Corrosion Evaluation of Steel Reinforcing Bar Using Electromagnetic Method

When corrosion happens with the steel reinforcing bar (rebar) in concrete, the magnetic properties of the corrosion products are different from that of the steel rebar. By measuring the electromagnetic response, it is possible to judge the corrosion of steel rebar in concrete. We developed an electromagnetic method to evaluate the corrosion of steel rebar. AC magnetic field was produced by an excitation coil when AC current flow in it. Then, eddy current was induced in the surface of the steel rebar. A detection coil was used to measure the magnetic field produced by the eddy current. The signal after the amplifier was sent to a lock-in amplifier. From the lock-in amplifier, two signals were obtained: X signal (the same phase signal with the excitation current) and Y signal (90 degree phase difference signal with the excitation current). From the slope of the plotted X-Y graph using the X and Y signals, the corrosion of the steel rebar can be judged. We developed a small compact system for the corrosion evaluation of steel rebar, which will be suitable for the field experiments.