Infrared thermography as a non-destructive test for the inspection of reinforced concrete bridges: A review of the state of the art
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paper_title: Nondestructive test methods for concrete bridges: A review

paper_content:

Abstract NDT methods applicable to concrete bridges are reviewed. The methodology, advantages and disadvantages along with up to date research on NDT methods are presented. Different damage levels, having less dependence on inspector judgment, are suggested. Moreover, a flow chart based on damage level along with NDT methods and potential remedial measures are proposed for periodic health monitoring of structures. NDT methods are also suggested to address specific problems related to structures. Finally, the relation between some of the well-known NDT methods and most common problems encountered by the field engineers is proposed. Hence, the importance of structural health monitoring is highlighted.
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paper_title: Bridge deck delamination identification from unmanned aerial vehicle infrared imagery

paper_content:

Abstract The rapid, cost-effective, and non-disruptive assessment of bridge deck condition has emerged as a critical challenge for bridge maintenance. Deck delaminations are a common form of deterioration which has been assessed, historically, through chain-drag techniques and more recently through nondestructive evaluation (NDE) including both acoustic and optical methods. Although NDE methods have proven to be capable to provide information related to the existence of delaminations in bridge decks, many of them are time-consuming, labor-intensive, expensive, while they further require significant disruptions to traffic. In this context, this article demonstrates the capability of unmanned aerial vehicles (UAVs) equipped with both color and infrared cameras to rapidly and effectively detect and estimate the size of regions where subsurface delaminations exist. To achieve this goal, a novel image post-processing algorithm was developed to use such multispectral imagery obtained by a UAV. To evaluate the capabilities of the presented approach, a bridge deck mockup with pre-manufactured defects was tested. The major advantages of the presented approach include its capability to rapidly identify locations where delaminations exist, as well as its potential to automate bridge-deck related damage detection procedures and further guide investigations using other higher accuracy and ground-based approaches.
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paper_title: Integrated health assessment strategy using NDT for reinforced concrete bridges

paper_content:

This paper presents the results of the application of several Non-Destructive Techniques (NDT) on the Pentagon Road Bridge, in Chatham, Kent, England. This provides crucial structural information such as rebar position, moisture ingress and deflection. A FEM (Finite Element Model) of the bridge was created using data from the visual inspection and was parameterised and calibrated using information gather from the NDT results. The results of all of the above are compared in order to identify the portion of the bridge which had undergone the greatest amount of deterioration. This process forms the basis for the integrated bridge health mechanism proposed by this paper.
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paper_title: Concrete bridge deck condition assessment using IR Thermography and Ground Penetrating Radar technologies

paper_content:

Abstract The current practice of bridge inspection relies heavily on visual inspection, which suffers from several limitations, including the safety of the inspection team, the accuracy of subsurface defects detection, and subjectivity. In visual inspection, data collection is time consuming and the collected data is typically documented by completing standard inspection reports. These reports do not provide sufficient visualization of locations and/or the extent of defects. Emerging combinations of non-destructive testing (NDT) technologies and Geographic Information Systems (GIS) have the potential to circumvent some of these limitations. More research is still needed to assess the potential of these technologies to be applied in the field and to address the challenges in deploying them. The challenges include data acquisition and processing, data interpretation to identify the location and extent of defects, and the integration of results obtained from multiple technologies. This research introduces an integrated method utilizing Infrared (IR) Thermography and Ground Penetrating Radar (GPR) technologies to enhance the detection of concrete bridge defects. Integrating results can improve confidence in defect detection and quantification, and as a result can enhance the reliability of the bridge condition rating process. The integrated system is implemented in a case study of a concrete bridge deck in the city of Laval, Quebec, Canada. The obtained results are compared to detailed and visual inspection results conducted on the bridge before its demolition. The study analyzes potential, limitations, and challenges of using the proposed integrated method. In addition, the study demonstrates the feasibility of integrating the collected data in ArcGIS for enhanced visualization of the inspection results.
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paper_title: APPLICATION OF INFRARED THERMOGRAPHY TO THE NON-DESTRUCTIVE TESTING OF CONCRETE AND MASONRY BRIDGES

paper_content:

Abstract Within recent years there has been an increase in the use of NDT methods to detect defects and anomalies in various civil engineering structures. Infrared thermography, which has been successfully used in the USA in civil engineering applications, is being increasingly applied in the UK as an NDT technique. For example, the technique is now included in the Building Regulations for the assessment of thermal insulation for all new non-domestic buildings from April 2002. One of the perceived limitations of infrared thermography is that in temperate climates it is too cold to use this technique since there is rarely the extreme solar exposure that has enabled the successful use of thermography to detect render debonding and concrete spalling utilising solar heating. However, with the advancements in modern technology it is now possible to detect smaller changes in temperature (down to 0.08 °C). This paper shows that even with the low ambient temperatures experienced in Europe it is possible to use infrared thermography to identify correctly known areas of delamination in a concrete bridge structure and also to investigate the internal structure of a masonry bridge.
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paper_title: Building defect detection: External versus internal thermography

paper_content:

publisher: Elsevier articletitle: Building defect detection: External versus internal thermography journaltitle: Building and Environment articlelink: http://dx.doi.org/10.1016/j.buildenv.2016.06.011 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.
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paper_title: Practical identification of favorable time windows for infrared thermography for concrete bridge evaluation

paper_content:

Abstract Infrared Thermography (IRT) is one of the nondestructive inspection techniques to detect delaminations in concrete bridge decks. These defects are identified by capturing the temperature gradient of concrete surfaces. In order for this technique to be effective in damage detection, IRT inspections should be conducted at certain time windows with favorable temperature conditions to get clear temperature gradients on inspected surfaces. This study is an experimental work examining the effects of ambient environmental conditions at different times of a day to locate subsurface delaminations and voids at a shallow depth, which is an additional influencing factor. This study also attempts to figure out a relationship between ambient environmental conditions and the temperature values of concrete surfaces to estimate the best time window with appropriate environmental conditions for IRT inspections. To this end, specially designed reusable concrete test plates with different thicknesses were manufactured to collect thermocouple sensor readings. Multiple regression analyses were employed to generate prediction models that seek a relationship between environmental conditions and temperature gradients on the test plates attached to a target bridge. Regression models also utilized sensor data collected at another location different than the target bridge location. It was found out that the most important aspect of sensor data collection was to accomplish a perfect contact of test plates with concrete bridge deck surfaces to get discernible temperature gradients. When this condition is not met, data analyses yield spurious results leading to futile conclusions. On the other hand, it was also observed that prediction models generated by regression analyses followed the same pattern as that of sensor readings. This makes it possible to have prediction equations based on sensor readings to determine suitable time window for conducting IRT inspections.
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paper_title: A comparison of nondestructive evaluation methods for bridge deck assessment

paper_content:

Concrete bridge deck deterioration is a significant problem that must be addressed to preserve highway infrastructure investments in bridges around the world. Reducing the cost of bridge deck maintenance is critical to government and private agencies responsible for maintenance of bridges. Maintenance challenges increase as many bridges begin to approach the end of their design life and traffic loads continue to increase. One means of reducing the cost of bridge deck maintenance is to accurately evaluate the condition of the structure and its constituent materials. Current methods used to evaluate deterioration of bridge decks include acoustic, electrochemical, electromagnetic, and visual inspection techniques. The purpose of this study was to assess the advantages and limitations of three available evaluation methods. The evaluation techniques included in this study were ground penetrating radar, the chain drag method, and IE. These techniques represent an important group of inspection methods currently used to evaluate in-service bridge decks. The bridge deck used in the study contains significant delaminations but exhibits virtually no outwardly visible signs of these deficiencies, so a detailed visual inspection survey of the deck was not included. Cores were taken from the bridge deck at selected locations to confirm the accuracy of the results obtained through each evaluation method. This paper presents the findings from each method and describes their respective advantages and limitations.
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paper_title: Updating Bridge Reliability Based on Bridge Management Systems Visual Inspection Results

paper_content:

