Detection of Air and Water-Filled Subsurface Defects in GFRP Composite Bridge Decks Using Infrared Thermography

Any discontinuity within a structural component influences the transmission of thermal energy through its thickness, which leads to differences in surface temperatures just above the defective and defect‐free areas. The variation in the surface temperatures are recorded using a digital infrared camera and the thermal images (thermograms) are analyzed to locate the presence of subsurface defects such as debonds and delaminations within the structure. While past studies focused on detection of air‐filled subsurface defects (debonds and delaminations) in fiber reinforced polymer (GFRP) composite bridge decks using infrared thermography, this paper includes the detection of fully and partially water‐filled defects as well. Simulated water‐filled defects were embedded within the flange‐to‐flange junction of adjacent GFRP bridge deck modules to create delaminations. The deck specimens were then tested before and after the application of a 3/8″ (9.5 mm) thick polymer concrete wearing surface. It was found that water‐filled delaminations as small as 2″ × 2″ × 1/16″ (51 mm × 51 mm × 1.6 mm) could be detected in case of specimens without wearing surface, but this was not possible after application of the wearing surface. The heating source considered included heater and solar radiation. Use of cooling sources such as cold water and liquid carbon dioxide were also explored. These results helped establish the limits of detection for fully and partially water‐filled delaminations using Infrared Thermograpy. Additional studies included the detection of debond between 2″ (51mm) thick asphalt overlay and the underlying composite deck and it was found that air‐filled debonds as small as 4″ × 4″ × 1/16″ (102 mm × 102 mm × 1.6 mm) could be detected using heater as well as solar radiation as heat sources.