Reinforced concrete structures - a comprehensive analysis of

Reinforced concrete structures in modern construction are, without exaggeration, a key component of almost any structure. For such products is characterized by an extremely wide variety, which allows them to be used in solving the most diverse tasks.

Below we describe the key features of parts made of reinforced concrete, describe the subtleties of their production, as well as consider the main advantages and disadvantages of this type of material.

Product classification

The basic document regulating the use of such products is a SNiP on reinforced concrete structures (2.03.01-84). This standard, as well as other documents governing certain aspects of the use of reinforced concrete in construction, determine its composition and key performance requirements.

According to these standards, reinforced concrete is a composite consisting of a cement or similar in binder, dense filler and metal reinforcement. This combination allows you to combine the massiveness and durability of real concrete with sufficient bending and compression strength, which steel possesses.

To facilitate orientation in the diversity of reinforced concrete structures, there are several options for their classification. At the core of each option is one or another fundamental feature.

 So, by the principle of construction of reinforced concrete products are divided into:

• Prefabricated - consist of individual elements produced in the factory and collected in a single system at the facility.
• Monolithic - settled by pouring directly on the spot. For the manufacture of monolithic structures, formwork of various forms is most often used.

Note! Also sometimes distinguish intermediate, precast-monolithic type of products, combining both described technologies.

Configuration classification usually includes the following varieties:

• Block - the most common and easy to manufacture. Represent corpulent or hollow blocks of regular geometric shape.
• Linear - a type of block modules elongated in length. Linear structures usually include beams, piles, posts, trusses, etc.
• Flat - slabs and floors of different size and strength. Like blocks, they can be made hollow to reduce mass with a slight decrease in strength.
• Spatial products - trays, pipes, rings for wells, etc. The main feature of such modules is the presence of an internal functional cavity.

Naturally, here is only an overview of the main types of products. SNiP on reinforced concrete structures contains a more detailed classification with precise characteristics, and therefore, when designing, specialists refer specifically to this standard.

Main components and production

Binder

The manufacture of reinforced concrete structures involves the use of four main components: binder, filler, reinforcement and water. In addition, to improve the quality of the material in the raw material, modifiers are often added - substances that optimize the composition, improve plasticity, accelerate the hardening, etc.

Binder is one of the most important components:

• Portland cement is commonly used as a binder that hardens after hydration (interaction with water). It is characterized by high strength and quite reasonable price.

Note! A separate group consists of so-called non-shrink cements, the volume of which does not change upon hydration. With their help, usually perform repair of reinforced concrete structures.

• For the production of concretes, which are used in mass construction, cement M400 or M500 is usually used. These types of material are usually oriented on calculating the proportions of other components of the mixture for the manufacture of w / w products.

• However, in some cases, the design requires increased mechanical characteristics. At the same time, higher quality cement (M600 - M800) can be involved. However, it should be remembered that the use of such compositions significantly increases the cost of construction. In addition, after solidification, such products are less amenable to processing.

Filler

The second most important component is the filler. And if a variety of materials can be used for building concrete without internal reinforcement, up to foamed polymers, then in the production of reinforced concrete structures, usually only those substances are used that will ensure the composition high density and strength.

They can be divided into several groups, which are listed in the table below:

When choosing a filler usually follow these rules:

• For the production of concrete M400 and below gravel is used, for more durable materials - crushed stone.
• Both crushed stone and gravel are subjected to fractionation before entering into the composition - separation according to particle size. The use of materials of one fraction helps to improve the uniformity of the composition and improve its properties.
• When calculating the mechanical characteristics, it is necessary to take into account that the strength of stone aggregate should be about 1.5 - 2 times higher than the strength of the cement composition.

Armature frame

Finally, an important element is the reinforcement cage:

• To improve the mechanical characteristics of the material, steel reinforcement is used - wire, rods, pipes or other elements, connected in frames of a certain shape. The configuration of the frame is determined by the outlines and dimensions of the structure itself, as well as the design requirements for strength.
• The instruction allows both the welded connection of the frame elements and their binding using a special wire. The second method is less reliable, but it is easier to implement independently, because it is widely used in private construction.

• According to the features of the bookmark, the reinforcement is divided into tense and unstressed. The reinforcement stress is called its preliminary stretching with the help of special devices: after the polymerization of concrete, such a framework retains its elasticity, and its ability to compensate for loads increases many times over.

Manufacturing technology

Prefabricated items

The scheme by which the production of reinforced concrete structures, depends on what result we plan to get.

