Bridge Deck Sub-Surface Defect Detection using Time-Lapse Thermography

A novel approach for evaluating subsurface condition of concrete structures has been developed using a relatively low cost microbolometer infrared camera. The approach is based on time lapse infrared thermography which produces a video sequence of surface temperatures (instead of a snapshot) by filming the same scene over an extended period of time. Time series analysis is then used to reconstruct the sequence of images into a high contrast composite image accurately delineating deep subsurface defects. A laboratory experiment evaluated time lapse thermography for detecting subsurface defects on two concrete slabs fabricated with different surface finishes, rebar locations and simulated defects at different depths. This study shows that time lapse thermography can be used to detect subsurface defects up to 6 inches deep irrespective of the type of surface finish (smooth or rough). Similar defect detection results were obtained for concrete slabs with surface overlays. The results indicate that time lapse thermography could be used as a practical option for accurate and consistent evaluation of the sub surface condition of bridge decks with overlays.