Title: Frequency and Geometry Effects on Ultrasonic Pulse Velocity Measurements of Concrete Specimens

Author(s): Piotr Wiciak, Giovanni Cascante, and Maria Anna Polak

Publication: Materials Journal

Volume: 117

Issue: 2

Appears on pages(s): 205-216

Keywords: dimension effects; laser vibrometer; nondestructive testing of concrete; ultrasonic pulse velocity

DOI: 10.14359/51722399

Date: 3/1/2020

Abstract:
The ultrasonic pulse velocity (UPV) method is commonly used as a nondestructive testing (NDT) method in civil engineering and is the ASTM standard for the relative evaluation of concrete quality. However, its limitations due to specimen dimensions or the frequency content of the transmitter excitation are not well understood. The only ASTM recommendation related to the specimen dimension is that the length should be larger than one wavelength. In this study, an experimental program is designed to specifically address the current gap in the understanding of transducer coupling and geometric effects on UPV testing. A state-of-the-art laser vibrometer and numerical simulations are used to evaluate a group of 30 specimens to give a comprehensive range of dimension-to-wavelength ratios. This study shows the response of the ultrasonic transducers in terms of the actual displacements, which indicate their complex character instead of the single pulse response typically assumed. In addition, to improve the reliability of the UPV test, the minimum specimen length-to-wavelength ratio should be greater than 4, instead of 1 as typically recommended, and the diameter-to-wavelength ratio should be greater than 3 instead of 1. If the new set of recommendations is not fulfilled, the error of the UPV measurements can reach up to 20%.