Explain the working of Ultrasonic System for Concrete Elements?

Ultrasonic methods can be used underwater for overall assessment of the strength of concrete based on sound velocity measurements through a large volume of structural element. It can also be used to detect and locate flaws and discontinuity in concrete elements. It is, however, recommended that the underwater ultrasonic system be used primarily for checking the uniformity of concrete from one test location to another in a given structure. If the data consistently indicates poor or very poor quality concrete, core samples must be taken and standard compression test performed to confirm the results.

The system consists of two different underwater transducer holders for direct and indirect sound velocity measurements. An umbilical cable connects either the direct or indirect transducer holder to the topside DAU. The DAU contains most of the signal conditioning electronics and data acquisition system. In ultrasonic testing, an electric pulse is generated in the test instrument and transmitted to a transducer that converts the electric pulse into mechanical vibration. The vibrations are transmitted into the object being tested. A portion of this energy is reflected to the receiving transducer, where it is reconverted to electrical energy and sent to the DAU. Sound velocity is calculated by measuring the time required for transmission of sound wave over a known path length. Table 5.2 presents suggested condition grading for concrete based on pulse velocity measurements.

Table: Criterion for concrete quality grading