NON-DESTRUCTIVE TESTING OF UNDERWATER CONCRETE STRUCTURES USING REMOTELY CONTROLLED DRONES

Concrete is a fundamental component in civil, commercial, and industrial infrastructure. Periodic inspection is mandated to ensure safe operation during the structure's lifetime. Recent innovations in inspection technology have enabled rapid characterization of the interior of a concrete specimen with techniques like ground penetrating radar and phased array ultrasonic tomography. A universal limitation of these conventional methods is that they are best documented for in-air application, with comparatively scant literature available for underwater deployment. Visual inspections and diver deployed semi-destructive tests are the main modes of underwater concrete inspection. Underwater, concrete structures encounter harsher conditions and larger weathering effects compared to those above. Underwater inspections sites often have poor visibility, strong currents and debris, making manned inspections risky. Divers also have limited inspection time and depth, decreasing scope and increasing asset downtime. To overcome those limitations, this paper proposes the use of remotely operated underwater vehicles (ROVs) to perform quantitative non-destructive tests on underwater concrete structures. ROVs developed by Planys Technologies are compact, lightweight, and versatile. They are capable of extended inspection times, and operational depths of up to 200 m. These ROVs can be deployed by a crew of 2-3 personnel and are remotely controlled from a safe location above water. One of the most well-known techniques, ultrasonic pulse velocimetry, was adapted for the marine environment. While foundational when compared to the state-of-the-art in-air techniques, it is still capable of providing a quantitative measure of a concrete structure's integrity. The paper describes experimental results from in-lab and in-field testing, as well as limitations to practical applications.