This extensive research was conducted to evaluate performance-based asphalt mixture design concepts for the New Jersey Department of Transportation (NJDOT). NJDOT has used performance-based design procedures for their “specialty” asphalt mixtures since 2006. However, performance criteria had not yet been developed for NJDOT’s “conventional” asphalt mixtures, which include dense-graded, stone matrix asphalt (SMA) and open-graded friction course (OGFC) mixtures.

The study also looked at the proposed method of “Balanced Mixture Design,” which does not use air voids as the determinate for optimum asphalt content. Instead, the procedure determines the range of asphalt contents where both rutting and fatigue-cracking performance is satisfied and recommends the middle of that range as the optimum.

Lastly, the study evaluated the Overlay Tester equipment from a second manufacturer, Troxler Electronics, and how well this new unit compared to the original device manufactured by Shedworks, Inc. A mini round robin study compared the two pieces of equipment and a brief statistical analysis conducted that compared the test data.

The research study resulted in proposed performance-based criteria for “conventional” asphalt mixtures that are sensitive to both traffic level and location in the pavement (surface, intermediate, or base). The criteria also maintain consistency in test procedures and limits with other performance-based asphalt mixtures in New Jersey. The “Balanced Mixture Design” methodology indicated that NJDOT’s dense-graded asphalt mixtures fatigue life would greatly benefit from a one percent increase in VMA, while resulting in very little decrease in rutting resistance.

Upon review of the Troxler Electronics Overlay Tester and comparing it to the Shedworks device through round robin studies confirmed that the Troxler device could be utilized to determine the fatigue life of asphalt mixtures in accordance with the NJDOT B-10 test procedure.

After evaluation, the unit was delivered to NJDOT, where the researchers held a two-day training course to familiarize NJDOT engineers with the required sample preparation, testing, and data analysis.