A study that validated the field performance of ground-penetrating radar (GPR) as a nondestructive tool to predict in situ asphalt mixture density is presented. New overlays using six types of asphalt mixtures were placed at Illinois Route 72 (IL-72) near the Chicago area. Both GPR and nuclear gauge data were collected from the construction site for density estimation. Six cores were extracted for each mixture, and their densities were measured in the laboratory. A density model named Al-Qadi, Lahouar, and Leng (ALL), developed in an earlier study by the authors, was used to predict the asphalt mixture density from GPR measurement. GPR performance was then verified by comparing the GPR-predicted densities with densities of 20 field cores measured with the nuclear gauge and in the laboratory. This study shows that GPR can provide reasonably accurate density prediction when an appropriate model is used. GPR's accuracy of density prediction is comparable with, or better than, that of the nuclear gauge when two calibration cores are used. GPR measurement of an asphalt mixture was not affected by temperature within the range of 90° to 190°F (32° to 88°C). The relationship between the GPR signal reflection amplitude and the number of roller passes could be used to monitor the asphalt mixture compaction process and determine the optimum number of roller passes.
This paper demonstrates that ground-penetrating radar (GPR) is an effective tool for quality assurance and quality control during flexible pavement compaction and after construction. Density is one of the most important properties of asphalt concrete layers in flexible pavement. It is critical to monitor the change in asphalt concrete density during compaction; GPR can be used to measure asphalt mixture density nondestructively and rapidly. However, it is challenging to apply the GPR method during compaction because of the unknown effect of roller-sprayed water on the GPR signal. This paper presents the results of a study on the effect of surface water on the GPR signal when a 2-GHz antenna is used. It was found that the higher-frequency components of the ultrawide band signal were affected by water; however, the lower-frequency components were not significantly influenced. The process consisted of a band-pass filter with a passing band from 200 to 800 MHz and extracting the surface reflection amplitude after filtering. The extracted feature was found to be insensitive to the presence of surface water. Therefore, this technology could be used effectively during the compaction process. Field data collected from two construction projects were used for validating this approach. The proposed approach was found to be feasible for monitoring compaction status. Pavement thickness and density profiles were also obtained by GPR after construction. The density values obtained by GPR were similar to those obtained by nuclear density gauge.
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