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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1.

Introduction.

In world practice, the method of strengthening building structures using composite materials is widely used. Unidirectional and bidirectional composites in the form of canvas have become widespread. Glass, carbon, organic or aramid, basalt fibers are used as fillers and thermosetting epoxy resin often acts as a binder. Composite materials based on carbon fiber (Carbon Fiber Reinforcement Polymers) are most widespread due to their high chemical and corrosion resistance to most aggressive environments, as well as high strength and Young’s modulus. Due to its high rigidity, CPRF have fairly high long-term strength and low creep, as well as high fatigue strength. Reinforcement technology using carbon fiber sheets can be used for reinforced concrete and stone, wooden and steel structures. The effectiveness of external reinforcement of reinforced concrete structures with composites has been confirmed by numerous experimental data. As noted, for example, in Esfahani, 2007, this method can significantly increase the load-bearing capacity and service life of a reinforced concrete structure. The work of Bykov, A., 2023 demonstrated the effectiveness of using external reinforcement of concrete structures using a CPRF sheets both to prevent the development of unwanted deformations and to restore damaged structures under load. During operation of such a reinforced structure, various destruction mechanisms can occur. This may be the flow of metal reinforcement, destruction of concrete, rupture of the canvas, delamination of the composite as a result of cracks opening in the concrete, etc. (Esfahani, 2007). As shown by Pellegrino, 2008, failures associated with coating delamination typically occur before the ultimate flexural or shear capacity of the structure is reached. Organizing continuous monitoring of the condition of such structures is an urgent task. There are various methods of non-destructive testing that have shown their effectiveness in monitoring the process of delamination of a composite coating from a concrete structure. The works of Basu, 2021, Lorenzi, 2020 provide examples of the use of ultrasonic testing of the integrity of concrete structures. The work of Shardakov I. et al., 2016 demonstrated the possibility of monitoring the delamination of CPRF layer from the concrete surface using thermography. However, these approaches are quite problematic to use for assessing the condition of building structures in situ over a long period of time. The use of the acoustic mission (AE) method seems promising in this direction. It is based on an analysis of the parameters of elastic waves that arise during the implementation of various deformation processes in a structure. As noted in the works of Maji, 1994, Grosse, 2003, AE signals during loading of reinforced concrete structures can be of a different nature. They can be associated with the occurrence of cracks of various orientations and types in the volume of the cement binder and fillers, discontinuities at the boundaries between the fillers and the binder; can be caused by plastic deformation of steel reinforcement, corrosion of various natures (Schechinger, B., 2006, Radhika V., 2024). Reinforcing composite elements can, in turn, initiate AE signals caused by the destruction of the matrix and fibers of the composite, delamination of the composite sheet, peeling of fibers from the matrix, disruption of adhesion at the boundary of concrete and composite (Degala, S., 2009, Aidoo, J., 2004). Its use is attractive due to the fact that it makes it possible to record the occurrence and development of defects over time, as well as to determine the places where they arise. Examples of the use of acoustic emission in the diagnosis of reinforced concrete structures can be found in the works of Colombo, 2003, Grosse, 2003. This paper presents the results of a series of experimental studies that allow us to evaluate the possibilities of using the acoustic emission method to control the deformation interaction of a composite sheet with the surface of a reinforced concrete beam subject to bending. The processes of acoustic emission that occur under sequential loading in the 4-point bending mode of a conventional reinforced concrete beam and a beam reinforced with a composite material were studied. A comparison of the data recorded in these 2 cases made it possible to identify features of the AE signals that could be considered as signs of the occurrence and development of detachments of the composite sheet from the concrete base. The possibilities of using this approach in organizing online monitoring systems for the deformation state of building structures reinforced with composite materials are assessed.

2.

Materials and methods.

The work investigated the processes of acoustic emission that occur during the deformation of a reinforced concrete beam with dimensions of 1270  220  120 mm, made of class B35 concrete reinforced with AIII steel. The experiment involved a beam without external reinforcement (Fig. 1a) and a beam reinforced with a longitudinal