Impact of Asphalt Concrete Properties on the Illinois Flexibility Index Cracking and Hamburg Wheel Tracking Test Rutting Potential

Abstract

Superpave balanced mix design (BMD) approaches have been adopted using the Illinois Flexibility Index test (I-FIT) for cracking and Hamburg wheel tracking test (HWTT) for rutting. The objective of this study was to evaluate the impact of the asphalt concrete (AC) properties on I-FIT’s flexibility index and HWTT’s rut depth. The study was intended to determine the most important parameters the influence the prediction of flexibility index and rut depth. An extensive database of I-FIT and HWTT results was collected from the Illinois Department of Transportation. A total of 18,594 I-FIT data sets were collected from 2061 mix designs. For HWTT, 8,263 data sets were collected from 3,782 mix designs. Data exploration analysis was conducted to evaluate the impact of the AC properties on the I-FIT and the HWTT results. Finally, feature ranking analysis was performed to determine the properties that significantly influence the flexibility index and rut depth. The result indicates that most of the AC properties identified in the database had an impact on flexibility index and rut depth. To rank the influential parameters, a random forest regression model was developed to execute recursive feature elimination analysis. The parameters Gmb, recycled content, air voids, and asphalt binder replacement were the most impactful on flexibility index and rut depth results. In this study, a large database of Illinois Flexibility Index and Hamburg wheel tracking data was collected. Then an evaluation of the impact of each AC property on the flexibility index and rut depth was conducted. Finally, a feature ranking analysis was conducted to identify the properties that impacted the flexibility index and rut depth more significantly. Contractors and AC designers may be challenged to adjust an AC mix design to control potential AC cracking or rutting. The results of this research identified the critical properties to predict flexibility index and rut depth. The outcome would allow the AC mix designer to achieve the required thresholds for cracking and rutting potential effectively by controlling the mix design parameters.