Evaluation of asphalt mixtures' viscoelastic properties using phase angle relationships

A recent study at Arizona State University has shown that the phase angle, φ, was a good laboratory parameter to distinguish the asphalt mixture's tyre/pavement noise characteristics in the field. The phase angle is obtained simultaneously from the E* dynamic complex modulus test (AASHTO TP 62-03). In particular, the peak or maximum phase angle obtained from the range of the E* test frequencies provided the best indication of the mixture's noise-dampening response. The objective of this study was to utilise the φ-E* relationships to develop appropriate master curves for the phase angle parameter. In addition, the objective was to develop predictive phase angle models so that they can be used to assess the dampening response, and therefore the tyre/pavement noise characteristics of the different asphalt mixtures. E*-φ results from 217 conventional and crumb rubber-modified asphalt mixtures were used in the analysis. The beta distribution was found to best fit the phase angle master curve relationship and the statistical goodness-of-fit parameters were found to be excellent. Phase angle predictive equations were modelled with combinations of mixture properties such as aggregate gradations, binder viscosity-temperature susceptibility parameters, asphalt content, mixture air voids, temperature and loading frequency. Over 6510 data points were included in the development of the phase angle predictive equations. They included equations for both conventional and crumb rubber-modified mixtures. The predictive equations had very good to excellent goodness-of-fit statistics.