Question:
What are the pros and cons of the Rapid Chloride Permeability Test?
Answer:
The so called “Rapid Chloride Permeability Test” is being used as a measure of the “permeability” of concrete to chloride ions. The more proper term would be chloride penetration. Many highway agencies have adopted the test and it has been included in HPC bridge specifications. The test was developed in the late 1970’s under an FHWA contract and has been standardized as AASHTO T277 and later as ASTM C 1202. There has been considerable debate regarding appropriate applications and interpretation of test results. Because of this, it is instructive to review the “pros and cons” of this test.
Pros:
• The test is rapid and can be completed in two days including specimen preparation. Other permeability tests take weeks or months to complete.
• Equipment for the test can be constructed from relatively simple components and is also commercially available.
• As the test has been in use for approximately 20 years, there is a large database of test results available.
• Though information is limited, the test has been correlated with chloride ponding and other tests of concrete permeability.
Cons:
• The test has poor correlation with ponding tests when different mixes are compared.
• The test is not a direct measure of chloride “permeability.” It only measures electrical conductivity of the concrete.
• Chloride ions only carry a small proportion of the current during the test, so the test is not specific to chloride.
• It has been claimed that the test yields erroneous results when applied to silica fume concrete.
• Self-heating of the specimen during the test affects test results.
Space prohibits addressing each pro and con. Most of the “cons” are related to the fact that this is not a direct test of chloride penetration. While this is scientifically correct, the test was developed as an empirical indicator of chloride penetration, not as an exact measure. ASTM C 1202 states: “This test method is applicable to types of concrete where correlations have been established between this test procedure and long-term chloride ponding procedures such as those described in AASHTO T259.” If such correlations have indeed been developed for a given concrete, then the Rapid Chloride Permeability Test can be confidently applied.
Answer contributed by David A. Whiting of Construction Technology Laboratories, Inc.