Piezoceramic-based Smart Aggregates Research Articles

A review on smart aggregate based structural health monitoring

Concrete structures are prone to damage and deterioration in their health due to environmental effects, aging, etc., leading to failure prior to their intended service life. Structural Health Monitoring (SHM) is an innovative technique adopted for assessing the structural health, damage identification and assessing the residual life of the structure. The conventional techniques have proved to be inefficient as they required prior information about the vicinity of the damage and accessibility to the damaged region of the structure. The development of various sensors such as fiber optical sensor (FOS), piezoelectric transducers have proved to efficient. This study presents the introduction and the fundamental concept of the latest sensor in trend in the domain of SHM, the piezoceramic-based Smart Aggregate(SA). The applications of SA under various loadings for concrete structures have been reviewed. Also, the damage indices developed for 1-D and 2-D structural components for assessing the damage status in the structure have been summarized. It was established that the smart aggregate is capable of damage detection, health monitoring (concrete columns, shear wall, frames) and impact detection(concrete piles).

Damage Monitoring of Engineered Cementitious Composite Beams Reinforced with Hybrid Bars Using Piezoceramic-Based Smart Aggregates.

In order to explore the crack development mechanism and damage self-repairing capacity of ECC beams reinforced with hybrid bars, the smart aggregate-based active sensing approach were herein adopted to conduct damage monitoring of ECC beams under cyclic loading. A total of six beams, including five engineered cementitious composite (ECC) beams reinforced with different bars and one reinforcement concrete counterpart, were fabricated and tested under cyclic loading. The ultimate failure modes and hysteresis curves were obtained and discussed herein, demonstrating the multiple crack behavior and excellent ductility of ECC material. The damage of the tested beams was monitored by smart aggregate-based (SA) active sensing method, in which two SAs pasted on both beam ends were used as actuator and sensor, respectively. The time domain analysis, wavelet packet-based energy analysis and wavelet packet-based damage index analysis were performed to quantitatively evaluate the crack development. To evaluate the self-repairing capacity of the beams, a self-repairing index defined by the difference of damage index at loading and unloading peak points was proposed. The results in time domain and wavelet packed analysis were in close agreement with the observed crack development, revealing the feasibility of smart aggregate-based active sensing approach in damage detection for ECC beams. Especially, the proposed damage self-repairing index can describe the same structural re-centering phenomena with the test results, showing the proposed index can be used to evaluate the damage self-repairing capacity.

Monitoring the Early Strength Development of Cement Mortar with Piezoelectric Transducers Based on Eigenfrequency Analysis Method

Monitoring the early strength formation process of cement is of great importance for structural construction management and safety. In this study, we investigated the relationship between the eigenfrequency and the early strength development of cement mortar. Embedded piezoceramic-based smart aggregates recorded the early strength of cement mortar. An eigenfrequency analysis model demonstrated the relationship between strength and frequency. Experiments were performed by using piezoelectric transducers to monitor the early strength formation process during the testing period. Three types of specimens with different strength grades were tested, and the early strength formation processes were recorded. The experimental results demonstrate that cement mortar strength has a good linear relationship with the resonance frequency, and the average square of the correlation coefficient is greater than 0.98. The results show that structural health monitoring technology is a feasible method of assessing structural safety conditions and has a broad market in the structural construction industry.

Detecting of the Crack and Leakage in the Joint of Precast Concrete Segmental Bridge Using Piezoceramic Based Smart Aggregate.

