Application Cases

Experiment Name: Research on Non-Destructive Detection Technology for Concrete Carbonation Based on Nonlinear Ultrasonic Method

Experiment Purpose: This paper proposes and implements a nonlinear ultrasonic technique for the non-destructive detection of concrete. The principle of this method is to utilize PZT sensors to detect the second harmonic during the propagation of pulses. Based on the changes in concrete density during the carbonation process, which cause alterations in the nonlinear ultrasonic parameters as ultrasonic waves penetrate the concrete, the second harmonic nonlinear parameters are obtained through FFT transformation to assess the degree of concrete carbonation. Experimental results indicate that the measured nonlinear parameters change significantly during the concrete carbonation process. Therefore, it is feasible to detect concrete carbonation using detection technology based on the properties of nonlinear ultrasonic waves.

Testing Equipment: Voltage amplifier, digital oscilloscope, etc.

Experiment Process:

Concrete cubic specimens measuring 100mm×100mm×100mm were cast according to the mix ratio to compare the influence of ultrasonic incidence frequency on nonlinear parameters. After curing the specimens for 28 days, rapid carbonation experiments were conducted. An arbitrary waveform generator was used to excite a three-cycle-long pulse electrical signal, which was then output to the voltage power amplifier. The power amplifier amplified the peak voltage of this electrical signal to 56V. The amplified electrical signal excited the PZT piezoceramic at the transmitting end of the medium (specimen), causing the PZT piezoceramic to emit ultrasonic waves after undergoing the "inverse piezoelectric effect." The encapsulation diagram of the concrete specimen is shown in Figure 1.

Figure 1: Schematic Diagram of Concrete Specimen Encapsulation

The PZT piezoceramic at the receiving end of the medium (specimen) received the ultrasonic wave signal, which was then converted into an electrical signal through the "direct piezoelectric effect" of the PZT piezoceramic. The signal was amplified by 46 dB and transmitted into the digital oscilloscope. For the three specimens, three-cycle-long pulse signals with incidence frequencies of 50 kHz, 75 kHz, and 100 kHz and an amplitude of 10 Vpp were used. The signals were collected in average mode with 256 averages, and the data results were averaged. The data were entered into a computer and transformed into the frequency domain using FFT to obtain the amplitudes of the fundamental wave (A1) and the second harmonic (A2). The relative nonlinear parameter βr was calculated to investigate the variation of nonlinear parameters with carbonation time.

Experimental Results:Figure 2 shows the variation of the nonlinear parameter. As the number of carbonation days increased, the amplitude of the first wave (A1) also increased, while the amplitude of the second harmonic (A2) decreased, resulting in a corresponding decrease in the nonlinear parameter. When the incidence frequency of the pulse ultrasonic wave was 75 kHz, the nonlinear parameter value was higher than that at 50 kHz and 100 kHz. However, the change in the nonlinear parameter at 75 kHz was smaller compared to that at 50 kHz and 100 kHz. This may be due to severe scattering and attenuation of ultrasonic waves at an incidence frequency of 50 kHz; when the incidence frequency was 100 kHz, the ultrasonic wave attenuated too quickly, and the amplitude of the second harmonic dropped rapidly.

Figure 2: Nonlinear Parameter Values of Specimens under Different Incidence Frequencies as Carbonation Time Changes

Figure 3 shows the degree of change in nonlinear parameters of pulse ultrasonic waves with incidence frequencies of 50 kHz, 75 kHz, and 100 kHz during the carbonation process. The maximum change in nonlinear parameters was 89.4% at an incidence frequency of 50 kHz, 67.1% at 75 kHz, and 95.2% at 100 kHz. The sensitivity of nonlinear parameters at incidence frequencies of 50 kHz and 100 kHz was higher than that at 75 kHz.

Figure 3: Changes in Nonlinear Parameters of Specimens under Different Incidence Frequencies as Carbonation Time Changes

Since the nonlinear parameter value was the highest at an incidence frequency of 75 kHz and the attenuation of the nonlinear parameter was smaller compared to that at 50 kHz and 100 kHz, an incidence frequency of 75 kHz can be selected as the fundamental frequency for measuring nonlinear ultrasonic parameters. The results show that the measured nonlinear parameters change significantly during the concrete carbonation process. Therefore, it is feasible to detect concrete carbonation using detection technology based on the properties of nonlinear ultrasonic waves.

Voltage Amplifier Recommendation: ATA-2048

Figure: Specification Parameters of the ATA-2048 High-Voltage Amplifier

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