In this article:

Concrete - main material construction, prepared using a certain technology. Additional ingredients in its composition help improve structural and technical parameters concrete.

This building material is usually classified according to 6 main characteristics: purpose, type of binder, medium density, strength, frost resistance and water resistance.

1. As intended

The production of various types of concrete mixtures depends on the conditions where future reinforced concrete structures will be used. The conditions can be very specific: fire resistance, sulfate resistance, resistance to stress, shock, vibration.

According to their intended purpose, the following types of mixtures are distinguished:

ordinary concrete used to create beams, columns, foundations, floors;
certain types are used for road, airfield pavements and sidewalks;
Hydraulic concrete is used for lining dams, locks, canals, and water supply structures;
concrete is isolated for special purposes, for example, heat-resistant or acid-resistant, as well as for radiation protection.

2. By type of binder

The most important factor that determines the properties of a concrete mixture is the type of binder.

The main types of concrete in this category:

Gypsum concrete

Based on gypsum it is obtained gypsum concrete, which is used in finishing elements, for the manufacture of suspended ceilings and internal partitions. Wide Application gypsum-cement-pozzolanic mixtures with high water resistance have been obtained; they are used to create bathroom blocks and various structures of low-rise buildings.

Cement concrete mortar

Based on cement components they produce cement concretes and mortars. The most common raw material component is Portland cement and its varieties. Also widely used concrete mixtures on Portland slag cement and pozzolanic cement. The use of this type is construction.

This category includes decorative concrete, which is produced on the basis of colored, white cements. The idea of creating a decorative building material came to us from Germany. Regarding color range concrete, it includes green, black, brown, blue, yellow, red and white shades. White concrete is considered especially expensive. There are also concrete mixtures based on non-shrinking, tensile and aluminous cement.

Slag-alkali concrete

Recently they began to use in construction slag-alkaline concrete. It is produced from slags mixed with alkali solutions. This type of concrete is indispensable when creating massive objects.

This is explained by the fact that when creating large structures A large amount of heat is released from the Portland cement mixture, and the temperature of building elements can reach 80°. If such an object cools very quickly, cracks may appear. The use of slag-alkaline concrete avoids this problem.

Polymer cement concrete

With a mixed binder base one gets polymer cement concrete. In this case, the base contains latexes, water-soluble resins and cement. When this mixture cools, a film appears on its surface, swelling in the presence of a large amount of moisture.

There are two types - framed and filled.

Application.

The material is actively used for landscape design, outdoor and interior decoration walls, building facades and when installing floors. Polymer-cement concrete is convenient to use, it is easy to apply both mechanized and manual.

Acid-resistant and heat-resistant concrete

Special binders will be needed to obtain special concrete. To obtain acid-resistant and heat-resistant concrete, use liquid glass, slag, glass-alkaline elements as binders.

Silicate concrete

A very rare type of concrete, practically unused in modern production – silicate concretes. Their production is based on the use of lime, where there is an autoclave hardening method.

Dense autoclaved silicate concrete is used to create load-bearing panels for internal walls and large blocks, as well as floor panels. Especially durable building materials are used to create railway sleepers and slate, which do not contain asbestos. Also, silicate concrete can be used for constructing road bases and in tubes for mine construction. There are also combined types concrete, made on the basis of a combination of 2-3 binder components. Such compounds can often be found in the composition of plaster mixtures, where lime, gypsum, cement and other elements are combined in a single composition.

3. By average density

The main factor influencing the water resistance, frost resistance, and resistance of a concrete structure to compression is density. The significance of density is determined by large aggregates: dolomite, expanded clay, diabase, gravel, granite, limestone. Following compliance with GOST, concrete grades are distinguished within the range M50-M800.