Precast concrete segmental bridges (PCSBs) have been widely used in bridge engineering due to their numerous competitive advantages. The structural behavior and health status of PCSBs largely depend on the performance of the joint between the assembled segments. However, due to construction errors and dynamic loading conditions, some cracks and leakages have been found at the epoxy joints of PCSBs during the construction or operation stage. These defects will affect the joint quality, negatively impacting the safety and durability of the bridge. A structural health monitoring (SHM) method using active sensing with a piezoceramic-based smart aggregate (SA) to detect the crack and leakage in the epoxy joint of PCSBs was proposed and the feasibility was studied by experiment in the present work. Two concrete prisms were prefabricated with installed SAs and assembled with epoxy joint. An initial defect was simulated by leaving a 3-cm crack at the center of the joint without epoxy. With a total of 13 test cases and the different lengths of cracks without water and filled with water were simulated and tested. Time-domain analysis, frequency-domain analysis and wavelet-packet-based energy index (WPEI) analysis were conducted to evaluate the health condition of the structure. By comparing the collected voltage signals, Power Spectrum Density (PSD) energy and WPEIs under different healthy states, it is shown that the test results are closely related to the length of the crack and the leakage in the epoxy joint. It is demonstrated that the devised approach has certain application value in detecting the crack and leakage in the joint of PCSBs.

A Novel Embeddable Tubular Piezoceramics-Based Smart Aggregate for Damage Detection in Two-Dimensional Concrete Structures.

Due to their multiple advantages, piezoceramic materials have been widely used in structural health monitoring (SHM). Piezoceramic patch-based smart aggregate (SA) and spherical piezoceramic-based smart aggregate (SSA) have been developed for damage detection of concrete structures. However, the stress waves generated by these two types of transducers are limited by their geometry and are unsuitable for use in two-dimensional concrete structures (e.g., shear walls, floors and cement concrete pavements). In this paper, a novel embeddable tubular smart aggregate (TSA) based on a piezoceramic tube was designed, fabricated and tested for use in two-dimensional (2D) structures. Due to its special geometry, radially uniform stress waves can be generated, and thus the TSA is suitable for damage detection in planar structures. The suitability of the transducer for use in structural health monitoring was investigated by characterizing the ability of the transducer to transmit and measure stress waves. Three experiments, including impedance analysis, time of arrival analysis and sweep frequency analysis, were conducted to test the proposed TSA. The experimental results show that the proposed TSA is suitable for monitoring the health condition of two-dimensional concrete structures.

A PZT-Based Electromechanical Impedance Method for Monitoring the Soil Freeze⁻Thaw Process.

It is important to conduct research on the soil freeze–thaw process because concurrent adverse effects always occur during this process and can cause serious damage to engineering structures. In this paper, the variation of the impedance signature and the stress wave signal at different temperatures was monitored by using Lead Zirconate Titanate (PZT) transducers through the electromechanical impedance (EMI) method and the active sensing method. Three piezoceramic-based smart aggregates were used in this research. Among them, two smart aggregates were used for the active sensing method, through which one works as an actuator to emit the stress wave signal and the other one works as a sensor to receive the signal. In addition, another smart aggregate was employed for the EMI testing, in which it serves as both an actuator and a receiver to monitor the impedance signature. The trend of the impedance signature with variation of the temperature during the soil freeze–thaw process was obtained. Moreover, the relationship between the energy index of the stress wave signal and the soil temperature was established based on wavelet packet energy analysis. The results demonstrate that the piezoceramic-based electromechanical impedance method is reliable for monitoring the soil freezing and thawing process.

Real-Time Monitoring of Early-Age Concrete Strength Using Piezoceramic-Based Smart Aggregates

AbstractIt is well known that concrete is the most common type of structural material, and a proper estimation of concrete strength in its early age can provide guidance for staged concrete constru...

A Study on the Influence of Stage Load on Health Monitoring of Axial Concrete Members Using Piezoelectric Based Smart Aggregate

Piezoceramic based smart aggregate (SA) has been employed to monitor the strength development of early age concrete. The validity of SA-based active sensing method was tested and verified with loading and unloading conditions. However, the early age concrete in buildings is subjected to many load increments during the construction process. The influence of incremental load on the properties of the propagating waves is still unclear. This study aims to investigate the effects of axial stage loads on the signal response of the SA. The concrete specimens that are embedded with SA’s were loaded step by step, and the amplitude and wave velocity of the sensing signals were measured at each stress state. The experimental results indicated that the amplitude of the received signal decrease with the increase of the stress level. As for the velocity of the propagated stress wave, however, the velocity shows an increasing trend before a sharp decline at high stress level.

