THE OVERLAY TESTER: A SENSITIVITY STUDY TO IMPROVE REPEATABILITY AND MINIMIZE VARIABILITY IN THE TEST RESULTS

Technical Report Documentation Page 1. Report No. FHWA/TX-12/0-6607-1 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle THE OVERLAY TESTER: A SENSITIVITY STUDY TO IMPROVE REPEATABILITY AND MINIMIZE VARIABILITY IN THE TEST RESULTS 5. Report Date Submitted: October 2011 Published: February 2012 6. Performing Organization Code 7. Author(s) Lubinda F. Walubita, Abu N. Faruk, Gautam Das, Hossain A. Tanvir, Jun Zhang, and Tom Scullion 8. Performing Organization Report No. Report 0-6607-1 9. Performing Organization Name and Address Texas Transportation Institute The Texas A&M University System College Station, Texas 77843-3135 10. Work Unit No. (TRAIS) 11. Contract or Grant No. Project 0-6607 12. Sponsoring Agency Name and Address Texas Department of Transportation Research and Technology Implementation Office P. O. Box 5080 Austin, Texas 78763-5080 13. Type of Report and Period Covered Technical Report: September 2009–September 2011 14. Sponsoring Agency Code 15. Supplementary Notes Project performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration. Project Title: Search for a Test for Fracture Potential of Asphalt Mixes URL: http://tti.tamu.edu/documents/0-6607-1.pdf 16. Abstract Hot mix asphalt (HMA) overlay is one of the most commonly used methods for rehabilitating deteriorated pavements. One major type of distress influencing the life of an overlay is reflective cracking. Many departments of transportation have implemented design-level tests to measure the rutting potential of HMA; these are typically wheel- tracking tests. However, currently, there is no national design-level test for measuring resistance to cracking. Currently, the Texas Department of Transportation uses the Overlay Tester (OT) to evaluate the cracking susceptibility of HMA mixes in the laboratory. While, the OT effectively simulates the reflective cracking mechanism of opening and closing of joints and/or cracks, repeatability and variability in the test results have been major areas of concern. In particular, variability in the OT test results poses a problem with most of the conventional dense-graded HMA mixes, such as Type C and D, which is approximately 75 percent of all the HMA used on Texas highways. This laboratory study presents a comprehensive sensitivity evaluation of the critical steps of the OT test procedure in an attempt to optimize the OT repeatability and minimize variability in the test results. In general, the study indicated that the sample drying method, glue quantity, number of sample replicates, air voids, sample age at the time of testing, and temperature variations are some of the key aspects that have a significant impact on the OT test repeatability and variability. Overall, findings from this study indicate that variability in the OT test results can be minimized if these aspects are improved and/or more clearly specified in the OT test procedure (Tex-248-F). 17. Key Words HMA, Cracking, Overlay Tester (OT), Peak Load, OT Cycles, Repeatability, Variability, Coefficient of Variation, Monotonic, Tensile Strength, Tensile Strain, Tensile Modulus, Fracture Energy (FE), FE Index, Pseudo Strain Energy, Air Voids, X-Ray CT 18. Distribution Statement No restrictions. This document is available to the public through NTIS: National Technical Information Service Alexandria, Virginia 22312 http://www.ntis.gov 19. Security Classif.(of this report) Unclassified 20. Security Classif.(of this page) Unclassified 21. No. of Pages 154 22. Price Form DOT F 1700.7 (8-72) Reproduction of completed page authorize

THE OVERLAY TESTER: A SENSITIVITY STUDY TO IMPROVE REPEATABILITY AND MINIMIZE VARIABILITY IN THE TEST RESULTS

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