PSI - Issue 65

I. Shardakov et al. / Procedia Structural Integrity 65 (2024) 241–247 I. Shardakov, I. Glot, A. Bykov, I. Panteleev A. Shestakov / Structural Integrity Procedia 00 (2024) 000–000

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sheet 6 cm wide and anchored with U-shaped clamps 20 cm wide (Fig. 1b). Reinforcement was carried out using SikaWrap-230 carbon canvas and Sikadur-330 epoxy resin. The beam, cleaned of cement dust, was covered with a layer of epoxy resin, and then a carbon canvas was laid on it and fixed with a finishing layer of epoxy. Two series of tests were performed: 4-point bending of the concrete beam without reinforcement and a similar test of the beam reinforced with composite sheet.

Fig. 1. Structural diagram of the experiment: (a) conventional concrete beam; (b) beam reinforced with CFRP sheet

The tests were carried out on a laboratory bench. Quasi-static loading of the beam was carried out in steps. During the test, 25 loading and unloading stages were performed. The load increment at each stage was 2 kN, which corresponds to 4-6% of the breaking load. Between loading stages, 5-10 minute exposures were made, during which the pattern of cracks and their opening width were recorded. Loading up to the 15th stage occurred without the formation of visible cracks. With a further increase in the applied load, cracks were recorded in the conventional beam (the first main crack was at the 15th loading stage, the second at the 16th stage). In the beam with composite reinforcement, in addition to cracks in the concrete, cohesive delamination was observed at the boundary of the composite and concrete and rupture of the composite tape. Damages in the concrete beam and carbon fiber canvas recorded at the final stage of loading are shown in Figure 2.

Fig. 2. Scheme of damage at the final stage of loading: (a) – a conventional beam, (b) – a beam reinforced with CFRP sheet

To record AE signals, the following equipment was used: an Amsy-5 Vallen acoustic emission recording system (Germany) with a signal sampling frequency of 2 MHz; AEP4 acoustic signal preamplifier with 34 dB gain; AE sensors SE2MEG-P (Deci, USA) with a frequency range of 200-2000 kHz; To ensure acoustic contact of the sensor with the surface of the beam, paraffin paste was used. In the experiment with a conventional concrete beam, 2 AE sensors were installed on the side surface of the beam (Fig. 1a). For a reinforced beam, 1 sensor was installed on the side surface of the beam and 2 sensors on the carbon fiber canvas (Fig. 1b).