Variability Analysis of the Bulk Resistivity Measured Using Concrete Cylinders

Many agencies are interested in using a rapid test method for measuring the electrical properties of concrete (i.e., the resistivity or conductivity) because the electrical properties can be related to fluid transport (e.g., ion diffusion). The advantage of electrical testing is that it is relatively easy to perform, and the test method is relatively fast (it takes less than a minute). Over the past century, many studies have investigated different approaches for measuring electrical properties. This paper describes the variability associated with measuring the bulk resistivity along the longitudinal axis of a cylinder after placing electrodes on either end. A multi-laboratory evaluation was performed at ten laboratories. Data from this evaluation provided variability data for 12 concrete mixtures at testing ages of 28, 56, and 91 days. Information on the variability is important in the development of precision and bias statements for standard test methods. In addition, this work discusses how the resistivity results obtained from this test can be correlated with surface resistivity measurements made using a Wenner probe. Linear agreement was noticed between the Wenner test and the measurement through the cylinder, but with a factor confirmed by previous research by Morris et al. (“Practical Evaluation of Resistivity of Concrete in Test Cylinders Using a Wenner Array Probe,” Cem. Concr. Res., Vol. 26, 1996, pp. 1779–1787). Additionally, the effect of electrode resistance is discussed, and for high resistivity concrete such as that used in much transportation infrastructure, this effect appears to be negligible; however, it can be accounted for easily.