## 1 Introduction
[5] comprehensively reviewed the structural monitoring and detection of civil infrastructure using optical fiber sensing technology. [PERSON] and [PERSON] [3], [PERSON] et al. [6] and [PERSON] et al. [7] have all reviewed the literature on other methods of structural monitoring and damage detection. The piezoelectric sensor is relatively a new technology for structural health monitoring with the advantages of a quick response, availability in various shapes, active sensing, low cost and simplicity of implementation. It has been shown to have great potential in local monitoring and detecting minor to major cracks in concrete structures. Owing to their multiple functions, piezoelectric sensors such as piezoceramic (PZT; lead zirconate titanate) sensors have been used successfully in many SHM applications for RC structures. Recently, piezoelectric material has been successfully used in SHM because of its aforementioned advantages. Moreover, piezoelectric sensors can be easily post-installed in critical parts of existing structures by mounting them on a surface or embedding them into the inner structure. They can function as actuators or sensors. Accordingly, piezoelectric material has been actively used in research into structural health monitoring. [PERSON] et al. developed novel nondestructive wave-based methods for measuring the modulus of elasticity of concrete using the wave-propagation characteristics and characteristics of the PZT transducer [8]. [PERSON] et al. [9], [PERSON] et al. [10], [PERSON] et al. [11] and [PERSON] et al. [12], developed an advanced multifunctional PZT-based sensor, smart aggregate (SA), to diagnose the structural health of RC structures. [PERSON] et al. [13] used pre-embedded piezoceramic-based sensors to measure dynamic stress and perform the SHM of a single concrete column underground excitation with gradually increasing acceleration. However, for locating probable damage or the failure of the existing structures, post-embedded piezoceramic-based sensors are more suitable than pre-embedded piezoceramic-based sensors. Therefore, [PERSON] et al. [14] utilized the post-embedded piezoceramic-based sensors for the on-site SHM of the large-scale RC piers of an existing bridge in Taiwan under cyclic loading. A feedback sensing network using active sensing property of SAs to reduce damage-location detection time was established by [PERSON] et al. [15]. [PERSON] et al. [16] proposed the concept of smart concrete slab with embedded tubular PZT transducer array for image-based damage detection. [PERSON] et al. [17,18] developed a novel embeddable spherical SA to monitor the health of concrete structures, providing a significant improvement in the detection aperture and additional functionality for health monitoring. To reveal the stress wave propagation in concrete structures, [PERSON] et al. [19] developed a simple and effective absorption attenuation model of stress waves in concrete based on the Rayleigh damping model and [PERSON] et al. [20] presented a dynamic model of an embeddable PZT transducer with a waterproof layer and a protecting layer. [PERSON] et al. [21] proposed a method using PZT enabled time-reversal method to monitor the grouting quality. [PERSON] et al. [22] proposed a method of simultaneously using piezoelectric transducers as strain gauges and acoustic emission sensors to monitor the health of concrete structures. [PERSON] et al. [23] proposed the relation between the damage volume ratio and the root-mean-square deviation damage index which can be used to predict the collision damage of the RC structures. Additionally, [PERSON] et al. [24,25] performed piezoceramic transducers on the successful application of SHM of structures. The use of post-installed surface-mounted PZTs or pre-installed embedded PZTs has recently been extended, not only for the evaluation of the concrete strength gain but also for health monitoring and damage detection.