Overlay Tester Results from Dense-Graded Asphalt Concrete Mixes: Accuracy in Characterizing Crack Susceptibility

Abstract

Several highway agencies have either implemented or considered implementing laboratory performance tests to estimate the cracking potential of asphalt concrete (AC) mixes during the mix design process. One such popular test, the overlay tester (OT), measures the number of cycles to failure of specimens that are caused by the repeated application of deformation. The major concern about using this test as a reliable characterization of the cracking susceptibility of AC mixes, especially for dense-graded mixtures, is the variability in the specified number of cycles to failure in the performance index. The main objective of this paper is to report a means for improving the consistency of the OT test results on dense-graded AC mixes. An assessment of a specimen preparation process that can yield more consistent results was conducted. The consistency of the traditional number of cycles to failure as well as of the load–displacement response and load reduction curves was investigated by using a modified specimen preparation process. The repeatability of alternative performance indexes, such as the critical fracture energy and crack progression rate, that can be measured from the OT test was also investigated and compared with that of the index for the number of cycles to failure. This study indicated that the raw data from the OT test seemed to be repeatable if the proposed specimen preparation process was consistently followed. Alternative performance indexes that yielded an acceptable degree of repeatability may be readily implemented in the OT test to assess the cracking characteristics of AC mixes.