Bridge management systems have become increasingly sophisticated over the past decade and provide valuable information about the structural condition of all bridges in the national database. At the same time, reliability methods have gained increasing prominence and are used to forecast life-cycle performance over many decades of structural life. Such reliability analyses need to be updated based on the results of inspections. Specifically targeted nondestructive evaluations are the preferred solution, but are not always available for every bridge. This paper examines how the visual inspection data provided from bridge management systems already in place can be used to update the reliability of a bridge. The limitations and necessary modifications to current practice are discussed. The superstructure of a Colorado highway bridge deteriorating due to corrosion is used as an example.
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paper_title: Infrared thermography for condition monitoring – A review

paper_content:

Temperature is one of the most common indicators of the structural health of equipment and components. Faulty machineries, corroded electrical connections, damaged material components, etc., can cause abnormal temperature distribution. By now, infrared thermography (IRT) has become a matured and widely accepted condition monitoring tool where the temperature is measured in real time in a non-contact manner. IRT enables early detection of equipment flaws and faulty industrial processes under operating condition thereby, reducing system down time, catastrophic breakdown and maintenance cost. Last three decades witnessed a steady growth in the use of IRT as a condition monitoring technique in civil structures, electrical installations, machineries and equipment, material deformation under various loading conditions, corrosion damages and welding processes. IRT has also found its application in nuclear, aerospace, food, paper, wood and plastic industries. With the advent of newer generations of infrared camera, IRT is becoming a more accurate, reliable and cost effective technique. This review focuses on the advances of IRT as a non-contact and non-invasive condition monitoring tool for machineries, equipment and processes. Various conditions monitoring applications are discussed in details, along with some basics of IRT, experimental procedures and data analysis techniques. Sufficient background information is also provided for the beginners and non-experts for easy understanding of the subject.
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paper_title: Application of Fuzzy Concepts to the Visual Assessment of Deteriorating Reinforced Concrete Structures

paper_content:

Data obtained using visual inspection are qualitative and subjective in nature. Reported methodology utilizes fuzzy sets for modeling qualitative data. Characteristic distress manifestations corresponding to various deterioration mechanisms in RC structures and associated repair priorities (conditions) are first classified. To deal with the subjective nature of associated data, independent responses on applicable repair priorities for different distress manifestations are obtained from experts through questionnaire survey. Data obtained from questionnaire responses are subsequently used for the development of corresponding fuzzy membership functions (MFs). Visual-inspection data for various characteristic distress manifestations (on the basis of deterioration mechanism) are recorded individually for every deteriorating element of the structure as per the prepared guidelines. Recorded data are used for the selection of corresponding MFs. Selected MFs are combined according to the proposed fuzzy rule using ...
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paper_title: Bridge Condition Assessment and Load Rating using Dynamic Response

paper_content:

This report describes a method for the overall condition assessment and load rating of prestressed box beam (PSBB) bridges based on their dynamic response collected through wireless sensor networks (WSNs). Due to a large inventory of deficient and aging bridges in the United States, the health monitoring of bridges can be very expensive; therefore, new tools for quick, efficient and response-based condition assessment and load rating of bridges will be helpful. The hypothesis is based on the assumption that the health of a bridge is associated with its vibration signatures under vehicular loads. Two WSNs were deployed on a 25-year old PSBB bridge under trucks with variable loads and speeds, and its dynamic response was collected at the current condition. The acceleration response of the bridge at its newest condition was collected from dynamic simulations of its full-scale finite element analysis (FEA) models mimicking field conditions. The FEA bridge model was validated by the field testing and numerical analysis. The acceleration data in time domain were transformed into frequency domain using Fast Fourier Transform to determine peak amplitudes and corresponding fundamental frequencies for the newest and current conditions. The analyses and comparisons of the bridge dynamic response between the newest and the current bridge interestingly indicate a 37% reduction in its fundamental frequency over 25 years of service life. This frequency reduction is linked to the reduction in condition rating of the current bridge. The analysis data, bridge structural dynamics and bridge geometric parameters have been used to calculate the in-service stiffness of the bridge to estimate its load bearing capacity. Using the results and algorithms from this research, application software is developed to instantly estimate the overall condition rating and load bearing capacity of a PSBB bridge under vehicular loads. The research outcome and the software will help in performing quick and cost-effective condition assessment and load rating of PSBB bridges, and may provide a better ability to plan replacements and develop load ratings.
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paper_title: Investigation of effective utilization of infrared thermography (IRT) through advanced finite element modeling

paper_content:

Abstract Infrared thermography (IRT) has been used experimentally for concrete delamination detection. The past studies were conducted with limited experimental conditions, which make a difference in delamination detection. As a result, there are inconsistencies in the results reported in the literature. In this study, heat transfer models of concrete blocks with artificial delamination used for a previous test are developed and analyzed to explore sensitive parameters for effective utilization of IRT. After these FE models are validated, critical parameters and factors of delamination detectability such as the size of delamination (area, thickness and volume), ambient temperature and solar irradiance conditions (different seasons), and the depth of delamination from the surface are explored. This study presents that the area of delamination is much more influential in the detectability of IRT than thickness and volume. It is also found that there is no significant difference depending on the season when IRT is employed. This study shows a potential to bring significant improvement to IRT use in the field for subsurface damage detection for concrete structures.
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paper_title: Review Paper: Health Monitoring of Civil Infrastructure

paper_content:

Increased awareness of the economic and social effects of aging, deterioration and extreme events on civil infrastructure has been accompanied by recognition of the need for advanced structural health monitoring and damage detection tools. Today, these tasks are done by visual inspection and very traditional methods such as the tap test. This labor-intensive task is done at a frequency of less than once every two years for bridges, and on an as-needed basis for other infrastructures such as buildings. Structural health monitoring techniques based on changes in dynamic characteristics have been studied for the last three decades. When the damage is substantial, these methods have some success in determining if damage has occurred. At incipient stages of damage, however, the existing methods are not as successful. A number of new research projects have been funded to improve the damage detection methods including the use of innovative signal processing, new sensors, and control theory. This survey paper hig...
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paper_title: Status of structural health monitoring of long-span bridges in the United States

paper_content:

This paper gives an overview of ongoing research and development in the field of structural health monitoring technologies in the US, with application to long-span bridges. Specifically, this paper attempts to review various key structural health monitoring technologies, including sensor development, data processing, damage detection algorithms, data analysis and information processing. Several examples are cited from the aerospace, civil and mechanical communities. Monitoring of constructed systems are of considerable interest since the consequences of failure can have a significant effect on the society at large. For instance, consider the 1100 major long-span bridges in the USA (those with spans of 100 m or longer), many are over 50 years old, and several notable ones are over 100 years old. These bridges fall outside the Standard Specifications issued by AASHTO (1998), and there is little generic experience related to maintaining their performance, especially after they age and/or following any damage. More than 800 of the long-span bridges in the National Bridge Inventory are classified as fracture-critical. It follows that structural health monitoring techniques may prove to be useful for maintaining and preserving this population of aging civil infrastructure. It is hoped that the following will stimulate additional discussion regarding the importance of structural health monitoring as an emerging research area for a variety of aerospace, civil and mechanical applications.
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paper_title: Effects of Solar Loading on Infrared Imaging of Subsurface Features in Concrete

paper_content:

This paper addresses the effect of solar loading on thermal imaging for the detection of subsurface deterioration in concrete bridge components. The deterioration of the concrete resulting from corrosion of embedded mild reinforcing and prestressing steel results in delamination and spalling that can affect the strength and serviceability of a concrete structure. The ability to detect this deterioration during its early stages, when mitigation efforts can be employed, can provide a useful tool for maintenance and inspection personnel. Infrared thermography is a tool that has the potential to detect these subsurface defects to compliment inspection efforts and provide an additional means of condition assessment for a bridge. However, the technique relies on thermal gradients developing in the concrete such that a temperature contrast exists between damaged concrete and sound concrete. The environmental conditions at the bridge, such as direct solar loading, ambient temperature variation, and wind affect the thermal gradient in the concrete, and hence, the ability to image subsurface features. The effects of direct solar loading on the detection of subsurface targets in a concrete test block have been studied. Quantitative measurements of the thermal contrast that appear in thermal images of the test block are reported and analyzed. The effect of the depth of the embedded target is discussed, as well as the timing of inspection (relative to sunrise) that resulted in maximum contrast in thermal images.
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paper_title: APPLICATION OF INFRARED THERMOGRAPHY TO THE NON-DESTRUCTIVE TESTING OF CONCRETE AND MASONRY BRIDGES

paper_content:

