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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observed. No cracks, cavities, or signs of internal structural decomposition (such as cold joints) of the concrete were noted. The range of ultrasonic velocity during through ultrasonic sounding of the core samples was 4,427 to 4,602 m/s, which corresponds to the range obtained during through-sounding of the columns K1 through K9 (4,444 to 4,580 m/s). Therefore, it has been confirmed that the defects are confined to the protective layer of the concrete up to a depth of 1.5 meters and do not extend into the interior of the column. Summarizing the results of the field study #2, we can conclude that the results obtained from ultrasonic testing correlate with the results of ground-penetrating radar (GPR) and are confirmed both by visual inspection and laboratory testing of core samples. The investigations have shown that defects were formed only in the surface concrete cover of the lower part of columns and do not occur in the deeper sections. Due to the positive results, the order for dismantling the columns was canceled. Defective layers were removed, and the concrete cover repaired with special compounds. A work performance project for repairing the defective columns was developed, and author's supervision over the restoration of structures was carried out. Columns were repaired using two compositions: thixotropic (MasterEmaco P5000 AP) and pourable (MasterFlow S5400), as shown in Figure 8. Before the repair of the columns, tests were conducted to determine the adhesion strength of the concrete on the repaired surfaces. The results revealed that all values of adhesion strength exceeded the required 1.5 MPa, and the type of failure (cohesion) confirmed the test data.

Fig. 10. Photofixing of repaired columns

4. Discussion According to the results of the study, both methods have good convergence, which is confirmed by the results of visual inspection of concrete cores extracted from structures. During this work, the use of ultrasonic inspection revealed a number of issues that complicated and delayed the research: • The need to determine the location of reinforcement bars in the structures being inspected; • Preparation of the surface and marking prior to conducting the inspection; • Requires comprehensive access in order to be able to install sensors facing each other; • Poor visualization of the results obtained. It is worth pointing out that the method of GPR allows for rapid, fast-paced field surveys and provides good imagine data; however, higher speeds of field measurements are offset by the complexity of the obtained survey data, which translates to time-demanding data processing. Acknowledgements The authors would like to express their acknowledgments to the China State Construction Engineering Corporation (CSCEC).