Evaluation of rheological performance and moisture susceptibility of polyphosphoric acid modified asphalt binders

The effects of modification of asphalt binders with polyphosphoric acid (PPA) were evaluated in this study. Mechanistic performance was evaluated by examining the stiffness, rutting, and fatigue properties of two selected binders modified with different dosages of PPA. A surface science approach, namely the surface free energy (SFE) technique as employed to evaluate moisture susceptibility of different PPA-modified asphalt binder and aggregate systems. Since PPA is a hydrophilic material, two different crude oil originated PPA modified binders with selected liquid antistripping agents (LAAs) were evaluated. Binders modified with PPA and Styrene-Butadiene-Styrene (SBS) were also included in the test plan to observe their performance with a simultaneous presence of acid and polymer. Laboratory test results reveal that SBS-modified binders are more rutting resistant than the corresponding PPA-modified binders. The effects of LAA are contingent upon the crude origin of the asphalt binder. Furthermore, PPA did not show any negative effects on fatigue behaviour of long-term aged asphalt binders. From the SFE analysis it was concurred that PPA-modified binders could be more susceptible to moisture damage than the corresponding SBS-modified binders. Higher amount of PPA made asphalt binders more susceptible to moisture damage than lower amounts. Furthermore, Fourier Transform Infrared Spectroscopy (FTIR) spectra revealed no changes in the functional groups due to the addition of PPA. The outcome of this study is expected to help Arkansas Department of Transportation (ArDOT) and other agencies in revising their quality control guidelines for possible inclusion of PPA as an approved modifier for asphalt binders.