Abstract Within recent years there has been an increase in the use of NDT methods to detect defects and anomalies in various civil engineering structures. Infrared thermography, which has been successfully used in the USA in civil engineering applications, is being increasingly applied in the UK as an NDT technique. For example, the technique is now included in the Building Regulations for the assessment of thermal insulation for all new non-domestic buildings from April 2002. One of the perceived limitations of infrared thermography is that in temperate climates it is too cold to use this technique since there is rarely the extreme solar exposure that has enabled the successful use of thermography to detect render debonding and concrete spalling utilising solar heating. However, with the advancements in modern technology it is now possible to detect smaller changes in temperature (down to 0.08 °C). This paper shows that even with the low ambient temperatures experienced in Europe it is possible to use infrared thermography to identify correctly known areas of delamination in a concrete bridge structure and also to investigate the internal structure of a masonry bridge.
---
paper_title: Practical identification of favorable time windows for infrared thermography for concrete bridge evaluation

paper_content:

Abstract Infrared Thermography (IRT) is one of the nondestructive inspection techniques to detect delaminations in concrete bridge decks. These defects are identified by capturing the temperature gradient of concrete surfaces. In order for this technique to be effective in damage detection, IRT inspections should be conducted at certain time windows with favorable temperature conditions to get clear temperature gradients on inspected surfaces. This study is an experimental work examining the effects of ambient environmental conditions at different times of a day to locate subsurface delaminations and voids at a shallow depth, which is an additional influencing factor. This study also attempts to figure out a relationship between ambient environmental conditions and the temperature values of concrete surfaces to estimate the best time window with appropriate environmental conditions for IRT inspections. To this end, specially designed reusable concrete test plates with different thicknesses were manufactured to collect thermocouple sensor readings. Multiple regression analyses were employed to generate prediction models that seek a relationship between environmental conditions and temperature gradients on the test plates attached to a target bridge. Regression models also utilized sensor data collected at another location different than the target bridge location. It was found out that the most important aspect of sensor data collection was to accomplish a perfect contact of test plates with concrete bridge deck surfaces to get discernible temperature gradients. When this condition is not met, data analyses yield spurious results leading to futile conclusions. On the other hand, it was also observed that prediction models generated by regression analyses followed the same pattern as that of sensor readings. This makes it possible to have prediction equations based on sensor readings to determine suitable time window for conducting IRT inspections.
---
paper_title: Infrared thermography for condition monitoring – A review

paper_content:

Temperature is one of the most common indicators of the structural health of equipment and components. Faulty machineries, corroded electrical connections, damaged material components, etc., can cause abnormal temperature distribution. By now, infrared thermography (IRT) has become a matured and widely accepted condition monitoring tool where the temperature is measured in real time in a non-contact manner. IRT enables early detection of equipment flaws and faulty industrial processes under operating condition thereby, reducing system down time, catastrophic breakdown and maintenance cost. Last three decades witnessed a steady growth in the use of IRT as a condition monitoring technique in civil structures, electrical installations, machineries and equipment, material deformation under various loading conditions, corrosion damages and welding processes. IRT has also found its application in nuclear, aerospace, food, paper, wood and plastic industries. With the advent of newer generations of infrared camera, IRT is becoming a more accurate, reliable and cost effective technique. This review focuses on the advances of IRT as a non-contact and non-invasive condition monitoring tool for machineries, equipment and processes. Various conditions monitoring applications are discussed in details, along with some basics of IRT, experimental procedures and data analysis techniques. Sufficient background information is also provided for the beginners and non-experts for easy understanding of the subject.
---
paper_title: Nondestructive test methods for concrete bridges: A review

paper_content:

Abstract NDT methods applicable to concrete bridges are reviewed. The methodology, advantages and disadvantages along with up to date research on NDT methods are presented. Different damage levels, having less dependence on inspector judgment, are suggested. Moreover, a flow chart based on damage level along with NDT methods and potential remedial measures are proposed for periodic health monitoring of structures. NDT methods are also suggested to address specific problems related to structures. Finally, the relation between some of the well-known NDT methods and most common problems encountered by the field engineers is proposed. Hence, the importance of structural health monitoring is highlighted.
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paper_title: Pulsed infrared thermography processing and defects edge detection using FCA and ACA

paper_content:

Abstract CFRP sheet with delamination defects was detected using pulsed infrared thermography. The principle of polynomial fitting the derivative time algorithm (FDA) and related coefficient algorithm (RCA) was described. A new polynomial fitting the derivative time-related coefficient algorithm (FCA) was formed by combining FDA and RCA, which improves the signal to noise (SNR) of feature images, and is benefit for the detection and identification of defects. The defects edge identification procedure using ant colony algorithm (ACA) is given, and the defect edge features in the infrared image have been extracted using ACA effectively.
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paper_title: Infrared thermography technique as an in-situ method of assessing heat loss through thermal bridging

paper_content:

Abstract A key aspect in assessing the thermal standard of building envelopes is the quantification of the heat loss though thermal bridging, which can be expressed in terms of the linear thermal transmittance Ψ. Values of Ψ may be obtained from tabulated values for standard building details, from numerical modelling or from measurement. Where the internal structure of the building envelope is unknown, which is very often the case, measurement is the only option. This study shows how the infrared thermography technique (ITT) can be used as a non-invasive and easy-to-use method to provide quantitative measures of the actual thermal bridging performance. The novelty of this approach includes evaluation of the actual heat flow rate caused by thermal bridge qTB and Ψ-value by means of the ITT solely, without any supporting methods. Another important aspect of the methodology is that it accounts for the correlation between the surface temperature and the convective and radiative heat transfer coefficients. Values for these coefficients are assessed for the whole range of the surface temperatures recorded on the thermogram resulting in improve accuracy. The qTB and Ψ-value calculated using the presented methodology fully mirrors the real thermal performance of the thermal bridge. The methodology has been tested under laboratory conditions in a steady state in a hot box with excellent agreement.
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paper_title: Quantitative determination of subsurface defects in a reference specimen made of Plexiglas by means of lock-in and pulse phase infrared thermography

paper_content:

Lock-in and pulse phase infrared thermography measurement techniques have been exploited for quantitative assessment of subsurface defects in a reference specimen made of Plexiglas. Radiometric thermal images were post-processed using a contrast approach in the frequency domain, allowing defect depth to be resolved with a combined standard uncertainty of about 5% for thicknesses up to 3.6 mm. Conversely, significant radial heat diffusion next to the boundary of the discontinuities made accurate sizing of deeper subsurface defects more difficult, resulting in a combined standard uncertainty of about 17% for a 10 mm diameter flat-bottomed hole of 3.6 mm deep. The obtained results demonstrate the potentiality of active thermography as a fast, powerful contactless NDE measurement tool.
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paper_title: Building defect detection: External versus internal thermography

paper_content:

publisher: Elsevier articletitle: Building defect detection: External versus internal thermography journaltitle: Building and Environment articlelink: http://dx.doi.org/10.1016/j.buildenv.2016.06.011 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.
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paper_title: Theory and Practice of Infrared Technology for Nondestructive Testing

paper_content:

Preface. Getting Started with Thermography for Nondestructive Testing. FUNDAMENTAL CONCEPTS. Introduction to Thermal Emission. Introduction to Heat Transfer. Infrared Sensors and Optic Fundamentals. Images. Automated Image Analysis. Materials. Experimental Concepts. ACTIVE THERMOGRAPHY. Active Thermography. Quantitative Data Analysis in Active Thermography. ACTIVE AND PASSIVE THERMOGRAPHY: CASE STUDIES. Applications. References and Bibliography. Appendix A: Computer Model. Appendix B: Smoothing Routing. Appendix C: Parabola Computations. Appendix D: Higher-Order Gradient Computations Based on the Roberts Gradient. Appendix E: Properties of Metals and Nonmetals. Appendix F: Matlab M-Scripts Available. Index.
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paper_title: Application of lock-in thermography for the inspection of disbonds in titanium alloy honeycomb sandwich structure

paper_content:

