IMPLICATIONS OF THE NEW LOW TEMPERATURE SPECIFICATION ON PG GRADING AND TESTING OF ASPHALT BINDERS

In this paper the effect of using various values of damage transfer functions (PC) on the low-temperature binder grades of "conventional unmodified" binders is discussed. The criteria developed to define a "conventional unmodified" binder is also explained. Using the PC value, the new specification was evaluated to determine the effect of various modification methods on the low temperature grading (Tcr). Generally it was observed that polymer modified asphalt exhibited higher fracture strengths, which resulted in improved Tcr. Whereas, excessive blowing and some unconventional modification techniques resulted in increased (warmer) values of Tcr. In practice, it was found that stiffness modification (i.e., reducing the base asphalt stiffness) may have a more significant effect on Tcr than strength modification. For practical purposes, it is critical that the testing and predictions of Tcr exhibit good reproducibility. To determine the precision of the new low-temperature grading procedure, a group of nine experienced laboratories participated in a round robin. Results indicate that the reproducibility of Tcr determined with the new specification was equal to or better than the current practice of using the S(60) and the m-value from the BBR. It was also observed that the BBR appears to control the precision and that the reproducibility of fracture strength does not significantly affect reproducibility Tcr determined using the new procedure. Polymer modified asphalt binders (PMAs) appear to be more reproducible than conventional binders of comparable stiffness. For the covering abstract see ITRD E107185.