What is the Chloride ion migration (PERMIT) test?
The PERMIT test is an in-situ, non-destructive assessment of the resistance of cover concrete to the migration of chloride ions and allows for the identification of corrosion risk.
How does the Chloride ion migration (PERMIT) test work?
The PERMIT ion migration test is based on the same principles as laboratory-based chloride migration tests but uses an all-in-one portable test system that can evaluate the chloride resistance of structures while in service and without damage.
The test is carried out by placing an anodic and cathodic chamber on the concrete surface and forcing chloride ions to migrate between them through concrete under the influence of a voltage.
The change in chloride concentration of the anolyte is monitored continuously and it is used to determine the rate of chloride movement through concrete and via the Nernst-Planck equation the chloride migration coefficient.
The PERMIT ion migration test has been validated against most laboratory-based test methods and can be related to the deterioration of concrete subjected to chloride induced reinforcement corrosion caused by external chlorides.
What is the Chloride ion migration (PERMIT) test used for?
Deterioration process | Defects | Control of repairs |
Variation in quality of concrete | Quality of concrete replacement |
How do I carry out the Chloride ion migration test?
The PERMIT test for chloride ion migration in concrete from Amphora NDT involves several steps, which generally include the following:
Attach the PERMIT device to the concrete structure using bolts or mechanical clamping.
Prepare the device by filling one chamber with a chloride source solution and the other with a neutral solution like deionized water.
The device will then apply a voltage across the chambers to migrate ions from the source to the neutral solution through the concrete and use electrical conductivity measurements to monitor the ion flow.
Once a steady state is reached, the device will analyse samples from the outer chamber to determine the flux. As the concrete's quality improves, the permeability decreases, potentially extending the chloride ion migration test duration from as short as 1.5 hours to as long as 10 hours.
This steady flux data is then converted into the ionic diffusivity or the coefficient of ion diffusion via the Nernst-Planck equation.
Transfer the test results from the device to a PC for further analysis.
This test is specifically designed for in-situ assessment without the need for core extraction. The device comprises two parts: the body that houses the testing solutions and electrodes, and the electronic controller for voltage application and data recording. The duration of the test can range from 1.5 to 10 hours, depending on the quality of the concrete.
What equipment and expertise are required for the Chloride ion migration test?
The PERMIT ion migration test system from Amphora NDT is the only in-situ chloride migration test on the market today and Is composed of:
The PERMIT body
This houses two reservoirs for the ion source solution and a neutral solution like deionized water, along with electrodes and a clamping ring for attachment to the concrete surface as well as an electronically controlled system to apply the test voltage, stir the solution, and measure conductivity and temperature in the outer chamber.
Electronic control box
This contains the custom-designed electronic control and data recording hardware. It has a digital display and test selection keys, sockets for connecting the PERMIT body and for connecting to a PC, and comes with a DC power supply unit.
Clamping mechanism
This secures the PERMIT body onto the test surface, which can be done either by bolting or using clamps, suitable for both horizontal and vertical surfaces.
Connection cables and carrying case
Cables for connecting the PERMIT body to the control box and for data transfer to a PC, and a portable carrying case to protect the device form external conditions.
Conducting PERMIT testing for chloride migration in concrete necessitates a blend of technical knowledge in chloride ion migration, diffusion processes, and electrochemistry; operational skills for device setup, solution preparation, and voltage application; data analysis capabilities to compute ionic diffusivity via the Nernst-Planck equation; and interpretative expertise to assess concrete durability, predict service life, and evaluate corrosion risks.
What are the advantages of the Chloride ion migration test?
Amphora NDT‘s PERMIT testing is the only in-situ test that measures chloride migration in concrete without extracting cores.
Low-cost method especially when compared with lab-based tests.
Rapid testing and results within 24 hours even for extremely impermeable concrete.
The device is portable and easy to handle, facilitating testing in various environments and locations.
PERMIT can measure the effectiveness of sealants, coatings, and the impact of different curing conditions on chloride penetration resistance.
Can be used to asses migration of all ionic species such as chlorides, sulphates etc.
What are the disadvantages the Chloride ion migration test?
PERMIT evaluates the surface and near-surface therefore might not indicate the internal condition of the concrete.
Test accuracy can be affected by the ambient environment, requiring controlled conditions for best results.
The proficiency of the operator and proper calibration of the device are crucial for obtaining accurate results.
Interpretation of the results requires a solid technical understanding of concrete behaviour and ion migration phenomena.
How accurate is the Chloride ion migration test?
The PERMIT test can be used to accurately measure ionic diffusivity in the range 1 x 10-8m2/s to 1 x 10-14m2/s. The results of these tests have been proven to be extremely accurate based on comparisons against lab tests including steady (Figure 6) and non-steady state migration (Figure 7).
The methodology behind the test of measuring the chloride concentration of the analyte solution through electrical conductivity has also been proven to be extremely accurate (Figure 8).
What are the limits of the Chloride ion migration test?
The PERMIT test is designed for a specific range of ion diffusivity and therefore may not cover all construction materials or scenarios. The test also assumes a certain saturation state of the concrete which, if not met, could lead to inaccurate results.
Ancillary information
Maturity of test: > 10 years
Qualification & interpretation : Inspector and specialist
Service disruption: No
Preliminary works: Yes
Time consumption Medium (one day)
Cost Low
Access to element 1 face
References and further information