Proposed Improvements to Overlay Test for Determining Cracking Resistance of Asphalt Mixtures

Abstract

There is an increasing need in evaluating the cracking resistance of asphalt mixtures with high recycled contents. 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. Specimens for this test can be prepared from laboratory-compacted specimens or field cores. This test can be conducted more quickly than other performance tests, and the data analysis is relatively simple. A study is underway at the National Center for Asphalt Technology (NCAT) to evaluate the overlay test conducted in the Asphalt Mixture Performance Tester (AMPT) for evaluating the asphalt mixture resistance to cracking. The purpose of this paper is to present a new method for determining the failure point (or the number of cycles to failure) and a higher test frequency for conducting the overlay test in the future. The study included five mixtures used in the bottom asphalt layers of the five test sections of the Group Experiment in the 2009 research cycle of the NCAT Pavement Test Track. The evaluation results showed that the alternative method proposed in this paper could better define the moment of failure in the overlay test, and therefore, more accurately determine the number of cycles to failure. It also showed that the overlay test could be conducted at 1 Hz instead of 0.1 Hz to reduce testing time without affecting the test results (and test variability at certain maximum opening displacement levels).