Construction today is very difficult to imagine without the use of concrete. He is fake diamond, which is used in the construction of buildings and structures, fences, as well as different designs and elements. Concrete is quite widely used for the manufacture of utility blocks, blind areas and pedestrian paths.

This material is universal and has a wide range of uses. You can make it yourself or order a ready-made mixture made in a factory. Mixing of components is carried out in metal or wooden boxes, mobile concrete mixers or bathtubs. Using concrete mixers construction site you can ensure the greatest productivity, high-quality mixing of ingredients and reduced operating time. It is important to prevent foreign impurities from entering the mixture. Experts recommend following technology and taking into account proportions.

Concrete - what is it

Concrete is an artificial building stone that is obtained by molding and hardening the mixture. Its ingredients must be rationally selected and well-compacted. The main ingredients are a binder, which can be cement. The process also uses fine and coarse aggregates as well as water. The composition may also contain additional additives, and some mixtures do not include the presence of water at all, in in this case We are talking about asphalt concrete.

Application of concrete

Where is it used? Concrete is a material that can be classified into several varieties. Each of them has its own area of ​​use. For example, especially heavy concrete is used in nuclear power plants. Its weight is 2500 kg/m3. If we are talking about heavy concrete, then it is used for the manufacture of foundations, as well as for construction work, where reinforced concrete structures are made. Heavy concrete has a weight ranging from 1800 to 2500 kg/m3.

Lightweight concrete is used to make panels, floors and wall blocks. Its weight is equal to the limit from 500 to 1800 kg/m 3. Particularly lightweight concrete is used for thermal insulation of building facades and structures. The weight of this material does not exceed 500 kg/m3. Among other things, today the use of concrete, which contains special admixtures, is common. The latter are designed to improve or change characteristics, among which we should especially highlight:

• density;
• strength;
• thermal conductivity.

If we consider such materials in more detail, we can highlight heat-resistant concrete, which during operation can undergo heating up to 1000°C. But road concrete has high stability and bending strength. The hydraulic mixture has high corrosion resistance, increased density and water resistance.

Concrete composition: main components

Concrete is a material that requires the presence of main components, among them sand, crushed stone, cement and water. As for sand, it can have a fraction ranging from 1.2 to 3.5 mm. Sand that is too fine cannot be used. When choosing this component, you should pay attention to cleanliness. If the material contains clay or silt, then they should be in a volume of no more than 5%. Otherwise, the concrete will be less durable, because it will be greasy due to clay. As a result, the material will simply crumble.

Before use, the quality of sand must be checked. To do this, pour it into a container with running water and shake it. If the water is cloudy, then there is no need to talk about the high quality of the sand. Concrete is a material made from gravel or crushed stone. This can be expanded clay, scrap brick and granite screenings. The particles in this case should have sizes ranging from 1 to 8 cm. If you plan to make the solution yourself, then this parameter should not exceed 2 cm.

It is important to make sure that the crushed stone is free of debris and clay impurities. If you use a larger fraction, this will cause a loss of strength, as well as inconvenience of the work being carried out. Cement is one of the main components. Its consumption depends on the brand. The amount of cement is determined by proportions. On sale you can find:

• Portland cement;
• Portland slag cement;
• pozzolanic cement.

The first type is used for all types of construction and for pouring foundations. For self-preparation of the solution, this variety is optimal. Portland slag cement has reduced frost resistance; in addition, it is moisture resistant. But pozzolanic cement is used in the construction of underwater and underground structures, because it has high moisture resistance. Concrete production is impossible without the use of water. It should not contain oils, impurities, enamels, paints and petroleum products. Absolute purity, however, is difficult to guarantee.

Concrete proportions

If you decide to make concrete on a construction site yourself, then you need to become more familiar with the proportions. They depend on the brand of concrete and cement used. If the latter is grade M400, then to obtain M100 concrete you need to add 7 kg of crushed stone and 4.6 kg of sand. Cement is added in an amount of 1 kg.

