Evaluation of New Dynamic Shear Rheometer Testing Geometry for Performance Testing of Crumb Rubber–Modified Binder

Crumb rubber modifier (CRM) has been used for many years in asphalt binder to provide improved field performance. Historically the increase in viscosity of CRM binder was measured with crude vane viscometers to quantify binder performance characteristics. The Superpave ® system introduced far more accurate tools in the asphalt binder testing system to measure performance characteristics. As a result of testing geometry limitations, Superpave binder tests, specifically high-temperature testing, have generally not been applicable in testing CRM binders. This inability to test the material fully has limited the use and adoption of CRM binders. Well-known geometries in the rheology field, specifically coaxial cylinder geometries or cup and bob, can handle the larger particle sizes typically used as CRM. However, these geometries are not familiar in the asphalt industry. This study investigated the ability of the cup-and-bob geometry to test neat, polymer-modified, and CRM binders to determine if it could provide similar rheological results for both Superpave and multiple stress creep recovery (MSCR) testing. It concluded that the cup-and-bob geometry could accommodate large CRM particles and provide similar results for Superpave as well as MSCR testing.