Study of Impact Damage in PVA-ECC Beam under Low-Velocity Impact Loading Using Piezoceramic Transducers and PVDF Thin-Film Transducers.

Compared to conventional concrete, polyvinyl alcohol fiber reinforced engineering cementitious composite (PVA-ECC) offers high-strength, ductility, formability, and excellent fatigue resistance. However, impact-induced structural damage is a major concern and has not been previously characterized in PVA-ECC structures. We investigate the damage of PVA-ECC beams under low-velocity impact loading. A series of ball-drop impact tests were performed at different drop weights and heights to simulate various impact energies. The impact results of PVA-ECC beams were compared with mortar beams. A combination of polyvinylidene fluoride (PVDF) thin-film sensors and piezoceramic-based smart aggregate were used for impact monitoring, which included impact initiation and crack evolution. Short-time Fourier transform (STFT) of the signal received by PVDF thin-film sensors was performed to identify impact events, while active-sensing approach was utilized to detect impact-induced crack evolution by the attenuation of a propagated guided wave. Wavelet packet-based energy analysis was performed to quantify failure development under repeated impact tests.

A primary study on the performance of piezoceramic based smart aggregate under various compressive stresses

The reliability of piezoceramic based smart aggregate (SA) used for damage detection of concrete structures has already been validated by laboratory tests. However, the in situ concrete members are generally under a big range of stress levels, and the performance of SA under various compressive stresses is still unclear. In this study, an electronic universal testing machine was employed to apply different stresses on the SAs. The received signals of SA sensor accompanying with different drive signals were recorded. The experimental results show that the amplitude of received signals increases firstly, and then tends to be stable with stress. This enhancement is mainly induced by the decrease in thickness of epoxy resin layer caused by compressive stress. It indicates that the change of load applied on monitored concrete members embedded with SAs may lead to a change in monitoring signal amplitude even in elastic range, but it does not stand for the change of health state of monitored concrete member.

Structural Health Monitoring (SHM) of Civil Structures

As newer and more reliable ways of construction were developed, civilization began to spread out further and retain functional infrastructure for longer periods of time.[...]

Cyclic Crack Monitoring of a Reinforced Concrete Column under Simulated Pseudo-Dynamic Loading Using Piezoceramic-Based Smart Aggregates

Structural health monitoring is an important aspect of maintenance for bridge columns in areas of high seismic activity. In this project, recently developed piezoceramic-based transducers, known as smart aggregates (SA), were utilized to perform structural health monitoring of a reinforced concrete (RC) bridge column subjected to pseudo-dynamic loading. The SA-based approach has been previously verified for static and dynamic loading but never for pseudo-dynamic loading. Based on the developed SAs, an active-sensing approach was developed to perform real-time health status evaluation of the RC column during the loading procedure. The existence of cracks attenuated the stress wave transmission energy during the loading procedure and reduced the amplitudes of the signal received by SA sensors. To detect the crack evolution and evaluate the damage severity, a wavelet packet-based structural damage index was developed. Experimental results verified the effectiveness of the SAs in structural health monitoring of the RC column under pseudo-dynamic loading. In addition to monitoring the general severity of the damage, the local structural damage indices show potential to report the cyclic crack open-close phenomenon subjected to the pseudo-dynamic loading.

Influence of axial loads on the health monitoring of concrete structures using embedded piezoelectric transducers

Piezoceramic-based smart aggregate has been widely used to evaluate early-age concrete strength and to detect damage in concrete structures. In these structural health monitoring systems, they are generally verified and calibrated through experiments under load-free condition. However, the stress levels of actual concrete members are different. The microstructures of concrete will change with the variation of external load, and the high-frequency waves used in the monitoring system may be highly sensitive to these changes. In this study, the effects of axial compressive loading on the monitoring results are investigated. Specifically, three loading cases, that is, single cycle load, cyclic load, and step-by-step load, are employed to stress the concrete specimens embedded with smart aggregates. The amplitude and velocity of monitoring signals were measured before, during, and after each loading case. The test results show that the axial load lower than 30% of failure load still have a significant impact on the received signals. The amplitude attenuation is dependent on both frequency and load history, while the velocity is highly stress-dependent. The results indicate that the baselines of monitoring signals obtained from the same concrete structure in its healthy state can vary under different stress levels. The axial load variation should be carefully considered during the monitoring process. This study also provides a potential method to assess stress state in concrete structures using smart aggregates.

