Remote Sensing of Concrete Structures Using Laser Sonic Waves

Abstract

A laser-based remote sensing system (LRSS) for detecting defects in concrete has been developed. The diffraction efficiency of a photorefractive crystal (PRC) in the LRSS was increased by an applied electric field. A stabilization system to stabilize the interference pattern in the PRC using the running hologram technique was constructed. Defects in concrete can be located using initiation and detection of impact echo and standing Lamb waves (or natural mode of vibration). The prototype of the LRSS was assembled and set on a small truck. Field experiments were carried out to investigate real concrete defects of a bridge in bullet-train line in Japan. The LRSS scan concrete surfaces to produce a two-dimensional map of real concrete defects. The observed predominant frequency of concrete vibration was consistent with data from impact hammering method.

Keywords: Concrete, photorefractive effect, laser interferometer, homodyne detection, hologram, vibration detection, Lamb wave, ultrasound, impact echo detection, defect detection.