Concrete crack assessment using unmanned aerial vehicle

Most of civil infrastructure has suffered from concrete cracks due to the diverse natural loading, structural aging, rebar corrosion, creep, and shrinkage. The structural damage caused by concrete cracks can bring national issues, such as loss of lives, economic loss, and performance loss as a failure of the structure. For the structural safety, concrete cracks are visually inspected from specialists who evaluate the current structural condition based on the shape, size, length, and width information of cracks. Although the specialists are highly trained to appraise concrete cracks with reasonable standards, visual inspection is inappropriate to crack assessment of large-scale structures in terms of high-cost, longtime, and safety of specialists. Recently, digital image processing has been introduced to identify concrete cracks from crack images which are captured using digital imaging devices (i.e., cameras and camcorders). While digital image processing is possible to assess crack information with short-time and low-cost, to capture crack images of some structural members is still limited due to the accessibility issue for capturing crack images. Recent advances in Unmanned Aerial Vehicle (UAV) technologies have proposed low-cost and high-performance UAVs that can be used for diverse fields. In this research, a prototype of UAVbased digital image processing is proposed to conduct concrete crack assessment. The proposed UAV is equipped with sensing and communication controller, camera, ultrasonic wave sensor, and WIFI module. The crack image and associated working distance information are measured by the adopted equipment of UAV. In addition, the optimized image processing strategy is introduced to identify crack information without non-crack elements in the original image, such as shadow, dust, spider web, and hole. The performance of the proposed prototype is evaluated from concrete structure