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.

Asphalt emulsion is the most widely used tack coat material in the U.S. The objective of this study is to investigate factors that may affect the interlayer bond shear strength of asphalt emulsion tack coats of both laboratory and field compacted samples. The laboratory study included six types of tack coat materials applied on two surfaces with two residual application rates. The field study phase involved validation of the interlayer shear performance findings using field cores extracted from paving projects. The field study included taking cores of the existing layer, emulsions used for interlayer bonding, and loose mixes of new asphalt layers. Materials were collected to produce the laboratory prepared specimens for comparison with the field cores. Results of the laboratory study demonstrate that there is a direct relationship between the roughness (texture) of the existing surface and the interlayer shear strength (ISS) between two surfaces. Statistical analysis provided a strong correlation and indicated that 79% of the data variance can be explained with surface texture, emulsion type, application rate, and replicate effects. Comparing field cores with laboratory produced samples showed no clear relationship between the shear strength of laboratory and field specimens. It is speculated that the difference in compaction of the upper layers in the laboratory and field, and effect of shearing during coring of the samples from the field, resulted in higher laboratory shear values relative to field core values. The study highlights major challenges in using laboratory prepared samples to predict field behavior of tack coats.