common problem
1. Record fast scan
With the popularization of structural entity inspection, the number of projects to be inspected is increasing, and the workload is also increasing, and the inspection before the acceptance of the main project is mostly aimed at the thickness of the protective layer of the steel bar, and the recording type fast scanning is more and more widely used. into the detection. However, with this method, sometimes there will be missing ribs, multiple ribs and the situation that the image cannot be analyzed. The reasons may be as follows:
(1) The axis of the probe is not perpendicular to the steel bar during detection. The scanner cannot detect steel bars parallel to its scanning direction. When the axis of the probe is not at an oblique angle to the steel bars, the peak value of the scanned signal will become flat, the overall signal will become weaker, and the area of the signal will become wider, etc., which will also cause the instrument to detect The thickness of the protective layer becomes larger;
(2) The spacing between the steel bars is very small. Theoretically, when the steel bar spacing is less than 36mm, it is easy to cause the instrument to leak bars;
(3) The thickness of the protective layer of adjacent steel bars is too different, which is the main reason why the image cannot be analyzed;
(4) The thickness of the protective layer is too small or the ribs are exposed. When the thickness of the protective layer is less than 10mm, the measurement accuracy will be reduced;
(5) The influence of other substances: additives or magnetic components in concrete, as well as embedded pipes in components will also affect the test results.
2. Image scanning
When the thickness of the protective layer of steel bars is too large, the image obtained by scanning will be unable to be analyzed by the instrument. In theory, the detection depth of the scanner is 100mm, but when the thickness of the protective layer is greater than 60mm, the overall signal will become weaker, which will affect the scanning accuracy. . The thickness of steel bar cover obtained by one image scan has several values, and there is subjectivity in the value selection.
solution
(1) Before on-site inspection, it is necessary to carefully analyze and study the drawings, determine a reasonable inspection location, be aware of the location of the steel bars in the component, and avoid the densely populated areas of steel bars such as beam-column nodes and joints of steel bars, so that the roots of the steel bars detected The data is in line with the actual situation, and complete and accurate detection data are obtained.
(2) When testing, it should be ensured that the surface of the concrete component is smooth and flat, the axis of the probe is parallel to the edge of the component as far as possible, and the surface of the scanner roller is clean without sand or gravel. Avoid conductive metals such as water pipes, electrical wires, and metal wire casings as much as possible.
(3) When there are missing ribs, multiple ribs and image cannot be analyzed in the fast recording scan, the image scanning can be used for further determination of the ribs. Especially in the case of structural components with exposed ribs, image scanning is required to truly reflect the engineering situation. As shown in Figure 3 and Figure 4, when recording a certain beam, the signal area becomes wider when scanning quickly, and it does not match the actual reinforcement situation. After scanning it with image scanning, it is found that there is a line between the bottom and the bottom of the bottom Scrap steel bars with bars at an angle of about 30° affected the test results.
