A Sensitivity Study to Evaluate Intermediate Temperature Cracking Tests for Vermont Asphalt Mixes

Abstract

The State of Vermont began implementing balanced mix design (BMD) in late 2019. Since 2020, both Hamburg wheel tracking test (HWTT) and Illinois flexibility index test (I-FIT) results were required to be included in the mix design submittal along with the traditional Superpave volumetric design. This paper presents a part of the ongoing benchmarking efforts in Vermont, among many other states around the country, and compares the sensitivity of the two popular intermediate temperature cracking tests [I-FIT and indirect tensile cracking test (IDEAL-CT)] to the design factors of mixes produced in Vermont. Both laboratory-produced and plant-produced mix data are evaluated, and the factors analyzed include mix type, design gyrations, production facility, binder grade, and binder supplier. We found that IDEAL-CT shows much higher sensitivity to the design factors than I-FIT according to the data presented in this study. Therefore, it is recommended that Vermont Agency of Transportation (VTrans) adopt IDEAL-CT as the intermediate temperature cracking test for BMD implementation rather than I-FIT, due to the higher sensitivity and simplicity of IDEAL-CT. Regression models are further developed for IDEAL-CT using selected mix properties to guide the mix design adjustment. Similar studies are highly recommended for other state agencies that are interested in implementing BMD.