Abstract This paper investigates the lock-in thermography testing of skin-to-core disbonds in titanium alloy honeycomb structure. A three-dimensional finite element model of titanium alloy honeycomb sandwich structure is built. The phase difference between the disbond defect region and the nondefective region is used to optimize the excitation frequency. The phase variation of the surface temperature because of the discontinuity of the honeycomb structure is analyzed. And the relationship between the phase difference of the defect and the nondefective region and the thickness of the disbond is obtained. Two titanium alloy honeycomb sandwich structure specimens with skin-to-core disbond defects were manufactured. Different from the conventional method of simulating disbond defects, two methods of prefabricating intimate contact disbond are proposed to form real defects. The lock-in thermography experiments are carried out on the specimens. The digital correlation method is used to process the infrared image sequence. The experimental results show that lock-in thermography is effective in inspecting the intimate contact disbond in titanium alloy honeycomb sandwich structure.
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paper_title: Medical applications of infrared thermography: A review

paper_content:

Abnormal body temperature is a natural indicator of illness. Infrared thermography (IRT) is a fast, passive, non-contact and non-invasive alternative to conventional clinical thermometers for monitoring body temperature. Besides, IRT can also map body surface temperature remotely. Last five decades witnessed a steady increase in the utility of thermal imaging cameras to obtain correlations between the thermal physiology and skin temperature. IRT has been successfully used in diagnosis of breast cancer, diabetes neuropathy and peripheral vascular disorders. It has also been used to detect problems associated with gynecology, kidney transplantation, dermatology, heart, neonatal physiology, fever screening and brain imaging. With the advent of modern infrared cameras, data acquisition and processing techniques, it is now possible to have real time high resolution thermographic images, which is likely to surge further research in this field. The present efforts are focused on automatic analysis of temperature distribution of regions of interest and their statistical analysis for detection of abnormalities. This critical review focuses on advances in the area of medical IRT. The basics of IRT, essential theoretical background, the procedures adopted for various measurements and applications of IRT in various medical fields are discussed in this review. Besides background information is provided for beginners for better understanding of the subject.
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paper_title: Non-destructive control of industrial materials by means of lock-in thermography

paper_content:

Lock-in thermography is employed for non-destructive control to evaluate several aspects of industrial interest: inclusions of spurious materials in both carbon-epoxy and glass-epoxy, impact damage and delaminations occurring around holes during drilling in carbon-epoxy, bonding improvements in Certran® after plasma treatments and steel modifications after welding. Phase images are analysed to find quantitative information for industrial characterization.
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paper_title: Recent progress in diagnosing the reliability of electrical equipment by using infrared thermography

paper_content:

Abstract Infrared thermography (IRT) has gained more attention and become an interesting method in electrical preventive maintenance due to its high precision and sensitivity imaging characteristics. This paper provides a review of the application of IRT for diagnosing electrical equipment, including their thermal anomalies and methods of measurement. Improvement of the inspection techniques is highlighted in order to investigate the reliability of electrical equipments due to the effect of the environmental factors and equipment condition. Factors related to the target equipment and the inspection tool together with their characteristics is also presented. Due to the complex analysis, various automatic diagnostic systems are proposed for faster and more accurate analysis. Typical engineering solutions using recent technologies are reviewed which could be used to improve the quality of IRT inspection.
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paper_title: Comparison of NDT Methods for Assessment of a Concrete Bridge Deck

paper_content:

The field application of three different nondestructive tests (NDTs)—air-coupled impact echo (IE), infrared (IR) thermography, and sounding (chain drag)—are evaluated in this paper, where an actual in-service concrete bridge deck is tested. Two different contactless IE test equipment sets are deployed as part of an effort to develop new rapid measurement methods. The IE data are presented as two-dimensional frequency maps, and the IR data are presented as temperature maps over the tested area. Sounding (chain-drag) result maps are also presented. For verification of the location of near-surface delamination damage, eight drilled core samples were extracted from the test area. The results obtained from each of the individual NDT methods show reasonably good agreement with the drilled cores in terms of locating near-surface delamination. Finally, the NDT methods are compared across general performance criteria, considering accuracy, testing practicality, and costs. The analysis shows that all of the evaluated NDT methods are comparable, and the chain-drag method is not more accurate and reliable for detection of shallow delamination in the deck.
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paper_title: Imaging of concrete structures

paper_content:

Abstract Demand for the development of non-destructive testing (NDT) techniques for concrete structures has increased with the growing concern about the deteriorating condition of the World's infrastructure. Efficient and accurate imaging techniques are needed for a reliable evaluation of safety and serviceability of concrete structures. Although, presently, imaging is routinely used in various fields, implementation of these technologies in NDT of civil engineering systems, especially of concrete structures, offers many challenges and requires additional development due to the composite nature of the concrete material and the complexities of reinforced or prestressed concrete systems. This paper presents the basic principles of various imaging techniques associated with several NDT methods applicable to concrete structures. The techniques considered are radiography, radioactive computerized tomography, infrared thermography, radar imaging and acoustic imaging. Special considerations regarding the applicability and accuracy of these techniques for the condition assessment of concrete structures are discussed, and examples of imaging applications are given.
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paper_title: Infrared thermography for assessing moisture related phenomena in building components

paper_content:

Abstract In this work the potential of infrared thermography (IRT) to assess moisture related phenomenon was tested. Initially, several set-ups and boundary conditions were created to compare IRT with other techniques and to understand the ideal conditions for accurate IRT. Afterwards, IRT was used to assess capillary absorption on a full-scale laboratory model and the drying process of two exterior walls. The main conclusions were that smaller differences are obtained for low reflectance surfaces and during the night, IRT can detect invisible moisture problems and can be used to assess the drying process, although the phenomenon complexity raises some difficulties if a quantitative approach is intended.
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paper_title: Nondestructive Bridge Deck Testing with Air-Coupled Impact-Echo and Infrared Thermography

paper_content:

Two different nondestructive test (NDT) methods, air-coupled impact-echo (IE) and infrared (IR) thermography are evaluated on a full-scale simulated reinforced concrete bridge deck containing simulated delamination and cracking defects. The IE data are presented as two-dimensional frequency maps and spectral B-scan lines. The IR data are presented as temperature maps on the concrete surface. The lateral boundaries of the detected delaminations are also indicated in the images. The results obtained from each of the individual NDT methods show reasonably good agreement with most of the actual defects. The advantages and limitations of each method to characterize defects are discussed. The consistency and sensitivity of each method are also investigated. Finally, a simple data fusion technique is proposed to improve effectiveness of the individual test data. The findings from this study demonstrate that the combination of air-coupled IE and IR thermography tests is a practical option for consistent and rapid in situ evaluation of reinforced concrete bridge decks.
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paper_title: Nondestructive test methods for concrete bridges: A review

paper_content:

Abstract NDT methods applicable to concrete bridges are reviewed. The methodology, advantages and disadvantages along with up to date research on NDT methods are presented. Different damage levels, having less dependence on inspector judgment, are suggested. Moreover, a flow chart based on damage level along with NDT methods and potential remedial measures are proposed for periodic health monitoring of structures. NDT methods are also suggested to address specific problems related to structures. Finally, the relation between some of the well-known NDT methods and most common problems encountered by the field engineers is proposed. Hence, the importance of structural health monitoring is highlighted.
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paper_title: Effects of Solar Loading on Infrared Imaging of Subsurface Features in Concrete

paper_content:

This paper addresses the effect of solar loading on thermal imaging for the detection of subsurface deterioration in concrete bridge components. The deterioration of the concrete resulting from corrosion of embedded mild reinforcing and prestressing steel results in delamination and spalling that can affect the strength and serviceability of a concrete structure. The ability to detect this deterioration during its early stages, when mitigation efforts can be employed, can provide a useful tool for maintenance and inspection personnel. Infrared thermography is a tool that has the potential to detect these subsurface defects to compliment inspection efforts and provide an additional means of condition assessment for a bridge. However, the technique relies on thermal gradients developing in the concrete such that a temperature contrast exists between damaged concrete and sound concrete. The environmental conditions at the bridge, such as direct solar loading, ambient temperature variation, and wind affect the thermal gradient in the concrete, and hence, the ability to image subsurface features. The effects of direct solar loading on the detection of subsurface targets in a concrete test block have been studied. Quantitative measurements of the thermal contrast that appear in thermal images of the test block are reported and analyzed. The effect of the depth of the embedded target is discussed, as well as the timing of inspection (relative to sunrise) that resulted in maximum contrast in thermal images.
---
paper_title: Practical identification of favorable time windows for infrared thermography for concrete bridge evaluation

paper_content:

