Virginia’s 2024 Implementation of Balanced Mix Design

About the report:

The Virginia Department of Transportation (VDOT) implemented balanced mix design (BMD) performance testing for asphalt mixture design and production in the 2024 paving season. The BMD approach seeks to achieve asphalt mixtures that have properties to resist both cracking and rutting distresses and to increase durability. This implementation of BMD follows years of research and trial projects evaluating the performance test procedures and thresholds. This study documents BMD implementation in Virginia to capture lessons learned after producing approximately 2 million tons of BMD-designed mixtures in 2024.

The BMD implementation was reviewed through data from contract locations, bid prices, performance test results, field density, mixture comparison to previous years, and a survey of stakeholders involved with BMD mixtures.

Collection of project information was challenging because the information was kept in disparate locations in different divisions within the agency. Given the concern for cracking performance, it was encouraging to see that BMD mixtures had slightly higher asphalt content than previous Superpave designs. BMD type D mixtures showed lower production air voids. Voids filled with asphalt values, especially for 12.5 mm mixtures, were found to be increasing toward the upper production limit as mixtures evolve to meet BMD cracking requirements. VDOT and producer performance results distributions aligned well for Cantabro and indirect tensile cracking tests, with indirect tensile cracking test results largely greater than the threshold limits, indicating improvements in cracking resistance. VDOT showed better results overall for indirect tensile at high temperature testing, and more producer labs indicated an issue with the indirect tensile at high temperature testing. BMD production samples consistently met all performance testing thresholds. In addition, BMD mixtures showed no overall change in field density. Finally, the survey provided a range of positive and negative feedback regarding the testing in 2024.

Based on the information collected, it is recommended that increasing the indirect tensile cracking test production threshold, allowing reduced frequency of production performance testing, and adjusting voids filled with asphalt requirements for BMD should be considered. Training on the indirect tensile at high temperature test should be continued because the test is still relatively new, and some technicians have experienced issues running the test. Finally, based on data collection challenges during the study, it is recommended that improved alignment of data sources and systems be pursued such that data can be easily accessed and compiled to allow for continued performance monitoring and fully informed maintenance decisions.

Supplemental materials can be found at https://library.vdot.virginia.gov/vtrc/supplements

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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