Effect of the Geometrical Constraints to the Wenner Four-Point Electrical Resistivity Test of Reinforced Concrete Slabs

Abstract

The main objectives of this study are to evaluate the effect of geometrical constraints of plain concrete and reinforced concrete slabs on the Wenner four-point concrete electrical resistivity (ER) test through numerical and experimental investigation and to propose measurement recommendations for laboratory and field specimens. First, a series of numerical simulations was performed using a 3D finite element model to investigate the effects of geometrical constraints (the dimension of concrete slabs, the electrode spacing and configuration, and the distance of the electrode to the edges of concrete slabs) on ER measurements of concrete. Next, a reinforced concrete slab specimen (1500 mm (width) by 1500 mm (length) by 300 mm (thickness)) was used for experimental investigation and validation of the numerical simulation results. Based on the analytical and experimental results, it is concluded that measured ER values of regularly shaped concrete elements are strongly dependent on the distance-to-spacing ratio of ER probes (i.e., distance of the electrode in ER probes to the edges and/or the bottom of the concrete slabs normalized by the electrode spacing). For the plain concrete, it is inferred that the thickness of the concrete member should be at least three times the electrode spacing. In addition, the distance should be more than twice the electrode spacing to make the edge effect almost negligible. It is observed that the findings from the plain concrete are also valid for the reinforced concrete. However, for the reinforced concrete, the ER values are also affected by the presence of reinforcing steel and saturation of concrete, which could cause disruptions in ER measurements

Exploring the Detection of Cl− Penetration in Portland Cement Mortars via Surface Electrical Resistivity

“…Table 3 provides details on the shape and dimensions of the different specimens. As is shown in Figure 2, the size of the prismatic mortar specimens was determined to minimize edge effects and to consider the space as semi-infinite, taking the value of a as less than 1/3 of the thickness of the specimens (approximately a = h/3) [21,30,31]. Parameters α and β are dependent on the electrode spacing.…”

“…Therefore, the dimensions were 25 cm in width, 40 cm in length, and 15 cm in height. A geometric correction factor of approximately 1.0 was obtained from the specimen size to minimize edge effects in the surface electrical resistivity measurements [21,31]. The specimens were cured via immersion in a calcium-hydroxide-saturated solution for 28 and 220 days.…”

“…Increased electrode spacing allowed deeper probing into the sample [21,31]; for example, by changing a from 38 mm to 46 mm, the fraction of the analyzed volume that had electrical properties of the "layer" containing chloride ions decreased and the measurements better reflected the properties of the zone that was free from these ions. Using this strategy, the current flow in the mortar is more homogeneous and the variability in the measurements is lower [22].…”

“…However, these methods do not improve the contact between the electrodes and the concrete surface to a significant extent [20]. Studies indicate that the best resistivity measurements are obtained using the Wenner configuration with the largest electrode spacing [21]. An increase in separation will result in a greater penetration of the current field, covering more volume that results in lower relative values.…”

Testing the Uniformity of Surface Resistance on Large-Format Transparent Heating Glass

“…This method is not new [27,28], but is still widely used in many fields. For example, in geophysics, to measure the shear strength of peat soil [29] or construction [30]. The exciting results of using this method to measure the in situ change in electrical resistivity during plastic deformation to characterise the deformation of metals were shown in [31].…”