Cracking performance predictions using index-volumetrics relationships with direct tension cyclic fatigue test and Illinois Flexibility Index Test (I-FIT)

Abstract

This paper introduces a methodology to predict fatigue cracking indices from asphalt mixture volumetric conditions using the index-volumetrics relationship (IVR). Two different tests, the Illinois Flexibility Index Test (I-FIT) and the direct tension cyclic fatigue test, were conducted using two North Carolina plant-mixed lab-compacted (PMLC) mixtures, RS9.5C and RI19.0C, obtained from field projects. Several mixture samples were collected from different truck loads for each mixture. The research team determined three sets of fatigue index values from the I-FIT, i.e., flexibility index (FI), cracking resistance index (CRI), and balanced cracking index (BCI) values, and determined another set of fatigue index values, Sapp index values, from the direct tension cyclic fatigue tests. IVRs for the individual mixtures and test indices were developed and then used to predict the fatigue index values at the volumetric properties that were not used in the IVR development. A good agreement was found between the predicted and measured index values. Except for the BCI values of the RS9.5C mixture, most of the I-FIT cracking test results showed counterintuitive trends with regard to air void content; however, the Sapp index showed more intuitive trends in both mixtures. The effect of binder content on the index values was not included in this study due to an inherent limitation of PMLC mixtures, which is the narrow range of binder content for the collected mixture samples compared to air void content.