Laboratory Evaluation of Asphalt Binder Rutting, Fracture, and Adhesion Tests
Fujie Zhou, Hongsheng Li, Peiru Chen and Tom Scullion, April 2014
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 softer but highly modified binders. Therefore, it is necessary to improve current asphalt binder performance parameters and associated specification limits, especially for modified binders.
This report documents the laboratory evaluation of several new tests for rutting, fatigue, and adhesion property of asphalt binders, including the multiple stress creep and recovery (MSCR) test, linear amplitude sweep (LAS) test, double edged notched tension (DENT) test, elastic recovery test, pull-off test, pneumatic adhesion tensile testing instrument (PATTI), dynamic mechanical analyzer (DMA) test, and surface energy test. It was found that the MSCR test and associated specification works better than the current G*/sin -based PG specification, especially for those highly modified asphalt binders (such as PG64 34). MSCR round robin results among five laboratories clearly indicated that both Jnr0.1 and Jnr3.2 results are very repeatable and reproducible, but both Jnrdiff and R0.1 have pretty high variability. Since Jnrdiff is one of the parameters for grading asphalt binder, caution should be exercised when applying the MSCR specification. The R3.2 results are acceptable in terms of repeatability and reproducibility. Based on the laboratory test results, users should exercise some caution when grading the slightly modified asphalt binders (such as PG64-28) using the MSCR test and associated specification. This study further confirms the poor relationship between the parameter G*sinδ and the binder fatigue resistance. Neither the MSCR nor the elastic recovery test shows good correlation with the asphalt mix OT cracking test. Both the LAST and the DENT tests provide similar ranking to that of asphalt mix OT cracking test. The DSR-based LAS test is recommended for asphalt binder fracture test, since the DSR has been widely used in the last 20 years. Additionally, only the PATTI test is a promising test for evaluating adhesive properties of asphalt binders. All three other tests (the pull-off test, DMA, and surface energy test) were not successful in this study for evaluating asphalt binder adhesion property.
Obviously, these laboratory findings need further field validation. Additionally, one needs always to keep in mind that the binder alone does not determine field performance of asphalt mixes. Mix characteristics as well as the pavement structure itself, traffic, and the environment within which it is located have a significant role in determining pavement performance.
Keywords: Asphalt Binder, Multiple Stress Creep Recovery Test, Fracture Test, Adhesion Test
ENTIRE REPORT (Adobe Acrobat File – 4.2 MB)