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 that starts at the surface and reaches the reinforcing parts.
It is used to protect reinforcing elements from corrosive changes, overheating, high humidity, negative environmental influences. Also, his task is to ensure high-quality adhesion of concrete mortar and reinforcement.
Design
In reinforced concrete buildings, the protective layer is formed using the remote location of the reinforcing elements from the common plane. It should be noted 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, the dimensions of the sections.
To prevent the beams from collapsing, steel reinforcement is laid in the stretched part of the structure. Concrete, when solidified, is carefully bonded to it and transfers most of the tensile forces.
Influencing factors
Observance of optimally suitable thickness is an important condition for the work. If the layer is thin, the rapid destruction of metal 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, as this contributes to an unjustified increase in the cost of the building. Therefore, you need to be able to correctly calculate the required size. Among the influencing factors, it is worth noting the following:
- Load on reinforcing elements. There are two options coming from this indicator. Non-stressed and stressed type of reinforcement refers to them.
- A variety of components. Both transverse and longitudinal views are used. The working and structural reinforcement also differs.
In addition to the above, the expected operating conditions have a big impact. Can be used indoors or outdoors, in high humidity conditions or in contact with soil. It also requires mandatory accounting.
Choice
To simplify the process of selecting the thickness, you should pay attention to the established norms specified in the SNiP. The reinforcing non-stressed longitudinal component must have a protective layer of concrete 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. In case of exceedingof this level, provided the height of the beams is up to 250 mm, the indicator is equal to 15 mm.
When building with a longitudinal prestressing type of reinforcement in those places where the load is transferred to the concrete part, the layer should be approximately two diameters thick. This applies to both reinforcing bars and wire ropes.
The rates and norms listed above require standard weather conditions. To check the existing 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. A protective layer of concrete with a thickness of 60 cm or more in this case is much easier to equip.
The most widespread today are plastic fixing devices, despite the fact that not so long ago they were used instead of rebar blanks. They had to be pre-made before the laying began. Today's options are relatively low cost and easy to install. They are designed to simplify the reinforcing work and subsequent concreting of monolithic structures as much as possible.
Pros of use
Thanks to the clamps, it became possible to secure the reinforcing elements in the required form with high quality. So there was an automated pouring of mortar from concrete. Atthere is no need to worry about the displacement of the reinforcement, as a constant uniform concrete cover is guaranteed. SNiP 2.01.02-85 contains the basic requirements for its creation. This tool becomes especially useful when resurfacing.
Using latches unlocks the following features:
- reducing building construction costs;
- requires less time for work related to concreting and reinforcement;
- protective coating of the foundation is always under control;
- quality of work is getting better.
It should also be noted that the reliability and quality of the final concrete structure is sufficiently influenced by the even level of protective coating.
Work in progress
Over time, even the maximum protective layer of concrete requires reconstruction work due to falling into an unsuitable state. The reservoir is restored using two methods:
- complete top replacement;
- partial repairs, which also includes patching up chips and cracks.
In the second option, it will not take much effort and time, here it is necessary to process the damaged areas, clean them and coat them with a primer. Patching can begin only after all preparatory work is completed.
Performing a complete replacement of the top cover must be subject to certain requirements and regulations. The need for completereconstruction 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 their environment.
Reservoir replacement
Work begins with the determination of the thickness, for this a concrete cover gauge is used. It makes it possible to measure the cement protective layer, the unusable parts of which are subsequently removed with the utmost care to the place where the steel frame is attached.
If necessary, metal surfaces in a reinforced concrete structure are cleaned from corrosive deposits, as well as from existing dust and dirt.
The application of concrete mortar begins after completion of the preparatory steps. Mechanical application of the mixture is used, which is the distribution of 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 fit of the smallest particles are ensured. The mortar must be at least 3 cm thick.
If there is significant damage on the surface of the building that cannot be eliminated with partial repairs, you can apply a new protective layer of concrete over the old one. Diamond tipped devices are used when machining is required.
Anchoring
For buildings fromreinforced concrete, the anchoring of reinforcing elements is of particular importance, which ensures the transfer of the design force in the established section. Its length is revealed in accordance with the fact that the force acting in the reinforcement must be taken over by its adhesion to the concrete surface along the entire length of the anchoring. As well as the resistance force of the fixing devices, depending on the tensile capabilities of the concrete, the profile and size of the reinforcement, the stress state of the materials.
Anchoring of transverse-type reinforcement is carried out by bending it and welding it to the longitudinal version or its coverage. In this case, the longitudinal reinforcement must have a diameter of at least half the size of the transverse one.
Lap fastening should be carried out at a distance that will ensure the transfer of the calculated force from one part to be joined to another. The length of the overlap along the main anchorage is set, while taking into account the space between the joints and the rods, the protective layer of concrete, the number of transverse-type reinforcement at the junction and the rods connected at one point.
