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Mastering Concrete Thickness of Protective Layer Control: Effective Strategies
March 01,2023

As we all know, buildings in earthquake-prone areas are mainly reinforced concrete structures, so considerable attention is paid to the concrete slab thickness, and LANGRY NDT can provide you with professional cover meterConcrete Scanning Instruments, we detail the control methods and measures for the floor slab thickness in these areas.

One. What is the concrete slab thickness?

The thickness of concrete slab is part of concrete that protects and avoids the direct exposure of reinforcement in the concrete member. The thickness of the protective layer is the minimum distance between the concrete surface and the outer edge of the nominal diameter of the outermost reinforcement (including hoops, structural reinforcement, distribution bars, etc.).

Two. What is the use of thickness of concrete slab?

1, to ensure durability: to prevent corrosion of reinforcing steel by air, moisture, and salt.2、Ensure the grip force: work together with the reinforcement to make the reinforcement play the design strength.

3, to ensure fire resistance so that the reinforced concrete elements in the fire resistance period will not lose workability.

It can be seen that the concrete protective layer directly determines the structure, durability, and functionality of the building, so it is quite an important construction measure.

Three. The provisions of the thickness of concrete slab

1, the protective layer is too small, easy to cause the floor to sink and crack, as well as the alkaline reaction in concrete in advance makes the steel oxidation, and rust expansion, resulting in a concrete burst.


2. The protective layer is too large, which makes the concrete in an unreinforced state and produces cracks.


3. the minimum value of the protective layer is 20, 30, 40, and 60mm. in addition, it is stipulated that the protective layer shall not be larger than 80mm. and there shall be no negative deviation.

Four concrete protective layer control has a good trick

1, reasonable choice and set the mat or shim, so that the reinforcement is laid in the correct location to ensure the thickness of the protective layer.

2, mat selection (concrete, steel, plastic): ① mortar mat due to low strength, durability is lacking, the provisions shall not be used; ② plastic mat stability, rigidity, fire resistance is lacking, limited to the wall side, column side, both sides; ③ concrete mat need to determine in advance the strength equal to or greater than the strength of the cast concrete.

3,Using customized steel support members, the concrete surface needs to do the anti-rust treatment.

4, pad (spacer) size, steel support members to develop a plan for each part of the pad using color identification to distinguish the size, and approved by the supervisory unit.

5,Pave horse path, dedicated construction channel to prevent random trampling steel.

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▲Set up a "horse path" on site, a special channel laid on the plate reinforcement to reduce the trampling on the reinforcement, not only to avoid the deformation of the surface reinforcement but also to reduce the impact on the bottom protective layer

Five, floor slab concrete protective layer construction method

1, using steel shims: generally used for the protective layer of the bottom reinforcement.

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2、Adopt shaped steel members: bottom reinforcement and surface reinforcement are available.

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▲ Style 1: a protective layer of bottom reinforcement with rust-proof bottom

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▲Style 2: Protective layer of surface reinforcement with rust prevention treatment at the bottom

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▲Style 3: Protective layer of face reinforcement with anti-rust treatment at the bottom

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▲Style 4: a protective layer of bottom reinforcement and face reinforcement with rustproof treatment at the bottom of the member

Six. The construction method of the protective layer at the bottom of the beam

1、Steel mat: Similar to the bottom of the slab.

2、Steel members.

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3、Steel bracket.

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Seven. beam side wall side column side protection layer construction method

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▲Using plastic round shims, and color to distinguish the thickness of the protective layer, the site can be seen at a glance

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▲Site Setup

Eight. Acceptance measures of concrete protective layer-

As the concrete pouring project is a hidden project and irreversible. Therefore, the protective layer of all components must be checked and accepted in full and photographed for the record.

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▲ Field acceptance of protective layer thickness

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▲Take photos for the record

Nine Summary

The defects of the concrete protective layer will lead to the concrete surface exposed reinforcement or section effective height reduction, which directly affects the structural bearing capacity and durability, the quality defects such as cracking of floor slab, rusting of exposed reinforcement at the bottom of the slab, leakage, etc., are very mostly caused by the insufficient control of reinforcement protective layer thickness.

Therefore, the project has strict control in both design and construction: based on the specification requirements, comprehensive consideration of durability, the effective height of the cross-section, and other factors, in strict accordance with the design requirements, member types, parts, etc. to determine the design value of the concrete protective layer thickness, and in construction to select the corresponding parts of the mat, bench type, reasonable layout spacing, strictly prohibit misplacement and omission; reasonable arrangements for interspersed construction, set up anti-stepping measures The concealed acceptance should be carried out strictly to ensure the accuracy of the thickness of the protective layer.



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