Damage detection of concrete piles subject to typical damage types based on stress wave measurement using embedded smart aggregates transducers

Concrete piles are the most common types of foundation structures. Pile damages, such as fractures, cracks, mud intrusion and secondary concrete pouring, are the leading causes of pile structural failure, which may directly result in casualties and economic loss. It is desirable to develop a monitoring system that can detect these pile damages. In this paper, embedded piezoceramic-based smart aggregates transducers along with the active sensing approach are developed to detect common types of pile damages, including crack, partial mud intrusion, secondary pouring, and full mud intrusion, based stress wave measurement. With the active sensing approach, one smart aggregate is used as an actuator to generate a stress wave that will propagate along the pile, and other smart aggregate(s) will measure the propagating wave. All damages, which introduce new interfaces and discontinuities, attenuate the stress wave propagation. The attenuations of the stress waves based on different pile damages were compared by the received sensor signal in time domain. A wavelet packet-based energy analysis was used to develop an energy index to assist the detection of damages. Experimental results demonstrated the feasibility that the proposed approach can detect all four types of common damages associated with concrete piles.

Water presence detection in a concrete crack using smart aggregates

Liquid migrating into existing concrete cracks is a serious problem for the reliability of concrete structures and can sometimes induce full concrete structural failures. In this paper, the authors present recent research on water presence detection in concrete cracks using piezoceramic-based smart aggregate (SA) transducers. The active sensing approach, in which one piezoceramic transducer is used to generate stress waves and others are used to detect the stress wave responses, is adopted in this research. Cracks formed in concrete structures act as stress reliefs, which attenuate the energy of the signals received by the SAs. In case of a crack being filled with liquid, which changes the wave impedance, the piezoceramic transducers will report higher received energy levels. A wavelet packet-based approach is developed to provide calculated energy values of the received signal. These different values can help detect the liquid presence in a concrete crack. A concrete beam specimen with three embedded SAs was fabricated and tested. Experimental results verified that the SA-based active sensing approach can detect a concrete crack and further detect the liquid presence in the concrete crack.

Monitoring the freeze–thaw process of soil with different moisture contents using piezoceramic transducers

Water content plays an active and important role in the performance of the soil freeze–thaw cycle to form frozen soil mechanical properties. Monitoring the freeze–thaw cycle of soil with various types of soil with varied moisture content will provide a direct observation of the properties of soil in cold regions. This paper presents new findings from monitoring the freeze–thaw process of soil using a piezoceramic-based smart aggregate (SA). For comparison, clay soil and medium sand with different moisture contents were used to study the behavior of the soil under the freeze–thaw process. Two SAs were embedded in the soil specimens with a pre-determined distance between them, one as an actuator to generate a stress wave and the other as a sensor to detect the propagated wave. As the propagation of the emitted wave is sensitive to soil status and properties, it is possible to monitor the soil freeze–thaw process by interpreting the SA sensor signal. Based on the attenuation of the energy, a freeze–thaw status indicator was established to describe the freezing–thawing condition. Indicator values of soil specimens with different types and different levels of moisture in freeze–thaw cycles were studied. The test results indicate that the freezing duration in the freezing–thawing process varied for different types of soil and different initial moisture content of the soil. Soil with different particle sizes and moisture content will determine the frozen soil microstructure and its corresponding mechanical properties. Our results illustrate that if soil particle size is bigger, then the signal indicator is stronger; if the moisture content is higher for the same soil, then the signal indicator is stronger. The research presents an innovative method to investigate the freezing–thawing performance of soil and potentially points to a new method to study the variation of soil mechanical properties during the freezing–thawing process, which is a critical problem for infrastructure in cold regions.

