Air void content is one of the most important characteristics of in-place asphalt concrete, substantially affecting early deterioration and long term performance. Destructive measures at limited locations, such as coring, are typically conducted as part of the air-void content evaluation after the pavement has been fully constructed. In this paper, use of an air coupled step-frequency array system for nondestructive assessment of air-void variability is explored. The dielectric properties of the asphalt were determined from the asphalt surface reflection amplitude of all 21 adjacent transmitting and receiving pairs of the array and related to air void content through plotting of dielectric changes with core measured air void content. This approach is an extension of the procedure developed for a single bistatic antenna pair determining properties within top millimeters of the asphalt surface. While cores provide information concerning bulk properties across the depth, the proposed method with an array system provides an opportunity for increased lateral coverage. The case study demonstrated good repeatability and correspondence with core measured air void content. The array-based method improves the coverage and productivity of the measurements, making it an attractive alternative to current state-of-the-practice procedures.
|Original language||English (US)|
|Number of pages||7|
|Journal||Case Studies in Nondestructive Testing and Evaluation|
|State||Published - Apr 1 2015|
Bibliographical noteFunding Information:
The work presented in this paper was conducted for a joint FHWA/MnDOT sponsored project 99008 under work order 139. Dr. Jacopo Sala from 3D Radar developed the software used in this study to convert the frequency domain data to the impulse time-histories analyzed in this study. Multiple MnDOT personnel assisted in the project. Matt Lebens assisted in data collection and provided the metal marking materials. Joe Voels obtained the forensic samples. Ray Betts conducted the core density testing.