Illinois Flexibility Index Test: Effect of Specimen Geometry and Test Configuration on the Asphalt Concrete Damage Zone

Abstract

The Illinois Flexibility Index Test (I-FIT) was developed as a standard test to predict the cracking potential of asphalt concrete (AC) materials. The test geometry is a semicircle with a precut notch. The effect of parameters on crack initiation and propagation was investigated. The parameters studied included the specimen’s thickness, air void content, notch length, and loading rate. The energy accumulation and dissipation in the damage region surrounding the notch were evaluated. A high-resolution camera was used to allow digital image correlation measurements of the strain and displacement fields of the specimen surface to provide an estimate of the fracture process zone (eFPZ). It was found that the thicker the specimen, the smaller the eFPZ area was. Similarly, the apparent size of the eFPZ increased as the air void content increased. The notch length should be maintained at 15 mm to avoid the overlap of the compressive and tensile strain regions under the loading head. As to loading rate, a slow loading rate should be avoided at intermediate temperature to allow a better control of the viscous and plastic deformations.