High Temperature Performance Grading of Asphalts through a Specification Criterion that Could Capture Field Performance

Since the realization that the Superpave specification parameter |\iE*|/sin δ is not adequate in rating polymer-modified binders for high temperature performance grading of paving asphalts, researchers have been seeking ways to refine this parameter to make it more sensitive to pavement performance and also find other possible parameters that may better relate to rutting resistance. Most of these efforts have led to positive results in the right direction, but each has its own set of limitations that is preventing immediate implementation of the suggested ideas. From among the various suggestions, the one that has the highest merit for possible use is the refinement of the Superpave specification parameter, namely, the term |\iE*|/(1—(1/tan δ sin δ)) that evolved through a theoretical derivation based on fundamental concepts. This performance-based specification term was shown to be more sensitive to the variations in the phase angle δ than the original Superpave specification parameter and thus described the unrecovered strain in the binders more accurately. Though this refinement led to better discrimination between rutting resistance of various asphalts, not all asphalts with the same performance-grade based on the new parameter behaved identically in their rutting performance in laboratory mixture test evaluations. By model fitting the master curve formed from |\iE*|/(1—(1/tan δ sin δ)) versus frequency data at various temperatures for each binder, a rut-controlling term was extracted that correctly graded the binders in terms of the mixture performance. However, this approach is not appropriate for routine use as it requires large sets of data generation at various temperatures to form the master curve before determination of the model parameters for the rut-controlling term. The present work proposes an alternative method of using the term |\iE*|/(1—(1/tan δ sin δ )) such that it can be easily adopted as a high temperature performance grading specification for asphalts and evaluates its efficacy through actual field performance data.