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The purpose of this work was to investigate how the impedance of concrete subjected to alternating current (AC) is affected by adding silica fumey reducing water-to-cement ratioy and adding polypropylene fibers. Based on the test resultsy it is possible to increase concrete impedance and decrease its susceptibility to degradation by AC voltage.
Concrete pores can act as capacitors and alternating current (AC) can pass through a capacitor. Thus, AC passes in concrete in two parallel ways-by capacitor and resistor paths. The capacitor paths consist of the pore network and resistor paths consist of the solid phase. If steel bars are embedded in the concrete, then the bars can also act as capacitors for passing AC.12 As shown in Figure 1, there are two kinds of capacitors in concrete's equivalent of an electrical circuit. Therefore, three steel bars embedded in concrete can be used as working, counter, and reference electrodes during an electrochemical impedance spectroscopy (EIS) test. According to Figure 1, the EIS spectrum of concrete consists of two arcs, one that is related to the capacitance of the steel bars and appears in the lowfrequency range, and another that is related to the capacitance of the bulk concrete and appears in the high-frequency range.13
At Point A in Figure 1, the imaginary part of impedance is very low compared to the real part, so that a higher amount of current can pass through the concrete and a high percentage of it will pass through the capacitance path (pores).1"3 So if the AC voltage is high enough and the concrete is saturated with water, then serious nonuniform current distribution forms in concrete. This will lead to thermal and shrinkage stress in concrete and cause the formation of cracks and an increase in the concrete's permeability.13 According to our results, the frequency of urban AC power (i.e., 50 Hz) is approximately equal to the frequency of Point A.
Under special conditions, including polluted air, rain, and low-quality concrete poles, high-voltage AC can leak from power lines to water-saturated concrete power poles.3"4 Figure 2 shows a concrete power pole after experiencing stray AC attack. The concrete surface has many cracks and in some areas the concrete cover has started to fall off. In dry concrete, AC stray...