Concrete

CONCRETE – it is one of the most common and important building materials that is obtained by hardening a mixture of binder, water, aggregates and additives.

Concrete is widely used in civil and industrial construction. In the case of the construction of a concrete structure, its types and brands are determined at the stage of project creation. For various elements of the building structure, different types and grades of concrete are used. It is necessary to determine for which specific structural element (foundation, load-bearing walls, internal partitions, floors) the concrete grade is selected.

The main characteristic of concrete is compressive strength, which determines the grade of concrete. By the type of binder, concretes are:
– cement;
– silicate;
– polymer concrete, etc..

By volumetric mass, concretes are divided into:
– heavy – bulk density above 1800 kg / m3, used in industrial construction;
– lungs – bulk density does not exceed 1800 kg / m3.

The price of concrete depends on:
– on the type of concrete (heavy concrete is cheaper than cellular concrete);
– from the grade of concrete (the higher the number indicated in the grade of concrete, the higher the price).

Do not do it:
– use heavy concrete for the construction of internal partitions or for building superstructures;
– use aerated concrete in the construction of underground structures (cellars, basements, etc.).

It is optimal to purchase concrete directly from the manufacturer, which will save significant money.

Preparation of concrete mix

In individual construction for the preparation of a concrete mixture, Portland cement of grade 400 is most often used as a binder..
It must be borne in mind that cement is very hygroscopic, i.e. quickly absorbs moisture from the air and hardens. Therefore, you should not buy cement in advance, and if you already bought it, then it should be stored in a sealed container (for example, tightly wrapped in polyethylene).
The sand used must be clean (free of clay, silt and organic inclusions) and coarse. To isolate foreign inclusions, it is recommended to sift the sand. The cleaner the sand, the higher the strength of the resulting concrete mix. The use of insufficiently cleaned sand will entail an increase in cement consumption by 10-20 percent of the recommended.
It is better to use small crushed stone (fraction 5-20 mm). Optimum results are obtained by using crushed stone from natural rocks, small river or crushed gravel. It is possible to use artificial crushed stone, slag, expanded clay, but it should be remembered that a concrete structure using this kind of aggregates will be less durable.

The approximate number of components for the preparation of 100 liters of concrete mixture:
Cement – 30 kg (3 buckets);
Sand – 70 kg (5 buckets);
Crushed stone – 100 kg (8 buckets);

The water for preparing the mixture must be clean, free of foreign matter. It is difficult to determine the amount of water in advance, because it depends on the initial moisture content of sand and gravel and on the moisture demand of the cement. Usually the required amount of water is determined during the preparation of the mixture. First, dry components (cement, sand, crushed stone) are mixed together, and then water is added in small portions until the mixture acquires the consistency of “thick cottage cheese”. The mixture should not spread, so it can be prepared by hand using a shovel or bayonet on a metal or wooden board, concrete floor. It should be remembered that work on the preparation of a concrete mixture must take place at a positive ambient temperature..

Reinforced concrete

Reinforced concrete structures are subdivided into prefabricated and monolithic. Precast concrete structures (for example, houses) are assembled directly on the construction site from individual elements (blocks, panels, etc.) manufactured in factories.
Monolithic reinforced concrete structures are concreted at the construction site and allow you to create a modern house with the most free planning with large areas of many rooms and high thermal insulation properties of the outer walls. For this type of construction, a rigid metal frame and monolithic structures of floors and walls are used.

note

Stressing cement is often used as a binder in reinforced concrete, which has the property of expanding in volume during hardening. As a result, the reinforcement receives tensile stress, concrete – compression, and the concrete structure becomes self-stressed. Concrete connected to a metal frame provides unlimited possibilities for use in so-called large-span structures, for example, rooms up to 100 sq. M, when one functional space flows into another, large indoor pools, etc. without additional intermediate supports, while maintaining a small wall thickness and high thermal insulation properties of the building envelope. Three-layer structures of external walls from two layers of monolithic reinforced concrete 5 cm thick with an effective insulation (expanded polystyrene) in the middle. This design is lightweight, with a high degree of thermal insulation properties and is much cheaper than any with the use of bricks..
In addition, concretes based on stress cements are practically waterproof, which allows them to be used in construction without additional waterproofing..

Advantages

• increased crack resistance;
• high strength;
• high water resistance;
• high corrosion resistance;
• durability

disadvantages

Metal reinforcement creates electrical fields inside the concrete that have adverse health effects.