An active sensing approach using piezoceramic induced stress wave is proposed to provide monitoring and early warning for the development of interface debonding damage of precast segmental concrete beams (PSCBs). Three concrete specimens with toothed interfaces were fabricated and bonded with high-strength epoxy resin adhesive to form PSCBs. Smart aggregates (SAs) embedded in concrete specimens are used as actuators and sensors. The PSCBs are subjected to periodic loading with hydraulic jack to test the different degrees of debonding damage. The experimental results of time-domain and frequency-domain analysis clearly show that the amplitude of the signal received by the piezoceramic sensor is reduced when debonding crack occurs. The energy analysis and damage index based on wavelet packet can be used to determine the existence and severity of interface debonding damage in PSCBs. The experimental research validates the feasibility of monitoring the interface debonding damage in PSCBs using SA transducers based on active sensing technique.
Precast segmental concrete beams (PSCBs) are widely applied to civil engineering [
The conventional detection techniques can be classified into destructive and nondestructive evaluation techniques [
The emergence of smart materials, such as piezoceramic materials, especially, lead zirconate titanate (PZT), makes structural health monitoring (SHM) possible through fully integrated transducers, offering real-time monitoring of structural health status and adding a new dimension to traditional structural detection technology [
Active sensing technology can identify the damage and defects of the structure by analyzing the difference between the received signal of the sensor before and after the structural damage [
At present, due to the limitations of the structure working environment and the difficulty of traditional monitoring instruments in practical applications, the damage identification or monitoring method of the PSCBs interface has not been established in practical engineering. Therefore, it is necessary to establish a real-time monitoring and damage assessment method.
Although many methods have been successfully proposed for condition monitoring of different structures, there has been no report on the interface condition monitoring of PSCBs. In this paper, three-array piezoceramic smart aggregates (SAs) are embedded in concrete to enable the active sensing approach, which is used to identify the interface damage of segmented bonded concrete specimens during the loading period. The occurrence and severity of cracks attenuate the propagation of waves which can be reflected by the received signal in time/frequency domain, meaning that wave energy dissipates when it passes through the interface. Wavelet packet analysis is used to analyze the change of received signal energy, and a periodic damage index is proposed. Experimental results demonstrate that piezoceramic SAs can timely monitor the development process of cracks in segmented concrete specimens, which lays a foundation for the identification of related interface states in the future.
The most typical characteristic of piezoelectric materials is the piezoelectric effect [
Based on the piezoelectric effect, transducers with dual functions of stress wave transmission and detection can be fabricated [
The selected PZT is specially processed and packaged in drum-shaped cement mortar or fine stone concrete block with a volume of approximately 8–10 cm3, which could be placed into the structure after curing. For the connection, a Bayonet Neill–Concelman (BNC) connector is welded at the end of the wire, as shown in Figure
SAs with a BNC connector.
SA parameters.
PZT plane size (mm × mm) | 15 × 15 |
PZT thickness (mm) | 0.3 |
SA diameter (mm) | 25 |
SA thickness (mm) | 20 |
Density ( |
7.75 |
PSC d33 ( |
381.6 |
PSC: piezoelectric strain constant.
The PZT-enabled active sensing approach requires at least a pair of piezoelectric actuator and sensor placed on the surface or inside of a concrete structure [
In this paper, the active sensing technology with piezoceramic SAs is used to detect debonding damage at the interface of PSCBs. The principle diagram of the active sensing approach in monitoring the debonding damage at the interface of PSCBs is shown in Figure
Principle of PSCB debonding damage using the active sensing approach.
In order to quantitatively describe the debonding crack damage of PSCBs during the loading process, the signal can be specially characterized based on wavelet packet analysis [
The energy vectors of subsignals in each frequency band of the final signal are defined after the signal is decomposed by a wavelet packet, as shown in the following equation:
Then, the sum of the energy vectors obtained from the reconstruction and decomposition of
The damage index is used to determine the health status of the concrete structure using the following formula to evaluate the damage area and extent of the specimens [
The specimens consist of three single-tooth concrete components, which are assembled with epoxy resin and embedded in the SAs in the concrete beam. The cement used for casting the concrete beam is type 32.5 Portland cement. The mixture ratio of the concrete is shown in Table
Mixture ratio of the concrete.
Cement (kg/m3) | Water (kg/m3) | Sand (kg/m3) | Stone (kg/m3) | Water reducing agent (kg/m3) |
---|---|---|---|---|
532 | 137 | 695 | 1046 | 14.5 |
Specimen 3D model.
