The risk of  corrosion of the reinforcement in the immediate region of the test location may be related empirically to the measured potential difference by the Half cell equipment.

The instrument consists of a Half cell, a Electrical junction device to provide a low electrical resistance liquid bridge, a Electrical contact solution to standardize the potential drop through concrete portion, a Voltmeter and some Electrical lead wires.

Applications

• Assessment of the durability of reinforced concrete members where reinforcement corrosion is suspected.
• Finding high reinforcement corrosion risk areas.
• It can also be used for investigating concrete contaminated with salts.

Codes

• ASTM C876 91

Methodology

Measurements are made in either a grid or random pattern. A direct low resistance electrical connection is made to the pre-exposed reinforcing steel  with a compression clamp or by brazing or welding a protruding rod. The bar is connected to the positive terminal of the voltmeter. One end of the lead wire is connected to the half-cell and  the other end to the negative terminal of the voltmeter. The electrical half-cell potentials are recorded to the nearest 0.01 V correcting for temperature if the temperature is outside the range 22.2 ± 5.5C

Limitations

• The method cannot indicate the actual corrosion rate.
• It may require to drill a small hole to enable electrical contact with the reinforcement in the member under examination, and surface preparation may also be required.
• Effect of protective or decorative coatings applied to the concrete need to be taken care