Based on density parameters, the following types of concrete can be distinguished:

Light or lightweight, which are produced on porous aggregates: tuff, expanded clay, pumice. Its density is 500-1800 kg/m3. The corresponding marking according to GOST is M50-M450. This type includes varieties of lightweight concrete - cellular concrete (aerated concrete and foam concrete), produced by swelling of a binder and water. This category includes large-porous concrete with lightweight aggregate. Their brands are M50-M150.
Heavy concrete produced from rock fillers: limestone, granite, diabase. Its density is 1800 - 2500 kg/m3. Compliance of this brand with GOST M50-M800. Heavy concrete was used in the construction of industrial and civil buildings as reinforced concrete and concrete structures, as well as in the construction of hydraulic projects, canals and transport structures.
Particularly heavy concrete with a density of over 2500 kg/m 3 is created from steel filings, shavings, and iron ore. It is used for special structures designed to withstand radioactive substances.

Each brand of concrete determines its strength class. For the construction of the least critical structures, grades with lowest value— M50, M75, M100. For example, this least durable concrete is suitable for building a blind area. To screed floors or railway floors, you will need concrete of higher strength, for example grade M200.

M550 concrete is considered the most durable.

The different strengths of all types of concrete depend on the proportions of sand, cement and crushed stone in its composition. High strength is achieved by the impressive presence of cement.

4. Frost resistance and water resistance of concrete

There are also grades of concrete according to frost resistance, which in GOST are marked with the letter F. Frost resistance is characterized by the largest number freezing and thawing with a decrease in mass and strength by a certain amount. The densest concrete mixtures are always the most frost-resistant. In this category there are concrete grades from F25 to F1000.

The ability of concrete not to allow water to pass through under pressure is called waterproof.

Concrete grades according to this classification are W2, W4, W6, W8, W12. Several years ago, the Russian letter V was used to denote this parameter.

Types of concrete and their classification

Concrete is an artificial stone material obtained as a result of hardening of the mixture binder material, water, fillers and special additives (in a certain proportion), thoroughly mixed and compacted.

Before hardening, this mixture is called concrete mixture .

One of the main properties of concrete is high resistance to compressive loads and low tensile loads: Rcom is 10 - 12 times higher than Rsol.

To increase tensile strength, reinforcement is placed in concrete structures, which mainly absorbs tensile forces. Reinforced concrete called reinforced concrete – it resists both compression and tension well.

Widely used in construction practice prestressed concrete . Essence prestress consists in the fact that the concrete zone subject to tension is compressed by tensioned reinforcement. As a result, tensile forces are absorbed by the reinforcement, reducing the compressive stress in the concrete. This technique ensures high crack resistance of concrete. Prestressed reinforced concrete structures are more economical than conventional reinforced concrete structures, since as a result of the effective use of high-strength materials (steel and concrete), the consumption of reinforcing steel is reduced.

Concrete is classified according to a number of characteristics.

A.) By average density concretes are divided into:

Particularly heavy over 2500 kg/m 3 ;

Heavy 1800 – 2500 kg/m 3 ;

Lightweight 500 – 1800 kg/m 3 ;

Particularly light less than 500 kg/m 3 .

For cooking especially heavy heavy aggregates from stone ore-containing rocks (magnetite, hematite) are used for concrete; in the form of steel filings or shavings, cast iron shot, scale, etc. Such concretes are used for radiation protection during the construction of nuclear power plants, and as cement concrete for filling excavations.

Heavy concrete has received the greatest application in construction practice for the construction of underground and above-ground load-bearing structures and structures (foundations, walls, columns, beams, trusses, covering and floor slabs, etc.). Crushed stone of dense rocks (granite, limestone, diabase, etc.) is used as a coarse aggregate for such concrete.

To the group lungs includes concrete with porous aggregates of natural or artificial origin, as well as cellular concrete (without aggregates) with a significant number of artificially created closed pores in the concrete body. This also includes concrete on porous aggregates in combination with porous cement stone. Used as a heat-insulating and structural material.

Extra light (thermal insulating) – these are predominantly cellular concretes with high degree porosity (sandless) and on light porous aggregates. Such concretes have low thermal conductivity and are used as an effective thermal insulation material.

B.) By structure Concrete comes with a dense, porous, cellular and large-porous structure.

Dense structure – when the ratio of components is selected so that there is no free space left in the concrete body (absolute volume method). Concrete consists of coarse and fine aggregate (or only fine) and dense cement stone(or other hardened binder) between aggregate particles.

Porous – when the space between the grains of inert components (large and small or one of them) is filled with a binder that has hardened in a porous state.

