Conference Paper

Considerations for Infrared Thermography Field Implementations and Data Analysis for Bridge Inspections

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Abstract

The main objective of this paper is to further explore infrared thermography (IRT) with advanced data analysis methods to overcome some of the limitations of IRT. A case study from a bridge in Jacksonville, FL is presented along with successful detection results as well as uncertainties for the bridge deck, underside, piers, and pier caps. In this study, IRT was utilized on this bridge for a number of locations, with hammer sounding validation to discuss the feasibility of IRT for certain scenarios such as discoloration, shading, reflection. For example, the uncertainties associated with IRT application, such as the effect of reflections from surrounding objects and solar radiation are presented and discussed. These areas were also cross-checked by visual examination of the physical site or the visual image of the surface. The delaminated areas of the bridge deck, underside of the deck and the pier were successfully detected by IRT and validated by hammer sounding. Next, this study presents an advanced IRT data analysis method using finite element modeling to estimate the approximate depth and severity of the delamination detected by IRT, which has been a shortcoming of IRT in the past.

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... 9 Concrete delamination is not only limited to the concrete bridge deck but also the concrete soffits, girders, piers, and abutments of the bridge. [10][11][12][13] In the past, fatalities have been reported due to concrete spall falling onto a motorist from the soffit of an overpass bridge. 11 Concrete is the second most used material in the world after water. ...
Article
Infrared thermography (IRT) has been widely used in detecting the subsurface delamination of bridge deck. However, IRT inspection on delamination zones of the bridge deck which have limited exposure to direct solar radiation (e.g., the bottom surface of the bridge deck) is rather challenging due to the relatively low thermal contrast (∆T) development in these zones. Therefore, the purpose of this study is to conduct a series of experimental studies in conjunction with numerical modeling for investigating the effectiveness of IRT in delamination detection of bridge deck components which are normally not exposed to direct solar radiation. Specially, the effects of different environmental conditions, thickness of bridge deck, and defect characteristics on the absolute thermal contrast (∆T) development were systematically investigated. The results show that IRT can effectively detect the subsurface delamination of concrete bridge deck located in regions that are not exposed to the direct solar radiation. In addition, the development of detectable thermal contrast (>0.5°C) is much dependent on the rate of change in ambient temperature with a suitable detection period between 8 am and 4 pm. Furthermore, it shows that the value of ∆T increases with the increase of bridge deck thickness and delamination size.
... Fig. 18(b) shows another example of the effect of sunlight during daytime. This IR image was taken at a sidewalk of a bridge deck in Jacksonville, FL, around noon time [44]. The enclosed area was de- tected by IRT, and the delaminated area was validated by hammer sounding. ...
Article
Capturing the temperature difference between sound and defective parts under ambient conditions is key for infrared thermography (IRT) on concrete bridges. This study explores the favorable time windows for concrete bridge deck inspections by IRT through field experiment and finite element model simulations. Based on the numerical simulations and experimental IRT results, the preferable thermal contrast to detect defects occurs during both daytime and nighttime. However, available time span during daytime is much shorter than that of nighttime due to interchange periods between cooling and heating cycles in the morning and in the evening. Furthermore, IRT is affected by sunlight during the daytime resulting in possible misdetections. Moreover, effects of clouds and radiative cooling are observed, and it is found that the clear sky is a preferable condition for IRT. Therefore, optimal conditions for IRT implementation on concrete bridge decks can be concluded that nighttime application under the clear sky condition. In addition, the effect of obstacles on a bridge surface such as gravel, wood chips that bring additional challenges to IRT are also evaluated experimentally.
