Infrared thermography inspection of fiber-reinforced polymer composites bonded to concrete

The use of fiber-reinforced polymer (FRP) composites to strengthen existing civil infrastructure is expanding rapidly. Many FRP systems used to strengthen reinforced concrete are applied using a "wet layup" method in which dry fibers are saturated on-site and then applied to the surface. Air voids entrapped between the FRP system and concrete as a result of improper installation reduce the integrity of the repair.; The objective of this study was to investigate the use of infrared thermography (IRT) for evaluating bond in FRP composites applied to reinforced concrete. Phase I of this study examined FRP strengthening systems that were applied to full-scale bridge girders. IRT inspections were performed on four AASHTO type II girders with simulated impact damage that were loaded to failure. Phase I also contained a field inspection of an in-service bridge that was strengthened with FRP composites. The results of the field studies indicated that as the overall thickness of the FRP system increased the detectability of defects was diminished. In addition the installation procedures influenced IRT results. The use of excessive epoxy tack-coat was shown to reduce detectability and increase the required observation time.; A second experimental study (Phase II) was conducted in which 34 small-scale specimens (15 cm x 30 cm) containing fabricated defects were inspected in a laboratory environment. These specimens were constructed using different FRP composite thicknesses (1 mm to 4 mm) and matrix saturation levels. Four heating methods were investigated (flash, scan, long-pulse, and sinusoidal), and quantitative analyses were performed on the thermal data using currently available techniques.; Data were used to establish detection limits for air and epoxy-filled voids in carbon FRP composites. It was shown that IRT is capable of detecting 19 mm diameter and larger defects in carbon FRP composites up to 4 mm thick. Quantitative data analysis techniques were also used to estimate the depth and material composition of defects up to 2 mm below the surface. These data analysis techniques were also effective for enhancing detection of defects up to 4 mm below the surface.