Quantitative Infrared Thermography Inspection for FRP Applied to Concrete Using Single Pixel Analysis

Abstract This research investigated infrared thermography (IRT) as a nondestructive testing method for FRP systems applied to concrete. Twenty-seven small-scale specimens (15 cm × 30 cm) were constructed using carbon and glass FRP composites with thicknesses ranging from 1 mm to 4 mm. Different wet lay-up procedures were used to saturate dry fibers and the level of matrix saturation was also varied (weight fractions for fibers ranged from 0.4 to 0.67). Infrared thermography inspections were performed by heating samples for 60 s with halogen lamps and an existing normalization technique was applied to the resulting temperature vs. time history for each pixel in the resulting series of thermal images. This method was shown to be effective for minimizing the effects of non-uniform heating as well as establishing the relative depth of fabricated defects with respect to the FRP/concrete interface. The normalized temperature response for defect-free regions in each specimen was also shown to be dependent on matrix saturation levels, the presence/absence of a thickened epoxy tack-coat, and the uniformity of matrix saturation.