Piezoelectric Smart Aggregates Research Articles

Advances in the development of piezoelectric smart aggregates for structural health monitoring

Advances in the development of piezoelectric smart aggregates for structural health monitoring

Two-Dimensional Damage Localization Using a Piezoelectric Smart Aggregate Approach-Implementation on Arbitrary Shaped Concrete Plates.

This paper presents the application of a hybrid approach for damage localization in concrete plates of arbitrary geometric shapes and a constant thickness. The hybrid algorithm utilizes fast discrete wavelet transformation, energy approach and time of flight criteria for the purpose of the localization of single- and multi-damage problems inside or on the periphery of concrete plates. A brief theoretical background of the hybrid method as well as numerical procedures for modeling the piezoelectric smart aggregate and ultrasonic wave propagation are presented. Experimental and numerical verification of the damage localization were performed on square samples/models with one or two damages and with 16 positions of piezoelectric smart actuator/sensor aggregates. After the verification of the hybrid method, a numerical simulation was performed on models with one or two damages for plates of arbitrary geometric shapes. Based on the obtained results, it was concluded that the proposed method can be applied to damage localization in concrete plates of arbitrary geometric shapes. The presented method and numerical procedure can be further used in research through varying the geometry, number and position of damages as well as the number and position of piezoelectric smart aggregates.

Interface damage monitoring of assembled GFRP-UHPC composite beams using piezoelectric smart aggregate

Glass fiber reinforced plastic reinforcement (GFRP) and ultra-high performance concrete (UHPC) were combined into a new composite beam, which was applied in ocean engineering to improve the durability of structures. To enhance the stiffness and durability of composite beam and lower the cost of structure, prefabricated construction technology was adopted to reserve holes for pouring UHPC. Through the quasi-static test of prefabricated GFRP-UHPC composite beams, the interface between concrete and GFRP was monitored using piezoelectric smart aggregate. The damage index was obtained in accordance with wavelet packet energy analysis theory to examine the interface damage of prefabricated composite beams. Experimental results show that active monitoring of assembled GFRP-UHPC composite beams with piezoelectric smart aggregate can effectively reflect the degree of interface peeling damage of composite beams. The monitoring results reveal that interface damage of specimens with reserved continuous holes is less than that of specimens with reserved discontinuous holes. Moreover, peeling damage will occur not only between GFRP and UHPC, but also at the interface between concrete and UHPC.

Early-age concrete strength development monitoring using piezoelectric self-emission and detection (SED) and coda wave energy (CWE)

The property of concrete is very significant to structural safety, and the early hydration process plays a critical role in the final concrete property. This paper develops a self-emission and detection (SED) principle with a single piezoelectric smart aggregate (SA) transducer, which is used as both an actuator and a sensor, to monitor the concrete early age strength development. The signal analysis is carried out by the coda wave energy (CWE). Experiments of concrete specimens with and without the SAs were conducted. Experimental results show a high correlation between the strength of early-age concrete and the CWE and non-linear fitting is used to establish the relationship between them. The proposed CWE features a simple analysis method, and the SED principle does not require consideration of the matching between the transmitting transducer and the receiving sensor, such as frequency range, sensitivity. Furthermore, the proposed method can be used as a reference for health monitoring of other structures and has good application prospects.

Real-time monitoring of humidity inside concrete structures utilizing embedded smart aggregates

The moisture level of hydraulic concrete structures strongly influences their strength and durability, so the real-time monitoring of the concrete humidity is crucial to ensure the regular operation of such structures. To this end, this study used an active monitoring method to observe the concrete humidity in real time by embedding pairs of piezoelectric smart aggregates (SAs) in concrete. The monitoring platform based on smart aggregates was constructed and measured five concrete specimens of two dimensions. The time-domain signals of the concrete specimens at different water content levels were obtained, and the wavelet packet energy analysis characterized the sensor signal energy quantitatively. On this basis, a humidity index was defined to describe the variation in the humidity of the concrete specimens. The experimental results demonstrate that the humidity index is practicable to monitor and evaluate the humidity inside concrete structures. Compared with traditional methods for monitoring the moisture content, the proposed technique does not need manual external excitation and can realize real-time, lossless, and long-time monitoring of concrete humidity.

Energetski baziran trodimenzionalni indeks oštećenja za praćenje i otkrivanje oštećenja na betonskim građevinama

A novel approach to active structural health monitoring and damage detection of massive reinforced concrete structures using piezoelectric smart aggregates is presented in this paper. An innovative three-dimensional damage index, based on wavelet signal decomposition and energy of wave propagation, is derived in matrix form. Although the proposed three-dimensional damage index can be used for all types of reinforced concrete structures, it is primarily recommended for massive infrastructure buildings. The approach proposed in this paper is theoretically considered for an arbitrary shape of a reinforced concrete element, and it is numerically verified for various scenarios by varying the geometry of reinforced concrete elements, as well as the position, size and quantity of damage. Quasi-static analysis of piezoelectric smart aggregates is modelled using a standard finite element method, and the explicit finite element method is successfully applied in this research for modelling propagation of ultrasonic waves. The results based on numerically generated simulations indicate that the new approach to non-destructive damage detection using three-dimensional damage indexes is quite promising. However, an experimental verification of the proposed damage index will certainly be required in future research.

