by Definition of steel reinforcement protection layer: refers to the minimum distance between the surface of concrete and the outer edge of the nominal diameter of the outermost steel reinforcement (load-bearing steel reinforcement), which serves to protect the steel reinforcement from direct exposure in concrete components. For post tensioned prestressed steel bars, it is the distance from the outer edge of the casing or hole to the surface of the concrete. The minimum thickness of the protective layer is specified to meet the durability requirements of concrete structural components and the requirements for effective anchoring of stressed steel bars.
The thicker the concrete protective layer, the better the bonding and anchoring performance, durability, and fire resistance of the load-bearing steel bars in the component. However, excessive thickness of the protective layer can cause cracks to become too wide after the component is subjected to force, which will affect its performance. Moreover, since the tensile effect of concrete is not considered in the design, excessive thickness of the protective layer will inevitably lead to economic waste. Therefore, according to the “Code for Design of Concrete Structures” (GB50010-2010), the thickness of the concrete protective layer (the distance from the outer edge of the steel bar to the concrete surface) of ordinary steel bars and prestressed steel bars under longitudinal stress should not be less than the nominal diameter d of the steel bar (which can ensure the anchoring of the concrete in the gripping layer to the stressed steel bar), and should comply with the provisions in the table below. In general design, the minimum value is used..
The thickness of the protective layer is not fixed and can be reduced under certain conditions, such as:.
The surface of the component has a reliable protective layer (cement permeable crystalline waterproof material).
Adding rust inhibitors or cathodic protection measures to concrete to prevent rust.
There is a reliable waterproofing method, and the protective layer on the side in contact with the soil layer can be appropriately reduced, but should not be less than 25mm..
In order to effectively control cracks in concrete components and effectively bond with steel bars, effective construction measures should be taken for the protective layer of the stressed steel bar when it is greater than 50mm. When using steel mesh, the thickness of the protective layer of the mesh should not be less than 25MM.
The beam has a foundation of 20 sides, 15 sides, and 40 sides (70 is cancelled due to the 2010 version’s requirement for cushion layer).
A hundred year plan of 1.4, over 50 must be protected (1.4 times is determined by the carbonation rate of concrete)..
Unfortunately, the design specifications for reinforced concrete structures in version BJG21-1966 were not found, and the original version of BJG21-66 was found.
62nd edition specification requirements.
When the thickness of the wall panel is not greater than 100mm, the protective layer of heavy concrete is not less than 10mm, and the thickness of light concrete is not less than 15mm.
When the thickness of the slab wall is greater than 100mm and the beam height is below 250mm (without specifying whether it is the total height or the web), when the nominal diameter of the steel bar is greater than 20mm, it should not be less than 15mm. Compared to the current nominal diameter, the main reinforcement of the protective layer has increased. When the beam height is greater than 250mm and the nominal diameter of the steel bar in the column is greater than 20mm, it shall not be less than 20mm. (Column components are stricter than slabs), when the nominal diameter of the steel bar is greater than 20MM, it should not be less than 15MM..
The protective layer of steel bars with cushion layer in the foundation shall not be less than 35mm (less than the current standard of 40mm), and the protective layer of steel bars without cushion layer shall not be less than 70mm (this operation was cancelled until the 2010 version of the new regulations).
The distribution reinforcement shall not be less than 10mm, and the welding hoop reinforcement for beams and columns shall not be less than 15..
200 and above.
