If you need to reinforce any reinforced concrete structure, as a rule, use rod and wire reinforcement of a smooth and periodic profile and ropes made of low-carbon and low-alloy steels. For greater strength, these structures are hardened from rolling heating and subjected to cold or warm deformation..
Reinforced concrete structures are reinforced with wire, individual rods, meshes and space frames (Fig. 1).
Concrete is a complex material that is obtained as a result of the molding and hardening of a concrete mixture selected in a certain way, which provides the concrete itself with all the necessary characteristics: strength, water resistance, frost resistance, etc..
Typically, a concrete mix consists of the following ingredients: binder, water, aggregates and special additives. The concrete mix must comply with the main characteristics of the material: have good workability, corresponding to the method of compaction used, and during transportation and laying, maintain the homogeneity obtained during production. Ideally, the proportions by weight of the concrete mix should be 8-15% cement, 80-85% aggregates.
All concretes have different densities and, depending on this, are divided into the following groups:
– extra heavy concrete, with a density of more than 2500 kg / m3. Such concretes are made on the basis of especially heavy aggregates, for example, barite, magnetite, cast iron scrap and are used in the construction of protective structures of special design;
– heavy concrete, with a density of 2200-2500 kg / m3. They are made on the basis of sand, gravel, crushed stone from solid rocks and are used in the construction of all load-bearing structures;
– lightweight concrete, density of which is 1800-2200 kg / m3. These concretes are mainly used in load-bearing structures;
– lightweight concrete, with a density of 500-1800 kg / m3. In turn, these concretes are subdivided into:
– 1 lightweight concrete on porous natural and artificial aggregates;
– 2 cellular concrete (aerated concrete and foam concrete), which include an astringent base, water, a finely dispersed silica component and a converter;
– 3 coarse or sandless concrete, based on dense or porous coarse aggregate without the use of fine aggregate;
– especially lightweight concrete, density no more than 500 kg / m3. They are generally cellular and based on porous aggregates. Usually used for thermal insulation.
AND. Cement. Cement grade depends on the design grade of concrete for compressive strength.
The cement grade is determined as follows:
Concrete grade M150 – Cement grade MZOO
Concrete grade M200 – Cement grade MZOO M400
Concrete grade M250 – Cement grade M400
Concrete grade MZOO – Cement grade M400 M500
Concrete grade M350 – Cement grade M400 M500
Concrete grade M400 – Cement grade M500 M600
Concrete grade M450 – Cement grade M550 M600
Concrete grade M500 – Cement grade M600
Concrete grade M600 and higher – Cement grade M600
In the event that the marking of the cement is higher than the recommended one for a particular type of concrete, the highly active cement must be diluted with a finely ground active ingredient. This will avoid waste of high-quality cement..
B. Small filler. Sand is suitable as a fine aggregate. But at the same time, it is necessary to take into account the fact that small particles, such as dust, clay, silt, increase the water demand of the concrete mixture and the further consumption of cement. Thus, before adding sand, it must be cleaned of impurities by washing..
IN. Large filler. As a large aggregate for concrete, gravel, crushed stone, the grain size of which is 5-70 mm, is used. If concrete is intended for rather massive structures, the size of crushed stone grains can reach 150 mm.
Any aggregate, large or small, should be checked for the presence of radionuclides.
D. Water. The water that is used for mixing the concrete mixture and pouring the concrete must be free from harmful impurities that can reduce the setting and hardening of the binder. For these purposes, it is best to use tap drinking water or water from natural reservoirs. The pH value of water should be at least 4. The water should contain mineral salts in the composition of no more than 5000 mg / l (sulfates no more than 2700 mg / l). Use of marsh, domestic waste and industrial water should be avoided, or thoroughly purified.
In order to prepare a concrete mixture at home, the following materials and their proportions are recommended: cement – 1 part, sand – 2 parts, crushed stone – 2 parts, water – 0.7 parts.
It must be borne in mind that in order to avoid further stratification, the concrete mixture should not be too mobile..
One of the drawbacks of concrete, like any other stone material, is its low tensile strength. It is about 10-15 times lower than the compressive strength of concrete. In reinforced concrete, there is no such disadvantage, since the tensile stress falls mainly on the reinforcement. The proximity of the coefficients of thermal expansion and strong adhesion ensure the joint operation of concrete and steel reinforcement in a reinforced concrete structure as a whole.
That is why concrete and reinforced concrete structures are widely used in modern construction..
They are usually used for the construction of prefabricated strip foundations. Figures 2 and 3 show the dimensions of the wall blocks and foundation pads..
In order to reduce concrete consumption and minimize the weight of the entire structure as much as possible, the blocks used in the construction of basement walls are made hollow with narrow through voids. The width of such voids should be no more than 40 mm. Or hollow slabs can have wide, closed voids..
Blocks with voids cannot be used in soils that are oversaturated with moisture, since voids can accumulate water, which, when frozen, can destroy the walls of concrete blocks.