Monitoring and evaluation of the repair quality of concrete cracks using piezoelectric smart aggregates

Various crack repair methods have been studied, but monitoring and evaluation of crack repair quality are rarely reported. In this paper, a method was proposed to monitor and evaluate the repair quality of concrete cracks using piezoelectric smart aggregates (SAs). SA can be utilized as both the actuator and the sensor in the active sensing approach, and it can be safely embedded in concrete structures due to its encapsulation properties. Moreover, the principle of stress wave propagation in the repairing process of concrete cracks was explored. Three concrete specimens with embedded SAs were fabricated and a self-made SA-based monitoring platform was constructed. The effects of crack damage, crack repair height, and repair material on stress wave propagation in concrete specimens were studied by using the monitoring platform. An energy analysis method based on wavelet packet was developed to quantitatively characterize the signal energy. Accordingly, the crack repair index was defined innovatively. Furthermore, the axial compressive strengths of concrete specimens in different states were measured. The results show that the proposed repair index can monitor the crack repair process in real time and has the potential to evaluate the repair performance of different crack repair materials.

Early-age strength monitoring of the recycled aggregate concrete using the EMI method

At present, the recycled aggregate concrete (RAC) technology has served as an environment-friendly means to dispose the waste concrete. This paper mainly investigates the feasibility of the early-age strength monitoring of the RAC using the electro-mechanical impedance (EMI) method. Both the compressive test and EMI test utilizing the embedded piezoelectric smart aggregate (SA) transducers were conducted on the specimens with different recycled coarse aggregate (RCA) replacement ratios and loading ages. The compressive test results show the early-age strength of the RAC develops more slowly on the whole as the RCA replacement ratio increases. In addition, the EMI test results as well as the theoretical analysis show that the conductance resonant frequency (CRF) of the SA generally rises as the age goes on. By regression analysis, the linear relationship between the early-age strength of the RAC and the CRF increment was established. It validates the applicability of using the EMI method to monitor the early-age strength of the RAC in engineering practice.

Attenuation characteristics of stress wave in cracked concrete beam using smart aggregate transducers enabled time-reversal technique

Piezoelectric enabled stress wave methods for concrete structural health monitoring have been widely researched. However, the attenuation characteristics of stress wave in cracked concrete structures have barely been studied. As a result, it is hard to quantify the damage levels of the concrete structure. In this paper, the attenuation characteristics of stress wave in cracked concrete beam are studied using stress wave with the time-reversal technique. The attenuation model of stress waves related to the focused signal amplitude and the total crack width of concrete beam is proposed. In this study, a series of 18 concrete beams were tested using a four-point loading. During the test procedure, the signals of stress wave from the piezoelectric smart aggregate transducers in all the test specimens were collected to facilitate the proposed model. The test data of 12 beams are used to determine the attenuation coefficient of stress wave per unit crack width, and the test data of the other six beams are used to validate the accuracy of the proposed attenuation model. The results indicate that the prediction results based on the stress wave attenuation model are in good agreement with the test results of cracked concrete beams.

Monitoring of Interfacial Debonding of Concrete Filled Pultrusion-GFRP Tubular Column Based on Piezoelectric Smart Aggregate and Wavelet Analysis.

The concrete filled pultrusion-GFRP (Glass Fiber Reinforced Polymer) tubular column (CFGC) is popular in hydraulic structures or regions with poor environmental conditions due to its excellent corrosion resistance. Considering the influence of concrete hydration heat, shrinkage, and creep, debonding may occur in the interface between the GFRP tube and the concrete, which will greatly reduce the cooperation of the GFRP tube and concrete, and will weaken the mechanical property of CFGC. This paper introduces an active monitoring method based on the piezoelectric transducer. In the active sensing approach, the smart aggregate (SA) embedded in the concrete acted as a driver to transmit a modulated stress wave, and the PZT (Lead Zirconate Titanate) patches attached on the outer surface of CFGC serve as sensors to receive signals and transfer them to the computer for saving. Two groups of experiments were designed with the different debonding areas and thicknesses. The artificial damage of CFGC was identified and located by comparing the value of the delay under pulse excitation and the difference of wavelet-based energy under sweep excitation, and the damage indexes were defined based on the wavelet packet energy to quantify the level of the interface damage. The results showed that the debonding damage area of CFGC can be identified effectively through the active monitoring method, and the damage index can accurately reflect the damage level of the interface of GFRP tube and concrete. Therefore, this method can be used to identify and evaluate the interface debonding of CFGC in real time. In addition, if the method can be combined with remote sensing technology, it can be used as a real-time remote sensing monitoring technology to provide a solution for interface health monitoring of CFGC.

