Investigation of the Effects of Long-Term Aging and Testing Temperature Sensitivity on the Flexibility Index (FI) Parameter Obtained from the Illinois Flexibility Index Test (I-FIT)

Fatigue cracking, occurring at intermediate temperature, is the most prevalent mode of cracking in asphalt pavements. Due to recent significant progress in laboratory characterization of asphalt mixtures, testing notched specimens such as the one required by Illinois Flexibility Index Test (I-FIT) have shown promising to characterize intermediate cracking resistance of asphalt mixtures. I-FIT as per AASHTO TP124 standard was developed to assist in the asphalt mix design process, and at production level as a quality assurance tool. Since I-FIT is specified to be conducted at 25ºC, the effect of temperature sensitivity on I-FIT results is of interest. Currently, AASHTO R30 standard specifies forced-draft oven aging at 85ºC for 120 h of compacted asphalt mixture specimens for simulating long-term aging of asphalt pavements during service time. In this research, five plant-produced surface course asphalt mixtures that have been paved across Ontario were selected. The mixtures included asphalt binder grades of PG52-40, PG58-34, PG64-34, PG64-28, and PG70-28. First, the effect of two different laboratory forced-draft oven aging on I-FIT, at 85ºC for 120 h and at 95ºC for 72 h, was investigated. The statistical analysis of the results showed that both aging methods have comparable FI (Flexibility Index) values for five asphalt mixtures. Secondly, I-FIT was conducted at three temperatures, including 23ºC, 24ºC and 25ºC, to investigate the sensitivity of I-FIT parameters to testing temperature variations. The statistical analysis of the results showed that asphalt mixtures containing hard asphalt binders are more sensitive to the drop of testing temperature.