Surface resistivity as an alternative for rapid chloride permeability test of hardened concrete.

PDFTech ReportFHWA-KS-14-15Concrete pavementsDeicing chemicalsDurabilityPermeabilityElectrical resistivityBenefit cost analysisKansasKansas. Dept. of Transportation. Bureau of Materials & ResearchJenkins, AndrewKansas. Dept. of Transportation. Bureau of Materials & ResearchUS Transportation CollectionKansas experiences harsh winters that require frequent use of de-icing salts, making it critical to the long-termdurability of concrete structures that the permeability is kept under control. Under current KDOT specification, theRapid Chloride Permeability (RCP) test, as described in ASTM Standard C1202 (2012), or the Volume of PermeableVoids method, described in ASTM Standard C642 (2013), more commonly known as the boil test, must be performedto evaluate concrete permeability. Surface resistivity testing was investigated as an alternative to these tests.Testing for surface resistivity was set up to evaluate the correlation of surface resistivity with RCP and boiltests, the effect of loss of saturation on the sample, and the repeatability of surface resistivity testing. Results indicate astrong relationship (R-squared value of 0.84) between 28-day surface resistivity and 56-day C1202 RCP testing.Results also correlate well to a mathematical relationship derived through Ohm's Law. Surface resistivity did not havea strong relationship (R-squared value of 0.37) with C642 boil testing. Cylinders were cast to evaluate the effect ofsaturation levels and differential sample drying. Cylinders were allowed to dry for varying lengths of time at differentages. Results indicated that allowing the samples to dry, regardless of the length of drying time and the age at whichthe samples were drying, increased the surface resistivity results by an average of 15%. Through the course of thisstudy, including all samples tested, the standard deviation and coefficient of variation on any given set of cylinders is1.4 and 4.9%, respectively. If only samples used for the correlation of 28-day surface resistivity to 56-day RCP areused, the coefficient of variation is 4.2%. A cost-benefit analysis was performed to evaluate the monetary savingsresulting from this research. A triennial analysis indicates a total cost savings by KDOT and contractors ofapproximately $980,000 and a cost-benefit ratio of 9.2.As a result of this research, recommended specification limits have been developed for surface resistivitytesting. As of January 2014, surface resistivity testing has been added to KDOT Standard Specifications as an alternatetest method for concrete permeability