Estimation of phase angles of asphalt mixtures using resilient modulus test

• Phase angles were quantified for asphalt mixtures using resilient modulus test.
• Eleven different asphalt mixtures covering 297 data points were used in the study.
• Phase angle predictive model was established with very good correlations.
• Phase angle of resilient modulus test is a promising viscoelastic property assessor.

The main objective of this study was to develop, derive, and estimate the phase angle (ϕ) parameter from resilient modulus (Mr) test, designated ϕMr, 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. ϕMr were estimated for the eleven mixes with three replicates per mix totalling 33 samples at 15, 25 and 35 °C and at 0.5, 1, and 1.5 Hz. AR-Open mixes had the highest ϕMr 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 ϕMr, suggestive of the fact that the mixes that had higher asphalt contents have extra-viscous response or are highly viscoelastic. Furthermore, ϕMr predictive model was developed based on asphalt material properties totalling 99 data points provided by R2adj (adjusted coefficient of estimation) = 0.8390, and Se/Sy (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 ϕMr, and with low bias and high precision. Additionally, ϕMr master curves were constructed for the mixes with 35 °C as reference. Overall, it is envisioned that ϕMr parameter obtained in this study will be helpful to comprehensively understand the viscoelastic properties of different asphalt mixtures, and incorporate ϕMr as a viscoelastic characteristic assessor in futuristic flexible pavement designs.