**Van Ha Mac 1,**†**, Quang Huy Tran 2,**†**, Jungwon Huh 1,\*, Nhu Son Doan 1, Choonghyun Kang <sup>3</sup> and Dongyeob Han <sup>1</sup>**


Received: 28 October 2019; Accepted: 29 November 2019; Published: 2 December 2019

**Abstract:** In bridge structures, concrete decks have a higher risk of damage than other components owing to the direct impact of traffic. This study aims to develop a comprehensive system for bridge inspection using passive infrared thermography (IRT). Experiments were conducted on a concrete specimen (assumed as the surface of the bridge deck) embedded artificial delaminations with different width-to-depth ratios (WTDRs). Both professional handheld IR camera (H-IRC) and a UAV mounted with an IR camera (UAV-IRC) were employed simultaneously to capture the surface temperature of the structure. The present work indicates that the passive IRT technique with an H-IRC can be used to detect delaminations located at depths of 4 cm or less from the structure surface if the WTDRs are not lesser than 1.9 for daytime and 2.5 for nighttime when testing on a sunny day. In addition, the larger the WTDR, the higher the temperature difference can be produced, thus delaminations could be observed more clearly. Furthermore, our study suggests that the concrete bridge deck inspection using passive IRT can produce appropriate results if the inspection is performed from 10:00 to 15:00 or from 19:30 to approximately 2:00 on a sunny day. Good agreement between the results obtained from tests using H-IRC and UAV-IRC was observed, which validates the application of UAV-IRC in real structure inspection.

**Keywords:** delamination; width-to-depth ratio (WTDR); concrete bridge deck; handheld IR camera (H-IRC); UAV IR camera (UAV-IRC); passive IRT; non-destructive technique; concrete structure
