Investigating Thermal Imaging Technologies and Unmanned Aerial Vehicles to Improve Bridge Inspections

Bridge inspection is central to any transportation facilities maintenance program. A particular concern with bridge conditions is concrete delamination on the underside of bridge decks, especially on overpass bridges and on bridges that see pedestrian or boat traffic underneath. Current methods for inspecting overpass bridge decks include visual observations from the roadway underneath by maintenance personnel. Areas identified that may be prone to loosen and fall are then chipped off, before the concrete fails and lands on passing traffic. Sometimes the visual observations can miss deteriorated areas creating a potential safety hazard. A more robust method to determine these concrete delaminated areas will both increase safety and allow better use of limited staff and resources. Unmanned aerial vehicles (UAVs), or more popularly, “drones” are emerging as a practical and inexpensive alternative to traditional manual inspections. Although there is a significant push from FHWA through State DOT’s to explore effective use of UAVs, it has so far only been tested in a few states. Infrared thermal imaging (IR) is being successfully used to determine concrete delaminated areas on bridges. The FHWA Turner-Fairbanks Research Center is successfully using handheld IR on the top side of bridge decks. Iowa DOT has had success with high temperature hand held IR cameras on the underside of bridge decks. Despite some preliminary successes, several key gaps exist. First, despite a plethora of research going into different UAV-mounted imaging technologies and AI-based analysis of data, field studies in which the UAV condition assessment has been validated to actual bridge condition are limited. Second, UAV-based inspections of bridge undersides have been limited due to difficulties in maneuvering the UAV beneath the structure. This latter problem can be particularly acute in cases where deterioration leading to falling debris creates a hazard below the bridge. Finally, given the wide range of imaging technologies that can be applied to UAV-mounted systems (e.g. optical, infrared, lidar, GPR, etc.), which ones are best suited to identifying the types of deterioration likely to occur in different structures. The overall research objective is to focus on developing UAV-based inspection and analysis protocols using Infrared thermal imaging to determine concrete delaminations, with emphasis on the underside of bridge decks. In addition, other sensor technologies will be investigated should the IR technology not provide acceptable data and results.