Abstract Infrared Thermography (IRT) is one of the nondestructive inspection techniques to detect delaminations in concrete bridge decks. These defects are identified by capturing the temperature gradient of concrete surfaces. In order for this technique to be effective in damage detection, IRT inspections should be conducted at certain time windows with favorable temperature conditions to get clear temperature gradients on inspected surfaces. This study is an experimental work examining the effects of ambient environmental conditions at different times of a day to locate subsurface delaminations and voids at a shallow depth, which is an additional influencing factor. This study also attempts to figure out a relationship between ambient environmental conditions and the temperature values of concrete surfaces to estimate the best time window with appropriate environmental conditions for IRT inspections. To this end, specially designed reusable concrete test plates with different thicknesses were manufactured to collect thermocouple sensor readings. Multiple regression analyses were employed to generate prediction models that seek a relationship between environmental conditions and temperature gradients on the test plates attached to a target bridge. Regression models also utilized sensor data collected at another location different than the target bridge location. It was found out that the most important aspect of sensor data collection was to accomplish a perfect contact of test plates with concrete bridge deck surfaces to get discernible temperature gradients. When this condition is not met, data analyses yield spurious results leading to futile conclusions. On the other hand, it was also observed that prediction models generated by regression analyses followed the same pattern as that of sensor readings. This makes it possible to have prediction equations based on sensor readings to determine suitable time window for conducting IRT inspections.
---
paper_title: Infrared thermography for condition monitoring – A review

paper_content:

Temperature is one of the most common indicators of the structural health of equipment and components. Faulty machineries, corroded electrical connections, damaged material components, etc., can cause abnormal temperature distribution. By now, infrared thermography (IRT) has become a matured and widely accepted condition monitoring tool where the temperature is measured in real time in a non-contact manner. IRT enables early detection of equipment flaws and faulty industrial processes under operating condition thereby, reducing system down time, catastrophic breakdown and maintenance cost. Last three decades witnessed a steady growth in the use of IRT as a condition monitoring technique in civil structures, electrical installations, machineries and equipment, material deformation under various loading conditions, corrosion damages and welding processes. IRT has also found its application in nuclear, aerospace, food, paper, wood and plastic industries. With the advent of newer generations of infrared camera, IRT is becoming a more accurate, reliable and cost effective technique. This review focuses on the advances of IRT as a non-contact and non-invasive condition monitoring tool for machineries, equipment and processes. Various conditions monitoring applications are discussed in details, along with some basics of IRT, experimental procedures and data analysis techniques. Sufficient background information is also provided for the beginners and non-experts for easy understanding of the subject.
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paper_title: Verification and application of continuous surface temperature monitoring technique for investigation of nocturnal sensible heat release characteristics by building fabrics

paper_content:

This study verified and applied a novel technique, continuous surface temperature monitoring (CSTM), developed by the authors to investigate the nocturnal sensible heat release characteristics by building fabrics. The CSTM technique uses infrared technology to estimate the nocturnal sensible heat (SH) transfer between building finishes materials and the surrounding environment without knowing the physical and thermal properties of the tested materials. Forty-seven repeated indoor test were carried out for verification with the traditional internal energy equation (IE method), i.e. the product of mass, heat capacity and temperature change. The results were delightfully satisfactory with only 1.8–5.2% of average discrepancy. The R2 value of 0.972 between the two methods suggested that the developed CSTM technique statistically fits well with sensible heat release calculated by IE method. This means that the CSTM technique can be used to estimate sensible heat release from an object with insignificant error. CSTM technique was then applied for investigating 13 building surfaces in Central, Hong Kong. The findings proved that CSTM technique can be applied on number of buildings simultaneously to investigate the sensible heat release characteristics of different types of building fabrics. The results showed that granite walls release more sensible heat than ceramic walls.
---
paper_title: Infrared thermography for condition monitoring – A review

paper_content:

Temperature is one of the most common indicators of the structural health of equipment and components. Faulty machineries, corroded electrical connections, damaged material components, etc., can cause abnormal temperature distribution. By now, infrared thermography (IRT) has become a matured and widely accepted condition monitoring tool where the temperature is measured in real time in a non-contact manner. IRT enables early detection of equipment flaws and faulty industrial processes under operating condition thereby, reducing system down time, catastrophic breakdown and maintenance cost. Last three decades witnessed a steady growth in the use of IRT as a condition monitoring technique in civil structures, electrical installations, machineries and equipment, material deformation under various loading conditions, corrosion damages and welding processes. IRT has also found its application in nuclear, aerospace, food, paper, wood and plastic industries. With the advent of newer generations of infrared camera, IRT is becoming a more accurate, reliable and cost effective technique. This review focuses on the advances of IRT as a non-contact and non-invasive condition monitoring tool for machineries, equipment and processes. Various conditions monitoring applications are discussed in details, along with some basics of IRT, experimental procedures and data analysis techniques. Sufficient background information is also provided for the beginners and non-experts for easy understanding of the subject.
---
paper_title: Performance parameters for thermal imaging systems

paper_content:

Over the last few years we have been asked what typical performance characteristics should be considered while buying a thermal imaging system. The question set us thinking why such queries should arise, especially for IR systems. It is well known that for the last thirty years, there has been rapid advance in the capabilities of IR systems owing to the developments in the field of sensors, electronics, optics, instrumentation and computers. A survey of literature indicated that the terminologies used to define thermal imaging systems had also become quite complex, being borrowed from many fields such as electronics, physics, instrumentation, optics etc. This 'Back to Basics' article presents a brief but wide-ranging description of some of the important parameters used in the selection and characterisation of the performance of IR systems. A comprehension of the meaning and implications of these performance parameters is not only required for selecting appropriate equipment but it is also essential to understand the systems' capability and judiciously exploiting its full potential.
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paper_title: Nondestructive test methods for concrete bridges: A review

paper_content:

Abstract NDT methods applicable to concrete bridges are reviewed. The methodology, advantages and disadvantages along with up to date research on NDT methods are presented. Different damage levels, having less dependence on inspector judgment, are suggested. Moreover, a flow chart based on damage level along with NDT methods and potential remedial measures are proposed for periodic health monitoring of structures. NDT methods are also suggested to address specific problems related to structures. Finally, the relation between some of the well-known NDT methods and most common problems encountered by the field engineers is proposed. Hence, the importance of structural health monitoring is highlighted.
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paper_title: Thermographic measurement of the effect of humidity in mortar porosity

paper_content:

The objective of this analysis is to examine the influence of the moisture in the porosity measurement by means of thermal non-destructive test and ultrasound techniques. It is possible to determine the concrete durability by the calculation of its porosity. Porosity is determined in an indirect way, measuring mortar diffusivity by means of active thermography. Using ultrasound techniques, the porosity is related with the ultrasonic propagation of velocity. The diffusivity has been calculated using the W.J. Parker equation. In the ultrasound technique, using the pulse transmission method, ultrasonic propagation velocity was measured as a function of the water content. The conclusions express the correlation between both methods.
---
paper_title: Effects of Solar Loading on Infrared Imaging of Subsurface Features in Concrete

paper_content:

This paper addresses the effect of solar loading on thermal imaging for the detection of subsurface deterioration in concrete bridge components. The deterioration of the concrete resulting from corrosion of embedded mild reinforcing and prestressing steel results in delamination and spalling that can affect the strength and serviceability of a concrete structure. The ability to detect this deterioration during its early stages, when mitigation efforts can be employed, can provide a useful tool for maintenance and inspection personnel. Infrared thermography is a tool that has the potential to detect these subsurface defects to compliment inspection efforts and provide an additional means of condition assessment for a bridge. However, the technique relies on thermal gradients developing in the concrete such that a temperature contrast exists between damaged concrete and sound concrete. The environmental conditions at the bridge, such as direct solar loading, ambient temperature variation, and wind affect the thermal gradient in the concrete, and hence, the ability to image subsurface features. The effects of direct solar loading on the detection of subsurface targets in a concrete test block have been studied. Quantitative measurements of the thermal contrast that appear in thermal images of the test block are reported and analyzed. The effect of the depth of the embedded target is discussed, as well as the timing of inspection (relative to sunrise) that resulted in maximum contrast in thermal images.
---
paper_title: Square pulse thermography in frequency domain as adaptation of pulsed phase thermography for qualitative and quantitative applications in cultural heritage and civil engineering

paper_content:

