Abstract
High-speed laser remote sensing of defects inside a concrete specimen was demonstrated. In the proposed measurement setup, high-power laser pulses irradiated a concrete surface to generate vibration that can be detected by an optical interferometer, which was constructed using photorefractive crystal. The laser-based remote sensing system achieved inspection speeds of 25 Hz. The predominant frequency of a mock-up defect that was embedded in a concrete specimen was measured. The inspection result was identical to that obtained using a conventional hammering method.
Highlights
The degradation of infrastructure can cause serious accidents
We developed a high-speed laser remote sensing (LRS) system, which operates at 25 Hz, and demonstrated its ability to detect defects in concrete specimens
The induced vibration is detected by optical interferometer in the laser detection system, which is analogous to human ear
Summary
The degradation of infrastructure (e.g., tunnels) can cause serious accidents. Periodic inspection to detect internal concrete defects using the hammering method is recognized as a major preventive measure to eliminate accidents. Inspection methods for the detection of internal concrete defects employ ultrasound waves,[1,2,3,4] thermography,[5,6,7] and electromagnetic waves,[8,9,10] which have been proposed to overcome the above challenges. A laser remote sensing (LRS) system, based on the hammering method, has been demonstrated.[13,14,15] LRS was employed to detect defects in concrete wall of a train-tunnel; the inspection speed was ∼0.5 Hz.[14] Table 1 shows a comparison of the aforementioned methods. We developed a high-speed LRS system, which operates at 25 Hz, and demonstrated its ability to detect defects in concrete specimens.
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