations and field performance for full assurance that test threshold values are appropriate.  In addition, the differences in test results attributable to mixture reheating and different specimen types, such as laboratory-compacted specimens and field cores, should be addressed.  The study further recommends evaluating the Cantabro, IDT-CT, and APA test results to determine acceptable variability and establish precision statements.

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