Detecting Defects in Steel Reinforcement Using the Passive Magnetic Inspection Method

Abstract

Defects in steel reinforcement are critical factors in the evaluation of the service life of reinforced concrete (RC). Steel reinforcement (bar) defects or deterioration may lead to crack propagation and strength decrease in RC structural members. Deterioration also changes the steel magnetic properties; the evaluation of these changes can be investigated by an indirect passive and non-invasive method to locate and quantify defect in RC structures. Herein, a passive magnetic inspection (PMI) method is modified and used to examine its potential as a non-destructive testing (NDT) method for condition assessment of steel reinforcement. The passive magnetic flux density of steel bar with three small holes in three different positions and locations along the bar is measured in the laboratory. A signal processing methodology based on frequency spectrum analysis and filtering is applied to the experimental data, and the results are compared with the numerical simulation. The processed data from the experimental test shows the potential of PMI method to detect, locate and evaluate bar condition. Both experimental results (after signal processing) and simulation results show a good similarity for top and bottom holes. Cross-correlation of numerical simulation with experimental data was necessary to reveal detection of the side hole.

Simulation of Real Defect Geometry and Its Detection Using Passive Magnetic Inspection (PMI) Method

“…Natural magnetic fields and other influential local magnetic sources [37], combined with internal and external stresses, can change the scattered stray magnetic field of ferromagnetic materials [43]. Internal domain walls' displacement and magnetic-moment rotation in ferromagnetic materials happen under the influence of external magnetic fields [44], and there are relationships between the micro-magnetic characteristics of these materials and their mechanical responses [45].…”

“…Numerical simulation of the PMI method is performed based on the stray magnetic field (H d ) and the stray magnetic field energy (E d ) [37]. Hubert and Schäfer in 1998 [54] presented the relation for calculating the stray magnetic field (Equation (1)), based on summarizing Gauss's magnetic field law.…”

“…For conducting this research article, we scanned 373.87 mm of the surface of a ferromagnetic rebar (low-carbon steel), with a diameter of 16 mm, and two artificial defects (Table 1) [37], using a high-resolution 3D laser scanner ( Figure 1a) [56]. The shape of the rebar was created with cloud points (Figure 1b) that were modified and converted to a mesh by Mesh Lab V1.3.2 (http://meshlab.sourceforge.net/).…”

“…The laboratory flux magnetic density measurements were conducted using the PMI device that was specifically developed for this work in our lab, and is on its way to being commercialized. The PMI device works through scanning the SMFL arising from ferromagnetic structures [37].…”

“…We built a Passive Magnetic Inspection (PMI) tool to exploit the passive magnetic concept and examine the corrosion condition of embedded rebar by scanning from the external concrete surface [8]. Preliminary successes have been described [37] in which solid rebar was sketched in COMSOL R software version 5.3a (COMSOL Group, Stockholm, Sweden). based on a real rebar's geometry.…”