Sensitivity of the Illinois Flexibility Index Test to Mixture Design Factors

Abstract

The semicircular bend test was recently modified to develop the Illinois flexibility index test (I-FIT). The I-FIT test quantifies the cracking resistance of asphalt mixtures by using the flexibility index (FI), which includes the fracture energy and postpeak behavior of a mixture. This paper presents results from testing asphalt mixtures in Wisconsin. A statistical analysis approach was chosen for this study, in which the I-FIT procedure was used to differentiate between mixtures on the basis of changes in mixture composition and aging treatments. Mixtures included in this study varied in terms of the percentage of reclaimed asphalt pavement, design traffic levels, binder grades, modification levels, and aging conditions. In addition, a laboratory experiment to evaluate the effects of variability in mixture production, including asphalt content and filler content, on the I-FIT testing results was performed to provide a basis for evaluating the tolerance limits of the current production and for setting reasonable specification criteria. The statistical analysis indicated that the FI could discriminate between types of asphalt mixtures and aging conditions. The FI parameter was found to be a better parameter for capturing some of the critical changes in mixture variables and aging than the fracture energy and other parameters from the I-FIT procedure. It was also clear that the FI parameter was sensitive to the variation in production binder and filler contents within the tolerances of the current construction specifications of the Wisconsin Department of Transportation.