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.
Highlights
Non-destructive testing (NDT) techniques play a significant role in monitoring and diagnosing construction structures
The results indicate that the rebar diameters are all accurately estimated, and the cover thicknesses have a maximum error less than 5%, reflecting the developed ground-penetrating radar (GPR)-electromagnetic induction (EMI) dual sensor and proposed estimation method are effective for field rebar detection and characterization
We propose the integration of EMI and GPR for simultaneous estimation of rebar diameter and cover thickness, which is of significance for quality control and safety evaluation of concrete structures
Summary
Non-destructive testing (NDT) techniques play a significant role in monitoring and diagnosing construction structures. When an EMI sensor is used for rebar inspection, the induced secondary magnetic fields are sensitive to both the rebar diameter and cover thickness. A rebar locator or cover meter can estimate the rebar diameter or cover thickness, only if the other one is known, with the pre-calibrated data of the EMI strength stored in the instrument memory [6,7]. Ultrasonic echo was combined with EMI measurement for mapping the meshed reinforced concrete and estimating the cover thickness, where better results were obtained than those from an alone EMI survey [12]. This method requires to know rebar diameters in advance, and it cannot solve the rebar size
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