Nondestructive detection of cavities beneath concrete plates using ground penetrating radar and microphone

The objective of this study is to detect and estimate the size of a cavity beneath a concrete plate using ground penetrating radar (GPR) and microphone surveys in laboratory tests. A chamber in which a reinforced concrete plate is installed on one side, is filled with dry sand, and a cavity is placed between the concrete plate and sand. The GPR signals are measured at the surface of the concrete plate, and acoustic signals are acquired by impacting the concrete plate with an instrumented hammer and are measured by a microphone. Imaging methods are adopted for the GPR and acoustic signals, and the location and size of the cavity are evaluated using the images. The GPR survey results show that the evaluated location of the cavity may differ from the actual location, and the cavity size is underestimated because of the rebars. The microphone survey results show that the evaluated and actual locations match, and the estimated cavity size is slightly smaller than the actual size. This study demonstrates that microphones may be used efficiently for cavity identification and size estimation.