How to detect the thickness of concrete floor slab

According to Article 8.3.2 of Code for Acceptance of Construction Quality of Concrete Structure Engineering (GB 50204-2002), the inspection lot is divided by floors, structural joints or construction sections. For the same inspection lot, 10% of the walls and slabs shall be randomly selected according to the representative natural rooms, and there shall be no less than 3 rooms.

For large space structures, the inspection surface of the plate can be divided according to the longitudinal and transverse axes, and 10% is randomly selected, and there are no less than 3 surfaces. For the selected floor, not less than 5 survey areas should be selected for inspection. The sampling number of each unit project should not be less than 3 floors and 3 ladder components.

When measuring the thickness of the floor, turn on the power switch of the transmitting probe, lift the probe and place it on the pre-arranged measuring point at the bottom of the floor, and the top surface of the probe is close to the bottom of the floor. The receiving probe is located on the top surface of the floor. At this time, the receiving probe is located in a certain range above the transmitting probe. Press the instrument test key. If "≥999mm" appears in the thickness display position on the screen, it means that the receiving probe is far away from the transmitting probe.

Move the probe to scan, and when the thickness value is displayed on the screen during the movement (

Extended data

The allowable deviation of plate thickness is +8mm-5mm, which is expressed as a general project, and the qualified rate is above 80%.

The thickness value of the slab is 1/40 of the short span of the slab, and it is generally 120, 140, 160, 180 or 120, 150. Use secondary steel as much as possible, including secondary steel with a diameter of φ 10 (which is seldom used at present) and stressed steel bars with a diameter of ≥ 12. Except the hook, primary steel shall not be used. The diameter and spacing of steel bars should be larger, but the spacing should not be greater than 200, and the spacing should be 200 as far as possible.

The steel bars on the upper part of the slab with a span less than 2m need not be disconnected, and the steel bars can be omitted, which only means that the steel bars are bidirectional and double-row φ8@200. The spacing between the upper and lower steel bars on the slab should be equal, and the diameters can be different, but the types of steel bar diameters should not be too many. On the top floor, considering the crack resistance, the steel bars on the slab can be continuously connected or 50% connected, and the additional steel bars and pull-through steel bars in larger places should be overlapped by tensile steel bars.

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