Estimation of Fatigue Life Using Resilient Moduli of Asphalt Mixtures

The objective of this study was to determine the fundamental resilient moduli (M-r) parameters of four asphalt-rubber gap-graded (AR-gap), one asphalt-rubber open-graded (AR-open), four polymer-modified gap-graded (P-gap), and two conventional dense-graded asphalt concrete (DGAC) mixes at various temperatures and frequencies using ASTM D7369-11-based standard resilient modulus test [Standard Test Method for Determining the Resilient Modulus of Bituminous Mixtures by Indirect Tension Test, ASTM International, West Conshohocken, PA, 2011, www.astm.org]. M-r tests were conducted at 15 degrees C, 25 degrees C, and 35 degrees C and at 0.5, 1, 1.5, and 2 Hz on a total of 33 samples with three samples per mix. DGAC mixes had the highest M-r followed by P-gap and AR-gap, and then followed by the AR-open mixes. M-r master curves were constructed for the mixes with 25 degrees C as a reference. Furthermore, the M-r model was developed based on the material properties of 11 mixes totaling 121 data points provided by R-adj(2) = 0.9436 (adjusted coefficient of estimation), and S-e/S-y = 0.1579 (ratio of standard error to standard deviation indicative of relative accuracy of the predictive model), depicting excellent correlation between the measured and predicted M-r. Fatigue lives of each mix type was predicted using the obtained M-r and estimated tensile strains. The fatigue lives of the modified gap-graded mixes were found to be seven times higher than the conventional mixes. A novel approach was also devised to obtain fatigue lives of conventional and modified mixtures with a reduced thickness design concept based criterion with M-r being the major input parameter. Overall, it is envisioned that the M-r parameters obtained in this study will be helpful to understand the performance characteristics of the different mixes through future laboratory-field correlations.