Laboratory Evaluation of Asphalt Binder Rutting, Fracture, and Adhesion Tests: Fid-Bau Portal

Laboratory Evaluation of Asphalt Binder Rutting, Fracture, and Adhesion Tests

F Zhou / H Li / P Chen / T Scullion

The current performance grading (PG) specification for asphalt binders was developed based on the Strategic Highway Research Program (SHRP) and is based primarily on the study of unmodified asphalt binders. Over the years, experience has proven that the PG grading system, while good for ensuring overall quality, fails in some cases to predict rutting and cracking performance, particularly as it applies to modified binders (such as those with polymers or other types of modifiers). Specifically, recent studies on mixes from out of state (Minnesota) found that the mixes from Minnesota's Cold Weather Road Research Facility (MnRoad) have substantially improved cold weather cracking properties than mixes currently used in Texas. while these mixes still pass Hamburg rutting requirements, in spite of the binders being much softer, according to typical PG measurement, than would be used on Texas roads, according to typical PG measurement. To eliminate this type of apparent discrepancy on softer but highly modified binders, a new Multiple Stress Creep and Recovery (MSCR) test-based specification was proposed and has been adopted by the American Association of State Highway and Transportation Officials (AASHTO). It is believed that using the MSCR test which directly measures the permanent deformation properties of asphalt binder and the new specification, softer but highly modified binders will be allowed. However, these claims have not been verified with tests on Texas mixtures. Additionally, another weakness of the PG grading system is that it has no test method or criteria to screen out the premature adhesive or moisture damage failures of asphalt binder-aggregates. Therefore, it is necessary to improve current asphalt binder performance parameters and associated specification limits, especially for modified binders. Specifically, the major objectives of research project 0-6674 are: (1) Determine if the new AASHTO MSCR-based binder grading system is superior to the current TxDOT system. (2) Identify/develop a simple test method or methods to characterize fracture and adhesive properties of modified and unmodified asphalt binders and associated tentative specification limits. (3) Determine if asphalt binders not currently used in Texas would potentially improve overlay performance and conduct an associated cost-benefit analysis. (4) Identify optimal asphalt binder/aggregate combinations for different environmental zones in Texas. (5) Develop and initially populate a catalogue of all these measured (binder, binder/fine aggregate mastic, and asphalt mix) properties with relevant information that can be used to track the field performance of pavements constructed using these asphalt binders. This report documents the laboratory work focused on part of the first two objectives.