Development of machine compliance factor for the illinois flexibility index test (I-FIT)

The Illinois Flexibility Index Test (I-FIT) was developed to provide a practical and reliable parameter for the evaluation of asphalt concrete (AC) fracture resistance. The flexibility index (FI) can capture the behavior of AC in terms of their ductile or brittle fracture propagation. Although the test was proven to be a reliable and effective method and was accepted as provisional American Association of State Highways and Transportation Officials (AASHTO) standards, the effect of machine compliance on the test results was not investigated. This paper presents the outcomes of a study conducted to assess the impact of machine compliance on the results of the I-FIT. A procedure was developed to calculate the machine compliance factor by conducting tests on a standard reference material and numerical analysis. Using a standard material, machine compliance was assessed on four different devices, comparing the results obtained from finite element model (FEM) simulation and actual tests on the standard material. The procedure for calculating the machine compliance factor included testing and modeling a modified support configuration to minimize flexural deflections. Once the results were obtained, the values of the machine compliance were calculated for every device. The impact of machine compliance was then verified using data from an AC mixture: a statistical analysis was conducted on the results to assess significant differences of mean values among the machines before and after the correction. The effect of machine compliance was found to be insignificant on the results. The outcome of the study suggested that test fixture configurations and loading systems do not impact the results of the test.