Simultaneous Estimation of Rebar Diameter and Cover Thickness by a GPR-EMI Dual Sensor

Abstract

Precise characterization of reinforcing bars (rebars) in a concrete structure is of significant importance for construction quality control and post-disaster safety evaluation. This paper integrates ground-penetrating radar (GPR) and electromagnetic induction (EMI) methods for simultaneous estimation of rebar diameter and cover thickness. A prototype of GPR-EMI dual sensor is developed, and a calibration experiment is conducted to collect a standard EMI dataset corresponding to various rebar diameters and cover thicknesses. The handheld testing cart can synchronously collect both GPR and EMI data when moving on the concrete surface, from which a data processing algorithm is proposed to simultaneously estimate the rebar diameter and cover thickness. Firstly, by extracting the apex of the hyperbolic reflection from the rebar in the preprocessed GPR profile, the rebar position is determined and further used to extract the effective EMI curve. Then, the rebar diameter and cover thickness are simultaneously estimated from the minimum mean square error between the measured and calibrated EMI data under the constraint of the GPR-estimated cover thickness. A laboratory experiment is performed using four casted concrete specimens with 11 embedded steel rebars. The results show that the diameters of 10 rebars are correctly estimated out of the 11 rebars, and the maximum estimation error for the cover thickness is 6.7%. A field trial is carried out in a newly-constructed building, and the diameters of four tested rebars are all accurately estimated while the estimation errors of the cover thickness are less than 5%. It is concluded that the developed GPR-EMI dual sensor and the proposed algorithm can estimate the rebar diameter and cover thickness accurately by a single scan.

A Review of GPR Application on Transport Infrastructures: Troubleshooting and Best Practices

“…Those images can be obtained from a grid of B-scans obtained in profile lines separated by 10 cm [244]. Combining GPR with other techniques such as electromagnetic induction, it is possible to determine the position of the rebar, the cover thickness, and the rebar diameter [245]. The main limitation occurs in the case of a densely-meshed rebar, requiring antennas with narrower transmission energy cones.…”

A Machine Learning Scheme for Estimating the Diameter of Reinforcing Bars Using Ground Penetrating Radar

“…Due to that, additional NDT methods (e.g. eddy current [11], electromagnetic induction [14], [15]) need to be applied in the field to complement GPR, raising the overall computational and operational costs, and adding complexity to the acquisition.…”

Reverse-Time Migration Imaging of Ground-Penetrating Radar in NDT of Reinforced Concrete Structures

“…Zhou et al [16] used GPR in combination with the electromagnetic induction (EMI) method to accurately locate reinforcing bars. Chang et al [17] reported a physical model based on the use of digital image GPR for measuring the radius of reinforcing steel bars in concrete.…”

“…For detection and localization of reinforced bars, Remote Sens. 2021, 13, 2020 2 of 16 Liu et al [21] and Giannakis et al [22] utilized machine-learning methods to estimate the diameter of reinforcements. Moreover, the evaluation of concrete parameters is an essential research subject.…”