Evaluation of fatigue behavior in cold recycled mixture using digital image correlation method

Cold recycling (CR) is a reconstruction technique that produces a rehabilitated asphalt pavement without heating materials during the recycling process. It has been widely practiced in recent years, but the fatigue properties of CR mixtures are not fully understood. The objective of this study is to evaluate the laboratory fatigue behavior of CR mixtures with the application of digital image correlation (DIC) technique. The semicircular bending (SCB) and indirect tensile (IDT) fatigue tests were utilized to compare the resistance of CR and hot mix asphalt (HMA) mixtures to crack propagation in the stress-controlled mode of loading. According to the results of this study, the addition of cement to the CR mixture improves the overall fatigue performance; however it decreases the fatigue life of CR mixture under the same stress level. The SCB and IDT fatigue tests are in agreement with each other in ranking the fatigue resistance of different mixtures. The CR mixture has longer fatigue life and larger tensile strain at the failure point than the HMA mixture at lower stress levels. In addition, the contour plots of the horizontal tensile strain of CR specimen demonstrate the cracking path and the three stages of fatigue process. From the full-field strain results of the fatigue test, the two transition points in the fatigue curve are verified as the initial cracking point and fatigue failure point, respectively. Overall, this study provides a better understanding of the fatigue behavior of CR mixtures to improve the mix design and field performance.