Development of Laser-Based Remote Sensing System for Detecting Defects in Concrete

The noncontact acoustic inspection method using acoustic irradiation induced vibration and a scanning laser Doppler vibrometer can detect internal defects in the surface layer of concrete structures, etc., over long distances and without contact. Since this method uses flexural vibration in principle, it can be used as an alternative method to tapping inspection. Therefore, there has been an increase in requests for realizing movement measurement. Thus, an experiment was conducted to verify whether movement measurement was possible by mounting multiple LDVs and sound sources that did not have scanning mechanisms on a moving trolley. The experimental results revealed that by using cross-correlation processing between the transmitted and received waveforms, it is possible to perform movement measurements at low speeds of about 2 km/h.

Section: Inspection Methods That Can Be Performed From a Distancementioning

confidence: 99%

Study on movement measurement for internal defects in concrete structures by noncontact acoustic inspection method using correlation processing

Sugimoto,

Nakagawa,

Sugimoto

et al. 2024

“…Therefore, this method is difficult to use with a high ceiling. The laser remote sensing method 21) is a method utilizing shock excitation by a powerful pulsed laser and is suitable for inspecting a metal surface. Since the conversion efficiency from laser energy to vibrational energy is low, a high output is required to sufficiently excite the resonance of defects.…”

Section: Noncontact-type Nondestructive Testing Methodsmentioning

confidence: 99%

Detection of internal defects of concrete structures based on statistical evaluation of healthy part of concrete by the noncontact acoustic inspection method

Sugimoto

Utagawa

et al. 2018

A noncontact acoustic inspection method was developed to perform measurements from a long distance (usually about 5 to 7 m but even over 30 m) and detect internal defects (up to 10 cm in depth) of concrete structures using a long-range acoustic device and a laser Doppler vibrometer. An algorithm was also proposed to detect internal defects of concrete by combining two acoustic features, the vibrational energy ratio and spectral entropy obtained by our measurement. However, in actual concrete structures, it is difficult to distinguish a boundary between a healthy part and a defective part owing to influences such as the shape of internal defects, age-induced deterioration, and the surface condition of concrete. Therefore, we propose a method to statistically evaluate the distribution of the healthy part of concrete and extract the healthy part to identify the defective part. By this proposed method, the actual concrete floor slab bridge was measured from 33 m away and some internal defects were detected and visualized. Furthermore, a result for a railroad tunnel was compared with the Schmidt hammer rebound value and elastic wave velocity to verify the validity of the proposed method.

“…Therefore, a scaffold or an aerial work vehicle is necessary for a person to work at a high place. On the other hand, as a method of nondestructive inspection from a place more than 5 m away, the infrared and laser remote sensing methods 16,17) are known. Each method has its own difficulty.…”

Section: Introductionmentioning

confidence: 99%

High-speed noncontact acoustic inspection method for civil engineering structure using multitone burst wave

Sugimoto

Kosuge

et al. 2017

The noncontact acoustic inspection method focuses on the resonance phenomenon, and the target surface is measured by being vibrated with an airborne sound. It is possible to detect internal defects near the surface layer of a concrete structure from a long distance. However, it requires a fairly long measurement time to achieve the signal-to-noise (S/N) ratio just to find some resonance frequencies. In our method using the conventional waveform “single-tone burst wave”, only one frequency was used for one-sound-wave emission to achieve a high S/N ratio using a laser Doppler vibrometer (LDV) at a safe low power (e.g., He–Ne 1 mW). On the other hand, in terms of the difference in propagation velocity between laser light and sound waves, the waveform that can be used for high-speed measurement was devised using plural frequencies for one-sound-wave emission (“multitone burst wave”). The measurement time at 35 measurement points has been dramatically decreased from 210 to 28 s when using this waveform. Accordingly, 7.5-fold high-speed measurement became possible. By some demonstration experiments, we confirmed the effectiveness of our measurement technique.