Application Cases

Experiment Name: Concrete Damage Identification and Monitoring Based on Piezoelectric Ceramics

Experimental Principle:
This experiment utilizes piezoelectric ceramic-based wave propagation analysis to monitor internal concrete damage. The principle involves embedding piezoelectric smart aggregates at predetermined locations within the concrete. A specific voltage excitation signal is generated by a signal generator. Due to the inverse piezoelectric effect of the piezoelectric material, the smart aggregate undergoes axial deformation upon receiving the excitation signal, causing deformation in the surrounding concrete and generating stress waves. These stress waves propagate within the concrete specimen. When the stress waves reach other smart aggregates, they also undergo axial deformation, and under the direct piezoelectric effect, generate electrical signals that are received by a data acquisition device. When internal damage occurs in the concrete, changes in the propagation medium alter the waveform, propagation path, and energy of the stress waves, which are reflected in changes in parameters such as amplitude, energy, and waveform of the signals received by the sensors. By analyzing the differences between signals received under healthy and damaged conditions, the presence and extent of internal concrete damage can be determined.

Figure a: Experimental Setup

In this experiment, to simulate common internal defects in concrete in practical engineering, concrete specimens measuring 550×150×150 mm³ were designed. Plastic spheres of varying sizes were embedded in the concrete specimens to create areas of non-uniform media, simulating internal concrete damage. Each specimen contained a pair of smart aggregates, one serving as an actuator and the other as a sensor. The smart aggregates were fixed in the mold using iron wires to prevent loosening or displacement during vibration. The concrete was mechanically mixed, vibrated, and poured, followed by 28 days of water curing in a curing chamber. The distance between the smart aggregates was 400 mm, with their centers located 75 mm from the bottom surface of the specimen.

Figure b: Aggregate Arrangement

Testing Equipment:
Signal generator, ATA-P2010 power amplifier, smart aggregates, data acquisition card, laptop.

Experimental Procedure:
The piezoelectric ceramic actuator and sensor were pre-installed at predetermined positions within the concrete specimen. A signal generator was used to produce a specific voltage signal with a frequency range of 100 Hz to 20 kHz and an amplitude of 3 V. Due to the rapid attenuation of stress waves in concrete, a power amplifier was used to amplify the signal power to ensure the receiving sensor could fully capture the propagated signal. After amplification, the signal reached the smart aggregate actuator at the excitation end. Under the inverse piezoelectric effect, the actuator induced deformation in the surrounding medium, generating stress waves. These waves propagated through the specimen and eventually reached the smart aggregate sensor at the receiving end, causing deformation of the sensor. Under the direct piezoelectric effect, electrical signals were generated and received by the signal acquisition device for storage. During stress wave propagation, if internal damage existed in the specimen (i.e., changes in the propagation medium), phenomena such as reflection, diffraction, and refraction occurred at the damage site, altering the propagation path and energy of the waves. By comparing the differences between signals collected under different damage conditions, the health status of the concrete was assessed.

Figure c: Time-Domain Signals
(Figure c represents time-domain signals received by the sensor under (a) healthy condition, (b) damage extent of 30, (c) damage extent of 60, and (d) damage extent of 90.)

Figure d: Maximum Signal Amplitudes Under Different Damage Conditions

Experimental Results:
As shown in Figure c and Figure d, with the time-domain signal under healthy conditions as a reference, the time-domain signals under different conditions vary with changes in the extent of internal defects. By comparing the time-domain signals of specimens under different conditions, it is evident that the amplitude of the received time-domain signal is highest under healthy conditions. When internal defects exist in the specimen, based on the propagation characteristics of stress waves in concrete, phenomena such as refraction occur at the defect site due to changes in the propagation medium, and internal defects exacerbate signal attenuation. This is reflected in the received signals, where the amplitudes of the time-domain signals for specimens with internal defects show significant reductions. According to the trend of maximum amplitude reduction in time-domain signals, signal attenuation intensifies as the extent of internal defects increases. The maximum amplitudes of the time-domain signals under various conditions are ranked as follows: healthy condition > internal defect extent of 30 > internal defect extent of 60 > internal defect extent of 90. The experimental results demonstrate that changes in the amplitude of time-domain signals can effectively identify internal damage in concrete.

Figure: Specifications of the ATA-P Series Power Amplifier