Cellular – without fillers, with a significant number of artificially created pores in the concrete body in the form of closed cells filled with air.

High-porous concrete – with only coarse aggregate, without sand at all (sandless) or with a very small content of it.

B.) By type of binder There are different types of concrete: cement, silicate, gypsum, slag-alkaline, polymer concrete, polymer cement and special concrete.

Cement – concretes based on clinker cements, mainly Portland cement and its varieties, Portland slag cement and pozzolanic cement.

Silicate Concrete is made using lime binder. To ensure the hardening process of such concrete, autoclaves are used, where the concrete is subjected to heat treatment under pressure.

Plaster Concrete has low water resistance, so structures inside the building are made from it ( suspended ceilings, partitions).

Slag-alkali Concrete (binder - ground slag and alkaline solutions) have high strength and resistance to aggressive environments.

Polymer concrete (binder - epoxy, polyester, furan and other resins) highly resistant to aggressive environments, used in the construction of structures for the copper smelting and chemical industries, enterprises for processing agricultural products (sugar factories and breweries), acid storage tanks, mineral waters etc.

Polymer-cement concretes are made with the addition of aqueous dispersions of various polymers, which are introduced into the mixture along with mixing water. Polymers are deposited as a film on the surface of the aggregate, increasing the adhesion between the elements of the concrete structure. Such concretes have good tensile strength, increased frost resistance, water resistance and chemical resistance.

D.) By area of application and for appropriate purposes technical specifications The following types of concrete differ.

Structural – general purpose, used in structures that perceive external force influences (loads). The defining properties of such concrete are strength and deformation characteristics, as well as frost resistance when structures operate under conditions of alternating temperatures. These are foundations, columns, beam structures, covering and floor slabs, etc.

Structural and thermal insulation – used in enclosing structures (external walls, coverings). Such concretes should provide not only bearing capacity structures, but also their heat-shielding properties.

Thermal insulation – their purpose is to provide the necessary thermal resistance of enclosing structures with a relatively small layer thickness, while the load-bearing capacity of structures is provided by ordinary concrete (in two- and three-layer structures).

Hydraulic , which, along with the necessary strength and deformation characteristics, must have increased density, water resistance, frost resistance, and resistance to aggressive influences environment– water.

Road – for top surfaces of roads, airfield runways. They must have increased strength, high wear resistance, and have good resistance to alternating effects of temperature and moisture.

Chemical resistant – salt-, acid- and alkali-resistant. Along with the necessary indicators technical properties must be able to withstand for a long period without destruction or decline performance qualities exposure to concentrated solutions of salts, acids and alkalis and their vapors. Such concretes are used as the main material of structures, or for protective coatings structures made of ordinary concrete.

Heat resistant – maintaining their physical and mechanical properties within specified limits during prolonged exposure high temperatures. Applicable for industrial units And building structures subjected to heating to high temperatures during operation.

Decorative – for finishing layers with textured processing on front surfaces construction products. Such concretes (mortars) must meet the requirements regarding color, texture, and have sufficiently high weather resistance.

The types of concrete discussed above, despite significant differences in certain properties and their indicators, are subject to general laws that arise from the common principles of the formation of their structure and structure.

This material is an artificial stone, the production technology of which depends on the properties that need to be imparted. final product. The composition of the mixture for preparing concrete includes such basic components as binder (most often cement, sometimes other substances) and filler. As a rule, water is added, but in rare cases it can be done without it. In order to give concrete certain pronounced qualities, appropriate substances called additives are introduced into the mixture.

Already from this it becomes clear that by changing the proportional ratio of the components, selecting certain ingredients for preparing the solution, you can regulate various characteristics concrete. Therefore, such a variety of products should be classified to make selection easier optimal option for use in specific conditions. Mistakes here are unacceptable; a reinforced concrete truss requires a completely different class than, for example, the foundation of a bathhouse, otherwise the structure will be unreliable.

The fundamental document defining the classification of concrete is State Standard No. 25,192 of 1982. According to him, they all differ:

by structure;
by filler;
by astringent;
according to hardening conditions.

