Transducers frequency influence on ultrasonic velocity measurements in concrete specimens

Ultrasonic testing is a non invasive surveying technique suggested for concrete quality control. European standards concerning the determination of ultrasonic velocity in concrete take into account measurements stability, repeatability and reproducibility, and address the main factors influencing velocity measurements, but no exhaustive suggestion is given about the frequency characteristics of the transducers to be used in the test. Commercial measurements systems offer several types of transducers with different frequency characteristics, the choice of which is left with the operator, who has to decide without clear standards or guidelines. This work reports the preliminary results of an experimental campaign aimed at establishing the influence of transducers natural frequency on ultrasonic velocity measurements in concrete. Several concrete specimens have been made and tested by using transducers with different natural frequency. The correlation between transducers frequency and ultrasonic velocity has been exploited and discussed, also with relation to curing stage and concrete compressive strength