Infrastructure safety inspections rely on visual inspections and hammering inspections by inspectors. However, an important difficulty is that inspection results vary because of differences in the technical expertise of inspectors. An inspection method and preventive work using a coating type resin sensor and an infrared camera are proposed to overcome that difficulty. A nondestructive evaluation technique using thermography is used increasingly as a tool to maintain concrete structures. Most inspections only evaluate the defect locations and shapes on planes. No method has been developed for evaluating defect depths. After applying infrared reactive resin, thermographic images of a target area are taken sequentially. Then, temperature curves obtained at each pixel during cooling defect states in different parts of the temperature distribution are analyzed using Fourier transform. The temperature change is related to the defect size. Approximately 10% of aluminum powder mixed into the applied gel resin, because of its specific gravity, has the property of concentrating in areas damaged by compression failure or floating. This report describes technologies related to defect identification and size measurements in infrared reactive resin, and describes effects of preventive work to avoid the scattering and collapse of defects caused by structural degradation.