Abstract A methodical approach for qualitative and quantitative non-destructive testing of near-surface structures in civil engineering (CE) with active thermography is presented. It adopts the non-destructive testing (NDT) method of pulsed phase thermography (PPT) for the special requirements of CE and cultural heritage. The concept might be understood as a square pulse thermography (SPT) in frequency domain or an amplitude-expanded PPT with square pulse heating. After a discussion of the material spanning concept and qualitative results in cultural heritage a new approach for quantitative non-destructive testing (NDT) of near-surface structures in CE with active thermography is introduced and tested by investigations on concrete specimen with artificial defects. It is based on the thermal diffusivity of the material and the characteristic frequency of the first extrema of phase and amplitude contrast and aims at complementing the established approaches for defect depth calculation for measurements with long heating and observation times. It should be easily extendable to other fields of application.
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paper_title: Case Study on Rapid Scanning Techniques for Concrete Bridge Decks with Asphalt Overlay: Ground-Penetrating Radar and Infrared Thermography

paper_content:

AbstractAs of 2013, the Federal Highway Administration (FHWA) estimated that one-third of the total bridge deck area in the United States was structurally deficient. Providing for the effective management and repair of these decks requires transportation agencies to have access to the best available information about structural conditions. Bridge deck inspection has long relied on sounding techniques, such as tapping and chain drag, which can be time intensive and may not provide enough information for accurate repair estimating. Nondestructive evaluation (NDE) techniques may provide faster and more accurate data collection, but their value needs to be proven to transportation agencies and bridge owners. This paper describes a case study considering the two NDE techniques available for inspecting bridge decks with asphalt overlay: ground-penetrating radar (GPR) and infrared (IR) thermography. NDE scanning results and as-built repair data for four bridge decks were made available to the research team. Comp...
---
paper_title: APPLICATION OF INFRARED THERMOGRAPHY TO THE NON-DESTRUCTIVE TESTING OF CONCRETE AND MASONRY BRIDGES

paper_content:

Abstract Within recent years there has been an increase in the use of NDT methods to detect defects and anomalies in various civil engineering structures. Infrared thermography, which has been successfully used in the USA in civil engineering applications, is being increasingly applied in the UK as an NDT technique. For example, the technique is now included in the Building Regulations for the assessment of thermal insulation for all new non-domestic buildings from April 2002. One of the perceived limitations of infrared thermography is that in temperate climates it is too cold to use this technique since there is rarely the extreme solar exposure that has enabled the successful use of thermography to detect render debonding and concrete spalling utilising solar heating. However, with the advancements in modern technology it is now possible to detect smaller changes in temperature (down to 0.08 °C). This paper shows that even with the low ambient temperatures experienced in Europe it is possible to use infrared thermography to identify correctly known areas of delamination in a concrete bridge structure and also to investigate the internal structure of a masonry bridge.
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paper_title: Investigation of Mix-Variation Effect on Defect-Detection Ability Using Infrared Thermography as a Nondestructive Evaluation Technique

paper_content:

AbstractInfrared thermography (IRT) is a promising nondestructive evaluation technique that has been widely used for bridge deck inspection. It is a quick and fairly simple method for providing preliminary information about defected areas in bridge decks. However, detection capabilities and sensitivity to environmental conditions and material properties impose certain challenges for the application of IRT. In this paper, the effect of various concrete mixtures on passive IRT was investigated. Four concrete mixtures (i.e., conventional, high-strength, self-consolidated, and lightweight concrete) were considered in the evaluation. Various defects with relatively small sizes placed at different depths were simulated and planted in cast-in-place slabs. The casting and testing took place in the United Arab Emirates (UAE), which is considered a hot-weather region. The defected slabs were imaged, and the existence of defects was judged visually. A minimum of 0.8°C was used for successful detection to make a more...
---
paper_title: Verification and application of continuous surface temperature monitoring technique for investigation of nocturnal sensible heat release characteristics by building fabrics

paper_content:

This study verified and applied a novel technique, continuous surface temperature monitoring (CSTM), developed by the authors to investigate the nocturnal sensible heat release characteristics by building fabrics. The CSTM technique uses infrared technology to estimate the nocturnal sensible heat (SH) transfer between building finishes materials and the surrounding environment without knowing the physical and thermal properties of the tested materials. Forty-seven repeated indoor test were carried out for verification with the traditional internal energy equation (IE method), i.e. the product of mass, heat capacity and temperature change. The results were delightfully satisfactory with only 1.8–5.2% of average discrepancy. The R2 value of 0.972 between the two methods suggested that the developed CSTM technique statistically fits well with sensible heat release calculated by IE method. This means that the CSTM technique can be used to estimate sensible heat release from an object with insignificant error. CSTM technique was then applied for investigating 13 building surfaces in Central, Hong Kong. The findings proved that CSTM technique can be applied on number of buildings simultaneously to investigate the sensible heat release characteristics of different types of building fabrics. The results showed that granite walls release more sensible heat than ceramic walls.
---
paper_title: Principles of Thermography and Radar for Bridge Deck Assessment

paper_content:

Traditional methods of bridge deck condition assessment are slow, labor‐intensive, intrusive to traffic, and unreliable. Two new technologies, radar and infrared thermography, which have recently been introduced, show promise for producing rapid and accurate condition assessment for bridge decks. These technologies are being applied without the benefit of a firm physical understanding of their inherent capabilities and limitations. This paper discusses the physical principles upon which these techniques are based, and proposes simple physical models for the prediction of radar and infrared response to various bridge deck conditions. Parameter studies are carried out using these models to predict the radar and infrared response to moisture, chloride, delamination, and deck geometry. The model study results show the range of sensitivity and the inherent limitations of these two techniques. These results have led to the suggestion of a predictive technique that has been used in field studies of repaired and ...
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paper_title: Nondestructive Testing to Identify Concrete Bridge Deck Deterioration

paper_content:

This document presents the research results. The project consisted of two phases. In the first phase, a thorough literature search was performed to identify common forms of deterioration in concrete bridge decks, as well as the nondestructive testing (NDT) technologies that can effectively detect and characterize it. The following four defects were identified as those of the highest importance: rebar corrosion, delamination, vertical cracking, and concrete degradation. In addition, a framework for technology grading and ranking was developed, based on five performance measures: accuracy, repeatability, speed, ease of use, and cost. The focus of the second phase was on the validation of promising technologies in both laboratory and actual production-level conditions with respect to the five performance measures. The validated technologies were consequently graded and ranked. The ultimate product of this project was an electronic repository for practitioners, named “NDToolbox”. The repository provides information regarding recommended technologies for the detection of a particular deterioration type. It also provides information about particular technologies, including their description, physical principle of operation, applications, advantages and limitations, equipment, recommended protocols for data collection and analysis, and typical data presentation.
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paper_title: Comparison of NDT Methods for Assessment of a Concrete Bridge Deck

paper_content:

The field application of three different nondestructive tests (NDTs)—air-coupled impact echo (IE), infrared (IR) thermography, and sounding (chain drag)—are evaluated in this paper, where an actual in-service concrete bridge deck is tested. Two different contactless IE test equipment sets are deployed as part of an effort to develop new rapid measurement methods. The IE data are presented as two-dimensional frequency maps, and the IR data are presented as temperature maps over the tested area. Sounding (chain-drag) result maps are also presented. For verification of the location of near-surface delamination damage, eight drilled core samples were extracted from the test area. The results obtained from each of the individual NDT methods show reasonably good agreement with the drilled cores in terms of locating near-surface delamination. Finally, the NDT methods are compared across general performance criteria, considering accuracy, testing practicality, and costs. The analysis shows that all of the evaluated NDT methods are comparable, and the chain-drag method is not more accurate and reliable for detection of shallow delamination in the deck.
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paper_title: Imaging of concrete structures

paper_content:

