Laboratory performance of warm mix asphalt binder containing polyphosphoric acid

• Rheological and morphological properties of WMA-PPA binders were studied.
• Viscosity, Temperature and frequency sweep, creep stiffness, etc. were tested.
• The 1.5% of PPA was found to be the optimum content.
• The modification effect of PPA on WMA asphalt is a chemistry process.

In this study, the objective was to conduct a laboratory investigation of rheological and morphological properties of warm mix asphalt containing polyphosphoric acid (WMA-PPA). The Superpave binder tests (i.e., rotational viscosity test, dynamic shear rheometer (DSR) test and bending beam rheometer (BBR) test) as well as microscopic tests (i.e., Fluorescence microscopy, Fourier transform infrared spectroscopy (FT-IR) and Differential Scanning Calorimetry and Thermogravimetry (DSC/TG) test) were performed to determine the influences of polyphosphoric acid (PPA) on warm mix asphalt binders. The experimental design included six binders and four different polyphosphoric acid dosages (by weigh of neat asphalt). The test results indicated that, the addition of PPA into warm mix asphalt binders exhibited an increase in the viscosity at different test temperatures, giving clear indication of the modification effects of PPA on the warm mix asphalt binders’ high-temperature performances. Temperature and frequency sweep tests show that the WMA-PPA binders demonstrate lower value of phase angle and higher value of complex modulus compared with the WMA binder regardless of aging state, the WMA-PPA asphalt containing more PPA has higher values of complex modulus (lower values of phase angle) than the WMA-PPA asphalt with less PPA in original state and after RTFO aging state. Bending beam rheometer (BBR) test illustrates that the addition of PPA making the low temperature rheological properties of the WMA binder worse. Furthermore, the amount of PPA has a great effect on the microstructures and hot storage stability of WMA-PPA asphalts, and the modification effect of PPA on WMA asphalt is a chemistry process. The 1.5% of PPA was found to be the optimum content between the studied percentages due to the warm mix asphalt binder containing 1.5% PPA achieved comparative good intermediate and high temperature rheological properties and at the same time is considered economical.