Corrosion is a natural process that occurs when a structure is exposed to elements like CO2 or chloride, which can penetrate the concrete all the way to the steel reinforcement. This can have serious durability and safety consequences, which is why it is important to monitor corrosion using an accurate and trusted method.
The half-cell potential test is the only corrosion monitoring technique standardized in ASTM C876 – 15: Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete. It is used to determine the probability of corrosion within the rebar in reinforced concrete structures. This blog dives into the specifics of concrete corrosion, the half-cell potential technique for testing concrete corrosion, and the ways in which the data from the half-cell potential test can be interpreted.
Interpreting Half-Cell Potential Data
At first glance, this test method seems very simple and comprises of the following steps:
- Identify rebar location
- Make a connection with the reinforcement (more than one connection can be required if there is a discontinuity between reinforcements)
- Prepare concrete surface through wetting
Measurements are quick as potential values only take a few seconds to stabilize before the next measurement can be taken. However, there are important limitations in terms of data interpretation that need to be taken into consideration.
The effect of the concrete condition (dry or wet), presence of chloride, absence of oxygen at the rebar surface (due to saturation), cover thickness, concrete resistivity, and temperature are all factors that can influence the results by shifting their potential reading towards a more positive or negative value as shown in Table 2. This can make the data interpretation challenging when using the guidelines given in the ASTM C876 (Table 1), especially around the uncertain measurement ranges.
Table 2: Typical ranges of half-cell potentials of rebar in concrete (adapted from RILEM TC-154, 2003)
|Conditions||Potential values (mV/CSE*)|
|Humid, chloride free concrete||-200 to +100|
|Wet, chloride contaminated concrete||-600 to -400|
|Water saturated concrete without oxygen||-1000 to -900|
|Humid, carbonated concrete||-400 to +100|
|Dry, carbonated concrete||0 to +200|
|Dry concrete||0 to +200|