Evaluation of Interchangeability of Commercially Available Overlay Tester Devices

Several research and state highway agencies are using or considering to use the overlay tester (OT) test for assessing the cracking potential of asphalt concrete (AC) mixtures for flexible pavements. Although the OT test simulates effectively the cracking mechanism on AC specimens, the variability of the results from the same OT device, or the interchangeably of the results from different OT devices has been a challenge, especially for dense-graded mixtures. This paper reports on a comparative evaluation of the test results from three available OT devices. The repeatability and reproducibility of the testing mechanism of the three devices were first evaluated utilizing synthetic specimens with mechanical properties similar to typical AC mixtures. A typical dense- graded mixture with a 12.5 mm nominal maximum aggregate size was also used for this purpose. Eight specimens were tested on each device. Apart from the number of cycles to failure, the results were assessed with an alternative analysis methodology that specifies the critical fracture energy (CFE) and crack progression rate (CPR) as performance indices. The variability of the results from each individual OT device improved when the proposed parameters were used to analyze the test results. The reproducibility of the test results was acceptable among the three different devices. The paper concludes with practical recommendations to ensure that the OT test results from different devices are repeatable and reproducible.