PSI - Issue 5

Igor Shardakov et al. / Procedia Structural Integrity 5 (2017) 210–216 Igor Shardakov / Structural Integrity Procedia 00 (2017) 000 – 000

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1. Introduction Cracking is commonly observed in reinforced concrete structures during their service life. Crack formation significantly reduces the stiffness and strength properties of these structures. One way to repair the lost properties of concrete is by injecting epoxy resin into a crack (Keane B.F., 2009). The effectiveness of this technique is supported by the fact that new cracks appear outside the region of previously repaired cracks (NAHB Research Center, 2002). The success of this repair requires strict adherence to the repair technology, which includes proper filling of cracks and complete curing of the injected agent. At the first stage of the repair, a healing agent is injected into a crack to a depth of 5-10 mm along its entire length. Next, the space within the crack is filled completely with an epoxy composition. Inspection of the degree of crack filling and the quality of filler curing is a considerable challenge. One of the main crack control technique includes taking core samples from the rehabilitated fragments of the structure, strength testing of these samples and their comparison with the samples taken from the undamaged fragments. This method appears to be very tedious because it requires local damage of the structure already repaired. Among the non-destructive testing methods, we mention acoustic diagnostic techniques that detect defects and assess their current state (Fan and Qiao (2011), Stepinski et al. (2013)). The results obtained with these methods offer information about the filling degree of a crack, yet they cannot provide a proper estimate of the stiffness properties of the region filled with a repair agent. It is also interesting to consider the approaches which stem from the analysis of the parameters of natural vibrations (Salawu (1997), Quaranta et al. (2013)) of the examined structure and the transient vibration processes in it (Raghavan and Cesnik (2007), . Liu et al. (2013)). With these techniques, one can assess the changes in the parameters of natural vibrations depending on the crack opening or the degree of filling a crack space during the repair process (Bykov et al. (2015), Shardakov et al. (2016)). However, several specific features of these methods are worth noting. The measured parameters exhibit high sensitivity to the conditions of fastening of reinforced concrete structures, at which the process of crack healing takes place. What is more, significant changes in the measured parameters due to crack size changes occur under high frequency vibrations. The purpose of this paper is to develop further the existing non-destructive shock wave method used to monitor the state of reinforced concrete structures. This method includes the assessment of crack evolution under loading and the control over restoration of the stiffness properties of the structure during the elimination of cracks. In our version of the method, the parameters of elastic shock waves are recorded at instants when they are practically independent of structure fastening conditions and responded most adequately to the changes in cracks during their healing. Indicate references by Clark et al. (1962) or Deal and Grove (2009) or Fachinger (2006) in the text. 2. The proposed version of a non-destructive shock wave method for crack control The potential of the developed method is illustrated through its use in monitoring the crack state in a reinforced concrete beam represented schematically in Fig.1. The beam has the following dimensions: length 1.27m, height 0.22, and width 12m. It is assumed that a single crack develops across the central section of the beam.

Fig.1. Schematic diagram of the experiment