Experimental Research on Shear Failure Monitoring of Composite Rocks Using Piezoelectric Active Sensing Approach.

Underground space engineering structures are generally subject to extensive damages and significant deformation. Given that composite rocks are prone to shear failure, which cannot be accurately monitored, the piezoelectric active sensing method and wavelet packet analysis method were employed to conduct a shear failure monitoring test on composite rocks in this study. For the experiment, specimens were prepared for the simulation of the composite rocks using cement. Two pairs of piezoelectric smart aggregates (SAs) were embedded in the composite specimens. When the specimens were tested using the direct shear apparatus, an active sensing-based monitoring test was conducted using the embedded SAs. Moreover, a wavelet packet analysis was conducted to compute the energy of the monitoring signal; thus allowing for the determination of the shear damage index of the composite specimens and the quantitative characterization of the shear failure process. The results indicated that upon the shear failure of the composite specimens, the amplitudes and peak values of the monitoring signals decreased significantly, and the shear failure and damage indices of the composite specimens increased abruptly and approached a value of 1. The feasibility and reliability of the piezoelectric active sensing method, with respect to the monitoring of the shear failure of composite rocks, was therefore experimentally demonstrated in this study.

Early Age Concrete Strength Monitoring Using Power Spectral Density and Wavelet Packet Analysis

Concrete is a complex building material. Under normal curing conditions, concrete strength shows a nonlinear development process at an early age (1∼28 d). In the first few days after the completion of pouring, the strength of concrete increases slowly. Subsequently, the strength of concrete increases rapidly, reaching about 90% of its age strength. Finally, its strength gradually stabilizes. This paper introduces the experiment of 28‐day concrete age strength monitoring based on embedded piezoelectric smart aggregate (SA). Two piezoelectric SAs were embedded in a concrete‐filled GFRP (glass fiber reinforced polymer) tube column, one of which emitted a sinusoidal sweep signal and the other SA received the signal. With the hydration reaction of concrete, the stress wave would be significantly different when passing through concrete, and the received signal is changing constantly. Through power spectral density and wavelet packet energy analysis, the monitoring signal of concrete age within 28 days was analyzed. The experimental results show that the wavelet packet energy and power spectral density of the sensor monitoring signal show a nonlinear growth trend with time during the concrete target age. It can be divided into three stages, and the fifth day and the fourteenth day are the demarcation point of energy growth. And the trend of energy change corresponds well with the change of actual concrete strength and age. Comparing and analyzing the received signal energy of the sensor and the power spectral density function of the stress wave signal of the concrete specimen, the trend of the amplitude in the natural frequency domain is found to be the same in the three stages.

Smart aggregates for monitoring stress in structural lightweight concrete

Stress monitoring using piezo-electric smart aggregate (SA) provides a useful way to assess damage in concrete structures. Although the feasibility has been verified in normal weight concrete (NWC), efforts are needed for lightweight concrete (LWC) due to the differences in meso-scale factors that is key for SA-based monitoring. In this paper, SA sensors were tested for monitoring stress using four identical LWC cylinders with six SAs embedded in each specimen subjected to typical loading paths and load levels. Based on the test results, the effects of the related meso-scale factors on the feasibility of monitoring were evaluated. After that, the sensors’ sensitivity curve and the extent of SA output randomness were quantified. It can be concluded that SAs have potential for monitoring stress in LWC structures during the entire damage process.

Modeling of the attenuation of stress waves in concrete based on the Rayleigh damping model using time-reversal and PZT transducers

Wave-based concrete structural health monitoring has attracted much attention. A stress wave experiences significant attenuation in concrete, however there is a lack of a unified method for predicting the attenuation coefficient of the stress wave. In this paper, a simple and effective absorption attenuation model of stress waves in concrete is developed based on the Rayleigh damping model, which indicates that the absorption attenuation coefficient of stress waves in concrete is directly proportional to the square of the stress wave frequency when the damping ratio is small. In order to verify the theoretical model, related experiments were carried out. During the experiments, a concrete beam was designed in which the d33-model piezoelectric smart aggregates were embedded to detect the propagation of stress waves. It is difficult to distinguish direct stress waves due to the complex propagation paths and the reflection and scattering of stress waves in concrete. Hence, as another innovation of this paper, a new method for computing the absorption attenuation coefficient based on the time-reversal method is developed. Due to the self-adaptive focusing properties of the time-reversal method, the time-reversed stress wave focuses and generates a peak value. The time-reversal method eliminates the adverse effects of multipaths, reflection, and scattering. The absorption attenuation coefficient is computed by analyzing the peak value changes of the time-reversal focused signal. Finally, the experimental results are found to be in good agreement with the theoretical model.

