Electrical Properties of Cementitious Systems: Formation Factor Determination and the Influence of Conditioning Procedures

Abstract

The number of people wanting to use electrical tests to determine the transport properties of concrete has increased with advancements in the portability of hand-held testing devices. Electrical measurements are an attractive test method to quantify transport properties of cement-based materials since they can be performed rapidly. There is a high potential for using these tests in quality control or mixture qualification. However, electrical measurements can be significantly influenced by curing and storage conditions, which can impact the degree of saturation, degree of hydration, sample temperature, and pore solution chemistry. This study proposed a general equation that described the electrical resistivity measurements in cementitious systems and possible methods to account for some of these conditioning-induced changes. It is proposed that these tests are useful in the determination of the formation factor, a numerical quantification that describes the microstructure. A comparison of the formation factor obtained from rapid electrical measurements using the Nernst-Einstein relationship was compared to a migration test with the goal of proposing a curing methodology for rapid electrical tests that allows for the determination of a true transport property.

Leaching of conductive species: Implications to measurements of electrical resistivity

“…Previous work has demonstrated how finite layered effects can influence surface and bulk electrical measurements in different ways: half-space [44], or finite slab geometries [11,45–47]. One approach to investigate the effects of layered materials is to study the ratio of surface resistivity to uniaxial resistivity, as originally described by Morris et al [40].…”

“…If leaching occurs, as illustrated in Figure 1, the pore solution concentration (and resistivity) can change by a significant factor as ions migrate from the specimen into the surrounding storage solution. In a study by Spragg [11], this was shown, for the concrete considered, to be a factor of four. In this paper, experiments and modeling are combined to provide insights into the significance and magnitude of the influence of leaching on electrical properties measured in standardized tests.…”

“…Numerous research studies have shown a good correlation between this theoretical approach and experimental values, for a sealed sample, for ordinary portland cement (OPC) concretes, e.g. [11,20–24]. The primary concern with sealed specimens is they are not a saturated system, and Equation 1 is generally applied to a saturated system.…”

“…Frequently, electrical resistivity is used to determine the ionic transport properties of concrete as it can be related to the chloride ion diffusion coefficient [10,11]. The diffusion coefficient can be used with service-life prediction models to estimate service life of a concrete element [12-14].…”

“…In a previous study, a simplified linear mass balance approach was used to estimate the change in pore solution resistivity based upon the change in the resistivity of the storage solution [11]. …”