Application Cases

Experiment Name: Application of High-Voltage Amplifier in Research on Grouting Sleeve Compactness Detection Using Stress Wave Method

Research Direction: Nondestructive Testing

Test Objective:
The steel bar grouting sleeve connection technology is widely used in the connection of prefabricated building nodes. However, inadequate grouting compactness can lead to the risk of node failure. Therefore, detecting the compactness of sleeve grouting during construction is particularly important. However, because the sleeve is deeply buried within the component, it is not easy to detect. During construction, compactness is typically judged by observing the grout outflow from the vent hole, which lacks a scientific detection method. Thus, assessing the compactness of sleeve grouting faces significant challenges.

This chapter, based on active detection technology using the stress wave method, conducts experimental research on steel bar grouting sleeve connection joints under different compactness conditions. The wavelet packet energy method and the Hilbert-Huang transform method are employed to process the collected signals. Appropriate characteristic parameters are selected, and damage indicators are proposed to determine sleeve compactness. The experimental results indicate whether the damage indicators can accurately characterize grouting compactness and reflect grouting defects. Simultaneously, based on the experimental analysis, the propagation of stress waves in the steel bar grouting sleeve connection joint under signal excitation from piezoelectric sensors is simulated and analyzed. This reveals the stress wave propagation mechanism. The simulation results are compared with the experimental results to verify the reliability and accuracy of the numerical simulation.

Testing Equipment: ATA-2022B High-Voltage Amplifier, Sleeve and Grouting Material, Piezoelectric Ceramic Patches, Data Acquisition Card, Computer with LabVIEW Software, Test Specimens.

Experimental Procedure:
To effectively identify the grouting compactness of the sleeve, this section designs steel bar sleeve joints with different grouting levels. The specimens in this experiment simulate the horizontally connected steel bar grouting sleeve connection method used in practical engineering. Five compactness  conditions  were designed: 0%, 30%, 50%, 70%, and 100%, with three specimens for each condition. The steel bars had a diameter of 20 mm and a length of 400 mm. Manual pressure grouting was used. To ensure that the steel bar and sleeve were aligned on the same central axis during grouting and did not shift position, a fixing device was designed to hold the sleeve and steel bar in place with thin iron wire. At the same time, to ensure accurate control of grouting compactness, a dual-control method was adopted in the experiment: controlling the height of rubber plugs and controlling the grouting volume. Rubber plugs were placed at both ends of the sleeve, each with a thickness of 10 mm. The corresponding void area was cut from the rubber plugs. During grouting, the grout reached the preset height of the rubber plugs. Additionally, the volume of water required to fill the sleeve cavity was measured beforehand to determine the grout volume needed for 100% compactness. Then, a measuring cup was used to measure the grout volume for each compactness condition, which was sequentially injected into the respective sleeves. This dual-control method aimed to accurately control grouting compactness and reduce errors. After the grout inside the sleeve had completely solidified, the steel bar grouting sleeve joint specimens were cured in a standard environment for 28 days.

Figure: Sensor Fabrication Process

Next, PZT-5 piezoelectric ceramic patches were used to fabricate piezoelectric sensors. After the specimens were cured for 28 days, the sleeve grouting compactness detection test was conducted. During the experiment, LabVIEW software on the computer controlled the data acquisition card to generate a voltage signal. The signal was amplified by the voltage amplifier. The amplified signal excited the PZT sensor, generating stress waves. These stress waves attenuated inside the sleeve, and the attenuated signals were received by the PZT sensor on the other side. Finally, the signals were collected by the data acquisition card and displayed on the computer. The experimental setup and connections are shown in the figure below.

Figure: Experimental Setup

Experimental Results:

Figure: Energy Variation Diagram

It can be seen from the energy variation diagram that the total wavelet packet energy value obtained by the wavelet packet energy method and the Hilbert energy peak value obtained by the Hilbert-Huang transform method are both clearly related to the grouting compactness of the sleeve. As the grouting compactness increases, the energy  indicators  decrease, indicating that both signal processing methods are applicable for detecting the grouting compactness of steel bar grouting sleeve joints.

Figure: CI Values for the Two Signal Processing Methods

By comparing the two methods, it was found that as the grouting compactness increased, both the total wavelet packet energy value and the Hilbert energy peak value showed a downward trend. Furthermore, the decreasing slope of the Hilbert energy peak was greater than that of the total wavelet packet energy value. This indicates that compared to the wavelet packet energy method, the Hilbert-Huang transform method can better reflect the relationship between grouting compactness and the CI (Characteristic Index). Additionally, compared to the wavelet packet energy method, the Hilbert-Huang transform method does not require consideration of basis functions or decomposition levels. Therefore, it is recommended to use the Hilbert-Huang transform method for detecting the grouting compactness of steel bar grouting sleeve joints.

Figure: ATA-2022B High-Voltage Amplifier Specifications and Parameters