A three-dimensional coplanar capacitance imaging method for internal damage detection in asphalt layers

The two-dimensional (2D) dynamic coplanar capacitance imaging technologies have high imaging accuracy and detection efficiency in identifying internal damages in asphalt layers. However, these technologies are difficult to provide a three-dimensional (3D) visual damage distribution, and the reconstructed 2D damage images only refer to the 2D projection of the 3D damage. Thus, a novel direct 3D dynamic coplanar capacitance imaging method is proposed to image the 3D damage distribution in asphalt layers. Initially, the 3D dynamic sensitive field distribution is constructed. Secondly, the normalized coplanar capacitance of the measured electrode pairs is discussed. Finally, the 3D internal damages in asphalt layers are reconstructed and analyzed. It is concluded that the imaging accuracy of the middle-upper static and dynamic sensitive layers, which are closer to the sensor, is higher than that of their lower layers. The approximate spatial location of internal damages in asphalt layers is determined according to the maximum coplanar capacitance of adjacent diagonal electrode pairs in different scanning steps. Square damage exhibits the highest 3D imaging accuracy with an error of 13.25 %, followed by circular damage and triangular damage. As the depth of asphalt layers increases, the 2D slice imaging accuracy for circular and square damages improves, whereas the accuracy for triangular damage decreases. The findings of this investigation have the potential to assist engineers in the 3D visual identification of internal damages in asphalt layers combined with the ground-penetrating radar (GPR) method.