Correlating ultrasonic pulse velocity and compression resistance of dry concretes at 54 kHz and 500 kHz

Abstract

Nondestructive tests applying ultrasound in concrete is used for more than halfcentury. However, the difficulties in making transit time measurement in heterogeneous media have limited the spread use of these applications. The objective of this work is to present a metrological protocol to determine the correlation between the compressive strength of concrete specimens with about 1 year of cure with their respective longitudinal ultrasonic pulse velocity (UPV). From excitation signals sent through a tunable square wave using the direct transmission method, two pairs of transducers with central frequencies of 54 kHz and 500 kHz were used. UPV is determined by the relation between the length and the propagation time of flight the waveform travels within the concrete test specimens. The pieces were constructed according to ABNT NBR 5738:2015 (Concrete – Procedure for molding and curing of concrete specimens) and tested for compression according to ABNT NBR 5739:2007 (Cylindrical specimen compression test – Method of the test). The preliminary results obtained discloses a coherent increase in UPV and concrete strength. Moreover, the highest frequency leads to higher UPV. With the findings presented in this paper, it is possible to define a dual-frequency nondestructive ultrasound method to evaluate concrete resistance more reliable than the traditional approach.