NDTnet 1998 Aug, Vol.3 No.8

Abstract

Figure 1. A tomogram of a footing. Figure 2.. A tomogram of a concrete block.

The most suitable way to inspect the concrete structures with one side access is the ultrasonic pulse-echo method with tomographic presentation of output data. However it is very difficult to use this way because of necessity to ensure by liquid the qualitative acoustic contact between a large antenna aperture and the uneven concrete surface. Created lately an ultrasonic tomograph with dry acoustic contact has not such defect.The tomograph consists of an 36-element square matrix antenna array, a signal digitizer, a controller with computer interface and a Notebook computer. Each transducer of the antenna array has a cone-shaped protector having a point contact with the tested concrete surface. It allows to avoid the use of a contact liquid. The tomograph operations are based on pulse-echo method, in association with combinational sounding and data processing by the Combination Synthetic Aperture Focusing Technique (SAFT-C) (1). Operational ultrasonic frequency is 55 kHz.

Apart from reliable acoustic contact of all the antenna transducers with the surface, that ensures reproducibility of an obtained imagines, the point contact allows to measure the ultrasonic velocity in tested material during inspection process. For this purpose several pairs of the antenna transducers are used for registration a surface ultrasonic signals.
A tomogram of a reinforced concrete footing with friable concrete domain near an iron 1-bar is presented in Fig. 1. A tomogram in Fig. 2 illustrates an ability of the apparatus to imagine a local small flaws.
Thus the equipment enables in particular the detection in concrete of spherical flaws with diameters of 50 - 100 mm at depths 50 - 500 mm.

Reference
1. Kozlov, VN., Samokrutov, AA.,Evaluation. 1997,13: 73-84 Shevaldykir', VG. J. Nondestructive Testing and

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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