In order to ensure the accuracy of concrete protective layer thickness detection, testers should be proficient in the performance of the instruments they use and the degree of influence of various factors on the accuracy of concrete protective layer thickness detection. To avoid some of the factors that can be avoided, if there are no regulations, they should be based on the actual site Make records and perform simulation tests to correct them. According to long-term testing practice, before and during the testing of the rebar detector using the eddy current effect, the following operating points can be operated:
(1) Determine the number and location of tests in accordance with the procedures specified in the specification.
(2) Read the construction drawings, and grasp the cross-sectional dimensions of the structure at the inspection location, the direction of the force, the diameter and quantity of the reinforcing bars, and the thickness of the design protective layer.
(3) Investigate whether there are conductive metals such as water pipes, electric wires, and metal wire sleeves in the inspection location, and avoid them when selecting the test section.
(4) Check the flatness of the test surface. When the unevenness exceeds 0.5mm, it should be smoothed.
(5) Select a probe of appropriate size. Use a small probe when the thickness of the protective layer is less than 60 mm. Use a large probe when the thickness of the protective layer is greater than 60 mm.
(6) Set the parameters of the reinforcing bar size according to the construction icon, perform a rough survey in the detection location area, and draw the approximate position of the reinforcing mesh. Draw a detection line at the place where the distribution ribs have a relatively large distance and the effect of the distribution ribs is the smallest, and measure along the line.
(7) When determining the thickness of the protective layer of the main reinforcement at the bottom of the beam, the influence of dense steel bars on the detection accuracy is highly valued. When the number of rebars does not match the construction drawing or the position of the rebar cannot be determined, in addition to recording the readings of the bottom and two sides of the instrument, the thickness of the protective layer on the bottom surface should be calculated through the positioning of the reinforcing bars on both sides. Layer thickness, and align the bottom center of the probe with the bottom corner of the beam, and verify the measured values by measuring the distance from the bottom corner of the beam to the surface of the steel bar and the angle between the bottom of the instrument and the bottom of the beam. Among them, when measuring the distance from the bottom corner of the beam to the surface of the reinforcing bar, the displayed value of the instrument is least disturbed.
(8) Prepare a 10 mm thick plastic pad. When the thickness of the protective layer is less than the minimum value that can be displayed by the instrument, add a backing plate for testing, and subtract the thickness of the backing plate from the obtained value.
(9) When the negative deviation of the thickness of the protective layer exceeds the standard, the durability of the structure may be severely reduced, or the positive deviation of the protective layer may exceed the standard, which may cause the structural bearing capacity to be severely reduced, and if the test results are in doubt, excavation (micro damage) shall be checked and verified.
(10) The instrument should be checked on the standard block before and after use.