Cooling-excited infrared thermography for enhancing the detection of concrete filled steel tube interfacial debonding at concrete hydration

Interfacial Debonding occurring in concrete-filled steel Tube (CFST) arch bridges during construction is a critical issue, which can reduce the CFST carrying capacity and thus degrade the operational lifespan of the bridge. Timely detection of this type of defect during bridge construction can be highly cost-effective but rare sensing technology was reported for detection at this stage. Infrared thermography has been recognized as a potential detection method but still faces the challenge of low thermal contrast developed from concrete hydration. This research investigates the feasibility of using hydration heat as an internal heat source and proposes water-spray cooling as an external excitation to improve infrared debonding detection. The experimental study is carried out to investigate the detectability enhancement before and after the cooling excitation in terms of different debonding sizes and thicknesses. An image enhancement method is then proposed for debonding visualization based on the temperature difference matrix. In addition, the numerical simulation is conducted to analyze the cooling effect regarding the excitation intensity variation. The findings reveal that the thermal contrast of debonding ranges from 0.1~0.35℃ before cooling excitation and is enhanced by 2~3 times thereafter. In addition, the developed maximum thermal contrast of debonding can be characterized through a linear relationship to the cooling excitation intensity based on numerical analysis. The proposed method shows significant feasibility for early detection of debonding in CFST during arch bridge construction, which enables a new potential for structural inspection.