Working with researchers at the National Center for Asphalt Technology (NCAT), rheology specialists from Malvern Panalytical have played a pivotal role in the development of new test standards for the asphalt paving industry. As a result of the project, two new laboratory tests have been proposed for the characterization of modern polymer modified asphalt binders, for which conventional test methods are inadequate. These tests will be submitted to American Association of State Highway and Transportation Officials (AASHTO) for review and approval.
"Growth in the use of polymer modified binders has intensified the need for more appropriate testing, prompting the National Cooperative Highway Research Programme (NCHRP) to initiate this project," remarks Dr. Randy West, director of NCAT. "Malvern Panalytical's support for the work has been exemplary throughout, most especially in the development of a new oscillatory test method which was very much a product of their expertise. The new tests meet a key industry need for a simple method to determine appropriate mixing and compaction temperatures for these industrially important materials."
Polymer modified binders confer superior permanent deformation and fatigue resistance relative to conventional asphalt binders, and now have significant market share. Within the laboratory, rheological tests are used to determine optimum mixing and compaction temperatures. If mixing temperatures are too high then the product can be degraded and will likely result in emission problems at the plant and paving site; too low and the homogeneity of the mix is compromised. Compaction temperatures are important in the laboratory for fabricating paving mixture test specimens for mix design and quality control. Existing characterization techniques, used for decades with conventional asphalt, are ill-suited to newer polymer modified binders.
One of the new rheological tests is performed in oscillatory shear mode. Fast, easy to perform and well-suited to the QC environment, it has already been successfully adopted by a number of state agencies. The other new test is performed in steady shear flow mode. Both methods can be carried out on most rotational rheometers used for grading binder in the Superpave system.