Examining Different Alternatives to Delta Tc (ΔT_c) as a Parameter to Screen Asphalt Binders

The Superpave performance grading (or PG) framework or a variation of this framework is often used as a purchase specification in the United States and as a tool to evaluate the expected performance of modified and unmodified asphalt binders in many countries around the world. During the last decade and in response to changes in the use of modified binders and extenders, several modifications and improvements have been proposed and implemented to improve this framework. One such modification is the use of the ΔT_c parameter, which is based on the stiffness and m-value of an asphalt binder measured at low temperatures, as a metric to screen asphalt binders that contain higher concentrations of potentially deleterious refining products or as an indicator for susceptibility to premature cracking. The estimation of this parameter requires the determination of the true low temperature grade of the asphalt binder based on measurements carried out using a bending beam rheometer at multiple temperatures. This study explores the expected variability associated with the determination of this parameter as well as alternative metrics that can be more easily used on a routine basis as a quality control tool to screen binders with a low ΔT_c value. Based on the evaluation of nearly 200 binders from several different suppliers in and around the state of Texas, this study shows that a combined use of stiffness and m-value measured at the low grade test temperature of the asphalt binder can be used as an effective specification/screening tool to detect binders that result in a very low value of ΔT_c.