Protective layer of concrete: the choice of thickness,

06-08-2018

Building

When performing reinforced concrete work, it is necessary to pay attention to such an important parameter as the protective layer of the reinforcement cage. The fact is that many characteristics of the material depend on it. A protective layer of concrete is selected according to SNiP 2.03.01-84.

Next, we consider in detail what a protective layer of reinforcement in concrete is, what it is for, and how it should be in different situations.

General information

So, a layer of mortar from the surface to the metal frame is called a protective layer of reinforcement in concrete.

Its importance is due to the fact that it performs several functions at once:

Provides anchoring (fixing) reinforcement in concrete;
Provides joint work of concrete with iron;
Protects metal from environmental exposuresuch as heat, high humidity, various aggressive media, etc .;
Increases fire resistance and fire safety of reinforced concrete structuresTherefore, it is necessary to comply with these conditions by fire regulations.

It follows that it is impossible to ensure the strength and reliability of reinforced concrete without the optimal thickness of protection.

What determines the protective layer

If the protection is too thin, then, as it is easy to guess, the metal quickly begins to deteriorate, which leads to the gradual destruction of the entire structure. If, on the contrary, this layer is too thick, the cost of construction will increase substantially. Therefore, it is very important to determine the optimal value.

This parameter may depend on the following factors:

Roles of reinforcement in the design - it can be transverse or longitudinal, constructive or working.
Loads on reinforcement - the design may be unstressed or stressful.
Type of construction - it can be a foundation, beam, slab, support.
The dimensions of the cross section design.
Terms of use of the product - in the open air, indoors, in conditions of high humidity or in contact with the ground.

The distance from the formwork to the frame is allocated under a protective layer

Thickness selection

The thickness of the protective layer of concrete according to SNiP №2.03.01-84. governed by certain rules. With their help, you can accurately determine the desired value of protection in a particular case.

Next, consider the most common situations.

Longitudinal non-stressed reinforcement

If longitudinal non-strained reinforcement is used in reinforced concrete, the minimum layer must be at least the diameter of the rod.

In addition, there are the following rules:

If the slab thickness is less than 10 cm, the layer should be 1 cm.
In beams with a height of 25 cm and more - 2 cm.
With reinforced concrete thickness of more than 10 cm - 15 mm.
At construction of the bases - 3 cm.

Scheme of prestressed and non-stressed longitudinal reinforcement of beams

Longitudinal tensioned reinforcement

In reinforced concrete structures with longitudinal prestressing reinforcement in the field of load transfer to concrete, the formation thickness should be not less than 2d, i.e. at least two diameters of steel rods or reinforcing rope A-IV, At-IV. For rods At-V, AV, At-VI, A-VI, this indicator should be at least 3d.

Note! The minimum allowable diameter of the reinforcing rope is 20 mm, and the diameter of the rod is 40 mm.

When tensioning the longitudinal reinforcement on the concrete and its location in the channels, the distance from the surface to the channel should be at least half the channel diameter and at least 2 cm.

In industrial buildings

Protective layer in industrial buildings should be of the following thickness:

In the walls, flat and ribbed plates, wall panels - not less than 2 cm;
In beams, trusses and columns - not less than 25 mm;
Protective layer of concrete in foundations and foundation beams - at least 3 cm;
During the construction of underground structures - at least 2 cm.

Industrial reinforced concrete structures

To protect the ends of reinforcing bars, it is recommended to use a layer with a thickness of at least:

10 mm for structures up to 9 meters long;
15 mm for structures up to 12 meters long;
20 mm for structures over 12 meters long.

For collars and frames with transverse rods, it is necessary to take into account the height of the section:

If the height is less than 25 cm - the thickness of the layer should be 1 cm,
More than 25 cm –15 mm.

Under negative environmental conditions

In some special cases, the thickness may differ from the above values:

If there is a concrete foundation preparation - not less than 40 mm;
If the design is constantly in contact with the ground - 76 mm;
If the structure is in contact with the ground in conditions of adverse weather, when using d18-d40 fittings - 52 mm, for d10-d18 fittings - at least 25 mm and more;
If the structure is located in the open air - from 30 mm and more;
In rooms with a high level of humidity - from 25 mm and more.

Repair of the protective layer

Even if the reservoir thickness was chosen correctly, it may eventually become unusable over time. In such a case, restoration of the protective layer of concrete will help to save the entire structure.

Repair can be of two types:

Seal individual chips, shells, etc.
Complete replacement of the surface with your own hands.

If in the first case the repair does not cause any difficulties - it is only necessary to clean the damaged area of concrete, prime and impose a "patch", then in the second it is necessary to observe a certain technology.

Full replacement of the reservoir may be necessary in the following cases:

Material properties are reduced;
The metal is corroded;
The protective layer of the layer exfoliates.

A device for determining the thickness of concrete to reinforcement

In such situations, the old layer must be completely removed.

Instructions for the implementation of this work is as follows:

First of all, it is desirable to determine the thickness of the reservoir. To do this, you can use a special meter protective layer of concrete.
Next, the old layer is carefully removed before the reinforcement.
If necessary, the metal is cleaned from corrosion.
Then the surface is cleaned from dust and other contaminants.
After that, the solution is applied by the method of shotcrete. In this case, it is supplied under compressed air pressure. This allows cement particles to tightly interact with the surface of the structure and fill all existing cavities, pores, cracks, etc.

The thickness of the solution in this case must be at least 30 millimeters.

In the photo - the application of the solution

I must say that in some cases the old layer is not removed, but increased. This procedure makes sense in those cases where the surface is heavily damaged, and putting patches is impractical.

If the damaged area is small, then the horizontal surface can be “enlarged” using the usual screed method. To build up small vertical sections, the solution is applied on the principle of plastering concrete surfaces.

Tip! In some cases, there is a need to perform mechanical processing of reinforced concrete. In this case, use a tool with diamond nozzles. In particular, an effective method is diamond drilling of holes in concrete, which is used when carrying out communications, as well as cutting reinforced concrete with diamond circles, which may be required in different situations.

Conclusion

The protective layer of concrete for reinforcement plays an important role in reinforced concrete. The durability of the whole structure depends on it. Therefore, when performing concrete work, it is necessary to choose its thickness correctly, in accordance with the existing standards given above. From the video in this article, you can get more information on this topic.