## 1 Introduction  
Civil infrastructural systems are exposed to a wide range of loadings during their life, such as service loads, environmental conditions, and disasters. The safety and durability of the structures continue to be the primary concern of structural engineering, particularly in terms of life safety, economy, and functionality. Concrete, the most commonly used construction material, is a composite with heterogeneous and inherent complexities, making it more difficult to determine damage presence and progression [1]. Conventional structural assessment methods generally evaluate the condition on a member-by-member basis, which lacks the ability to identify possible damage possibilities and requires subjective assessments [2]. Moreover, the member from which the core is taken is also damaged, and it is not possible to determine the damages that occur in the inner area of the structural member with the existing methods. At this point, the use of structural health monitoring systems can provide an early detection of damages in structures and help engineers make informed decisions [3]. Nondestructive testing (NDT) methods allow comprehensive damage detection in inaccessible areas without harming the structure and can identify the location, size, and type of damage. They are categorized into two subcategories: active and passive methods [4]. Active NDT methods involve assessing damage characteristics by measuring changes within the material by applying external energy. For instance, ultrasonic monitoring uses mechanical sound waves, radiography utilizes radioactive radiation sources, and radar employs electromagnetic waves. Thus, this initiated energy transmission results in the measurement being controlled. Conversely, passive NDT methods utilize natural energy emitted within the material itself without requiring an external input. Acoustic emission (AE), which analyzes sound waves emitted due to energy release from the damage, and thermography, which assesses surface heat changes, are commonly used passive NDT methods for structural damage detection. The AE method, on the other hand, is the most effective technique for identifying potential active damage formation, particularly in nuclear power plants and bridges under dynamic loadings. By AE, significant information about damage can be provided, such as the type, location, and orientation of a crack, delamination, or dislocation [5; 6; 7]. This feature of the method allows one to monitor the structures in real-time and the ability to detect micro-fractures earlier, which will enable taking precautions by giving an alarm. Moreover, the AE method's usability with artificial intelligence technology, feasibility, and effectiveness on concrete damage inspection are proved in numerous studies found in the literature [8; 9; 10; 11]. In the AE phenomenon, energy release resulting from mechanisms (such as crack formation or propagation, reinforcement corrosion, etc.) propagates through the material as elastic waves, which are detected by sensitive sensors and converted into analyzable signals [12]. AE signals include typical parameters, such as amplitude (the peak voltage), duration (elapsed time between the first and last pulses exceeding the threshold), rise time (elapsed time between the first and peak pulses), and energy (area under the threshold-crossing envelope of the signal). Existing studies show the efficiency of using these parameters in the identification of critical information about damage in structures. The severity and orientation of the damage can be obtained by evaluating the amplitude and energy of the signal [13; 14; 15; 16]. These factors are crucial in AE detectability since they measure the damage size and intensity to which the signal originates. On the other hand, the type of damage is provided by analyzing rise time and frequency (i.e., average frequency, peak frequency, and frequency centroid) [17; 18]. Moreover, the location and time of the occurrence of the damage are determined using the signal arrival time [19; 20; 21; 22].