An improved ultrasonic computerized tomography (UCT) technique for damage localization based on compressive sampling (CS) theory

The traditional ultrasonic computerized tomography (UCT) method needs numerous measurements to detect the inside conditions of concrete. Considering the damage is sparsely distributed in the reinforced concrete, compressive sampling (CS) is applied to advance the UCT method at both the measurement stage and the imaging stage to localize damage part in the structure. The proposed detection algorithm requires much fewer measurements compared to the traditional UCT with the same accuracy. In the measurement stage, the pitch-catch paths are randomly selected to capture the travel time of ultrasonic wave from one side to the other side in the dense measurement net. When ultrasonic waves propagate in the structure, they will interact with the damaged part, prolong the propagation length, and delay the time of flight (ToF). In the imaging stage, the whole specimen is divided into small pixels based on the desired accuracy. The conventional Rando equation is advanced based on l1-minimization algorithm from CS method to solve the slowness of each pixel to reconstruct the damaged part. The functionality of the proposed algorithm is validated via both numerical model and experimental testing on a reinforced concrete beam in the laboratory. The results reveal the UCT based on CS is more efficient for localizing and imaging the damage with much fewer measurements, which has the immense potential in the development of structural health monitoring (SHM).