## 1 Introduction
Acoustic emission testing, a well-established and widely applied non-destructive technique, is used to monitor, detect, and pinpoint flaws and damage in mechanically stressed materials and structural components [60; 61; 62]. Alternative localized inspection techniques, such as X-ray testing, ultrasonic waves [63; 64; 65], laser scanning [66; 67; 68], infrared thermography [69; 70; 71], digital imaging, and image correlation techniques [72; 73; 74], have been explored to assess the condition of RC members. Additionally, strain-based approaches using fiber optic Bragg grating sensors effectively monitor changes in tensile forces within RC structures [75; 76]. Despite this, vibration-based and global methods, such as geodetic methods [77] and ground-penetrating radar (GPR) [78; 79; 80], are often inadequate for detecting localized structural damage due to their reliance on lower-order modal parameters [81; 82]. Some of the methods above offer unique advantages for monitoring the performance of retrofitted structures, and many employ a combination of sensors and algorithms for improved accuracy [1; 83; 84; 85]. However, conventional SHM methods are expensive and often insufficient, especially for challenging-to-access structural members, highlighting the importance of cutting-edge monitoring technologies. Among the various SHM techniques, the Electro-Mechanical Impedance (EMI) method is a localized SHM technique that has shown significant potential for detecting damage in RC structural components early, as highlighted in numerous studies [3; 86; 87; 88; 89]. Recent research has demonstrated its effectiveness in identifying structural issues, such as concrete cracking [1; 90], steel reinforcement yielding [91], and force quantification [92; 93]. Advanced SHM techniques using cutting-edge transducers and smart materials have demonstrated their ability to monitor structural damage in RC elements continuously [94]. Recent studies have shown that embedding a network of PZT patches in regions of an element prone to damage significantly enhances the effectiveness and accuracy of SHM methods for assessing damage levels and providing reliable diagnoses [95; 96; 97]. Notably, [PERSON] et al. [98] and [PERSON] et al. [99] expanded PZT-based SHM by introducing an advanced clustering technique that effectively evaluates multiple measurements from the PZT transducer network, enabling the diagnosis of damage in RC elements reinforced with FRP materials. [PERSON] et al. also investigated debonding failures in FRP-strengthened beams using PZT patches, demonstrating the technique's applicability for detecting such issues [100]. The EMI method primarily depends on piezoelectric materials, particularly piezoelectric lead zirconate titanate (PZT) patches, which offer several advantages for SHM applications. These include low energy consumption, cost efficiency, ease of installation, compact size, portability, and the ability to function as both sensors and actuators [63]. By leveraging the electro-mechanical coupling properties of PZTs, the EMI method detects irregularities in the structural integrity of the monitored structure [101]. The impedance signatures reflect the structural characteristics of the monitored region, so changes in the structure's properties lead to corresponding variations in impedance responses. Local deterioration can be identified effectively by comparing impedance signals recorded before and after a damaging event. A significant portion of the existing research has focused on evaluating the effectiveness of EMI-based monitoring for detecting various forms of concrete degradation. These degradation factors include, but are not limited to, rebar corrosion in RC members [102; 103; 104; 105], the effects of the heating duration [106; 107], and concrete mass loss [108; 109]. The EMI method has also been applied to assess the compactness of tendon duct grouting [96] and the setting time of fiber-reinforced concrete [110].