Abstract Demand for the development of non-destructive testing (NDT) techniques for concrete structures has increased with the growing concern about the deteriorating condition of the World's infrastructure. Efficient and accurate imaging techniques are needed for a reliable evaluation of safety and serviceability of concrete structures. Although, presently, imaging is routinely used in various fields, implementation of these technologies in NDT of civil engineering systems, especially of concrete structures, offers many challenges and requires additional development due to the composite nature of the concrete material and the complexities of reinforced or prestressed concrete systems. This paper presents the basic principles of various imaging techniques associated with several NDT methods applicable to concrete structures. The techniques considered are radiography, radioactive computerized tomography, infrared thermography, radar imaging and acoustic imaging. Special considerations regarding the applicability and accuracy of these techniques for the condition assessment of concrete structures are discussed, and examples of imaging applications are given.
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paper_title: Investigation of Mix-Variation Effect on Defect-Detection Ability Using Infrared Thermography as a Nondestructive Evaluation Technique

paper_content:

AbstractInfrared thermography (IRT) is a promising nondestructive evaluation technique that has been widely used for bridge deck inspection. It is a quick and fairly simple method for providing preliminary information about defected areas in bridge decks. However, detection capabilities and sensitivity to environmental conditions and material properties impose certain challenges for the application of IRT. In this paper, the effect of various concrete mixtures on passive IRT was investigated. Four concrete mixtures (i.e., conventional, high-strength, self-consolidated, and lightweight concrete) were considered in the evaluation. Various defects with relatively small sizes placed at different depths were simulated and planted in cast-in-place slabs. The casting and testing took place in the United Arab Emirates (UAE), which is considered a hot-weather region. The defected slabs were imaged, and the existence of defects was judged visually. A minimum of 0.8°C was used for successful detection to make a more...
---
paper_title: Practical identification of favorable time windows for infrared thermography for concrete bridge evaluation

paper_content:

Abstract Infrared Thermography (IRT) is one of the nondestructive inspection techniques to detect delaminations in concrete bridge decks. These defects are identified by capturing the temperature gradient of concrete surfaces. In order for this technique to be effective in damage detection, IRT inspections should be conducted at certain time windows with favorable temperature conditions to get clear temperature gradients on inspected surfaces. This study is an experimental work examining the effects of ambient environmental conditions at different times of a day to locate subsurface delaminations and voids at a shallow depth, which is an additional influencing factor. This study also attempts to figure out a relationship between ambient environmental conditions and the temperature values of concrete surfaces to estimate the best time window with appropriate environmental conditions for IRT inspections. To this end, specially designed reusable concrete test plates with different thicknesses were manufactured to collect thermocouple sensor readings. Multiple regression analyses were employed to generate prediction models that seek a relationship between environmental conditions and temperature gradients on the test plates attached to a target bridge. Regression models also utilized sensor data collected at another location different than the target bridge location. It was found out that the most important aspect of sensor data collection was to accomplish a perfect contact of test plates with concrete bridge deck surfaces to get discernible temperature gradients. When this condition is not met, data analyses yield spurious results leading to futile conclusions. On the other hand, it was also observed that prediction models generated by regression analyses followed the same pattern as that of sensor readings. This makes it possible to have prediction equations based on sensor readings to determine suitable time window for conducting IRT inspections.
---
paper_title: A data processing methodology for infrared thermography images of concrete bridges

paper_content:

Abstract This study presents a methodology to improve the usability and efficiency of infrared thermography (IRT) for subsurface damage detection in concrete structures. A practical and more objective approach to obtain a threshold for IRT data processing was developed by incorporating finite element (FE) model simulations. Regarding the temperature thresholds of sound and delaminated areas, the temperature of the sound part was obtained from the IR image, and the temperature of the delaminated area was defined by FE model simulation. With this methodology, delaminated areas of concrete slabs at 1.27 cm and 2.54 cm depths could be detected more objectively than by visually judging the color contrast of IR images. However, it was also found that the boundary condition affects the accuracy of the method, and the effect varies depending on the data collection time. On the other hand, it can be assumed that the influential area of the boundary condition is much smaller than the area of a bridge deck in real structures; thus, it might be ignorable on real concrete bridge decks. Even though there are some limitations, this methodology performed successfully paving the way towards automated IRT data analysis for concrete bridge deck inspections.
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paper_title: Application of impulse-thermography for non-destructive assessment of concrete structures

paper_content:

Abstract Impulse-thermography is an active method for quantitative investigations of the near surface region of various structures. It has recently been applied and optimised to applications in civil engineering. By using either an internal or external heat source, parts of the structure under investigation are heated up and the transient heat flux is observed by recording the temperature change at the surface as a function of time. This method is very well suited for the detection of voids and honeycombing in concrete, up to concrete covers of 10 cm as well as for the location of delaminations in multi-layered systems (e.g. plaster on concrete, CFRP-laminates on concrete, asphalt on concrete). Also safety relevant defects like voids in tendon ducts and cracks in concrete could be recognised.
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paper_title: Investigation of effective utilization of infrared thermography (IRT) through advanced finite element modeling

paper_content:

Abstract Infrared thermography (IRT) has been used experimentally for concrete delamination detection. The past studies were conducted with limited experimental conditions, which make a difference in delamination detection. As a result, there are inconsistencies in the results reported in the literature. In this study, heat transfer models of concrete blocks with artificial delamination used for a previous test are developed and analyzed to explore sensitive parameters for effective utilization of IRT. After these FE models are validated, critical parameters and factors of delamination detectability such as the size of delamination (area, thickness and volume), ambient temperature and solar irradiance conditions (different seasons), and the depth of delamination from the surface are explored. This study presents that the area of delamination is much more influential in the detectability of IRT than thickness and volume. It is also found that there is no significant difference depending on the season when IRT is employed. This study shows a potential to bring significant improvement to IRT use in the field for subsurface damage detection for concrete structures.
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paper_title: Nondestructive Bridge Deck Testing with Air-Coupled Impact-Echo and Infrared Thermography

paper_content:

Two different nondestructive test (NDT) methods, air-coupled impact-echo (IE) and infrared (IR) thermography are evaluated on a full-scale simulated reinforced concrete bridge deck containing simulated delamination and cracking defects. The IE data are presented as two-dimensional frequency maps and spectral B-scan lines. The IR data are presented as temperature maps on the concrete surface. The lateral boundaries of the detected delaminations are also indicated in the images. The results obtained from each of the individual NDT methods show reasonably good agreement with most of the actual defects. The advantages and limitations of each method to characterize defects are discussed. The consistency and sensitivity of each method are also investigated. Finally, a simple data fusion technique is proposed to improve effectiveness of the individual test data. The findings from this study demonstrate that the combination of air-coupled IE and IR thermography tests is a practical option for consistent and rapid in situ evaluation of reinforced concrete bridge decks.
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paper_title: Bridge deck delamination identification from unmanned aerial vehicle infrared imagery

paper_content:

Abstract The rapid, cost-effective, and non-disruptive assessment of bridge deck condition has emerged as a critical challenge for bridge maintenance. Deck delaminations are a common form of deterioration which has been assessed, historically, through chain-drag techniques and more recently through nondestructive evaluation (NDE) including both acoustic and optical methods. Although NDE methods have proven to be capable to provide information related to the existence of delaminations in bridge decks, many of them are time-consuming, labor-intensive, expensive, while they further require significant disruptions to traffic. In this context, this article demonstrates the capability of unmanned aerial vehicles (UAVs) equipped with both color and infrared cameras to rapidly and effectively detect and estimate the size of regions where subsurface delaminations exist. To achieve this goal, a novel image post-processing algorithm was developed to use such multispectral imagery obtained by a UAV. To evaluate the capabilities of the presented approach, a bridge deck mockup with pre-manufactured defects was tested. The major advantages of the presented approach include its capability to rapidly identify locations where delaminations exist, as well as its potential to automate bridge-deck related damage detection procedures and further guide investigations using other higher accuracy and ground-based approaches.
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paper_title: Combined use of thermography and ultrasound for the characterization of subsurface cracks in concrete

paper_content:

