Estimation of phase angles of asphalt mixtures using resilient modulus test

The main objective of this study was to develop, derive, and estimate the phase angle (phi) parameter from resilient modulus (M-r) test, designated phi(Mr), at various temperatures and frequencies for eleven types of asphalt mixtures: two conventional dense-graded (DGAC), four polymer-modified gap-graded (P-Gap), four asphalt-rubber gap-graded (AR-Gap), and one asphalt-rubber open-graded (AR-Open) mix. phi(Mr) were estimated for the eleven mixes with three replicates per mix totalling 33 samples at 15, 25 and 35 degrees C and at 0.5, 1, and 1.5 Hz. AR-Open mixes had the highest phi(Mr) followed by AR-Gap and P-Gap, and then followed by DGAC mixes. Principally, with an increase in the asphalt content from conventional to modified mixes, there was an increase in phi(Mr) suggestive of the fact that the mixes that had higher asphalt contents have extra-viscous response or are highly viscoelastic. Furthermore, phi(Mr) predictive model was developed based on asphalt material properties totalling 99 data points provided by R-adj(2) (adjusted coefficient of estimation) = 0.8390, and S-e/S-y (ratio of standard error to standard deviation indicative of relative accuracy of the predictive model) = 0.3820; depicting very good correlation between the estimated and predicted phi(Mr), and with low bias and high precision. Additionally, phi(Mr), master curves were constructed for the mixes with 35 degrees C as reference. Overall, it is envisioned that phi(Mr) parameter obtained in this study will be helpful to comprehensively understand the viscoelastic properties of different asphalt mixtures, and incorporate phi(Mr) as a viscoelastic characteristic assessor in futuristic flexible pavement designs. (C) 2015 Elsevier Ltd. All rights reserved.