Evaluation of the Influence of Production Tolerance Limits on Virginia Balanced Mixtures

The Virginia Department of Transportation (VDOT) is implementing balanced mixture design (BMD) to increase the longevity and durability of asphalt pavement structures. As of the time of publication VDOT has a design specification to balance common modes of pavement distress including durability issues, rutting, cracking, and stripping. This is achieved by assessing asphalt mixture performance through testing with the Cantabro mass loss test, asphalt pavement analyzer rut depth, and indirect tensile cracking test. The next step in the implementation process is to develop a quality assurance program to ensure that balanced mixtures in the laboratory remain balanced during production. The objective of this study was to evaluate the influence of current production tolerance limits for gradation and binder content on BMD performance tests results to determine if mixtures balanced in design can become unbalanced during production through plant and material variability. To simulate production variability, 14 mixture designs were altered to produce a coarse and fine gradation and high and low binder content based on current allowable tolerance limits and tested for performance. For most Virginia mixtures evaluated, it was determined that designs could become unbalanced during production. All the performance tests were sensitive to changes in asphalt content, while the Cantabro was also sensitive to a coarse gradation, and the APA was sensitive to a fine gradation. Results from this analysis are specific to the State of Virginia; however, the methodology of evaluating production tolerance limits is transferable to other agencies interested in assessing performance during production.