Guidelines for Thermographic Inspection of Concrete Bridge Components in Shaded Conditions

Abstract

Infrared thermography has the potential to detect subsurface delaminations before spalling develops and could be used to improve the visual inspection of concrete bridges. The technology has traditionally been applied to bridge decks, which are exposed to radiant heating from the sun that helps develop the necessary thermal gradients in the concrete. Thermal gradients can also be developed from normal diurnal temperature variations. Convective heat transfer develops the thermal gradients, although these thermal gradients are of much lower magnitude than those developed through radiant heating from the sun. This paper presents the results of a study to develop thermal imaging for the detection of subsurface deterioration in the soffit areas of bridges; these soffit areas are shaded and therefore are not exposed to radiant heating from the sun. Experimental studies and field testing were conducted and are described. This paper reports on guidelines developed for this application of the technology; the guidelines address the necessary environmental conditions to enable the detection of damage in bridge soffit areas. Specifically, the paper discusses the rates of change in ambient temperature needed to ensure that subsurface damage can be detected in shaded conditions. The paper also discusses the effect of wind speed on the detectability of subsurface damage in the shaded areas of a bridge, as well as the camera settings needed to ensure that an inspector can detect temperature anomalies associated with subsurface damage. A field example is provided to illustrate the application of the technology and highlight the required camera settings.

Clustering-Based Threshold Model for Condition Assessment of Concrete Bridge Decks Using Infrared Thermography

“…The reason for this is that, during the day, a warming trend existed such that the targets had positive thermal contrasts, which meant that the delaminated regions were at a temperature higher than that of the sound concrete. This is the anticipated behavior based on the fundamental heat transfer theories and complies with previous results reported by Washer et al (2013) and Chase et al (2015).…”

“…For instance, Maser et al (2009) reported that in most bridge structures, areas of severe corrosion are associated with delamination even if cracks are not detected directly. Washer et al (2013) reported that not all delamination can be observed in GPR images and both GPR and IRT can be used together for accurate identification of anomalies in highway bridges. The hammer sounding results showed 40% total delaminated areas on the bridge deck (40% of the total delaminations is common between these two surveys).…”

Infrared thermography for civil structural assessment: demonstrations with laboratory and field studies

“…Since concrete structures do not always have homogeneous temperatures due to differences of locations and orientations with respect to the sun as discussed by Washer et al [4], sometimes IRT makes it difficult to interpret the data from raw IR images due to a lot of noise depending on the time of photography as reported in [5]. As Washer et al [19] argued, if the temperature span for IR images is setup around 2°C, while some defects can be detected clearly, some anomalies generate higher/lower temperature than the temperature span and IRT cannot detect them at the temperature span. Therefore, they recommended adjusting the temperature span of IRT continuously throughout inspections.…”

“…Furthermore, delaminated areas are enclosed by dotted line. The temperature range of the IR images was set up to 3.0 K for all images as Washer et al suggested in [19], and the level setting was adjusted manually for each IR image to figure out the color contrast between the middle and surrounding areas.…”

In-Service Performance and Behavior Characterization of the Hybrid-Composite Bridge System

“…Thermography is often used to search for voids or delamination in concrete because the thermal properties of air are quite disparate from those of concrete. This type of NDE testing will be discussed in section 4.3.3 below in regards to potential delamination of the FRP shell (Washer, Fenwick & Nelson, 2013).…”