Sketch of the specimen plane (unit: cm).
The experiment equipment for the PSCB interface damage monitoring system used in this experiment mainly includes concrete specimens with epoxy resin joints, a data acquisition system (NI-USB 6366), a laptop with supporting software, and a hydraulic jack loading device, as shown in Figures
Experimental setup.
Specimen loading system.
Parameters of swept sine wave signal.
Configuration | Differential |
Amplitude (v) | 10 |
Duration (s) | 1 |
Number of steps | 5000 |
Sampling rate (MHz) | 1 |
Start frequency (Hz) | 100 |
Stop frequency (kHz) | 150 |
During the experiment, S1-1 and S1-2 were installed on the left and right sides of the beam, respectively. This type of aggregate can be regarded as a monitoring signal transmitter. S2 installed in the middle of the beam acts as a receiver. Figure
The hydraulic jack is used to load the specimen, and the pressure transducer is used to control the load in the experiment, which is then converted into shear force to carry out a damage test on the concrete beam. The purpose of this experiment is to study the trend of monitoring signal damage index changing with the development of cracks at the interface joint when the damage degree is strengthened. The selected parameters are shown in Table
Explanation of experiment parameters.
① | Epoxy resin adhesive is used for interface joint |
② | The interface joint is single-tooth mode |
③ | The thickness of the interface joint is 2 mm |
④ | The transverse compressive stress is adjusted by N1 and N2 |
The damage monitoring system consists of signal generation, signal acquisition, and signal analysis, as shown in Figure
Monitoring system for experiment.
The concrete reached the standard strength after 28 days of curing and the loading experiment was started. During the experiment, the loading method shown in Figure
In the shear experiment, SA1-1 and SA1-2 are used as actuators, respectively, and the received signals of sensor SA2 are shown in Figures
Time-domain signal of SA1-1 sensor in different operating conditions.
Time-domain signal of SA1-2 sensor in different operating conditions.
State of concrete beams at various stages. (a) Health status. (b) Mild damage. (c) Severe damage.
Frequency-domain signal of SA1-1 sensor in different operating conditions.
Frequency-domain signal of SA1-2 sensor in different operating conditions.
In order to quantify the signal energy detected in the loading process, the wavelet packet energy analysis method is used to calculate the signal energy. The energy levels of SA1-1 and SA1-2 sensors during loading are shown in Figure
Wavelet packet energy of SA1-1 and SA1-2 sensors in different operating conditions.
Similarly, in order to quantitatively analyze the interface damage degree of PSCBs, the wavelet packet damage indices of SA1-1 and SA1-2 are calculated, as shown in Figure
Damage index of SA1-1 and SA1-2 sensors in different operating conditions.
This paper presents an active sensing approach for detecting the interface debonding damage of PSCBs. Actuators and sensors for interface damage detection can be formed by embedding SAs in PSCBs. The relationship between interfacial debonding damage and energy consumption is studied by the shear test using wavelet packet theory. Based on the experimental results, the following conclusions can be drawn: The method given in this study can well reflect the development trend of damage and timely monitor the development of cracks in the joint of epoxy resin adhesive. The results show that the PZT-enabled active sensing approach based on the damage index of wavelet packet can effectively monitor the debonding state of the PSCB interfaces. Experiments have demonstrated that embedded SA-induced stress waves are sensitive to the debonding conditions of the interface. The occurrence of debonding damage leads to cracks, which greatly reduces the energy of stress waves propagating at the interface. It can be seen that the amplitude of the signal received from SA sensor decreases with the increase of debonding damage from the time-domain and frequency-domain analysis. The energy analysis and damage index based on wavelet packets can quantitatively evaluate the bonding state of the PSCB interface. With the increase of severity of debonding, the energy value of wavelet packet decreases and the value of damage index increases correspondingly. The initial and complete debonding stages can be successfully reflected in the damage index.
In addition, the damage index defined by wavelet packet theory is highly sensitive to damage. The predicted structural failure occurred earlier than the real failure. The proposed active sensing approach based on wavelet packet damage index has great potential to be applied in practice for inaccessible damage detection of PSCB interfaces.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors are grateful for the partial financial support received from the Major State Basic Research Development Program of China (973 Program, grant no. 2015CB057704), the National Natural Science Foundation of China (grant no. 51378081), the Natural Science Foundation of Hunan Province (grant no. 2019JJ40313), and the Hunan Provincial Innovation Foundation for Postgraduates (CX20190651).