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An experiment involving three neat asphalts and their mixtures with 1.5 wt % of polyphosphoric acid (105%) was conducted to investigate the effect of polyphosphoric acid (PPA) on the long-term aging characteristics of asphalt binders. Analytical techniques including dynamic shear rheometry, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance (NMR) spectroscopy were performed on unaged and aged PPA-modified asphalts. Rheological properties of unaged and aged modified asphalts were measured with a dynamic shear rheometer at various temperatures. The concentration of carbonyl-containing compounds present in the various unmodified and PPA-modified binders was determined by FTIR spectrometry. The thermal properties of the unmodified and PPA-modified binder were obtained by using differential scanning calorimetry. The results indicate that PPA-modified asphalts reduce rutting potential by increasing initial stiffness and reduce fatigue or low temperature cracking, or both by improving the low-temperature flow properties. The correlation between rheological properties and chemical properties of unmodified and PPA-modified asphalts is also presented. The results show a linear relationship between physical properties and chemical properties of asphalt binders with respect to oxidative aging. However, addition of PPA to asphalt alters the linear relationship. NMR results showed no new chemical species formed in the asphalt-PPA mixture.

Two different particle sizes of crumb rubber at three different concentrations were mixed with two asphalts to investigate the effect of rubber particles on the fundamental internal microstructure of asphalt binders with respect to their long-term aging performance. The rheological, morphological, and chemical properties of unaged and aged unmodified and rubber modified asphalt binders were studied as a function of long-term oxidative aging. Based on the limited study, the results indicate that the amounts of rubber particles added into asphalt binder are asphalt dependent. For highly incompatible asphalt, rubber concentration has substantial effect on the long-term flow properties of asphalt binders. For compatible asphalt, addition of rubber increased the elasticity of asphalts and also reduced viscosity buildup with aging. In addition, particle size of rubber does not show significant differences in terms of its effect on the long-term aging characteristics of asphalt binder. Furthermore, results from atomic force microscopy (AFM) showed that some fractions of the rubber particles may be dissolved in the asphalt due to devulcanization of the rubber, and hence, could explain the appearance of "new" material in the AFM image of the recovered asphalt samples.