Abstract Corrosion of metal reinforcement in concrete structures leads to cracks extending towards the surface. These cracks do not show any visual sign until they break the surface, exposing the structure to more accelerated deterioration. In order to develop a methodology for subsurface damage characterization, a combination of nondestructive testing (NDT) techniques was applied. Thermography is specialized in subsurface damage identification due to anomalies that inhomogeneities impose on the temperature field. Additionally, ultrasonic Rayleigh waves are constrained near the surface and therefore, are ideal for characterization of near-surface damage. In this study, an infrared camera scans the specimen in order to indicate the position of the crack. Consequently, ultrasonic sensors are placed on the specified part of the surface in order to make a more detailed assessment for the depth of the crack. Although there is no visual sign of damage, Rayleigh waves are influenced in terms of velocity and attenuation. Numerical simulations are also conducted, to propose suitable parameters like frequency for more accurate testing. The combination of the NDT techniques seems promising for real structures assessment.
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paper_title: Concrete bridge deck condition assessment using IR Thermography and Ground Penetrating Radar technologies

paper_content:

Abstract The current practice of bridge inspection relies heavily on visual inspection, which suffers from several limitations, including the safety of the inspection team, the accuracy of subsurface defects detection, and subjectivity. In visual inspection, data collection is time consuming and the collected data is typically documented by completing standard inspection reports. These reports do not provide sufficient visualization of locations and/or the extent of defects. Emerging combinations of non-destructive testing (NDT) technologies and Geographic Information Systems (GIS) have the potential to circumvent some of these limitations. More research is still needed to assess the potential of these technologies to be applied in the field and to address the challenges in deploying them. The challenges include data acquisition and processing, data interpretation to identify the location and extent of defects, and the integration of results obtained from multiple technologies. This research introduces an integrated method utilizing Infrared (IR) Thermography and Ground Penetrating Radar (GPR) technologies to enhance the detection of concrete bridge defects. Integrating results can improve confidence in defect detection and quantification, and as a result can enhance the reliability of the bridge condition rating process. The integrated system is implemented in a case study of a concrete bridge deck in the city of Laval, Quebec, Canada. The obtained results are compared to detailed and visual inspection results conducted on the bridge before its demolition. The study analyzes potential, limitations, and challenges of using the proposed integrated method. In addition, the study demonstrates the feasibility of integrating the collected data in ArcGIS for enhanced visualization of the inspection results.
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paper_title: Case Study on Rapid Scanning Techniques for Concrete Bridge Decks with Asphalt Overlay: Ground-Penetrating Radar and Infrared Thermography

paper_content:

AbstractAs of 2013, the Federal Highway Administration (FHWA) estimated that one-third of the total bridge deck area in the United States was structurally deficient. Providing for the effective management and repair of these decks requires transportation agencies to have access to the best available information about structural conditions. Bridge deck inspection has long relied on sounding techniques, such as tapping and chain drag, which can be time intensive and may not provide enough information for accurate repair estimating. Nondestructive evaluation (NDE) techniques may provide faster and more accurate data collection, but their value needs to be proven to transportation agencies and bridge owners. This paper describes a case study considering the two NDE techniques available for inspecting bridge decks with asphalt overlay: ground-penetrating radar (GPR) and infrared (IR) thermography. NDE scanning results and as-built repair data for four bridge decks were made available to the research team. Comp...
---
paper_title: Combined Imaging Technologies for Concrete Bridge Deck Condition Assessment

paper_content:

Evaluating the condition of concrete bridge decks is an increasingly important challenge for transportation agencies and bridge inspection teams. Closing the bridge to traffic, safety, and time consuming data collection are some of the major issues during a visual or in-depth bridge inspection. To date, several nondestructive testing technologies have shown promise in detecting subsurface deteriorations. However, the main challenge is to develop a data acquisition and analysis system to obtain and integrate both surface and subsurface bridge health indicators at higher speeds. Recent developments in imaging technologies for bridge decks and higher-end cameras allow for faster image collection while driving over the bridge deck. This paper will focus on deploying nondestructive imaging technologies such as the three-dimensional (3D) optical bridge evaluation system (3DOBS) and thermal infrared (IR) imagery on a bridge deck to yield both surface and subsurface indicators of condition, respectively. Spall and delamination maps were generated from the optical and thermal IR images. Integration of the maps into ArcGIS, a professional geographic information system (GIS), allowed for a streamlined analysis that included integrating and combining the results of the complimentary technologies. Finally, ground truth information was gathered through coring several locations on a bridge deck to validate the results obtained by nondestructive evaluation. This study confirms the feasibility of combining the bridge inspection results in ArcGIS and provides additional evidence to suggest that thermal infrared imagery provides similar results to chain dragging for bridge inspection.
---
paper_title: Comparison of NDT Methods for Assessment of a Concrete Bridge Deck

paper_content:

The field application of three different nondestructive tests (NDTs)—air-coupled impact echo (IE), infrared (IR) thermography, and sounding (chain drag)—are evaluated in this paper, where an actual in-service concrete bridge deck is tested. Two different contactless IE test equipment sets are deployed as part of an effort to develop new rapid measurement methods. The IE data are presented as two-dimensional frequency maps, and the IR data are presented as temperature maps over the tested area. Sounding (chain-drag) result maps are also presented. For verification of the location of near-surface delamination damage, eight drilled core samples were extracted from the test area. The results obtained from each of the individual NDT methods show reasonably good agreement with the drilled cores in terms of locating near-surface delamination. Finally, the NDT methods are compared across general performance criteria, considering accuracy, testing practicality, and costs. The analysis shows that all of the evaluated NDT methods are comparable, and the chain-drag method is not more accurate and reliable for detection of shallow delamination in the deck.
---
paper_title: Nondestructive Bridge Deck Testing with Air-Coupled Impact-Echo and Infrared Thermography

paper_content:

Two different nondestructive test (NDT) methods, air-coupled impact-echo (IE) and infrared (IR) thermography are evaluated on a full-scale simulated reinforced concrete bridge deck containing simulated delamination and cracking defects. The IE data are presented as two-dimensional frequency maps and spectral B-scan lines. The IR data are presented as temperature maps on the concrete surface. The lateral boundaries of the detected delaminations are also indicated in the images. The results obtained from each of the individual NDT methods show reasonably good agreement with most of the actual defects. The advantages and limitations of each method to characterize defects are discussed. The consistency and sensitivity of each method are also investigated. Finally, a simple data fusion technique is proposed to improve effectiveness of the individual test data. The findings from this study demonstrate that the combination of air-coupled IE and IR thermography tests is a practical option for consistent and rapid in situ evaluation of reinforced concrete bridge decks.
---

Title: Infrared thermography as a non-destructive test for the inspection of reinforced concrete bridges: A review of the state of the art

Section 1: INTRODUCTION
Description 1: Describe the importance of the inspection and maintenance of reinforced concrete bridges, the limitations of visual inspections, and the role of non-destructive testing methods like infrared thermography.

Section 2: Historic review and operation principle
Description 2: Provide a historical background of infrared thermography, its basic principles, and how it detects infrared radiation.

Section 3: Methodology and analysis
Description 3: Explain the different types of infrared thermography (active and passive), the distinctions between quantitative and qualitative measurements, and the associated methodologies and analyses.

Section 4: Advantages and limitations
Description 4: Discuss the benefits of using infrared thermography for bridge inspections, along with its limitations and challenges.

Section 5: Thermographic cameras
Description 5: Detail the evolution and important performance parameters of thermal cameras used in infrared thermography.

Section 6: INSPECTION OF BRIDGES
Description 6: Elaborate on how infrared thermography is applied for the inspection of bridges, including concepts of heat transfer in concrete and defect detection through thermal gradients.

Section 7: Depth and size of delamination and inspection time
Description 7: Summarize research on the detection of delaminations and defects, their depth and size, and recommendations on the optimal time for data collection.

Section 8: Combination with other non-destructive tests
Description 8: Illustrate how infrared thermography can be combined with other non-destructive testing methods to provide a comprehensive assessment of bridge conditions.

Section 9: CONCLUSIONS
Description 9: Conclude by summarizing the effectiveness, advancements, limitations, and future potential of infrared thermography in the inspection and maintenance of reinforced concrete bridges.

Section 10: ACKNOWLEDGEMENTS
Description 10: Acknowledge the contributions and financial support received for the study, if any.