On the Internet you can find some other criteria by which artificial stone is distinguished. So that a person who does not have special knowledge in the field of building materials can better understand the variety of characteristics of concrete, we present a generalized (more complete) classification of them.

Concrete by structure

Dense.
Large porous.
Porized.
Cellular.

By astringent

Cement.
Lime (silicate concrete).
Gypsum.
Slags.
Mixed compositions (cement + lime, slag + lime, cement + polymer and a number of others).
Special. There are inorganic and organic binders, which are used to adjust the characteristics of concrete in order to give the product special qualities.

By density

Extra light

Their density does not exceed 500 kg/m3, and such products are used mainly for additional insulation structures and for sealing seams, joints, sealing large cracks. They are produced by the “expanding” method (gas, slag, foam concrete).

Lungs

They are mainly used in the construction of elements that are not subject to heavy loads, since their density is from 500 to 1,800 kg/m3. “Light” fractions (expanded clay, tuff, pumice, agloporite and others) are used as filler.

Lightweight

1,800 – 2,200 kg/m3. Thanks to this characteristic, concrete is more versatile and can be used in the construction of load-bearing parts. Their filler is crushed stone of various fractions.

Heavy

The most commonly used types, as they are suitable for the installation of load-bearing elements (from 2,200 to 2,500 kg/m3). They include fractions of rocks (diabase, limestone, granite).

Particularly heavy

Their density (more than 2,500 kg/m3) determines the specific application. They are practically not used in the private sector, since various special-purpose structures are erected from them (underground storage facilities, bunkers, dams, etc.). Fractions of “heavy” materials (for example, cast iron shot, metal shavings, iron ore, barite) are used as filler.

By filler type

Special, giving special properties artificial stone(heat resistance, resistance to radiation or low temperatures and a number of others).
Porous (for example, lightweight concrete).
Dense (heavy concrete).

By granule size

Fine-grained (less used).
Coarse grain (more common).

According to manufacturing technology

Processed in autoclaves. They are considered the highest quality products, since the required characteristics of concrete are achieved by maintaining specified pressure and temperature throughout the entire hardening process (cellular concrete and some others).
Natural hardening.

The same, but with the use of artificial heating.

By purpose

Special

These include materials that provide thermal insulation, resistance to critical temperatures, radiation exposure, and so on.

Structural

They are used to produce various reinforced concrete products and construct loaded parts of structures (for example, various floors, supports, foundations).

Hydraulic

They are used for the construction of dams, artificial reservoirs, underground reservoirs and a number of other objects.

What to look for when choosing a concrete class

1. Curing time. As the grade of concrete increases, it decreases. This should be taken into account if the product is not prepared at the pouring production site, but is delivered to the site by transport. In addition, it is determined by the conditions of use, because you will have to organize its installation. How will this be done - manually or using mechanisms and devices (gutter, concrete pump).

It is also important at what weather conditions work is underway. It is often necessary to organize insulation of the poured solution in order to achieve its reliable “setting”.

2.Fraction sizes. It is clear that the larger they are, the more difficult it will be to mix the solution and compact the mass loaded into the form (formwork). You may have to organize vibration compaction, and this is not always convenient or possible. In addition, there is the concept of “fluidity” of a solution. This must be taken into account if the formwork has a complex configuration, since you may have to spend time and effort “pulling” the concrete throughout the entire volume.

3. Availability of additives, how do they affect the characteristics of concrete? For foundations, such indicators as frost resistance and water repellency are especially important.

4. Strength of concrete. It largely depends on the brand of binder used to prepare the mixture.

What types of concrete are there? General information and classification of concrete

The classification of concrete can be based not only on the type of main components of the solution and characteristics, but also take into account the scope of its use. For those who are not too well versed in chemistry building mixtures, this is the most convenient way decide on the material that is suitable for a particular type of work. Only after this should you move on to searching for a brand with the required technical parameters.

The main division of concrete provides for only two types: general construction and special. Lungs go in a separate line porous materials, whose scope of application directly depends on density indicators. At the same time, the same grades of concrete can often be found in several groups at once according to their intended purpose, so this feature should always be taken into account and when choosing, focus not only on strength.