Monitoring the Soil Freeze-Thaw Process Using Piezoceramic-Based Smart Aggregate

AbstractMonitoring the soil freeze-thaw process is of great importance to engineering design of infrastructure, observation of hydrology, variation of climate, and existence of vegetation in cold regions. This paper presents experimental results to describe the soil freeze-thaw process using piezoceramic-based smart aggregate (SA) transducers. Two SAs are embedded in predetermined locations: one is used as the actuator and the other is used as a sensor. The active-sensing method is applied to excite a stress wave propagating between the two SAs. The alteration of the mechanical properties of the soil during the freeze-thaw process has an important effect on the stress-wave propagation, and the transition between the freeze and thaw states of the soil is monitored in real time. A wavelet packet-based soil freeze-thaw status indicator is established to quantitatively describe the soil status during the freeze-thaw process. Potentially, this freeze-thaw status indicator can be linked to soil mechanical prope...

An Experimental Study on the Performance of Piezoceramic-Based Smart Aggregate in Water Environment

A number of smart aggregate (SA)-based monitoring systems have been developed to monitor the early age hydration process of concrete. In these systems, the embedded SAs act as sensors and work in a solid-liquid mixture. However, the influence of water on the performance of SA is still unclear. This letter presents some efforts to study the working performance of SA in water environment. A SA-based monitoring system, with the SA sensors immersed in tap water for various periods, was designed to monitor the variation of sensing signals. The test results show that the influence of water on SA is vital. The amplitude of sensing signals increases greatly for the early hours in water, and is tending toward stability for subsequent time. This can thus explain why the amplitude of sensing signals increases fast during early hours in concrete hydration monitoring process.

PZT-Based Detection of Compactness of Concrete in Concrete Filled Steel Tube Using Time Reversal Method

A smart aggregate-based approach is proposed for the concrete compactness detection of concrete filled steel tube (CFST) columns. The piezoceramic-based smart aggregates (SAs) were embedded in the predetermined locations prior to the casting of concrete columns to establish a wave-based smart sensing system for the concrete compactness detection purpose. To evaluate the efficiency of the developed approach, six specimens of the CFST columns with the rectangular cross-section were produced by placing some artificial defects during casting of concrete for simulating various uncompacted voids such as cavities, cracks, and debond. During the test, the time reversal technology was applied to rebuild the received signals and launch the reversed signals again by SAs, to overcome the issue of the lack of the prototype. Based on the proposed nonprototype, two indices of time reversibility (TR) and symmetry (SYM) were applied to relatively evaluate the level of concrete compactness in the range of the two SAs. The experimental results show that the developed method can effectively detect the compactness of concrete in CFST columns.

Innovative Data Fusion Enabled Structural Health Monitoring Approach

Piezoceramic-based active sensing is a useful approach to structural health monitoring. This approach often involves a large number of distributed piezoceramic transducers. It may be confusing to incorporate each sensor data. It is desired to develop an automated health monitoring approach to obtain a comprehensive and accurate health monitoring result by simultaneously interpreting data from all sensors. In this paper, an innovative data fusion enabled structural health monitoring (SHM) approach based on the Dempster-Shafer (D-S) evidence theory is proposed to obtain comprehensive SHM results for a distributed sensor network in a civil infrastructure. Considering that evidence from multiple different information sources (sensor data) has different levels of significance, not all evidence is equivalently effective for the final decision. A weighted fusion damage index (WFDI) is proposed to perform damage identification based on the authors’ recently developed piezoceramic-based smart aggregates. Experimental data of a two-story concrete frame was used to study the effectiveness of the proposed weighted fusion damage index. Analyses show that the proposed weighted fusion damage index can reveal the damage status of different areas of the frame. The results are consistent with the visual inspection of the cracks on the concrete frame.