Development of Long-Term Aging Factor For Asphalt Mixtures’ Cracking Resistance

To characterize the cracking resistance of asphalt mixtures, semi-circular bend (SCB) test has been developed and subsequently accepted as a routine test in mixture design in Louisiana. However, SCB test requires specimens to be aged for five days in laboratory, which makes it not implementable in quality control (QC)/quality assurance (QA). The primary project objective was to develop an aging factor to transfer the unaged SCB Jc to the aged SCB Jc. Specific objectives were to: (1) investigate the effect of laboratory aging on asphalt mixtures’ cracking resistance and asphalt binders’ rheological and chemical properties, (2) develop an aging factor to represent the laboratory aging effect on asphalt binder property; and (3) develop a cracking resistance prediction model based aging index. To achieve the objectives, SCB test was performed on five plant-produced mixtures that laboratory-aged for designated durations (0, 2, 5, and 7 days) to obtain the Jc values at various aging levels. Then, the asphalt binder were extracted and recovered from each mixture. After that, the rheological and chemical properties of extracted binders were evaluated by using dynamic shear rheometer (DSR) and Gel permeation chromatography (GPC) test. SCB test results indicated that the cracking resistance of asphalt mixtures decreased with aging, and 5 day aging SCB Jc values were found to be comparable to that of 7 days aged mixtures. The aging index of Glover-Rowe (G-R) parameter obtained from DSR test increased with aging, and the G-R parameter values at 5 days aging level were comparable to that of 7 days aged mixtures. GPC test indicated that asphaltene fraction increased while maltene fraction decreased with the aging. By considering the remarkable correlation between of G-R parameter with SCB Jc, an aging factor of 1.62 based on G-R parameter was proposed for mixture containing polymer modified binder. The aged SCB Jc values were transferred from unaged SCB Jc by utilizing proposed aging factor, and the transferred SCB aged Jc were found in good agreement with the measurement. Furthermore, a preliminary cracking resistance prediction was explored and validated by considering other mixture characteristics