PSI - Issue 64

Hideki Oshita et al. / Procedia Structural Integrity 64 (2024) 48–55 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

50

3

Coil

Coil

AC power supply

AC power supply

supression Corrosion protection current

Line of magnetic induction rebar

Line of magnetic induction

Induced current

rebar

Corrosion current

(cathodic reaction) (anode reaction)

Concrete

Concrete

Electric potential high

Electric potential

Potential after cathodic protection

0 + -

Electric potential distribution (before cathodic protection) Electric potential distribution (after cathodic protection)

Shift

disappear

Potential of non-corroded rebar

0 low Surface potential distribution of rebar

Potential after cathodic protection

Surface potential distribution of rebar

Fig. 2. (a) Before corrosion of rebars; (b) After corrosion of rebars

supplied. As a result, magnetic flux lines are generated around the coil and reach the embedded reinforcing bars within the concrete. An electric current (induction current) is induced on the reinforcing bar surface, creating magnetic flux lines that cancel out the existing ones. The higher the frequency of the AC current, the faster the direction of the induction current changes. This induction current serves as the protective current, inhibiting the formation of anodes and cathodes (localized cells) on the reinforcing bar surface. Even if anodes and cathodes were to form on the reinforcing bar surface, suppressing the flow of electrons (corrosion current) between them would also mitigate the corrosion reaction. The details of this method are explained based on Fig 2. When the reinforcing bar is not corroded, no localized cells (anodes or cathodes) form on the reinforcing bar surface, resulting in no potential difference. In this state, induced current (alternating current) generated by electromagnetic induction flows across the reinforcing bar surface, forcibly shifting the potential in both positive and negative directions, as shown in Fig.2 (a). However, when the reinforcing bar is corroded, localized cells form on the reinforcing bar surface. In this case, the healthy region’s potential decreases to a level similar to that of the corroded area, as depicted in Fig.2 (b), effectively neutralizing the potential difference and disrupting the formed localized cells. This method leverages electromagnetic induction to prevent corrosion by inhibiting the formation of localized cells on the reinforcing bar surface. 2.2. Electromagnetic Induction Analysis for Various Structural Components The method to prevent the corrosion using electromagnetic induction operates on the same mechanism as conventional cathodic protection methods. However, its significant feature lies in the use of electromagnetic induction and the non-destructive and non-contacted method without the need to expose reinforcing bar by chipping away concrete. When applying the electromagnetic induction corrosion prevention method to RC structures, the shape of the coil varies depending on the structural type. Specifically, as shown in Fig.3, spiral coils are suitable for columns and beams, while planar coils are more appropriate for beam members from a construction perspective. Here are the definitions for each type of coil: Spiral Coil: A three-dimensional coil formed by winding copper wire in a spiral shape Planar Coil: A two-dimensional coil where copper wire is wound in a spiral pattern within a plane The direction and density distribution of the induced current on the reinforcing bar surface differ based on the coil shape. In this section, we will analytically examine the impact of coil shape on the direction and density distribution of the induced current at the reinforcing bar surface using a three-dimensional electromagnetic induction method. For the sake of space limitations, our explanation will focus on column members in this study.