Bridge Deck Inspection Utilizing Infrared Thermal Imaging Technique

Abstract

Infrared Thermography (IRT) is a promising Non-destructive Evaluation (NDE) technique that has been widely used in bridge deck inspection. It is a quick and easy alternative to provide preliminary information of possible defected areas in bridge decks. However, detection capabilities and sensitivity to environmental conditions and material properties impose some challenges for the application of IRT. In this study, the effect of varying concrete mixtures on passive IRT was investigated. Four different concrete mixtures, conventional, high-strength, selfconsolidated and lightweight concrete, were included in the evaluation. Various defects with relatively small sizes and depths were simulated and planted in cast-inplace slabs. The casting and testing took place in the United Arab Emirates (UAE), which is considered a hot weather region. The defected specimens were imaged, and the images were compared to non-defected specimens to enhance the judgment on defect detection. Thermal conductivity of each mix was estimated using the Maxwell- Eucken 2-phase composite material model, and Rapid Chloride Penetration was tested and used as an indication of density. The slabs were imaged during the cooling cycle. Results indicated that mix variation had a significant effect on IRT. High strength concrete achieved the highest detection possibility among the mixes. Furthermore, results showed that the higher the density and thermal conductivity coefficient, the better the defect detection using IRT at ideal imaging conditions is. For the UAE, ambient conditions are favorable for passive IRT, as the results indicated minimal sensitivity to wind, relative humidity, and temperature as opposed to other locations in the world where passive IRT would not be applicable. Nevertheless, because of IRT limitations, it would be better employed as a health monitoring technique with baseline comparisons rather than an independent primary inspection NDT tool for bridges.