An Elastic-Wave-Based Imaging Method with Synthetic Aperture Focusing Technique for Scanning Defects inside Concrete Structure

Abstract

In this paper, a new elastic-wave-based NDT system was developed and then applied to reveal the defects in the concrete specimens by imaging method. This testing system integrates the point- source/point-receiver scheme with the synthetic aperture focusing technique (SAFT) to achieve the effect like scanning with a phase array system; hence it is equipped with large functioning depth because of the high-energy feature that transient elastic wave method possesses in comparison to traditional ultrasonic method. This NDT system is mainly composed of an impacting force generator, a displacement or velocity transducer, a signal capturing unit and operation software. To evaluate the feasibility of this system for scanning concrete structures, a concrete plate with embedded void was calibrated for experiment. Numerical simulations using 2D plane stress finite elements were performed for comparison purpose. Experimental results show good agreement with the numerical ones not only on the B-scan diagrams but also on the processed scanning images. It is concluded that the elastic- wave-based scanning system incorporated with SAFT scheme proposed in this paper exhibits high potential in inspecting the defects of in-situ concrete structures by imaging.