At the same time, the techniques for casting individual blocks and monolithic structures differ significantly:

• For the production of prefabricated modules, we need forms. If you need to make only a few pieces (for example, to form an overlap), then you can assemble a form of boards and thick plywood. Otherwise, the best choice would be to purchase a prefabricated metal structure with an adequate margin of safety.
• From the inside we process the form with machine oil. Wooden structures can also be lined with polyethylene to prevent swelling from moisture.

• Next, collect the reinforcement cage, which is installed in the tank at a distance of about 30-50 mm from the bottom plane. For distancing it is best to use special stands.

Pay attention! Do not forget about mortgages for fastening and transporting modules using a truck crane!

• Then pour the prepared solution based on cement, sand and aggregate. The proportions of the main components are determined depending on the desired strength of concrete.
• Using a deep vibrator or vibrating table, compact the material. At the same time, excess air is removed from it, due to which the density increases and the adhesion of hydrated cement to reinforcement and gravel is improved.

At the last stage, the product is dried, and in the industry for this purpose special high-temperature chambers are used. Constant heating above 500C contributes to a faster set of strength. In everyday life it is necessary to withstand the block before using it for at least 28 days.

Before use in the construction of industrial products must pass a multi-stage test. Tests on reinforced concrete structures make it possible to determine the compliance of the strength parameters with the planned ones, as well as to identify possible defects.

Monolith fill

Production of monolithic structures is faster, but at the same time - more labor intensive:

• First, the reinforcement cage is assembled, which is installed on a predetermined section and is welded to the already erected elements.
• Then a formwork is erected around the frame, the power of which allows it to withstand the mass of the filled solution without deformation and destruction.

• We pour concrete into the formwork, distributing it in such a way as to avoid the formation of "air pockets". We condense material, increasing its durability.
• Next, perform the drying of concrete, making sure that it retains a sufficient amount of liquid for hydration. To do this, cover the material with polyethylene, periodically moistening the surface.

Note! Drying should take place at positive temperatures. If it is planned to fill the monolith during the winter period, then the electrically conducting cables for heating the mixture are additionally placed in the construction, or the heat-insulating formwork is equipped.

After a set of strength, it is desirable to perform instrumental quality control of the material. This will allow us to use its calculated bearing capacity with confidence, without fear of collapse.

Advantages and disadvantages

Speaking about this variety of materials, one should not lose sight of the analysis of their strengths and weaknesses. As we know, reinforced concrete in capital construction is in great demand, therefore it is quite logical that it has quite objective merits.

Among them:

• Long service life. GOST for reinforced concrete structures used in construction implies a division into three categories of durability: the first is over 100 years old, the second is 50-100 years old and the third is 30 years old.

Note! Regulatory documents limited to the minimum allowable life of the structure. Subject to the rules of operation, timely prevention and repair, this period can be repeatedly increased.

• Relatively low cost. If we take into account only the financial component, the reinforced concrete structure will come out much cheaper than the steel one with the same performance indicators.
• High temperature resistant. Taking into account the low thermal conductivity of concrete, it is safe to say that such a structure will be much more fire resistant than a product of steel beams.
• Resistance to chemical and biological factors. Inert concrete reliably isolates the steel frame from the external environment, due to which the structure is destroyed several times slower due to corrosion. Yes, and bacterial lesions of concrete are found only in exceptional conditions (constant high humidity at high temperature).

• Good load resistance - static and dynamic. This advantage is due to the optimal combination of concrete and steel reinforcement properties.
• Manufacturability - if necessary, and the availability of the necessary resources of reinforced concrete, you can make almost any architectural form. In private construction, it is also possible to fill structures with your own hands: of course, labor costs will be substantial, but not at all transcendental.

However, reinforced concrete structures have several disadvantages:

• First, paradoxically, the minus is considered to be low strength with a significant mass. According to this indicator, reinforced concrete is seriously inferior to steel trusses and beams, since the product carries significantly less payload per unit mass.
• Secondly, the performance of the material (thermal conductivity, sound insulation, etc.) make it impossible to use it in residential construction without additional finishing.

However, these disadvantages are not fatal, and therefore this kind of building materials will be widely used, apparently for quite some time. Moreover, it is not expected yet that they are comparable in characteristics.

Conclusion

When producing reinforced concrete structures according to SNiP, attention should be paid to all the nuances, starting with the composition of the solution and ending with the mode of curing. Only in this case, the erected structure will have all the positive qualities characteristic of the material described.

The video in this article contains additional information on this issue, so for beginners (and not only!), We strongly recommend that you read it.