Validation of empirical changes to asphalt specifications based on phase angle and relaxation properties using data from a northern Ontario, Canada pavement trial

Abstract

Polymer modified asphalt is generally accepted to provide positive benefit/cost outcomes in terms of extending pavement service life. It has recently been claimed that higher modification levels perform better. A 13-year-old pavement trial in Ontario, Canada is providing valuable insights on this issue. Dynamic shear rheometer (DSR) tests were conducted to monitor rheological changes upon oxidative aging. Gelled binders exhibit more solid-like response leading to less ability to relax thermal stress, and hence an accelerated decay in performance. This was further verified from relaxation spectra calculated from stress relaxation data. A test section constructed with a gel-type binder containing 7 % styrene-butadiene-styrene (SBS) modifier has a predicted service life of 23 years, nearly the same as the control which was tainted with recycled engine oil bottoms (REOB). In contrast, sol-type 3.5 % SBS modified binder and straight-run Cold Lake asphalt binder are expected to last around 60 % longer at 36 and 38 years, respectively. Conclusions from this study reiterate that current specifications fail to correlate with field performance. Improved binder grading is possible by limiting the slope of the phase angle master curve between 30° and 45°.