Hybrid approach for two dimensional damage localization using piezoelectric smart aggregates

In the paper, a novel approach for damage localization in reinforced concrete plates, based on the computational analysis of piezoelectric smart aggregates, has been presented. The hybrid approach for damage localization is based on two criteria: wave propagation energy and time of flight. The comprehensive numerical analysis using standard and explicit finite element method has been conducted. In addition, the proposed algorithm of the hybrid method has been coded in MATLAB. The approach has been verified numerically using different square reinforced concrete plate models, considering different number, position and size of damage, as well as different number and position of the piezoelectric smart aggregates. Obtained results confirm the successful application of the novel approach to the damage localization.

Damage monitoring of the RC frame shaking table test and comparison with FEM results

Piezoelectric smart aggregate (SA) is an internal stress sensor capable of full range seismic damage monitoring for concrete structures. In this study, the structure model is a one-bay-two-story RC frame, which is subjected to one direction horizontal excitation in a shaking table test. Stresses of four cross sections at the top and bottom of the two columns in the first floor which were symmetrical about the central axis along the excitation direction were monitored. Strain of rebar, acceleration, displacement of the structure was also monitored. The RC frame underwent Loma Prieta earthquake record with a peak value of 0.8g. After the simulated ground motion, only moderate damages were observed in the structure. Finite element analysis (FEA) using OpenSEES were conducted to simulate the shaking table test. By the comparison between the test and numerical results, the influence of the randomness of the material property identified by the SA-based stress monitoring on the failure pattern was discussed and the parameters of finite element model were checked.

Numerical modeling of damage detection in concrete beams using piezoelectric patches

Research and development of active monitoring systems for reinforced concrete structures should lead to improved structural safety and reliability. Numerical models of active monitoring and damage detection systems can help in the development and implementation of these systems. Modeling of damage detection process in a concrete beam with piezoelectric sensors/actuators based on wave propagation is investigated in this paper. Numerical modeling process is divided into two parts: (1) piezoelectric smart aggregates (SA), and (2) wave propagation models. Displacement obtained in the SA model is used as an input parameter for the modeling of wave propagation. Wavelet analysis is used as a signal processing tool and the damage index is calculated based on the wave energy. In this paper root-mean-square deviation (RMSD) damage index is used. Damage indices obtained by this numerical analysis are compared with experimental results. Very good fit between the finite element (FE) results and experimental results confirm a good FE approach of this problem.

A Bridge Health Monitoring System Based on Wireless Smart Aggregates

Researches on health monitoring technology of concrete structures by using piezoelectric smart aggregates have achieved a great development. However, the technique is not widely used so far in practical engineering. Because when constructing large-scale structural health monitoring (SHM) system using wire-based sensors, it requires a lot of cables to form a monitoring network, resulting in huge cost of abundant material of wires and labor for wire placement, and the relatively heavy maintenance work in case of failure of the SHM system. A kind of wireless sensor network based on the protocol for Zigbee802.15.4 and the passive piezoelectric smart health monitoring technology is developed in the paper. Through internal load monitoring tests of a concrete bridge model under impact loading, the developed wireless smart aggregate (WSA) health monitoring system is experimentally validated. The finite element method (FEM) is used to simulate the process as the same as the bridge model test, and the numerical results are consistent with those of the experiment. The experimental results show that the developed wireless system is stable and reliable, and can be applied in concrete bridge structure health monitoring under impact loading.

Statistical algorithm for damage detection of concrete beams based on piezoelectric smart aggregate

The functional piezoelectric ceramic smart aggregate (SA) sensors and actuators, based on piezoelectric ceramic materials such as lead zirconium titanate (PZT), were embedded into the reinforced concrete beams with three-point bending under static loading for purposes of damage detection. The SA actuators generated the desired sine sweep excitation signals online and the SA sensors received and detected real-time signals before and after damage. The wavelet analysis and statistical characteristics about damage signals were used as a signal processing and analysis tool to extract the optimal damage information and establish a statistical damage detection algorithm. The damage index-based wavelet analysis and damage probability-based probability and statistics were proposed by PZT wave-based theory and active health monitoring technology. The results showed that the existence of cracks inside largely attenuated the amplitude of active monitoring signal after the damage of beam and the attenuation was related to the severity degree of damage. The innovative statistical algorithm of damage pattern detection based PZT-SA can effectively determine damage probability and damage degree, and provide a prediction for the critical damage location of reinforced concrete structures. The developed method can be utilized for the structural health comprehensive monitoring and damage detection on line of various large-scale concrete structures.