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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1. Introduction The use of geophysical techniques has increased in recent years, not only for investigating foundation soils but also for inspecting reinforced concrete structures. Ground penetrating radar (GPR) is a geophysical technique that can be used to find internal concrete defects such as cold joints, double row reinforcement, and even fiber-reinforced polymer (FRP) bars. Despite this, the widespread use of GPR for inspection purposes is hindered by the lack of regulatory documents for these surveys. The previous version of GOST 31937 standard, which outlines the rules for technical inspection, did not include any guidelines or regulations for using GPR to inspect structures. However, new technologies such as subsurface holographic GPR, which uses microwave methods to nondestructively test various materials and structures, including FRP (fiber-reinforced polymer) ones, are available. At the same time, the use of ultrasound for quality control and inspection of RC structures has been well-established for a long time (Ulybin and Fedotov, 2009). In addition to the traditional ultrasonic techniques for quality control and inspection of building structures, ultrasonic tomography (De La Haza, Samokrutov and Shevaldykin, 2016) and vibroacoustic techniques (Kunin, Y., 2023) are also employed. The disadvantages of ultrasonic methods include their relatively slow work speed and lack of visual representation of results. GPR techniques, on the other hand, allow for high-speed acquisition of data on the structural composition and presence of anomalies with clear visual representation. However, both these methods are indirect and require verification of data obtained through direct methods or calibration relationships. It should be noted that the joint use of ultrasonic and GPR methods for determining defects in load-bearing structures was known earlier (Nigel and Sambuelli, 2011), but the number of such works is relatively small, so it is of interest to further develop such works. 2.1 Ultrasonic methods The ultrasonic method is based on recording the velocity of ultrasound waves in the medium being studied. The speed of ultrasound wave propagation depends on the density of the material. The higher the density, the faster the speed, and vice versa. The lower the density, the slower the speed. By comparing the wave propagation velocity in different areas, it is possible to indirectly localize areas with internal defects, such as caverns or pores. The method of end-to-end ultrasound sounding is based on placing the transducers opposite each other, allowing us to estimate the velocity of sound waves traveling through the entire thickness of the inspected structure. This method is especially useful for detecting internal defects in concrete structures, as ultrasound waves travel a distance equal to the thickness of the concrete and allow us to determine its homogeneity over the entire structure's thickness. 2. Methods

Fig. 1. End-to-end ultrasonic sounding

Prior to ultrasonic testing, it is mandatory to carry out preparatory works, which includes: • Determination of the location of the reinforcement bars, e.g. by electromagnetic induction; • Preparing the surface of the structure to be tested, i.e. scraping the area of the structure to form a flat and even surface to ensure good contact between the transducer and the surface. Often, to ensure the best contact between the sensor and the surface, adhesive compounds such as lithol are applied to the surface or to the sensor itself.