Passive and active infrared thermography techniques in nondestructive evaluation for concrete bridge

Abstract

Deteriorations are normally developed in concrete bridge structural components during long-term operations under various factors such as cyclic loading, weather and environmental conditions, wind loading, and water flow. The conventional nondestructive test (NDT) methods, i.e. chain dragging and hammer sounding, might be less accurate to predict the subsurface delamination when the size of sub-surface defects is small. Out of the advanced NDT methods, Infrared thermography (IRT) has been proven to be an effective way to detect delamination. The Passive IRT method is effective to detect a large area of the structure in a short time, but the inspected structural components should be exposed to the sunlight, i.e. bridge deck. While the Active IRT method can be used to test the structure without facing the sun; However, this method is time-consuming. In an effort to apply the IRT technique for bridge health monitoring, both active and passive IRT methods were considered in this study. The tests were conducted on a concrete specimen embedded in various artificial delaminations with different sizes and depths. The results showed that the optimum observation time for the passive IRT test is from 11:00 am to 2:00 pm on a sunny day. In addition, both active and passive IRT methods resulted that the thermal contrast above the defect increases with the increase of the size of the defect and the heating duration which can be the halogen lamps of the active method or the solar energy of the passive method. Finally, the results of the active IRT indicated that the depth of the delaminations can be predicted by using the linear relationship between the observation time and the square depth proposed in this study.