Detection of subsurface defects in fiber reinforced polymer composite bridge decks using digital infrared thermography

Fiber reinforced polymer (FRP) bridge decks are rapidly emerging as potential alternatives to conventional reinforced concrete (RC) bridge decks. The FRP decks offer higher strength-to-weight ratios compared to RC decks. However, presence of subsurface defects such as debonds and delaminations formed during initial construction and in service can adversely affect the structural integrity and service performance of the FRP bridge decks. Hence, a field monitoring technique such as infrared thermography is required to evaluate the in situ condition of these FRP decks. This paper investigates the use of digital infrared thermography for subsurface defect detection in FRP bridge decks. Air-filled and water-filled debonds were inserted between the wearing surface and the underlying FRP deck in the laboratory. Simulated subsurface delaminations (of various sizes and thickness) were also created at the flange-to-flange junction between two FRP deck modules. The infrared technique was used to detect these embedded subsurface defects. Surface temperature-time curves were established for different sizes of delaminations and debonds. In addition, field study was conducted on a FRP bridge deck to detect debonds between the wearing surface and the underlying deck. The laboratory and field testing results show that infrared thermography is a potentially useful tool for defect detection in FRP composite bridge decks. The technique can possibly be used for several applications such as quality control during pultrusion of new decks (in factories), during field construction, and for field inspection of in-service decks.