Application Cases

Experiment Name: Ultrasonic Guided Wave Detection Technology for Interface Debonding Damage in Reinforced Concrete Structures

Experimental Principle:
This method utilizes the ability of ultrasonic waves to penetrate deep into steel reinforcement materials and reflect at interface edges when passing from one cross-section to another to detect defects in components. When an ultrasonic beam propagates from the component surface into the metal interior via a probe, it reflects upon encountering defects or the component's bottom surface. These reflected waves form pulse waveforms on the fluorescent screen, which are used to determine the location and size of defects.

Testing Equipment:
The complete setup, as shown in the figure below, consists of the specimen, a circular piezoelectric ceramic wafer (PZT 20×2 mm), a waveform generator, an ATA-8202 RF power amplifier, and a digital oscilloscope.

Experimental Process:
The concrete specimen used in this experiment has dimensions of 100×100×560 mm. A steel reinforcement bar (HRB335, diameter φ=18 mm, length L=700 mm) is placed at the center of the specimen cross-section, with an embedded length of 560 mm and exposed lengths of 70 mm at both ends to minimize the leakage of guided wave energy into the air, thereby improving accuracy. Based on empirical values, the concrete mix ratio is sand:cement:water = 3:1:0.5. The cement used is ordinary Portland cement (325R). The prepared specimen is shown in the figure below. PVC pipes with inner and outer diameters of 25 mm and 22 mm, respectively, are used to artificially simulate debonding damage at the steel-concrete interface. After concrete pouring, the pipes are rotated 360 degrees every 6 hours to prevent adhesion to the concrete. After 48 hours, when the concrete has partially solidified, the pipes are removed. Specimens 1–4 have debonding lengths of 140 mm, 280 mm, 420 mm, and 560 mm, corresponding to 25%, 50%, 75%, and 100% of the total embedded length, respectively. The specimens are cured in a standard curing chamber for 28 days before testing.

Data acquisition is performed using an oscilloscope with two signal channels: one receives the waveform output from the power amplifier, and the other receives the waveform from the sensor at the receiving end of the specimen. The excitation signal is a 5-cycle sinusoidal signal modulated with a Hanning window. The setup is used to test specimens with different debonding lengths.

The dispersion curve of ultrasonic guided waves in steel reinforcement is obtained through numerical simulation, and a modal guided wave at 120 kHz is successfully employed for effective detection of the steel-concrete interface.

By analyzing the ultrasonic guided wave waveforms received from the steel-concrete interface damage, the peak amplitude of the first wave is examined in the time domain to determine the influence of debonding length on the ultrasonic guided wave signal. In the frequency domain, the relationship between the debonding length ratio and the peak amplitude of the center frequency signal is established. Analysis of the correlation curve reveals that as the debonding length increases, the signal peaks in both the time and frequency domains decrease. Therefore, trends in the received signals can indicate the debonding condition between the steel reinforcement and concrete.

For longitudinal modal guided waves propagating in cylindrical waveguides, energy attenuation analysis serves as a more effective parameter. According to the energy attenuation curve, the energy value decreases linearly with increasing debonding length. It should be noted that the experimental results presented in this study are based on a specific sensor arrangement and concrete specimens of uniform strength. Factors such as sensor placement, concrete strength, steel reinforcement diameter, temperature, humidity, and external stress, which may affect the detection of the steel-concrete interface condition, were not considered.

Recommended Power Amplifier: ATA-8000 Series

Figure: Specifications of the ATA-8000 Series RF Power Amplifier