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Newly developed ultrasonic imaging technology for large concrete elements, based on tomographic reconstruction, is presented. The developed 3-D internal images (velocity tomograms) are used to detect internal defects (polystyrene foam and pre-cracked concrete prisms) that represent structural damage within a large steel reinforced concrete element. A hybrid air-coupled/contact transducer system is deployed. Electrostatic air-coupled transducers are used to generate ultrasonic energy and contact accelerometers are attached on the opposing side of the concrete element to detect the ultrasonic pulses. The developed hybrid testing setup enables collection of a large amount of high-quality, through-thickness ultrasonic data without surface preparation to the concrete. The algebraic reconstruction technique is used to reconstruct p-wave velocity tomograms from the obtained time signal data. A comparison with a one-sided ultrasonic imaging method is presented for the same specimen. Through-thickness tomography shows some benefit over one-sided imaging for highly reinforced concrete elements. The results demonstrate that the proposed through-thickness ultrasonic technique shows great potential for evaluation of full-scale concrete structures in the field.

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A comprehensive visualization scheme to characterize reinforced concrete structures, based on integrated ultrasonic tomography and 3-D computer vision, is presented. A recently developed hybrid air-coupled/contact ultrasonic transducer system enables the generation of internal tomographic images that characterize the interior condition, for example the presence of voiding defects, of full-scale reinforced concrete elements. Based on tomographic crosssectional slice images, 3-D volumetric internal images are built up to obtain full stereoscopic analysis. An automated image-based 3-D reconstruction technique is applied to the same structure to visualize external condition. Both internal and exterior visualizations of full-scale concrete column are integrated in a single three-dimensional image. The approach is demonstrated on a reinforced concrete column sample that exhibits exterior geometric inconsistency with the original design and also includes controlled internal defects. The experimental results demonstrate that the proposed integrated visualization technique provides holistic characterization of the interior and exterior of the test sample and thus demonstrates great potential for facilitating inspection of existing structures in the field.