Detection of Delamination with Various Width-to-depth Ratios in Concrete Bridge Deck Using Passive IRT: Limits and Applicability

Abstract

In bridge structures, concrete decks have a higher risk of damage than other components owing to the direct impact of traffic. This study aims to develop a comprehensive system for bridge inspection using passive infrared thermography (IRT). Experiments were conducted on a concrete specimen (assumed as the surface of the bridge deck) embedded artificial delaminations with different width-to-depth ratios (WTDRs). Both professional handheld IR camera (H-IRC) and a UAV mounted with an IR camera (UAV-IRC) were employed simultaneously to capture the surface temperature of the structure. The present work indicates that the passive IRT technique with an H-IRC can be used to detect delaminations located at depths of 4 cm or less from the structure surface if the WTDRs are not lesser than 1.9 for daytime and 2.5 for nighttime when testing on a sunny day. In addition, the larger the WTDR, the higher the temperature difference can be produced, thus delaminations could be observed more clearly. Furthermore, our study suggests that the concrete bridge deck inspection using passive IRT can produce appropriate results if the inspection is performed from 10:00 to 15:00 or from 19:30 to approximately 2:00 on a sunny day. Good agreement between the results obtained from tests using H-IRC and UAV-IRC was observed, which validates the application of UAV-IRC in real structure inspection.

Application of the Machine Vision Technology and Infrared Thermography to the Detection of Hoof Diseases in Dairy Cows: A Review

“…IRT images provide indisputable advantages for direct retrieval of the surface temperature distribution of the observed object, but also for detection and identification of objects emitting thermal radiation under low-light conditions, when recording of the visible spectrum is insufficient [57,58], or for detection of defects of the observed object that cannot be recorded by conventional photosensors [59][60][61]. However, images captured with thermal imaging sensors currently still have a significantly lower resolution than images taken with standard image sensors designed to capture the visible spectrum [62].…”

“…Resolution of Thermal Images [64] 60 × 80 (0.005 MP) [65,66] 160 × 120 (0.019 MP) [67][68][69][70][71][72][73][74][75][76][77][78][79][80] 320 × 240 (0.077 MP) [63,81,82] 320 × 256 (0.085 MP) [83,84] 336 × 256 (0.086 MP) [85,86] 384 × 288 (0.111 MP) [59][60][61][62][87][88][89][90][91][92][93][94] 640 × 480 (0.307 MP) [95,96] 640 × 512 (0.328 MP)…”

Thermography-Based Deterioration Detection in Concrete Bridge Girders Strengthened with Carbon Fiber-Reinforced Polymer

“…In active IRT, four traditional contrast definitions, including absolute, running, normalized, and standard contrasts, are commonly employed to quantitatively evaluate the defect detection on thermal images [12][13][14]18,[34][35][36][37][38][39][40]. In addition, another contrast method called differential absolute contrast (DAC) was proposed and applied successfully to investigate the structural health [41,42].…”

“…The surface temperature was recorded during not only the heating time but also the cooling duration at a capturing frequency of 0.5 Hz using a long-wavelength IR camera (FLIR SC660) with a thermal sensitivity of 0.03 • C [56]. The technical specifications of the IR camera are described in detail in our previous studies [14,35,36].…”

Principal Component Thermography for Defect Detection in Concrete

“…If one considers real conditions in-situ, detection of defects using IRT is hindered by the solar irradiance variations, shading caused by clouds or the surrounding objects, as well as the condition of the concrete’s surface (color variations, texture and possible rubble) [ 25 , 26 , 27 ]. The problem also emerges when IRT is intended to be used in shaded areas or concrete elements that cannot be naturally thermally excited by the Sun.…”