A Study on the Detection of Internal Defect Types for Duct Depth of Prestressed Concrete Structures Using Electromagnetic and Elastic Waves

Abstract

Prestressed concrete (PSC) is widely used for the construction of bridges. The collapse of several bridges with PSC has been reported, and insufficient grout and tendon corrosion were found inside the ducts of these bridges. Therefore, non-destructive testing (NDT) technology is important for identifying defects inside ducts in PSC structures. Electromagnetic (EM) waves have limited detection of internal defects in ducts due to strong reflections from the surface of the steel ducts. Spectral analysis of the existing impact echo (IE) method is limited to specific conditions. Moreover, the flexural mode in upper defects of ducts located at a shallow depth and delamination defects inside ducts are not considered. In this study, the applicability of the elastic wave of IE was analyzed, and multichannel analysis of surface, EM, and shear waves was employed to evaluate six types of PSC structures. A procedure using EM waves, IE, and principal component analysis (PCA) was proposed for a more accurate classification of defect types inside ducts. The proposed procedure was effective in classifying upper, internal, and delamination defects of ducts under 100 mm in thickness, and it could be utilized up to 200 mm in the case of duct defect limitations.

A method to detect uniformity of road base course based on impact imaging technology

“…The wave will be reflected strongly or transmitted for difference of wave impedance in different medium boundary or flaws position (like hollow, cavity and other damages) [15][16][17] . Impact imaging method is analyzing reflected waves and tracking the change to detect and judge the details inside the road 18 .…”

Evaluation of Unfilled Sheath in Concrete Structures Using Response Waveform in Time Domain

“…The elastic wave is emitted by hitting the surface of the structure with the steel ball, and the response is measured on the surface in the vicinity of the hitting point. From the response of the surface, it is possible to evaluate the thickness of the structure and the presence of internal defects on the plate-like structures [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In addition, if excitation is given by the generally used steel ball size, the input frequency range is about 2 kHz to 20 kHz, which is lower than that of ultrasonic waves; input wavelength is long and the attenuation is small as a consequence.…”

“…On the other hand, if the structure has internal defects, the boundaries are the surface of the structure and internal surface at the defect, and the dominant frequency is determined by the depth of the defect as a consequence. This evaluation method is called "Impact-Echo", and research on this technique has been actively conducted [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. However, generally speaking, evaluation using Impact-Echo would be difficult if the size of the defect is relatively small or the location of the defect is deep since the multiple reflections are not formed clearly under the conditions [7,21].…”

Analytical Study of SH Wave Scattering by a Circular Pipeline in an Inhomogeneous Concrete with Density Variation

“…They used PZT (lead-zirconate-titanate) sensors to record the changing state of elastic waves caused by cracks and crack propagation in GFRP reinforced concrete structures, considering the material discontinuity caused by cracks and the influence of strain field on wave propagation. Yoon [ 16 ] analyzed the applicability of the elastic wave of impact echo (IE) and evaluated six types of prestressed concrete structures using multichannel analysis of surface waves, electromagnetic waves, and shear waves. A more accurate classification method for internal defects in pipelines was proposed by using electromagnetic wave, IE, and principal component analysis (PCA).…”