**1. Introduction**

The most common problem associated with coastal infrastructure in metro cities like Mumbai, Bangalore, and Chennai is corrosion, which leads to cracking (micromacro) and resulting in gradual ageing of the structure and its components, as a result of climate change and sea-level rises [1]. Moreover, the National Association of Corrosion Engineers (NACE) has detailed the adverse impact on the Indian economy for the corrosion of reinforcement in structural components about U.S. \$26.1 billion (2.4% of the nations).

Gross domestic products (GDP) is spent annually for the corrosion of infrastructure by the government of India [2]. Numerous strategies have been proposed to postpone corrosion in reinforced concrete structures to minimise these huge

expenditures. Commonly suggested methods include the use of stainless steel [3] and epoxy-coated rebars [4] in place of conventional steel bars, admixing corrosion inhibitors [5], self-healing compounds in concrete [6], and use of polymer concrete. It is important to note that these methods only delay the onset of corrosion and do not prevent it entirely. Recently some researchers have also suggested the use of self-healing micro-capsules for corrosion protection of metal [6, 7]. Apart from that, these specific methods have scalability issues in structural applications and are not cost-effective. Steel corrosion is a major problem in the construction industry, and several approaches have been tried to combat it, but they have proven to be either expensive or ineffective. Civil engineers from all over the world are challenged and in search of new and non-corroded affordable construction materials as well as innovative approaches and systems to problem-solving [8].

In many civil engineering applications, fibre-reinforced polymer (FRP) composites reinforcement has been introduced as an alternative or substitute material that can replace traditional reinforcing steel [9–11]. Apart from all this, FRP is a non-corrosive material consisting of a polymer matrix reinforced with fibres [12]. The fibres are usually aramid, basalt, carbon, and glass, although other fibres such as asbestos or paper, or wood have been sometimes used. On the other hand, the polymer is usually an epoxy, vinyl ester, or polyester thermosetting plastic and phenol-formaldehyde resins are still in use. FRPs are commonly used in the aerospace, automotive, marine, and construction industries. Glass fibre polymer (GFRP) bars have been predominantly suggested for engineering applications vis-àvis economy and specific strength properties among other fibres [13].

Being non-corrosive, GFRP composite bars has many advantages such as high strength-to-weight ratio, electromagnetic-neutrality, light-weight, ease of handling, high longitudinal tensile strength, and non-magnetic characteristics, are easily constructed, and can be tailored to satisfy performance requirements [14, 15]. FRP composites have been used as internal reinforcement in concrete, bridge decks, modular structures, formwork, and external reinforcement for strengthening and seismic upgrading in modern construction and restoration of structures due to their favourable qualities. GFRP bars can be utilised in place of steel rebars in harsh exposure situations such as coastal settings, as well as in a variety of other structural applications such as wharves, box culverts, dry docks, and retaining walls [16]. Furthermore, due to their linearly elastic stress-strain relationship up to failure, GFRP reinforcing bars react differently from typical steel reinforcing bars. Furthermore, as compared to steel-reinforced concrete members, the lower modulus of elasticity of GFRP reinforcing bars produces a significant drop in flexural stiffness of GFRP-RC members after cracking and, as a result, greater deflection/deformations under service or loading circumstances [17, 18].

As a result, the serviceability limit state is frequently used to guide the design of GFRP-RC flexure members. In addition, relevant design codes and guidelines for the use of GFRP bars in RC structures have been developed [8]. More research is still needed to provide the required confidence through a better understanding of the flexural behaviour of GFRP-RC [8] using the non-destructive acoustic emission (AE) technique. The AE technique (AET) is considered as one of the most promising techniques from various types of Non Destructive Testing (NDT) methods [19]. The AE method and other NDT methods differ in two main features. First, in AE, the energy signal originates from the sample itself making its own signal, in response to stress. Second, the AE can detect the dynamic process because of its capability to detect movement or strain, whereas most of the other methods can detect existing geometrical discontinuities or fractures [20]. Thus, AE techniques have been applied to detect the crack location [21, 22] to quantify the degree of damage [23] and to determine the crack classification [24] in concrete structures.

*Crack Classification in Steel-RC and GFRP-RC Beams with Varying Reinforcement Ratio Using… DOI: http://dx.doi.org/10.5772/intechopen.101305*

These efforts, which will greatly improve our understanding of how concrete members reinforced with GFRP bars should be analysed, as well as the combination of these techniques, is expected to overcome the shortcomings of the respective techniques, increasing the efficiency of structural inspection and allowing for more frequent monitoring of structures.
