Protective layer of concrete to protect the reinforcement from the environment

The protective layer of concrete and its thickness are of interest to many people who are engaged in the construction of reinforced concrete structures. In fact, it is a coating beginning at the surface and reaching the reinforcing parts.

It is used to protect reinforcing elements from corrosive changes, overheating, high humidity, negative environmental effects. Its task is also to provide high-quality adhesion of concrete mortar and reinforcement.

Design

In reinforced concrete buildings, a protective layer is formed by the remote location of reinforcing elements from a common plane. It is worth noting that the protective layer of concrete for reinforcement has a thickness that is set depending on the elements used, their size and type. In addition, the index affects other factors, such as the type of concrete, the dimensions of the sections.

To prevent the collapse of the beams, steel reinforcement is laid in the stretched part of the structure. Concrete at hardening is carefully fastened with it and carries most of the tensile forces.

Impact factors

Observance of the optimum thickness is an important condition of the work. If the layer is thin, rapid destruction of the metallic elements will begin, which can lead to subsequent changes in the entire structure.

At the same time, too much thickness of the protective layer of concrete becomes not the best option, since this contributes to an unreasonable increase in the cost of the structure. Therefore, you need to be able to competently calculate the required size. Among the influencing factors, it is worth noting the following:

• Load on the reinforcement elements. There are two options coming from this indicator. Refers to them is the relaxed and stressed type of reinforcement.
• A variety of components. Used as a transverse as well as a longitudinal view. There is also a working and constructive armature.

Great influence, in addition to what is indicated above, is provided by the expected operating conditions. It can be used indoors or outdoors, in conditions of high humidity or in contact with the soil. This also requires mandatory accounting.

Selection

To simplify the process of selecting thickness, it is worth paying attention to the established norms specified in the SNiP. The reinforcing non-tensioning longitudinal component must have a concrete protective layer that is greater than or equal to the diametrical size of the rod. If the walls and slabs have indicators less than 100 mm, then the coating should start from 10 mm. If this level is exceeded, if the height of the beams is up to 250 mm, the indicator is equal to 15 mm.

When building with a longitudinal tension type of reinforcement where the load is transferred to the concrete part, the layer should have a thickness of approximately two diameters. This applies both to reinforcing bars and to steel ropes.

The indicators and norms listed above require standard weather conditions. To test the available thickness, special measuring devices have been developed, the work of which is based on the magnetic principle.

Fixation

Of particular importance is the retainer of the protective layer, which allows to create exact dimensions for the structure during its reinforcement. On such adaptations are placed reinforcing underlying networks while the foundation is being formed. The protective layer of concrete with a thickness of 60 cm in this case is much simpler.

The most widespread today are plastic fixation devices, although not so long ago they used instead of them billets from the armature. They had to be pre-made before the very beginning of laying. Today's options are relatively inexpensive and easy to install. They are designed for maximum simplification of reinforcing works and subsequent concreting of monolithic structures.

Advantages of use

Thanks to the locks, it became possible to fix the reinforcement elements in the required form. So there was an automated filling of mortar from concrete. At the same time, there is no need to worry about the displacement of the reinforcement, since a constant identical protective layer of concrete is guaranteed. SNiP 2.01.02-85 contains the basic requirements for its creation. This device becomes particularly useful in restoring the coating.

The use of latches opens the following possibilities:

• Reduction of construction costs;
• It takes less time to carry out works that are related to concreting and reinforcement;
• The protective covering of the foundation is always under control;
• The quality of work performance becomes higher.

It should also be noted that the reliability and quality of the final concrete structure has a sufficient influence and a uniform level of protective coating.

Carrying out work

With time, even the maximum protective layer of concrete requires reconstruction work because of coming to an unsuitable condition. The formation is reconstructed using two methods:

• Complete replacement of the upper part;
• Partial repair work, which also includes patching chips and cracks.

In the second variant, it does not take much effort and time, here it is necessary to treat the damaged areas, clean them and smear with a primer. You can start patching only after completing all the preparatory work.

Complete replacement of the upper part of the protective layer should occur when certain requirements and rules are met. The need for a complete reconstruction appears in the following situations:

• Separation of the protective layer;
• Changing the characteristics of materials;
• Metals began to break down due to chemical interactions with the environment surrounding them.

Replacement of the reservoir

Work begins with the detection of thickness, for this purpose a measuring instrument of the protective layer of concrete is used. It makes it possible to measure the cement safety layer, the unsuitable parts of which are subsequently removed with extreme caution until the anchoring point of the steel frame.

If necessary, the metal surfaces in the reinforced concrete structure are cleaned from corrosive layers, as well as from the existing dust and dirt.

The application of the concrete solution begins after the completion of the preparatory actions. A mechanical application of the mixture is used, which is the distribution of the material under pressure in the form of compressed air. Thanks to the use of this technique, a more dense interaction of the solution with the plane of the structure and the adherence of the smallest particles are ensured. The solution must have a thickness of at least 3 cm.

If there are significant damages on the surface of the building, which can not be got rid of in case of partial repair, it is possible to apply a new protective layer of concrete to the previous one. Devices with diamond tips are used when machining is necessary.

Anchoring

For reinforced concrete structures, the anchoring of reinforcing elements is particularly important, which ensures the transfer of the design force in the established section. Its length is determined in accordance with the fact that the force acting in the reinforcement must be transferred by its adhesion to the concrete surface located along the entire length of the anchoring. As well as the resistance of the fastening devices, depending on the possibilities of stretching the concrete, the profile and size of the reinforcement, the stress state of the materials.

Anchoring of the transversal type reinforcement by means of its bending and welding to the longitudinal version or its coverage is carried out. In this case, the longitudinal reinforcement must have a diameter not less than half the size of the transverse reinforcement.

The overlapping must be carried out at a distance that will ensure the transfer of the design force from one part to the other. The length of the overlap along the main anchoring is determined, taking into account the space between the joints and the rods, the protective layer of concrete, the number of reinforcements of the transverse type at the junction and the rods connected at one point.