Quantification of the Effect of Binder Source on Flexibility of Long-Term Aged Asphalt Concrete

Asphalt concrete (AC) aging reduces the resistance of flexible pavements to fatigue, thermal, and block cracking. Therefore, it is critical to understand the effects of AC aging on flexible pavement serviceability. Binder source has a significant effect on AC long-term aging. Therefore, it is necessary to develop a reliable, practical, and systematic method to quantify the effect of binder source on AC cracking resistance. Seven laboratory mixes were designed and produced at three asphalt binder replacement (ABR) levels using various binders, but same binder performance grade (PG). The AC mixes were tested using the Illinois Flexibility Index Test (I-FIT) under unaged and long-term aged conditions. Standard Superpave tests and temperature-frequency sweep tests, were conducted on virgin binders under various aging conditions. By comparing the binder rheological parameters and flexibility index (FI) of long-term aged AC specimens, the Delta T-c and m-value after 40-h of aging using a pressure aging vessel (PAV) were identified as valid indicators to reflect the effects of the binder source on AC long-term flexibility. A minimum Delta T-c of -8 degrees C and m-value of 0.280 were proposed as the preliminary thresholds. A new parameter, Delta m, which is defined as the m-value of 20-h PAV-aged binder minus the m-value of a 40-h PAV-aged binder, correlates well with the aging rate of AC. A binder with a high Delta m may induce an excessive drop in flexibility after long-term aging.