Using Infrared Imaging and Ground-Penetrating Radar to Detect Segregation in Hot-Mix Overlays (0-4126-1)

Segregation of any type is a serious problem in hot-mix asphalt and typically leads to poor performance, poor durability, shorter life, and higher maintenance costs. This project focused on using both infrared (IR) imaging and ground-penetrating radar (GPR) to evaluate the uniformity of newly placed hot-mix overlays. Both techniques provide a distinct advantage over existing nuclear techniques in that they provide 100 percent coverage of the new surface. In this project IR and GPR measurements were made in test sections on four newly placed asphalt overlays. Cores were taken where anomalies were detected in the mat. These cores were returned to the laboratory to identify changes in both the volumetric and engineering properties. Analysis showed that significant changes in both IR and GPR values are related to changes in hot-mix properties, primarily air void content. Based upon current Texas Department of Transportation (TxDOT) specifications significant changes in the hot-mix asphalt are expected if temperature changes of greater than 25 °F are measured in the field. If the surface dielectric changes by more than 0.8 for coarse-graded mixes and 0.4 for dense-graded materials, significant changes in mix properties are expected. The approach used in Finland to use a calibration core to convert GPR surface dielectric to mat air void contents worked well. TxDOT should consider future implementation of these technologies. Neither of the devices used in this project was thought optimal for full implementation. The research team has provided schematics and recommendations for future implementation efforts.