Surface and Uniaxial Electrical Measurements on Layered Cementitious Composites having Cylindrical and Prismatic Geometries

Abstract

Electrical measurements are becoming a common method to assess the transport properties of concrete. For a saturated homogenous system, the surface resistance and the uniaxial resistance measurements provide equivalent measures of resistivity once geometry is appropriately taken into account. However, cementitious systems are not always homogenous. This article compares bulk and surface resistance measurements in cementitious materials intentionally composed of layered materials (i.e., layers with different resistivities). For this study, layered systems were composed of paste and mortar layers, representing the heterogeneity that can exist in the surface layers of field applications as a result of differences in moisture content, segregation, ionic ingress, carbonation, finishing operations, or ionic leaching. The objective of this article is to illustrate that these electrical measures can differ in layered systems (with sharp layer boundaries) and to demonstrate the impact of the surface layer properties on the estimation for the underlying material properties, for both cylindrical and prismatic specimens. Accounting for the effects of a surface layer requires a separate correction in addition to the overall specimen geometry corrections.

Electrical Resistivity of Concrete for Durability Evaluation: A Review

“…In this approach, if there is heterogeneity, the values from the two tests will be different. This difference can give an indication as to whether the surface layer is more or less resistive [21]. Similarly, correlation between surface and bulk resistivity found in other studies indicated a strong relationship between the resistivity values when the appropriate geometry factor was applied [8,37]:…”

“…Based on the reported data, it can be concluded that a strong relationship exists between resistivity measured by surface and bulk tests. However, in practical cases, caution is needed for multilayered cementitious composite systems as electrical current flows differently in these two techniques and for the types of layered electrical properties that can occur due to moisture gradients, chemical changes, and ionic gradients [21]. More complicated situations for resistivity measurement that arise during field measurements where seasonal and wet/drying might take place at the tidal section on partially …”

“…As it is discussed in previous sections, every electrical resistivity ( ) measurement is composed of a resistance ( ) and a geometry correction factor ( ) that convert the resistance to resistivity which is a geometry independent intrinsic material property [21]. The correction factor ( ) depends on the geometry and size of the sample and the electrodes location.…”

“…Authors have found a similar correlation between bulk and surface resistivity ( 2 = 0.979). Both surface and bulk resistivity measurement methods have been used to determine the presence of a heterogeneity problem [21]. To investigate the heterogeneous systems, the surface and uniaxial resistivity tests were performed on the cylindrical specimen with a 10-mm thick white cement paste on outer layer and the prismatic specimens with two separate layers of white and grey cement pastes setup in parallel and series configurations, as illustrated in Figure 14 [21].…”

Design and performance of ternary blend high-volume fly ash concretes of moderate slump

“…Surface and uniaxial measurements of the resistance of hardened concrete cylinders are performed at various ages, while twin steel (screw rod) probes are embedded in a cylinder of each fresh concrete mixture to monitor its ''bulk'' resistance during the first day of curing [3]. The goal of the electrical measurements on the hardened concretes is to provide an indication of their expected durability, capitalizing on the relationship between conductivity and diffusivity [4][5][6] and the observations that reinforced concretes with higher resistivity generally exhibit lower corrosion rates [7]. For the fresh concrete, the goal is to use the initial measurements of electrical resistance to anticipate the subsequent setting time of each concrete mixture [3,8].…”