Development of an ultrasonic experimental device to characterise concrete for structural repair

Various non-destructive testing methods, based on the propagation of ultrasonic waves, can be used to characterise the mechanical properties of structural concrete in situ. The results obtained however are heavily influenced by both water content and concrete mix design. To overcome these biases, it is necessary to recalibrate the results on a small number of cores, whose water content has been laboratory-controlled. To this end, an experimental device designed around the transmission of bulk waves has been developed. The aim of this paper is to introduce and describe such a device, which is able to take into account specimen size, centre frequency and ease of use. The studied mixes herein are composed of wet shotcrete, dry shotcrete and concrete that has been formed and manually set. Measurement results show the evolution in wave velocities relative to four degrees of saturation. Moreover, measurement uncertainties in the values of velocities, Young’s modulus, shear modulus and Poisson’s ratio are quantified.