Nondestructive evaluation of fiber reinforced polymer bridge decks using digital infrared imaging

Fiber reinforced polymer (FRP) bridge decks are currently being explored as an alternative to the traditional reinforced concrete bridge decks because of their higher strength-to-weight ratio and better corrosion resistance properties. However, the long-term degradation behavior of FRP bridge decks is not very well understood. For ensuring continued structural integrity of these FRP decks, it is important to employ periodic field monitoring technique such as infrared thermography. The technique allows rapid data collection and interpretation in the field. Also, recent advances in digital infrared imaging has opened the door for using more advanced image enhancement techniques, which can lead to better sensitivity and reliability in the use of the infrared technique. This paper presents an example of the use of digital infrared thermography on a laboratory specimen of FRP bridge deck. The specimen was cast with embedded subsurface defects (debonds) which were successfully located using the infrared technique. The paper also demonstrates the use of digital signal processing methodology to aid in the defect detection process. The results show that infrared technique can be a useful tool for defect detection in field composite decks, and also for quality control during pultrusion of new decks (in factories) and during field construction.