According to the electrochemical characteristics of steel bar corrosion, electrochemical method determines the electrical parameters through certain detection methods and summarizes the corresponding laws under different corrosion conditions, so as to determine the degree or speed of steel bar corrosion. At present, such methods mainly include spontaneous potential method, AC impedance method, linear polarization method, concrete surface resistivity method, constant current method, electrochemical noise method and so on.

1. 1 spontaneous potential method

Spontaneous potential method is a widely used method to detect the corrosion of steel bars in Zi District. Taking reinforced concrete as electrode, the corrosion of steel bar is judged by measuring the equivalent potential of steel bar electrode and reference electrode.

The advantages of spontaneous potential method are simple equipment and convenient operation. The disadvantage is that only the possible degree of steel bar corrosion can be judged qualitatively, but the proportion of steel bar corrosion can not be measured quantitatively; When the surface of concrete is covered with insulator or can't be soaked in water, it can't be tested in this way.

1.2 AC impedance method

The AC impedance method is to apply a small AC signal to the concrete member, and judge the performance of the concrete electrode system by measuring and comparing the relationship between the amplitude and phase of the input and output signals. It can not only determine various electrochemical parameters of the electrode, but also determine the control steps of electrochemical reflection. We can also study the changing law of electrode process through the evolution of AC impedance spectrum with time. The disadvantages of this method are long measurement time, expensive instruments and equipment, low-frequency AC signal required by low-rate corrosion system, and difficult measurement. The analysis method is complex, and the measured impedance spectrum is related to the geometric size of the component, which is not suitable for field test.

1.3 linear polarization method

The linear polarization method is based on the fact that the overpotential is very small (

1.4 concrete surface resistivity method

When steel bars are corroded, electrons will migrate, which leads to the difference of electron distribution on concrete surface. By measuring the resistivity distribution of concrete surface, the possibility of corrosion of steel bars can be judged. This method is influenced by the water content and chemical composition of concrete surface.

2. Laws of physics

The corrosion status of steel bars is mainly reflected by measuring the changes of physical characteristics such as resistance, electromagnetism, heat conduction and sound wave propagation related to steel bar corrosion. Commonly used methods include resistance bar method, eddy current detection method, ray method and acoustic emission detection method. The advantages of this method are simple operation and little environmental impact. The disadvantage is that it is easily disturbed by other damage factors in concrete; Moreover, it is difficult to establish the corresponding relationship between physical measurement indexes and corrosion of steel bars.