United States Department of Transportation
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The Overlay Tester (OT): Comparison with Other Crack Test Methods and Recommendations for Surrogate Crack Tests [and supporting files]
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2012-10-01
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[PDF-7.78 MB]
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and Performance;NTL-HIGHWAY/ROAD TRANSPORTATION-Construction and Maintenance;
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Abstract:Presently, one of the principal performance concerns of hot-mix asphalt (HMA) pavements is premature cracking, particularly of HMA surfacing mixes. Regrettably, however, while many USA transportation agencies have implemented design-level tests to measure the rutting potential of HMA mixes; there is hardly any standardized national design-level test for measuring and characterizing the HMA cracking resistance potential. Currently, the Texas Department of Transportation (TxDOT) uses the Overlay Tester (OT) to routinely 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. As an effort towards addressing these repeatability/variability issues, this laboratory study was undertaken, namely to: 1) conduct a comprehensive sensitivity evaluation of the OT test procedure so as to improve its repeatability and minimize variability in the OT test results; 2) recommend updates and modifications to the Tex-248-F specification including development of OT calibration and service maintenance manuals; 3) explore other alternative OT data analysis methods; 4) comparatively evaluate and explore other crack test methods (both in monotonic and dynamic loading modes) that could serve as supplementary and/or surrogate tests to the OT test method; and 5) develop new crack test procedures, specifications, and technical implementation recommendations. As documented in this report, the scope of work to accomplish these objectives included evaluating the following crack test methods: 1) the standard repeated (OTR, Tex-248-F) and monotonic loading OT test (OTM); 2) the monotonic (IDT) and repeated loading indirect-tension (R-IDT) test; 3) the monotonic (SCB) and repeated loading semi-circular bending (R-SCB) test; 4) the disk-shaped compaction tension test (DSCTT); and 5) the monotonic (DT) and repeated loading direct-tension (R-DT) tests.
The supporting files in the Zip include: close out meeting slides, Texas OT test procedures, an OT calibration manual, spreadsheet macros, and video files.
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