Thesis
Full-text available
Deterioration of road infrastructure arises from aging and various other factors. Consequently, inspection and maintenance have been a serious worldwide problem. In the United States, degradation of concrete bridge decks is a widespread problem among several bridge components. In order to prevent the impending degradation of bridges, periodic inspection and proper maintenance are indispensable. However, the transportation system faces unprecedented challenges because the number of aging bridges is increasing under limited resources, both in terms of budget and personnel. Therefore, innovative technologies and processes that enable bridge owners to inspect and evaluate bridge conditions more effectively and efficiently with less human and monetary resources are desired. Traditionally, qualified engineers and inspectors implemented hammer sounding and/or chain drag, and visual inspection for concrete bridge deck evaluations, but these methods require substantial field labor, experience, and lane closures for bridge deck inspections. Under these circumstances, Non-Destructive Evaluation (NDE) techniques such as computer vision-based crack detection, impact echo (IE), ground-penetrating radar (GPR) and infrared thermography (IRT) have been developed to inspect and monitor aging and deteriorating structures rapidly and effectively. However, no single method can detect all kinds of defects in concrete structures as well as the traditional inspection combination of visual and sounding inspections; hence, there is still no international standard NDE methods for concrete bridges, although significant progress has been made up to the present. This research presents the potential to reduce a burden of bridge inspections, especially for bridge decks, in place of traditional chain drag and hammer sounding methods by IRT with the combination of computer vision-based technology. However, there were still several challenges and uncertainties in using IRT for bridge inspections. This study revealed those challenges and uncertainties, and explored those solutions, proper methods and ideal conditions for applying IRT in order to enhance the usability, reliability and accuracy of IRT for concrete bridge inspections. Throughout the study, detailed investigations of IRT are presented. Firstly, three different types of infrared (IR) cameras were compared under active IRT conditions in the laboratory to examine the effect of photography angle on IRT along with the specifications of cameras. The results showed that when IR images are taken from a certain angle, each camera shows different temperature readings. However, since each IR camera can capture temperature differences between sound and delaminated areas, they have a potential to detect delaminated areas under a given condition in spite of camera specifications even when they are utilized from a certain angle. Furthermore, a more objective data analysis method than just comparing IR images was explored to assess IR data. Secondly, coupled structural mechanics and heat transfer models of concrete blocks with artificial delaminations used for a field test were developed and analyzed to explore sensitive parameters for effective utilization of IRT. After these finite element (FE) models were validated, critical parameters and factors of delamination detectability such as the size of delamination (area, thickness and volume), ambient temperature and sun loading condition (different season), and the depth of delamination from the surface were 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. Then, FE model simulations were used to obtain the temperature differences between sound and delaminated areas in order to process IR data. By using this method, delaminated areas of concrete slabs could be detected more objectively than by judging the color contrast of IR images. However, it was also found that the boundary condition affects the accuracy of this method, and the effect varies depending on the data collection time. Even though there are some limitations, integrated use of FE model simulation with IRT showed that the combination can be reduce other pre-tests on bridges, reduce the need to have access to the bridge and also can help automate the IRT data analysis process for concrete bridge deck inspections. After that, the favorable time windows for concrete bridge deck inspections by IRT were explored through field experiment and FE model simulations. Based on the numerical simulations and experimental IRT results, higher temperature differences in the day were observed from both results around noontime and nighttime, although IRT is affected by sun loading during the daytime heating cycle resulting in possible misdetections. Furthermore, the numerical simulations show that the maximum effect occurs at night during the nighttime cooling cycle, and the temperature difference decreases gradually from that time to a few hours after sunrise of the next day. Thus, it can be concluded that the nighttime application of IRT is the most suitable time window for bridge decks. Furthermore, three IR cameras with different specifications were compared to explore several factors affecting the utilization of IRT in regards to subsurface damage detection in concrete structures, specifically when the IRT is utilized for high-speed bridge deck inspections at normal driving speeds under field laboratory conditions. The results show that IRT can detect up to 2.54 cm delamination from the concrete surface at any time period. This study revealed two important factors of camera specifications for high-speed inspection by IRT as shorter integration time and higher pixel resolution. Finally, a real bridge was scanned by three different types of IR cameras and the results were compared with other NDE technologies that were implemented by other researchers on the same bridge. When compared at fully documented locations with 8 concrete cores, a high-end IR camera with cooled detector distinguished sound and delaminated areas accurately. Furthermore, indicated location and shape of delaminations by three IR cameras were compared to other NDE methods from past research, and the result revealed that the cooled camera showed almost identical shapes to other NDE methods including chain drag. It should be noted that the data were collected at normal driving speed without any lane closures, making it a more practical and faster method than other NDE technologies. It was also presented that the factor most likely to affect high-speed application is integration time of IR camera as well as the conclusion of the field laboratory test. The notable contribution of this study for the improvement of IRT is that this study revealed the preferable conditions for IRT, specifically for high-speed scanning of concrete bridge decks. This study shows that IRT implementation under normal driving speeds has high potential to evaluate concrete bridge decks accurately without any lane closures much more quickly than other NDE methods, if a cooled camera equipped with higher pixel resolution is used during nighttime. Despite some limitations of IRT, the data collection speed is a great advantage for periodic bridge inspections compared to other NDE methods. Moreover, there is a high possibility to reduce inspection time, labor and budget drastically if high-speed bridge deck scanning by the combination of IRT and computer vision-based technology becomes a standard bridge deck inspection method. Therefore, the author recommends combined application of the high-speed scanning combination and other NDE methods to optimize bridge deck inspections.
