Detection of grouting condition of prestressed pipeline with variable thickness prestressed box girder

2. Introduction of methods and instruments

The basic principle of IE (impact echo) test: as shown in Figure 1. A small hammer or impactor is used as an excitation source to impact on the concrete surface to generate a compression wave, and then a receiving sensor placed near the impactor receives the reflected compression wave. After analysis, the thickness of the concrete is calculated, and the defects such as holes, cracks and peeling are detected. A large number of tests and papers at home and abroad show that the IE method is one of the most effective methods for non-destructive inspection of the grouting in the prestressed pipe. However, because they were all single-point tests at that time, the efficiency was low and the workload was large, so they were not widely used.

Figure 1: Schematic diagram of shock echo principle

(Where source is the excitation source that generates the compression wave and receiver is the receiver of the reflected wave)

After Olson invented the IES scanning impact echo method, it completely solved the efficiency problem and made it possible to detect large areas. The IE Scanner scanning impact echo system is based on the principle of the impact echo, using the unique technology of the rolling sensor, and close to the continuous test of the internal condition of concrete at 2.5cm intervals, which has the following advantages:

1. Only one test surface

2. No couplant required

3. The test is rapid, and can measure 2000 ～ 3000 points per hour

4. The detection structure is reliable and accurate

5. Three-dimensional imaging of the results can be used to display defects quickly and intuitively

3. Analysis of test results

According to the site conditions and the performance characteristics of the instrument, we selected the pulp outlet and the mid-span for testing.

To analyze the grouting condition of the pipeline, you can make a comparison by testing the data at the outlet of the slurry and the data at the mid-span.If the slurry is filled at the outlet, it means that the whole prestressed pipeline is filled with grouting. , We then analyze the grouting situation across the mid-position. The test was divided into two tests, the first test was scanned from B1-1 to B1-4, and 4 lines were tested at the outlet of the slurry. 3 lines were tested across the midpoint. The data was saved in 5B1. The second test scanned the test from B1-8 to B1-5, 4 lines were tested at the outlet and 3 lines were tested at the midpoint .Data saved in 5B2.

5B1 data analysis: the starting point of our test is about 40cm away from the first prestressed pipeline (B1-1). We analyze the situation of four tubes 5B1-1, 5B1-2, 5B1-3, B51-4. From 0.4m At 0.5m, the frequency domain diagram corresponding to the test point has a small secondary peak, corresponding to the 5B1-1 prestressed tube. According to the thickness calculation formula, d = vp / 2f, the corresponding thickness value at the secondary peak is 18.35cm The location is exactly at the location of the pipeline (the centerline of the pipeline is 20cm away from the test surface). It means that the grouting at this location is not very full, and there may be voids. 0.6-0.7m (B1-2), 1.4-1.5m (B1-3) , The frequency domain diagram corresponding to the test point also has small secondary peaks. Similarly, the thickness value corresponding to the small secondary peak is at 20-25cm, which is also located at the location of the pipeline.The corresponding prestressed pipelines at this location are 5B1-2 and 5B1. -3, the position of the two pipes on the first test line is also that the grouting is not full enough, and there are defects. The corresponding pipe at 1.7-1.8m (B1-4) is 5B1-4, and the test point is There is only one obvious main peak on the corresponding frequency domain graph, and the secondary peak is not obvious, indicating that there is no defect there, and the grouting is very full.

Next, we analyze the remaining test line.We found that there is a very obvious secondary peak on the frequency domain diagram corresponding to the test point of the 5B1-3 tube at the 1.5-1.6m of Line2, and the height of the secondary peak is almost the same as the main peak. After calculation, the thickness position corresponding to the frequency is also inside the pipeline. According to the thickness and waveform analysis, there may be no grouting or grouting is very unsatisfactory. The same situation exists at 0.7-0.8m (B1-2) of Line3, 1.5-1.6m (B1-3); Line4 1.5-1.6m (B1-3); Line5 0.75-0.85m (B1-2), 1.55-1.65m (B1-3); Line6 0.75-0.85m (B1-2), 1.55-1.65m (B1-3); Line7 is 1.55-1.65m (B1-3) .Line5, 6, 7 are measured at the mid-span position, Line1, 2, 3, 4 are measured at the location of the slurry outlet.According to experience, these grouting conditions at the measurement points corresponding to the frequency domain diagram with the same high-order peak of the main peak are very unsatisfactory, and may also be prestressed and outside the tube. The concrete structure is emptied. Therefore, the grouting conditions of B1-2 and B1-3 are very unsatisfactory. It may also be that the prestressed pipeline is not well combined with the external concrete structure and completely emptied. The remaining two pipelines have varying degrees of grouting and are not dense, but it is not very serious.

We then analyze the data of 5B2, measuring line LINE2D at 0.75-0.85m (B1-7), LINE3 at 1.55-1.65m (B1-6), 1.85-1.95m (B1-5); LINE4 at 0.75-0.85 m (B1-7); LINE5 at 0.75-0.85m (B1-7), 1.85-1.95m (B1-5), the secondary peaks are as obvious and the same height as the main peak, indicating that these positions The grouting conditions of prestressed pipelines are very unsatisfactory or empty from the external concrete. You can refer to the following image. Many other places have grouting that is not very ideal, and there are defects at different levels. In addition to the mentioned locations, the frequency domain maps corresponding to the other measurement points are relatively normal, there are no obvious secondary peaks, which is a case of full pressure.

4. Summary

This test result is limited by some objective conditions, which affects the accuracy of the test result, but it can also analyze some situations based on the test data.If we need to get a more accurate conclusion, we need to make a more detailed test area. For precise positioning, and can provide better field test conditions. It can be seen from the above analysis that IES can accurately find the location of each tube, and compare the location of the tube according to the relative position of the location and the surface of different structures. The grouting situation of the tube can be analyzed, which can provide good efficiency for the test. And accuracy.