Investigation of cracking behavior of antioxidant-modified asphalt mixtures

Age-hardening is a major cause of cracking and other distresses in asphalt pavements. One approach to controlling age-hardening in the asphalt binder and its detrimental effects on pavement performance is through the use of antioxidants. Investigation of cracking potential in asphalt binders containing various levels of antioxidants through a suite of rheological tests suggests that cracking of asphalt pavements can be significantly reduced through the use of antioxidants. In this study, asphalt mixtures containing antioxidants were prepared in the laboratory and subsequently subjected to two levels of aging in a forced-draft oven to simulate short-term and long-term aging. Dynamic modulus tests were conducted in the indirect tensile (IDT) mode to determine the stress-strain behavior of the mixtures at three temperatures and seven frequencies. In addition, creep tests were conducted in the IDT mode to obtain the creep compliance of the mixtures at three temperatures. The indirect tensile strength tests were performed to determine the tensile strength of the mixtures at -10 C. From the test results, thermal cracking in a hypothetical 12 in. thick asphalt pavement located in Frazee, MN was simulated using the Thermal Cracking Model (TCMODEL). Cracking susceptibility of the mixtures was also evaluated using the unified performance-based fracture mechanics analysis developed at the University of Florida. The results of the testing and analysis indicate that asphalt aging significantly reduces the cracking resistance of asphalt mixtures. The use of antioxidants substantially lowered the predicted cracking susceptibility. The results of this study suggest that a larger investigation of the effect of antioxidants in reducing cracking in asphalt mixtures is warranted, including full-scale field trials.