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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• Image by variable density method, i.e. when zero signal amplitude corresponds to one color, positive amplitudes correspond to the second color, and negative signal amplitudes correspond to the third color. Reflective boundaries on radargrams are represented not by a single phase of the electromagnetic wave, but by several, which is determined by the shape of the probing signal. When analyzing the data from the GPR survey, the travel time of the wave from the observation point to the reflection point and back is measured, and the depth is calculated using the formula: = 2 ср (1) ср = √ (2) where t - is the measured time, V - is the velocity of electromagnetic wave propagation in the medium on the interval from the observation point to the reflection point, с - is the speed of light in vacuum, ε is the dielectric constant of the medium. 3. Results For the purpose of comparative analysis of the mentioned methods, the studies of the mentioned ultrasonic and GPR methods on an existing constructions site were carried out. 3.1. Field study #1. Circular cross section RC columns. The subject of the study was cast-in-situ RC columns with a height of more than 7 meters of circular cross-section Ø580 mm, reinforced with the longitudinal reinforcement Ø32 mm grade A500, and transverse spiral smooth reinforcement Ø12 mm grade A240 with a spacing of 100 mm in the lower part of the columns at a height of 1.2 meters and a spacing of 200 mm in the central zone of the columns. The cross-section of the columns and reinforcement is shown in Figure 3.

Fig. 3. The cross-section of the columns and reinforcement.

The survey was performed to determine the presence or absence of internal defects and confirm the result by direct method by taking concrete core samples from the body of structures. To fulfill this task, it was decided to use in parallel the method of ultrasonic flaw detection and GPR profiling. GPR profiling was carried out along the columns from bottom to top, with a scanning spacing of 150-200 mm. Transverse ultrasonic examination was carried out along the pre-marked cells, in places free of reinforcing bars. According to the results of the work carried out by the ultrasonic scanning method, areas were found where the average ultrasonic wave velocity is 2200-2800 meters per second, which is 45% less than the normal ultrasonic wave velocity in concrete for the structures under investigation. GPR scanning was also conducted on the same section. The survey showed decrease of dielectric permittivity at the site by 25%, which suggests the presence of internal defects in the form of pores, caverns or voids.