Nondestructive Inspection of Voids in Concrete by Multi-layered Scanning Method with Electromagnetic Waves

The tiles that are used to protect the exterior of a building may separate from the concrete substrate and fall off as they age. To prevent accidents, a tiled wall can be inspected using various methods. In this paper, nondestructive inspection (NDI) with microwave electromagnetic waves (EMWs) is used for detecting tile separation, and the chance of detecting separation by this method is discussed. Here, the inspection apparatus is used to detect voids in concrete including voids that simulates tile separation. An antenna attached to the apparatus transmits and receives microwaves to obtain a reflection intensity from the concrete. In addition, the distribution of reflection intensity is obtained using a proposed scanning method, multi-layered scanning. This involves several scans along the concrete surface at different antenna-to-surface distances. Typically, EMWs have to be analyzed with an expensive network analyzer in the time or frequency domain. However, we demonstrate that voids are detected from the obtained distribution of reflected intensity of EMWs measured by a simple device without a network analyzer. The proposed method of NDI with EMWs is cheaper and simpler than conventional inspection methods.