Effect of specimen geometries on asphalt mixtures' phase angle characteristics

The main purpose of this research study was to obtain the phase angle ϕ* of three different asphalt mixtures at varying aspect ratios. The phase angle of an asphalt mixture describes the viscoelastic behaviour of the mixture and has been shown to be correlated to the tyre/pavement noise characteristics in the field. The motivation of the study was aimed at evaluating field cores specimens that have lower thicknesses for estimating ϕ* of asphalt mixtures. The experimental program comprised of dynamic modulus tests performed on conventional dense graded (CONV), asphalt rubber gap graded (ARAC), and asphalt rubber open graded (ARFC) mixtures at different temperatures and frequencies. A total of 27 CONV, 45 ARAC, and 105 ARFC samples were used to obtain their ϕ* at aspect ratios of 1.5, 0.75 and 0.35 totalling 1062 test data points. Statistical analysis revealed that the ϕ* variation with aspect ratios is dependent on the mixture type. Furthermore, ϕ* were correlated with pavement noise of field-cored samples with varying aspect ratios. ϕ* and noise levels had excellent correlation in that the measured field-noise decreased with increasing ϕ* corroborating previous studies.