Assessment technique for the degradation of heavy-duty anticorrosion coatings on long-span bridges utilizing near-infrared measurement

Long-span steel bridges are coated with heavy-duty anticorrosion coatings consisting of several layers of paint to prevent the corrosion of steel materials. When maintaining heavy-duty corrosion-resistant paint, the early detection of the loss of the top coat and exposure of the undercoat is important because deterioration progresses rapidly if the top coat is lost. However, the current maintenance method relies on visual inspection; therefore, more efficient and accurate detection methods need to be developed. Furthermore, paints of similar colors are often used for the top and intermediate coats for color matching; therefore, it is difficult to distinguish them in the visible range. Therefore, we focused on the differences in the near-infrared spectral characteristics between the top coat with a weather-resistant paint, such as a fluorine resin paint, and the intermediate coat with an epoxy resin paint. To develop a method for evaluating the deterioration of heavy-duty anticorrosion coatings, we conducted an experimental study on an actual long-span bridge. First, we employed a near-infrared hyperspectral imaging system to obtain the spectral characteristics of the top and intermediate coats and identified the wavelength range where the spectral characteristics of each paint differed. Next, we employed a near-infrared camera attached to a band-pass filter that transmitted only the wavelength range and cut other wavelength ranges, and we obtained near-infrared images. Consequently, we were able to confirm the exposure of the intermediate coat using near-infrared measurements.