To obtain concrete grade M200, mix 4.8 parts of crushed stone and 2.8 parts of sand. Cement is added in the same volume. In order to obtain concrete grade M300, you should combine 1.9 kg of sand and 3.7 kg of crushed stone. Cement is added in a constant volume. As for preparing M450 concrete. But sand and crushed stone in this case should be added in the following ratios: 1.1: 2.5.

Preparation of concrete

If you decide to make concrete yourself, then you need to pour a pile of sand and gravel onto a clean floor or into a special tank. It is important to maintain the required proportions; at the next stage, cement is poured. The mixture is mixed, and a crater-shaped depression is made in the upper part of the slide. Water is poured there.

To obtain a homogeneous solution, the dry mixture must be poured from the edges. When making construction concrete using a concrete mixer, you first need to pour 10 liters of water into the tank, and then add gravel and sand. The composition is mixed for several minutes, and then another 2 liters of water and cement are added. The liquid is added in the required quantity until the required concrete consistency is obtained.

Factory production

Construction concrete is produced in mobile mini-plants, which are equipped with automatic equipment. This allows you to produce a finished product High Quality. A stationary plant for the production of a mixture can produce up to 60 m 3 per hour. The process of producing concrete looks the same as when making it yourself.

At the first stage, the volumes of the components are determined, which are then mixed until homogeneous mass. Water is added to the mixture to obtain the consistency of thick sour cream. This composition is used for civil, multi-storey and private construction. Its strength characteristics are determined by the design, as is its composition.

Additives for concrete

Additives to concrete can improve the quality of the solution without significant material costs. Such components are divided into several groups, including:

• additives for frost resistance;
• strength gain accelerators;
• self-compacting additives;
• superplasticizers;
• mobility supplements;
• modifiers;
• complex supplements.

As for superplasticizers, they are necessary to increase the mobility of the mixture and increase the strength of the material. Superplasticizers give the material density and water resistance. This reduces the consumption of expensive cement to ensure strength.

When studying concrete additives, you should pay attention Special attention for strength gain accelerators. They allow you to increase the speed of strength characteristics. This happens within the first three days. Quite often during the production process of the solution, additives are used to maintain mobility. They are in demand during long-term transportation and in the hot season.

At low temperatures additives are used for frost resistance. But modifiers improve performance characteristics. This makes it possible to obtain high-strength concrete based on cement and aggregates. Concrete production may involve the use of self-compacting admixtures. This simplifies the concreting of thin-walled and reinforced structures.

On concrete mixture appropriate additives have a complex effect. They are convenient in that they relieve the manufacturer from the need to purchase components to ensure required properties. The use of such ingredients eliminates the interaction of some chemical elements, which can lead to negative consequences.

Types of pigments and their properties

Pigments are usually dry powders based on iron oxide or copper phthalocyanine. The latter base is slightly better in quality; it is able to provide maximum brightness and durability of the shade. Concrete pigments operate on the same principle: the process involves the absorption and reflection of certain light waves.

Pigments are characterized by corrosion, temperature, light and chemical resistance. For example, there are pigments that are most vulnerable to heat, among them: blue, green, iron oxide yellow. In this case, losses from light occur at 700°C. Standard dyes are environmentally friendly, which is why they are used for finishing residential premises. In industrial conditions, the following concrete pigments are used in the production of concrete mixtures:

• carbon black;
• titanium dioxide;
• umber;
• chromium oxide.

These ingredients are selected and dosed not according to the volume of the mass, but according to the amount of cement. Using the selected composition, you must check its effect on reference samples. This will avoid unpleasant surprises, because many powders are simply not capable of coloring large fractions of aggregates like crushed stone. In addition to the above-mentioned pigments, acid dyes are known today, which are used by etching hardened concrete. Sometimes such compositions are used for structures that have been in use for a long time.

Concrete grade M200: state standards and some features

This material can be of light or heavy varieties, depending on the aggregate. Proportions are regulated technical documentation and remain unchanged. The composition of M200 concrete includes:

• cement;
• aggregate;
• sand;
• additives.

The filler can be crushed stone or gravel, but additives are used to increase wear resistance, strength and setting speed. In general, the material has water resistance class W2, while mobility is class P2. This mixture corresponds to frost resistance level F50.

