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 starting at the surface and reaching the reinforcing parts.
It is used to protect reinforcing elements from corrosion changes, overheating, high humidity, negative environmental influences. Also, his task is to high-quality adhesion of concrete mortar and reinforcement.
Design
In reinforced concrete buildings, a protective layer is formed using a remote arrangement 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, other factors affect the indicator, such as the type of concrete and the dimensions of the sections.
To prevent the collapse of the beams, steel reinforcement is laid in the stretched part of the structure. When hardening, the concrete is carefully bonded to it and transfers most of the tensile forces.
Impact factors
Adherence to an optimum thickness is an important prerequisite. If the layer is thin, rapid destruction of metal elements will begin, which can lead to subsequent changes in the entire structure.
In this case, too large a protective layer of concrete is not the best option, as this contributes to an unjustified increase in the cost of the structure. Therefore, you need to be able to correctly calculate the required size. Among the influencing factors, it is worth noting the following:
- The load on the reinforcing elements. There are two options based on this indicator. Relates to them unstressed and stressed type of reinforcement.
- A variety of components. Both transverse and longitudinal views are used. The working and structural fittings also differ.
In addition to what is indicated above, the expected operating conditions have a great influence. It can be used indoors or outdoors, in conditions of high humidity or in contact with soil. It also requires mandatory accounting.
The choice
To simplify the process of selecting the thickness, it is worth paying attention to the established standards specified in SNiP. The reinforcing non-tensile longitudinal component must have a protective layer of concrete greater than or equal to the diametrical size of the rod. If walls and slabs have indicators less than 100 mm, then the coating should start from 10 mm. If this level is exceeded, provided the beam heights are up to 250 mm, the indicator is equal to 15 mm.
During construction with a longitudinal tensile type of reinforcement, in those places where the load on the concrete part is transferred, the layer should have a thickness of about two diameters. This applies to both reinforcing bars and steel ropes.
The indicators and norms listed above require standard weather conditions. To check the available thickness, specialized measuring devices have been developed, the operation of which is based on the magnetic principle.
Fixation
Of particular importance is the retainer of the protective layer, which allows you to create accurate dimensions for the structure during its reinforcement. Reinforcing underlying networks are placed on such devices while the foundation is being formed. The protective layer of concrete with a thickness of 60 cm in this case is much easier to equip.
The most widespread today are plastic fixing devices, despite the fact that not so long ago blanks from reinforcement were used instead of them. They had to be pre-made before the start of the installation. Today's options have a relatively low cost and easy installation. They are designed to maximize simplification of reinforcing work and subsequent concreting of monolithic structures.
Advantages of using
Thanks to the clamps, it became possible to qualitatively fix reinforcing elements in the required form. So there was an automated pouring of mortar from concrete. In this case, you do not need to worry about the displacement of the reinforcement, since a constant uniform protective layer of concrete is guaranteed. SNiP 2.01.02-85 contains the basic requirements for its creation. This device becomes especially useful when restoring the coating.
Using latches opens the following possibilities:
- reducing the cost of building a building;
- less time is required for work related to concreting and reinforcement;
- the protective coating of the foundation is always under control;
- the quality of work is getting higher.
It should also be noted that the reliability and quality of the final concrete structure is sufficiently influenced by the uniform level of the protective coating.
Work
Over time, even the maximum protective layer of concrete requires reconstruction work due to coming into an unsuitable condition. Formation recovery is performed using two methods:
- complete replacement of the upper part;
- partial repair work, which also includes patching of chips and cracks.
In the second version, it does not take much effort and time, here it is necessary to treat the damaged areas, clean them and grease with a primer. Patching can begin only after completion of all preparatory work.
The complete replacement of the upper part of the protective layer must occur in accordance with certain requirements and rules. The need for a complete reconstruction appears in the following situations:
- separation of the protective layer;
- changing the characteristics of materials;
- metals began to degrade due to chemical interactions with the environment surrounding them.
Reservoir replacement
Work begins with the identification of thickness, for this a meter of the protective layer of concrete is used. It makes it possible to measure a cement protective layer, unsuitable parts of which are subsequently removed with extreme caution to the point of attachment of the steel frame.
When the need arises, metal surfaces in the reinforced concrete structure are cleaned from corrosion deposits, as well as from existing dust and dirt.
The application of concrete mortar begins after the completion of preparatory actions. The 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 denser interaction of the solution with the plane of the structure and the adhesion of the smallest particles are ensured. The solution should have a thickness of at least 3 cm.
If there are significant damages on the surface of the building that cannot be eliminated during partial repairs, a new protective layer of concrete can be applied to the previous one. Diamond tip devices are used when machining is required.
Anchoring
For structures made of reinforced concrete, the anchoring of reinforcing elements, which ensures the transfer of the design force in the established section, is of particular importance. Its length is revealed in accordance with the fact that the force acting in the reinforcement should be adopted by its adhesion to the concrete surface located along the entire length of the anchoring. As well as the resistance force of the fixing devices, depending on the possibilities of stretching the concrete, the profile and size of the reinforcement, the stress state of the materials.
The reinforcement of the transverse type is anchored using its bending and welding to the longitudinal version or its coverage. In this case, the longitudinal reinforcement should have a diameter of not less than half the size of the transverse.
Overlap fastening should be carried out at a distance that will ensure the transfer of the design force from one connected part to another. The overlap length is set according to the main anchoring, while the space between the joints and the rods, the protective layer of concrete, the number of transverse reinforcement at the joint and the rods connected at one point should be taken into account.