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Supplanting the Rapid Chloride Permeability Test with a Quick Measurement of Concrete Conductivity
D. Stephen Lane
D. Stephen Lane
Year: 2005
VTRC No.: 05-R22
Abstract: The rapid chloride permeability test (RCPT) (AASHTO T 277, ASTM C 1202) is increasingly being used as an acceptance test for concrete constructions in the transportation industry. As more and more projects are subject to such testing, the capabilities of agency laboratories to conduct the test in a timely fashion are strained. A literature review regarding the RCPT revealed that the electrical conductivity of concrete is a more valid indicator of its quality than the RCPT result and that the conductivity can be determined from a measurement of the current taken 1 to 10 minutes after the voltage is applied using the standard equipment setup. A series of tests was conducted that estimated the within-laboratory precision of the conductivity measurement and the standard 6-hour RCPT. Comparison of the estimates indicated that the conductivity measurement is more precise than the RCPT. Conductivity values were calculated from a large block of RCPT data, and regression analysis was used to examine the relationship between the two measures. Confidence limits for the regression can be used to determine the range of RCPT values expected from a given conductivity value to facilitate shifting from an RCPT-based criterion to one based on concrete conductivity. The benefits of implementing these recommendations provided would be as follows: - Routine acceptance testing of concrete for chloride permeability would be streamlined without increased cost - Such acceptance testing could be conducted within 1 to 10 minutes, as compared to 6 hours for the existing test procedure, thus greatly reducing the backlog associated with such testing. This would permit the timely reporting of test results to project personnel and allow more effective management. - The new test recommended has improved repeatability when compared with the current test.