Proposed Improvements to Overlay Test for Determining Cracking Resistance of Asphalt Mixtures
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There is an increasing need in evaluating the cracking resistance of asphalt mixtures as more recycled materials are used in the mixes. A promising method that has been used to evaluate the mixture cracking resistance is the overlay test conducted in accordance with the Texas Department of Transportation procedure (Tex-248-F). This test can be conducted on specimens prepared from gyratory-compacted samples or from field cores. It can be conducted in an Overlay Tester or in the Asphalt Pavement Performance Tester (AMPT) with an Overlay Test Kit. The overall objective of this thesis is to evaluate and refine the overlay test conducted in the AMPT for determining the cracking resistance of asphalt mixtures. The evaluation was conducted using five plant-produced mixtures that were used in the bottom asphalt layers of five test sections at the NCAT Pavement Test Track. Key findings of this study include (1) a modified method for better determining the number of cycles to failure (i.e., the failure point) and (2) a higher test frequency (1.0 Hz) for reducing the testing time without significantly affecting the test result and its variability. Furthermore, the overlay test results were compared with those of the bending beam fatigue (BBF) test. Good correlation was found between the overlay test results and the BBF test results determined at 800 and 400 µԑ.