Development of a portable measuring system using ultrasound guided and surface waves to characterize concrete structures

Abstract

A portable system was developed to be used in lab and on field. The system is composed of one emitter and 60 receivers. All of them are Dry Point Contact sensors, P-wave, S1803 from ACSYS, with a nominal frequency of 100kHz and a wide frequency range from 15kHz to 175kHz. The 60 receivers are equally spaced of 5mm which enables to make measurements over 30cm. The acquisition is made with a two-channels A1560 ACSYS device. We developed an electronic part to multiplex the acquisition of all the receiver signals. A Raspberry-Pi device is used to control four 16-channels analogic multiplexers. We designed and manufactured with a 3D-printer a holder for the DPC sensors and the electronic part. The A1560 device and the Raspberry-pi are controlled with a Python program on a digital tablet. For one acquisition, which lasts a few seconds, 60 a-scans are registered. Several acquisitions are repeated by moving the system of a few centimeters. The results are averaged to lower the incoherent part of the signals due to multi-scattering effects on concrete aggregates. The result is processed with a p-w Transform to get the dispersion diagram and to assess the dispersion curve. In the case of surface waves, when the structure thickness is larger than the smallest wavelength, the dispersion curve can be inversed with a tool like Dinver from Geopsy. The final result is the ultrasound speed profile with depth. In the case of Lamb waves, the dispersion curve is compared to A0 and S0 modes calculated with a tool like Disperse form Imperial College or CIVA frome CEA. This efficient tool is used to study different concrete structures: - thick structure with concrete cover affected by carbonation or leaching, - thin structure like 6cm-thickness and 60cm-diameter concrete/steel/concrete pipes used in the nuclear industry.