General construction concrete

The largest group of building materials, which includes all types of mixtures and finished products, widely used in different areas civil engineering, as well as for the production of reinforced concrete products. Foundations are cast from them, walls are erected, beams, ceilings and columns are formed. When choosing compositions for specific conditions, it is necessary to pay attention to brands that characterize concrete in terms of density, strength, as well as frost resistance and water resistance after hardening.

The strength of the monolith is indicated by the numbers after the letters “M” or “B”. In the first case, the data are given in units of kgf/cm2. And although such a classification is considered insufficiently accurate and outdated, it is still actively used. In the second option, the values are indicated in MPa, and these are no longer average figures with the error allowed by GOST, but guaranteed strength. From these simple records it is easy to determine the characteristics of mixtures without any tables or reference books.

Different types of concrete grades find their application in construction:

M100 - most often used for concrete footings. IN preparatory work We need inexpensive liquid solutions with low strength and density. All that is required of such mixtures is to bind together the grains of the sand and gravel cushion, preventing them from spreading under load.
M150 - this composition is stronger, so it is in demand in the manufacture of sidewalks, blind areas, cement screed and small-sized reinforced concrete products.
M200 - a type of concrete popular among private owners, has sufficient strength to be selected for small foundations and walls in low-rise construction.
M250 - in demand in manufacturing flights of stairs, as well as most supporting and load-bearing structures.
M300 is the most widely used concrete in construction for this brand. It can be used in almost any work: from foundation construction to casting monolithic walls and floors.
M350 – enough durable concrete to make structures from it that can withstand increased loads (columns, beams).

The use of other brands from M400 and above is already in the professional field, since their characteristics are more suitable for various designs special purpose: from pool bowls and tunnels to bridges and dams.

In addition to strength, the classification of general construction concrete takes into account its other properties. For example, frost resistance not only determines the scope of use of the monolith, but also its durability:

F15 – suitable for interior works(pouring floor screed, erecting partitions).
F25 - minimum indicator for construction external walls heated buildings.
F50 and higher - such concrete is just right for the foundation, since seasonal freezing and thawing of the soil will inevitably have a thermal effect on it. Moreover, in northern regions this figure should be even higher.

The water resistance class is of particular importance when choosing building materials for installations, swimming pool bowls or fonts, as well as drinking and septic wells. It is designated by marks from W2 to W20 and indicates the pressure of the water column that concrete can withstand (units of measurement - atm·10 -1).

There is also a division of monoliths by density (letter D). The strength of concrete, and therefore the possibilities of its use, partly depends on it. Heavy varieties from D2000-D2500 kg/m3 are used for the construction of critical structures, lightweight ones - for general construction work. Light products up to D1200 kg/m3 go mainly as thermal insulation materials, since they have a low load-bearing capacity, barely reaching the brand strength M50-M75.

Special

Here, the varieties of concrete are as numerous as the scope of its application. building material. Let's look at the most common of them:

Heat-resistant concrete.

It is made from finely ground components with a high content of active silica or alumina. Works great under severe temperature changes and prolonged heating up to +700-1700 °C (depending on your own fire-resistant properties mineral fillers). It is used in the construction of thermal power plants and metallurgical shops, as well as industrial furnaces. It has good strength properties and is graded at least M250, but is susceptible to acid corrosion.

Hydraulic.

Frost-resistant (up to F300) type of concrete with minimal water permeability. Used in the production of sewerage and drainage systems, dams and some underground structures. Traditionally divided into additional subgroups: underwater and above-water, as well as variable-level concrete. They all work in different conditions environment, and therefore differ in composition and characteristics.

Road.

This group of concretes includes high-strength, weather-resistant mixtures. They are used as road surfaces, for the development of industrial sites with intensive use, as well as for the construction of runways (runways).

Acid-resistant type of concrete.

It also has low water absorption due to the addition of liquid glass to the solution. Withstands heating up to +1000 °C and is resistant to most aggressive media, except alkalis. Found widespread use in finishing objects chemical industry. However, it is almost never used as an independent building material due to its relatively low mechanical strength, not exceeding B12.5-15.

Anti-radiation.

Has very high tensile and compression resistance. It is made on the basis of PC or ShPC with heavy fillers - usually metal-containing. The fine components here are barite ores, shot from cast iron or lead. All this can increase the density grade to D6000.

