Evaluation of Ultrasonic SH-Waveform Tomography for Determining Cover Thickness and Rebar Size in Concrete Structures

• Published in: Journal of nondestructive evaluation 2022-06, Vol.41 (2), Article 35
• Main Authors: Chen, Ruoyu, Tran, Khiem T., Dinh, Kien, Ferraro, Christopher C.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Classical Mechanics; Concrete; Concrete structures; Control; Diameters; Dynamical Systems; Engineering; Quality assurance; Quality control; Rebar; Solid Mechanics; Synthetic apertures; Thickness; Tomography; Vibration; Waveforms
• ISSN: 0195-9298; 1573-4862
• DOI: 10.1007/s10921-022-00866-1

The simultaneous detection of cover depth and rebar diameter are among the most frequently encountered issues for inspecting concrete for quality control and assurance, or evaluating a concrete structure. This paper presents a novel application of 2D full-waveform inversion of ultrasonic SH-waves (2D SH-FWI), for determining cover depth and size of embedded rebar. The method was applied to ultrasonic SH-wave datasets collected by a commercial shear-wave tomography system (MIRA) on four concrete specimens. Two of them had 10 steel bars of the same size (#5) embedded at various depths, and the other two had 10 steel bars of various sizes (#3 to #14) placed at the same cover depth of 65 mm. The results showed that the presented 2D SH-FWI was able to characterize both the depths and sizes of rebars. Except for the smallest rebar # 3, the difference between the inverted and true sizes is less than 30% for 9 rebars (#4 to #14 at 65-mm cover depth), and less than 33% for all 10 rebars (#5) at various depths from 25 to 140 mm. For comparison, the rebar sizes could not be obtained with the ultrasonic synthetic aperture focusing technique and GPR method, which only detected the cover thickness.