On the use of empirical phase angle limits for the grading of asphalt binder

In recent years, Ontario paving contracts have specified asphalt binders based on limits for: (1) critical crack tip opening displacements (CTOD) obtained in the double-edge-notched tension (DENT) test, (2) limiting low temperature performance grades (LLTPG) obtained in the extended bending beam rheometer test (EBBR), and (3) EBBR grade losses, in addition to (4) regular American Association of State and Highway Transportation Officials (AASHTO) M320 criteria. While the enhanced performance measures are expected to provide significant improvements in pavement performance, both DENT and EBBR protocols are cumbersome. A total of 371 sets of binder test results are used to assess if CTOD, EBBR LLTPG and grade losses can be replaced with limiting phase angle temperatures T30??? and T45???, in an effort to make the binder specification more practical. The CTOD, LLTPG and grade loss correlate strongly with phase angle but variation for softer grades were found to be significant, which likely relates to differences in aging mechanisms in the laboratory and service (chemistry and/or thermal history, exudation of oils). A phase angle specification for the control of pavement cracking deserves further consideration for its accuracy, sensitivity, precision and thus usefulness.

Automated summary

In recent years, Ontario's paving contracts have specified higher standards for asphalt binders, including requirements for CTOD, LLTPG values, in hopes of improving pavement performance. The study found that phase angle can replace CTOD, EBBR LLTPG, and grade losses, with significant variations for softer grades, warranting further consideration of phase angle specifications.