Lightweight concrete

There is another classification principle, which is more often applied to light and especially light varieties of cellular concrete. Here everything is tied to their density (or rather, porosity). It characterizes the thermal insulation properties of artificial stone and allows you to automatically divide such concrete into groups according to its intended purpose:

D600 kg/m3 and above are structural mixtures and ready-made building blocks. They have sufficient strength indicators that they can be used to create a not too massive box of a house with 2-3 floors. But their ability to maintain temperature inside is more likely to be a pleasant bonus to the main characteristics and does not allow one to completely abandon insulation.
D400-D600 are so-called structural and thermal insulation materials that combine very average strength and more decent energy efficiency. Any type of concrete with these density values is suitable for construction internal partitions, but should be used with caution when constructing even lightly loaded enclosing walls.
Up to D300-D400, thermal insulation compounds and products with high porosity can only be used in self-supporting and non-load-bearing structures. Their main purpose is to reduce energy loss through the main walls. They are produced in the form of large and lightweight blocks, which are suitable for insulating multi-layer masonry.

Various tables with technical characteristics of concrete do not give a complete picture of the possibilities of their use in construction. Therefore, before choosing such materials, it is necessary to study their description operational properties and scope of application.

Currently, concrete is the most important building material, produced depending on the conditions of use using a specific technology. Additional ingredients included in concrete improve its technical and structural parameters.

● Classification of concrete is carried out according to six main characteristics:

1. Purpose.
2. View binder.
3. Density.
4. Durability.
5. Frost resistance.
6. Waterproof.

● The characteristics of the concrete mixture directly depend on the places and conditions where it will be used both by itself and as part of reinforced concrete structures. The places and operating conditions of concrete can be quite unusual, and from this arise the specific properties of concrete mixtures: resistance to vibration and loads, fire resistance, impact resistance, sulfate resistance.

● The type of binder is the main factor determining the properties of the concrete mixture.

● Cement concrete And cement mortar- based on cement components. The most common components here are all types of Portland cement, Portland slag cement, and pozzolanic cement. Concrete made on the basis of non-shrinking, tensile and aluminous cement is also used. Here you can also highlight decorative concrete, made on the basis of white and colored cements. The color palette of concrete mixtures includes blue, red, yellow, black, brown, green and white (the most expensive) colors.

● Slag-alkali concrete began to be used relatively recently. This type of concrete is created on the basis of slag mixed with alkali solutions. Places of use: construction of large objects. During the construction of massive structures using a concrete mixture based on Portland cement, the release of large quantity thermal energy, which contributes to heating building elements up to 80 º C. But with rapid cooling in a concrete structure, there is a high probability of cracks appearing. The use of slag-alkaline concrete helps to avoid this negative.

● Acid-resistant and heat-resistant concrete contains as binders liquid glass, glass-alkaline and slag elements. Used in the construction of special construction projects.
GOST 25881-83 Chemically resistant concrete. Test methods.

● Polymer cement concrete is produced as a result of the use of a mixed binder base that contains latexes, water-soluble resins and cement. When the concrete mixture cools, a film appears on the surface, which tends to swell in the presence of a significant amount of moisture. Polymer cement concrete is used to create landscape design, for internal and external finishing works, as well as when installing floors. This type of concrete can be worked either manually or mechanically. There are framed and filled polymer-cement concrete.

● Combined types of concrete include a base of several binding elements. Scope of application - in the composition plaster mixtures, which contain gypsum, cement, lime and other components.

● Gypsum concrete , made on the basis of gypsum, is used for the manufacture of suspended ceilings, internal partitions and finishing elements. In the construction of bathrooms, gypsum-cement-pozzolanic mixtures are used, which are highly water-resistant.

● Silicate concrete currently used extremely rarely. The production of silicate concrete involves the use of lime and the autoclave curing method. This type of concrete can be used in floor panels, in load-bearing panels of large blocks and internal walls, in tubes for mine construction, and in the construction of road foundations. Particularly durable types of silicate concrete are used in railway sleepers, as well as in the production of asbestos-free slate. GOST 25214-82 Dense silicate concrete. Technical conditions.
● Characteristics such as compression resistance, frost resistance and water resistance directly depend on the density of concrete. The density is affected by large aggregates of the concrete mixture - expanded clay, gravel, diabase, dolomite, limestone, granite. Concrete grades by density from M50 to M800.

