Simple and Practical Tests for Rutting Evaluation of Asphalt Mixtures in the Balanced Mix Design Process

About the report:

The Virginia Department of Transportation (VDOT) is currently using the asphalt pavement analyzer (APA) as a testing tool to screen the rutting potential of asphalt mixtures as part of its balanced mix design (BMD) method. However, the cost and availability of APA equipment in VDOT and contractor laboratories and the speed of testing are main barriers to the routine use of APA in the BMD process, especially during the production of asphalt mixtures.  The existence of alternative tests that are simple, practical, and performance indicative can help facilitate the implementation of BMD into practice.  The monotonic loading tests (hereinafter“ monotonic tests”) have been proposed to address the need for simpler tests.

This study was undertaken to assess the feasibility of using monotonic tests as a screening tool to evaluate the rutting potential of dense-graded asphalt surface mixtures as part of the BMD initiative in Virginia.  In this effort, three monotonic tests, the indirect tensile at high temperature (IDT-HT) test, rapid rutting (RR) test, and Marshall stability and flow (MS) test, identified from the literature, were evaluated using 17 plant-produced asphalt mixtures with “A” and “D” designations.  The results were used to assess the monotonic tests and the APA test relative to each other through several performance metrics and correlations with fundamental rutting tests and mechanistic-empirical–based simulations. The results were also used to develop performance threshold criteria for the considered tests. 

The results showed that the IDT-HT and RR tests can be used to screen the rutting potential of asphalt mixtures meeting VDOT mixture volumetric and gradation requirements for the A and D mixtures.  The initial performance criteria for the IDT-HT and RR tests were established for these mixtures.  Based on the results, the IDT-HT test was found to be the most suitable alternative test to the APA test. 

The study recommends using the IDT-HT test as part of the BMD initiative with a corresponding minimum strength of 133 kPa as a performance criterion based on the testing conditions used in this study. Implementation of traffic-based performance criteria for the A and D mixtures should be explored, as the current practice does not differentiate the performance between these mixtures.  The results of the IDT-HT, RR, and the APA tests should be compared and correlated with those from fundamental rutting tests and with performance predictions obtained from mechanistic-empirical pavement design simulations using a larger number of mixtures to verify the findings of this study. In addition, the results should be compared to field performance results for full assurance that the implemented tests and associated threshold values are appropriate.  Fine-tuning the testing process for the IDT-HT, RR, and APA tests and establishing precision estimates and statements are necessary for proper quality assurance practices.  The study further recommends hands-on training and demonstration of the tests being considered by VDOT as part of the BMD implementation.

Authors