Comparison between SCB-IFIT, un-notched SCB-IFIT and IDEAL-CT for measuring cracking resistance of asphalt mixtures

Abstract

In the last few years two types of tests have been proposed to estimate cracking resistance of asphalt mixtures at intermediate temperatures. The Semi-Circular Bending Illinois Flexibility Index Test (SCB-IFIT) is becoming widely used and it has been accepted as a quality control test in one state. However, the preparation of test specimen for SCB-IFIT is somewhat complicated and requires cutting and notching which could cause unexpected testing variance. In addition, the recently developed indirect tensile asphalt cracking test (IDEAL-CT), which requires no cutting or notching of specimen is also becoming widely considered as a possible practical test. In this paper, the need for the notch in the SCB-IFIT procedure is evaluated. In addition, the IDEAL-CT is compared to the SCB tests with and without notch. The comparison is focused on the specimen preparation, testing set-up, testing variance, and the capability of discriminating between different mixtures. The flexibility index (FI) results from the SCB with and without notch show a strong linear correlation (R2 of 0.95). The notched specimens have a larger variance in their results than un-notched specimens, indicating that the notch can be eliminated to reduce the variance of results. The cracking tolerance index (CTindex) results from IDEAL-CT are found to correlate very well with the FI from SCB-IFIT, and CTindex results show less variation than the FI results (average COV of 5.3% versus 23.0%). Since the IDEAL-CT requires no specimen cutting or notching, it could be a promising alternative to evaluate cracking resistance of asphalt mixtures.