PSI - Issue 10

M. Petrov et al. / Procedia Structural Integrity 10 (2018) 303–310

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M. Petrov et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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of determining the technical state of the structure is extremely acute. At the present time, various nondestructive testing methods have been developed and used to evaluate damage to concrete. Among them: the acoustic emission method (Alam and Loukili (2017)), electrical and electromagnetic emission (Gade et al. (2017); Stergiopoulos et al. (2013)), impact echo methods (Krzemień and Hager (2015)), ultrasonic and laser methods (In et al. (2015); Song and Popovics (2017)), and the impedance technique (Dai et al. (2016)). Along with the specified methods, a method for evaluating damage to reinforced concrete structures based on the parameters of the electric response that occurs in concrete as a result of weak mechanical impact has been developed (Fursa et al. (2017a; 2017b; 2017c)). The method relies on measurement of electrical responses from testing samples to a single impact by an attached capacitive transducer. The essence of the method is that the material under test is exposed to a weak elastic shock action that results in acoustic waves starting to propagate within the sample. The mechanical stresses caused by acoustic waves produce an alternating electric field as a consequence of the elastic wave deforming and displacing double electric layers located at the boundaries of the concrete components, and the polarization of piezoelectric quartz contained in the sand and gravel. The electric response to mechanical impact is the sum of these effects. The conducted research has established that piezoelectric inclusions play a decisive role in mechanoelectric transformation in concrete (Fursa et al. (2017b)). The electric measuring receiver placed next to the sample and within the range of this field registered the electric response parameters related to the characteristics of elastic waves and therefore reliably reflecting the processes of their interaction with internal structural heterogeneities and defects. The purpose of the research presented in this paper is to study the patterns of changes in the parameters of the electric response, the elastic and mechanical characteristics of the concrete reinforced with steel and fiberglass reinforcement during testing under compression conditions, and to determine diagnostic criteria for evaluating the dynamics of damage processes in reinforced concrete. The research was carried out using laboratory samples simulating reinforced concrete with different rein forcement materials (steel, fiberglass), various forms of reinforcement (1 reinforcing bar, 2 reinforcing bars, a cage made of 12 reinforcing bars), and various concrete compressive strengths. The sample size was 100 × 100 × 100 mm. The periodic profile reinforcement with a diameter of 10 mm was used for manufacturing concrete samples. The concrete samples were manufactured in accordance with GOST 7473-2010. The cement/sand/coarse aggregate ratio was 1:1.7:3.5 with a maximum aggregate size of 20 mm. The water-cement ratio was 0.55. Increasing the concrete strength was achieved by using a plasticizer and reducing the water-cement ratio to 0.45. Also, concrete samples without reinforcement were produced for comparative analysis. The researches were carried out in the conditions of complex mechanical effect to the specimen consisting from quasistatic loading with a constant speed and a periodic impulse shock excitation. Within the boundaries of current research, we analyze the electrical response on a weak elastic impact at a discrete time moments. The IP-500 press was used in the compression testing of concrete samples. The load rate was 0.3 kN/s. The re cording of load and displacement with the time increment of 1 s has been performed throughout the loading process using custom software. In the process of quasistatic uniaxial compression, from the beginning of loading until failure, a periodic (every 10 seconds) additional weak impact excitation along the lateral sample surface was carried out and the electric response to this action was measured. To measure the electric response during the loading process, the measuring probe was attached to the lateral sample surface by rubber bundles. Periodic measurement of the electric response to impact under increasing external compressive load made it possible to study the nature of the changes in the response parameters throughout the loading process, up to the failure of the sample. Fig.1 shows the scheme of the experiment and the photo of the compression test setup. Measurement of the electric signal has been carried out using a laboratory hardware and software system capable of generating mechanical impact on concrete sample and recording the electric response. The system consists of a remote measuring probe, a power supply, an I/O board and a notebook. The remote probe is a metal cup inside which there are a differential electrical sensor and an impact device. 2. Measurement procedure