Characterization of Effect of Aging on Polymer- and Polyphosphoric Acid-Modified Asphalt Binders Using X-Ray Diffraction (XRD)

Abstract

Abstract Over the last decade, modifying asphalt binders with polymers and Polyphosphoric Acid (PPA) has become an essential part of the asphalt industry. There is a need to study the effect of polymer and PPA on asphalt binders’ compositions and mechanical properties. Changes in the rheological properties of modified binders due to oxidative aging are another important concern for pavement engineers. Although significant efforts have been made to characterize the rheological properties of modified asphalt binders in the past, the influence of molecular structure on these properties is still unknown. In the present study, three different types of asphalt binders, namely unmodified, polymer-modified, and PPA-modified, were tested. The Dynamic Shear Rheometer and Rotational Viscosity test results indicate an increase in stiffness and viscosity due to polymer and PPA modifications. Aging was also found to increase the binder’s stiffness and viscosity, irrespective of the binder type. The effect of the molecular structure on the asphalt binder’s properties was investigated by the X-ray Diffraction (XRD) technique. The aromaticity and crystallite parameters for unaged, short-term aged, and long-term aged binders were determined from the XRD spectra. The XRD analysis was able to detect the change in molecular structure because of aging, but no specific trend for the change in crystallite parameters was observed. The aromaticity and crystallite parameters were found to increase with polymer modification and decrease with PPA modification when compared to the unmodified binder. It was also found that asphalt binder loses its aromatic characteristic upon the addition of PPA.