PSI - Issue 64

Alexander Shuvalov et al. / Procedia Structural Integrity 64 (2024) 445–455 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Transverse sounding is carried out on two mutually parallel planes (sides) of the column. The transducers on both sides should be placed mirror to each other between the reinforcing bars in the direction perpendicular to the direction of the main reinforcement. The results of this method are the values of the velocity of the ultrasonic wave, which are subsequently recorded in the memory of the device. After that the results are processed and the results are given in tabular and graphical form. 2.2 GPR methods The GPR method is a geophysical method based on transmitting radio wave pulses at select center frequencies into the medium to study it. The method of GPR relies on the effects that the electrical properties of matter (e.g., dielectric permittivity) have on the propagation of electromagnetic waves. If a wave pulse encounters a material interface of sufficiently different electromagnetic properties, a portion of the energy is reflected back while the remainder continues its path, which allows to determine the double travel time of the sounding pulse (the time required for the sounding signal to travel from the source to the reflecting surface and return to the receiver), which can be translated in depth under certain circumstances, and the amplitude of the received reflected sounding signal (which is indicative of how big the portion of reflected back energy was). An important physical parameter is the dielectric permittivity of the elements of the investigated medium, on which the speed of propagation of electromagnetic waves in the medium depends. The result of field GPR observations resembles a cross-section comprised of the wave patterns that depict the subsurface electrical structure and can reveal features of interest, like irregularities and defects in concrete strictures. In this case study, considering that the travel distance of the sounding signal is known, in the case of searching for defects in concrete structures, the main indicator is the deviation of dielectric properties calculated from the time of arrival of the reflection from the concrete-air boundary: the velocity of propagation of electromagnetic waves in air is higher than in concrete; if it takes less time for the EM-wave to travel a set distance (the thickness of a column in this case), it would mean a higher content of air on the EM- wave’s path. So lower values of dielectric permittivity are associated with an increase in volumetric porosity, whereas higher values, on the contrary, are associated with a decrease in volumetric porosity.

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Fig. 2. Different methods of representing amplitudes on radarograms: A - representation of amplitudes by deviation method with blackening of positive amplitudes (deviations to the right); B - representation of amplitudes by variable density method (blue-red with transition through white color scale); C - representation of amplitudes by variable density method with alternative color scale. Representation of electromagnetic wave amplitudes on radarograms can be done in several ways: • Representation of amplitudes by deviations, that is, the greater the amplitude of the signal, the greater the deviation of the trace from the zero position;