Article
Full-text available
A detailed investigation of infrared thermography (IRT) for civil structures is presented by considering different technologies, data analysis methods and experimental conditions in the laboratory and also in the field. Three different types of infrared (IR) camera were compared under active IRT conditions in the laboratory to examine the effect of photography angle on IRT along with the specifications of cameras. It is found that when IR images are taken from a certain angle, each camera shows different temperature readings. However, since each IR camera can capture temperature differences between sound and delaminated areas, they have a potential to detect delaminated area under a given condition in spite of camera specifications even when they are utilized from a certain angle. Furthermore, a more objective data analysis method than just comparing IR images was explored to assess IR data, and it is much easier to detect delamination than raw IR images. Specially designed laboratory and field studies show the capabilities, opportunities and challenges of implementing IRT for civil structures.
Article
The main objective of this study is to comprehensively evaluate the utilization of infrared thermography (IRT) considering different technologies, critical environmental parameters, and uncertainties for bridge deck evaluation. For this purpose, a real bridge was scanned and the results were compared with other nondestructive evaluation (NDE) technologies that were implemented on the same bridge. There are a number of considerations and factors that affect the utilization of IRT, such as thermal contrasts, camera specifications, distance, and utilization speed, and these are evaluated by using three different infrared (IR) cameras with different specifications. These considerations are discussed and results are presented. When compared at fully documented locations with eight concrete cores, a high-end IR camera with cooled detector distinguished sound and delaminated areas accurately. Furthermore, indicated location and shape of delaminations by three IR cameras were compared with other NDE methods from past research, and the results revealed that the cooled camera showed shapes almost identical to other NDE methods including chain drag. It should be noted that these data were collected at a normal driving speed without any lane closures, making it a more practical and faster method than other NDE technologies. It is also presented that the factor most likely to affect high-speed application is integration time of the IR camera.
Article
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.
Article
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.
Article
The author experimented to make the following relation clear about the external wall which is finished with the tile, the kind of tile, the condition of the removement, the environment at taking a thermograph, the wavelength of thermo-camera and the characteristic of the thermographs and the precision to distinguish removed parts. By the experiments using the test walls, the following item became clear. (1) The removement of tiles and the removement of fundamental mortar differ in the temperature response speed to the change of solar radiation. (2) As for the walls without solar radiation, it is possible to apply the thermography method, but it is rather unclear. (3) When the solar radiation lashes to the wall, as dark as the color of tile, it is easier to distinguish the removed part. The distinction precision by LW machine is better than the SW machine, when noise is small. (4) When the solar radiation doesn't lash, the wavelength influence to precision of distinction. On the LW machine, when taking the thermograph luster tile, the precision of distinction declines by the noise. (5) It is necessary about 1.0 ℃ to distinguish the shape of the removed part when the solar radiation lashes, and about 0.5 ℃ when the solar radiation dosen't lash. The removment of tyle can be distinguished with smaller temperature difference than removment of mortar. (6) The SW machine is influenced by the reflection of the sun and the contrast of the sunshine and the shade. The LW machine is influenced by the object such as the sky and the opposite building. (7) The author ordered apply-ability for each measurement wavelength, in the thermography method.
Article
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.
Article
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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