Asphalt Density Monitoring during Compaction Using GPR

Abstract: A direct relationship exists between asphalt concrete (AC) density and pavement performance. Consequently, quality thresholds have been established for AC mat density by Departments of Transportation (DOTs) in 50 states in the U.S. During flexible pavement construction, remedial actions to increase the achieved density become limited as AC cools down. Therefore, it is crucial to monitor AC to achieve the desired density during compaction. Ground-penetrating radar (GPR) technology can be used to monitor AC densification during construction with every roller pass. Contractors may use GPR as a quality control measure to optimize their rolling pattern, and ensure they receive pay incentives and avoid penalties, and agencies may use it for quality assurance. In this study, GPR data was collected for small- and large-scale tests. The small-scale test included the construction of a test slab inside the laboratory. Whereas the large-scale test included the construction of six AC sections of variable mix designs and aggregate types. Additionally, a roller-mounted GPR prototype was developed and used for data collection during the large-scale tests. The accuracy of AC density results predicted by GPR were verified using ground truth cores and nuclear gauge measurements. An accuracy of (+/-) 0.7% in determining AC percent compaction was achieved. The applied signal processing techniques to predict AC density from raw GPR signals are presented in detail. The use of recycled materials and additives in AC was not considered in this study.