Basic electrical quantities used to describe the behavior of materials to an electric field are bulk resistivity and conductivity. As opposed to DC testing, AC testing is conducted by applying alternating current, typically in a sequence of different frequencies, on the sample and by measuring the current flowing through the sample. This is achieved by electrodes covering the extremities of the specimen. They consist of a maximum of 7 calibrated standards with nominal conductivities of 59.5, 36, 22.5, 18.5, 14, 9.6, and 2.2 MS/m (58.0 MS/m = 100.0 %IACS on the International Annealed Copper Standard).
Factors affecting conductivity
Several parameters have been identified to influence the electrical conductivity of concrete: water-cementitious materials ratio, type and quantity of supplementary cementitious materials, presence of polymeric admixtures, presence of admixtures containing soluble salts, specimen-age, air-void system, type of aggregate, degree of consolidation, degree of saturation, and type of curing. In this test method, different curing methods are applied depending on whether the concrete has any supplementary cementitious materials.
Specifications of Specimen
The sample specimen has to be saturated adequately, whose measured electrical conductivity should give some account of the resistance of the concrete against chloride ion penetration. Since the electric conductivity varies with the extent of saturation, prior to testing, specimens are vacuum saturated to provide a common reference state at which to compare. In case the test is conducted on a partially saturated, or “as delivered” specimen, it will be indicated in the test report. The bulk resistivity, denoted as Rb, is measured using the circuit shown below.
Bulk Resistivity Measurement
Non-contact non-destructive techniques can be used to measure the bulk resistivity of silicon wafers, ingots, and blocks. The magnetic field within a flowing current of AC induces circulating (Eddy) currents within a sample. In fact, the Eddy current measure is the measure of the electrical loss of the material. The measuring head passes over the sample in a continuous movement without any contact with it. Since the measured signal is a function of sample resistivity, thickness, and distance between the probe and sample, it incorporates an inbuilt distance sensor (capacitance measurement) that measures at the same point as the Eddy sensor.
Applications
Conductivity meters are used to determine the ion capacity of an aqueous solution to conduct electrical current. The use of conductivity is common in determining the number of contaminants in water supplies for domestic consumption, wastewater, water quality testing, and even in industrial applications. The resistivity is a key parameter to determine when dealing with or preparing purified water, including deionized, distilled, or reverse-osmosis water. In the application, purified water can also be referred to as reagent water, reagent grade water, clinical lab reagent water, or Type I water.