● Depending on the density, the following types of concrete are distinguished:

1. Light or lightweight concrete. This type of concrete is produced using porous aggregates - expanded clay, pumice, tuff. In accordance with GOST, markings range from M50 to M450. Lightweight concrete includes cellular concrete, large-porous concrete with lightweight aggregate, foam concrete, aerated concrete, and materials that are produced by swelling of the binder.

2. Heavy concrete is produced by using rocks- granite, diabase, limestone. The density of heavy concrete is 1800-2500 kg/m³. According to GOST, the marking of heavy concrete varies from M50 to M800. Scope of application: concrete and iron concrete structures in civil and industrial buildings and structures, including hydraulic and transport facilities.

3. Particularly heavy concrete is obtained by using iron ore, shavings, and sawdust. It is used in the construction of special facilities with the ability to withstand radioactive contamination. The density of such concrete is above 2500 kg/m³.

● The strength of concrete is determined by its grade. Differences in the strength of concrete grades depend on the proportions of cement, sand and crushed stone in its composition. The high strength of concrete is obtained by the significant presence of cement. The strength of concrete indicates its mechanical properties and resistance to loads. This resistance limit indicator is measured in kgf/cm².

● Concrete grades M15-M50 are used for the construction of enclosing and thermal insulation structures. For construction simple designs(for example, for the blind area of the foundation) concrete with low grades is used: M50-M100. When constructing monolithic foundations, M100-M150 concrete is used. For reinforced concrete panels and blocks that do not experience serious loads, concrete M200-M250 is used, and for pre-stressed structures it is used concrete mortar with a brand no lower than M300. Concrete M200 is used for the construction of railway floors and in the process of screeding floors. Concrete grade M550 is considered the most durable.

● According to another classification, concrete is divided into compressive strength classes from B1 to B22. Both systems are designed to take into account the same thing. But there is one difference: concrete classes (B) indicate a guaranteed value, and concrete grade (M) indicates an average value for compressive strength. A guaranteed density value means that the concrete has a strength no less than the declared one. Although the classification of concrete by grade (M) is more common, when developing project documentation the guaranteed strength value (B) is indicated.

● The grade of concrete for frost resistance is designated by the letter F followed by a number indicating the number of freezing and thawing cycles that this type of concrete has withstood without destroying its characteristics. The moisture in the pores of concrete in a frozen state turns into ice and increases in volume. The expansion of frozen moisture leads to an increase in the internal stress of the concrete - i.e., to the destruction of structural integrity. Frost resistance is directly affected by the level of capillary porosity - the larger the pore volume in the concrete structure, the lower its frost resistance.

● Depending on the differences in construction projects in different climatic conditions, the requirements for frost resistance of concrete also vary: from F 25 to F 1000. Frost resistance is also affected by the density of the concrete mixture.

● Increased frost resistance is achieved by reducing porosity, using aluminous cements and special hydrophobic air-entraining additives, which form reserve pores that are not filled with moisture under normal conditions, but only at low temperatures.

● GOST 10060.1-95 Concrete. Basic method for determining frost resistance.
● GOST 25192-82 Concrete. Classification and general technical requirements.

● The water resistance of concrete is its ability to resist water under pressure. Moisture, as well as acidic components contained in water, have negative influence on concrete structures due to the fact that water has the property of washing away easily soluble components from almost any material. One of the components of the concrete mixture is slaked lime- calcium oxide hydrate. Washing out this component leads to the destruction of the structure of both foundations and concrete blocks.

● Water resistance is indicated by the letter W: from W2 to W20, although previously the Cyrillic letter B was used for this. Concrete grades are characterized by one-sided hydrostatic pressure in kgf/cm².

● To increase the water resistance of concrete, pozzolanic or sulfate-resistant Portland cement is used, the use of special film-forming coatings, and the addition of hydrophobic additives to the concrete solution.