Rutting Performance of PPA-Modified Binders Using Multiple Stress Creep and Recovery (MSCR) Test

In this study, the effect of modifying an asphalt binder using Polyphosphoric Acid (PPA) on its rutting performance was studied using the Multiple Stress Creep and Recovery (MSCR) test. The MSCR test provided the non-recoverable creep compliance and percent recovery of the tested binder blends at the test temperature(s). Those parameters were then used to evaluate the stress sensitivity and rutting potential of the PPA-modified binders and were utilized to determine the binder grade based on the level of traffic. For this purpose, a PG 58-28 binder was blended with different amounts of PPA, namely 0, 0.5, 1.0, 1.5, and 2.0% using a high shear mixer. The MSCR tests were conducted at two different stress levels (0.1 and 3.2 kPa) and two different temperatures (58 and 64 °C). It was found that adding PPA decreases the non-recoverable creep compliance of the neat binder. Consequently, the MSCR grade of the neat binder was found to improve from PG58S-XX to PG58E-XX, when blended with 2.0% PPA. Additionally, the percent recovery of the neat binder was found enhanced due to PPA modification. Therefore, it is anticipated that the mixes containing PPA would sustain a higher level of traffic without undergoing a significant amount of rutting compared to mixes containing non-PPA modified binders. Also, it was observed that the PPA-modified binders can exhibit stiffness similar to polymer-modified binders.