HALF-CELL POTENTIAL TEST
Electrical methods are used to evaluate the probability of corrosion activity of steel reinforcement. Corrosion is an electrochemical process involving the flow of charge (electrons and ions) between active sites on the bars, through. In short, an electrochemical cell is formed. At the anode, iron atoms loose electrons and move into the surrounding concrete as ferrous ions. This process is called a half cell oxidation reaction, or the anodic reaction. The electrons remain in the bar and flow to sites, called cathodes. Where electrons are combine with water and oxygen that are present in the concrete. The reaction at the cathode is called a half cell reduction reaction.
To maintain electrical neutrality, ferrous ions migrate through the concrete to the cathode sides where they combine with water and oxygen to form hydrated iron oxide or rust. When the bar is corroding, there is a flow of electrons through the bar and a flow of ions through the concrete. When the bar is not corroding, there is no flow of electrons and ions.
As the ferrous ions move in to the surrounding concrete, the electrons that are left behind in the bar give the bar a negative charge. Half Cell potential method is used to detect this negative charge and thereby provide an indication of the corrosion activity.
The half-cell potential readings are indicative of the probability of corrosion activity of reinforcement located beneath the reference cell. If the potential is more positive than – 0.20 V, there is a possibility that no corrosion is occurring at the time of measurement. If the potential is more negative than – 0.35 V, there is a possibility that there is active corrosion. Corrosion activity is uncertain when the voltage is in the range of – 0.20 to – 0.35 V. Half-cell potential method does not measure the rate of corrosion. It only provides an indication of the corrosion activity at the time of measurements.
