## 2 Test Samples and Methods
### Transmission Wave Method  
In this study, the transmission wave method was used. The transmission wave method is a rapid qualitative inspection method in the longitudinal direction, and it allows for a quick evaluation of the grouting quality of pre-stressed pipelines in a short period of time. For engineering structures, such as box girders, T-beams, and beam slabs, if the two anchoring ends of the pre-stressed pipelines in the beam body are not sealed, the reflection method can be used to detect the grouting quality of the pre-stressed pipelines, thus determining the quality of the grouting. The principle of transmission method detection is shown in Figure 4. One detector is fixed to each anchor exposed at both ends of the corrugated pipe. At one end (the transmitting end) of the beam plate, a known source signal (hammering signal) is excited and triggered by a detector at that end for timing. When the signal propagates to the other end (the receiving end), it is received by another detector. A signal analysis of the receiving end signal can be carried out separately, and the characteristic values of the hammering signal, such as the wave velocity, energy attenuation, and frequency change, can be obtained [16]. The relationship between the wave velocity, energy attenuation, and frequency change and the grouting compactness can be established to evaluate the grouting compactness. In this study, the AGI-BWG tester was employed. The AGI-BWG pre-stressed pipeline grouting quality detector [17] is a sophisticated system designed for monitoring and assessing the quality of grouting in pre-stressed pipelines. This detector comprises several essential components that work together seamlessly to ensure accurate data collection and analysis, as shown in Figure 5. The key components of the detector system are as follows:  
Figure 4: Schematic diagram of transmission wave method. Figure 3: Model diagram of pre-stressed beam (unit: m). Figure 2: Model design drawing of pre-stressed beam (unit: mm). 1. Computer Processing Terminal: The computer processing terminal serves as the central hub for data processing and analysis. It receives raw data from the wireless data acquisition device, processes and interprets the data, and generates meaningful insights for further action. 2. Wireless Data Acquisition Device: The wireless data acquisition device is responsible for wirelessly capturing data from the acceleration sensor and transmitting them to the computer processing terminal. This device enables the real-time monitoring of grouting quality parameters, facilitating prompt decision making based on the collected data. 3. Coding Signal Transmitter: The coding signal transmitter plays a crucial role in transmitting coded signals from the acceleration sensor to the wireless data acquisition device. This component ensures seamless communication between the sensor and the data acquisition unit, enabling accurate data transmission. Acceleration Sensor (JM Series IEPE-Type Sensor): The acceleration sensor used in the detector is from the JM series IEPE-type sensor family, known for its high sensitivity of 1200 mv/g. This sensor is instrumental in detecting and measuring the acceleration levels experienced by the pipeline, providing valuable data for assessing the structural integrity and grouting quality. Wireless Router (TP-LINK 150M Wireless Portable Router): The wireless router employed in the system is a TP-LINK 150M wireless portable router. It establishes wireless communication links between the components of the detector system.