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Overlay Tester: A Rapid Performance Related Crack Resistance Test

The focus of many asphalt mixture design procedures over the past 10 years has led to the development of stiffer, drier mixtures. However, these mixes are more difficult to construct and are potentially more prone to reflective cracking. In this research the upgraded overlay tester is introduced and proposed as a simple performance test on reflective cracking. The overlay tester can be run on standard size samples, typically 6 in. (150 mm) long by 3 in. (75 mm) wide by 1.5 in. (38 mm) high. These specimens can be prepared from either field cores or from Superpave Gyratory Compactor (SGC) molded specimens. The test is rapid and repeatable, and poor samples fail in minutes. It characterizes both crack initiation and crack propagation properties of asphalt mixtures. Based on repeatability study results, three replicates are recommended for the overlay tester. Sensitivity studies indicate that the overlay tester provides reasonable test results. Increasing asphalt content will significantly improve the reflective cracking resistance of asphalt mixtures. In a series of tests on Texas mixtures, it was determined that aggregate absorption has a major impact on the performance of specimens in the overlay tester. This topic has not received much attention recently but it obviously needs to be investigated. In the lab these highly absorptive aggregates did not severely impact the rutting performance but they had a major impact on cracking life. The effectiveness of the overlay tester was validated by five case studies in Texas. The overlay tester results all correlated well with the field performance. Furthermore, the overlay tester results have good correlations with beam fatigue test results and low temperature performance of asphalt mixtures in the field. A preliminary framework of asphalt overlay mixture designs and associated criteria have been proposed. Based on the framework, two examples of asphalt overlay mixture designs are presented in this report. This framework and the associated criteria are preliminary and they will need further refinement. Finally, a brand new overlay tester has been manufactured and delivered to the Texas Department of Transportation's central lab at the Cedar Park office. In addition, training for the operation and analysis has been provided.