Development of Fracture Resistance Curves for Asphalt Concrete

To date, a significant portion of research investigating the fracture characteristics of asphalt concrete has consisted of calculating a single number. This number includes values such as the stress intensity factor, fracture energy, or the J-integral. Unfortunately, by using only a single number, it can be confounding to differentiate between different types of asphalt concrete mixtures, especially at different testing temperatures. This research used a common fracture analysis technique, called resistance curves, or R-curves, to construct fracture resistance curves that include fracture characteristics of asphalt concrete at multiple testing temperatures. Sets of R-curves were collected at three testing temperatures and joined together to form a single R-curve, encompassing fracture characteristics across a temperature range, similar to the concept of constructing master curves collected for dynamic modulus testing. The technique was developed using data collected from the disk-shaped compact tension testing geometry. The effect of polymer modification type, air voids, aggregate type, and asphalt cement content were analyzed. Using R-curves instead of a single number allowed for a deeper understanding of the fracture characteristics of asphalt concrete. Unlike previous research, it was found that the effect and type of polymer modification can be better understood using R-curves, 4% air voids have a higher cracking resistance versus 7% air voids, and energy specific turning points were found that can influence the choice of asphalt concrete material components by local and federal agencies. Although this study is a preliminary analysis of the use of fracture R-curves for the analysis of the cracking resistance of asphalt concrete, it does identify the potential power of this method.