15443Testing Device [28 154431 Basic Principle

The principle of electrodeless resistivity measurement apparatus is illustrated in Figure 15.13. It can be seen from Figure 15.13 that the apparatus mainly consists of primary coil, secondary coil, and transformer core. In this study, a cement paste specimen was used as the secondary coil. When applying a voltage on the primary coil, another voltage was induced in the secondary cement specimen. In order to obtain the resistivity of the cement paste specimen, toroidal voltage measurement and current sensor were employed to monitor the inductive voltage and current of the cement specimen. It should be noted that toroidal voltage and current measurement did not touch cement specimen. As a result, the resistance Rt was calculated based on Ohm's law. It is of great concern for getting the resistivity rather measurement V, oin

oin measurement V,

Secondary concrete specimen

FIGURE 15.13 Schematic of resistance measurement.

FIGURE 15.13 Schematic of resistance measurement.

TABLE 15.9 The Dimensions of the Ladder-Shaped Polycarbonate Container (Unit: cm)

than resistance, because resistance is related to the specimen shape and size. It is easy to obtain the resistivity of the specimen (p) by the following equation:

where p is the electrical resistivity, Rt is the electrical resistance, S is the cross-section area of the specimen, and L is the length of specimen.

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