Infrared Testing: The Complementary Dual Camera System

How our high resolution video complements the abilities of Infrared.

Infrared data is collected using a FLIR thermographic camera, which measures surface temperature and can provide information regarding subsurface damage in bridge decks.  The camera is mounted to a vehicle and data can be collected at highway speeds with clear and accurate results.  After surveying each lane, the data is stitched together to create a comprehensive plan-view thermography image.

Figure 1. IR stitch of two inner spans of a two-lane bridge with clear delamination/debonding

Figure 1. IR stitch of two inner spans of a two-lane bridge with clear delamination/debonding

The areas that appear white in Figure 1 are hot spots resulting from debonding or delamination.  When an overlay debonds or a delamination exists at the rebar-level, the resulting air void acts as a thermal barrier, producing relatively higher temperature (white blotchy areas) in the IR image.  We delineate these areas to provide both subsurface defect quantities and maps to our clients. High resolution video is also collected with the infrared data, and used to filter out surface features that produce thermal anomalies but are unrelated to subsurface conditions.   Similar to the infrared, the video data can be stitched together to create a plan-view image for a bridge deck. This image can be used to identify, quantify, and map areas of patching, spalling, and cracking.

Figure 2.  Video proof that thermal anomaly in IR image is surface obstruction

Figure 2.  Video proof that thermal anomaly in IR image is surface obstruction

Figure 2 shows an area of thermal activity in front of the vehicle that was found to match the shape and location of surface staining in the high resolution video.  As a result, this area was delineated and categorized as a "thermal obstruction" instead of a delamination.  Obstructions can include discoloration, oil stains, rust deposits, debris, shadows, etc.

 

Figure 3.  Video proof that thermal anomaly in IR image is due to subsurface deficiency

Figure 3.  Video proof that thermal anomaly in IR image is due to subsurface deficiency

Figure 3 shows a few areas of thermal activity, similar to what we see in Figure 2.  Playback of the video in this location shows no surface obstructions, meaning that these ‘hot spots’ are due to a subsurface thermal barrier.  These were delineated and categorized as delaminated areas.  With the aid of a visual to go with the IR data, we are able to confidently distinguished areas of subsurface distress.