This solution is used in monolithic and frame construction. It is common when it is necessary to install floors, form concrete bases and lay screeds. Concrete M200 has proven itself to be excellent in the construction of strip foundations. The solution is used for the production of prefabricated elements such as flights of stairs and paving slabs.

If concrete is manufactured according to state standards 7473-94, then it complies regulatory requirements. The proportions of this mixture are as follows: 1 unit of M500 cement, 4.8 units of crushed stone and 3.2 units of sand. In other words, in order to obtain a cube of concrete, it is necessary to prepare 860 kg of sand, 265 kg of cement and 1270 kg of fine crushed stone. The volume of water used should be 180 liters. Its amount should not exceed 20% of the weight of all ingredients.

This concrete, the GOST of which was mentioned above, can be supplemented with plasticizers, stabilizing substances, a water repellent, frost-resistant components and additives to increase strength. The main advantage of the brand described is its low cost compared to durable options. Therefore, if the structure will not be strongly impacted during operation, then you should pay attention to this particular grade of concrete. It has good adhesion to metal surfaces and is suitable for pouring reinforced concrete foundations.

This concrete, the GOST of which must be complied with, may turn out to be more frost-resistant if thermal insulation work is carried out. Among the negative properties of this material, one should highlight the low degree of water resistance.

About the strength of heavy concrete

Heavy concrete can have different strengths, which can be determined by the brand. It indicates compressive strength. This value is expressed in kgf/cm2. The number after the letter indicates the approximate strength value. For example, for M250 grade concrete this figure is 261.93 kgf/cm 2 , while M400 grade concrete has a strength that is equivalent to 392.9 kgf/cm 2 .

The strength of concrete grade M450 is 458.39 kgf/cm2. Whereas if the brand looks like this: M500, then the strength in this case reaches 523.87 kgf/cm 2.

The strength of concrete and its grade depend on the amount of cement that is included in the composition. The larger its volume, the higher the brand will be and vice versa.

Conclusion

Now you know how many components need to be combined to get a cube of concrete of a certain brand. These proportions must be observed, only then in the end it will be possible to obtain a high-strength structure. The quality of the entire building sometimes depends on its reliability and durability. But first, you need to determine which brand of concrete is best to use to solve certain problems.

If you do not take into account the grade of concrete, you may encounter problems during the operation of the structure. This is due to the fact that some concretes are suitable, for example, for foundations, while others can only be used for the construction of lightweight partitions. In addition, structures used outdoors require special additives in the form of those that provide frost resistance. And if work is carried out in winter, then a plasticizer is required.

A volcanic country where components from which concrete can be made are readily available, including pozzolans and crushed lava rocks. The Romans used concrete in mass construction public buildings and structures, including the Pantheon, whose dome is still the largest in the world made of unreinforced concrete. At the same time, this technology was not widespread in the eastern part of the state, where stone was traditionally used in construction, and then cheap plinth - a type of brick.

Due to the decline of the Western Roman Empire, large-scale construction of monumental buildings and structures came to naught, which made the use of concrete impractical and, combined with the general degradation of crafts and science, led to the loss of the technology for its production. During the early Middle Ages, the only major architectural objects were cathedrals, which were built from natural stone.

The world leaders in concrete production are China (430 million m³ in 2006) and the USA (345 million m³ in 2005 and 270 million m³ in 2008). In Russia in 2008, 52 million m³ were produced.

Manufacturing

Cement concrete is produced by mixing cement, sand, crushed stone and water (their ratio depends on the brand of cement, fraction and moisture content of sand and crushed stone), as well as small quantities of additives (plasticizers, water repellents, etc.). Cement and water are the main binding components in the production of concrete. For example, when using 400 grade cement to produce 200 grade concrete, the ratio is 1:3:5:0.5. If grade 500 cement is used, then this conventional ratio produces concrete grade 350. The ratio of water and cement (“water-cement ratio”, “water-cement module”; denoted “W/C”) is an important characteristic of concrete. The strength of concrete directly depends on this ratio: the lower the W/C, the stronger the concrete. Theoretically, W/C = 0.2 is sufficient for cement hydration, but such concrete has too low plasticity, so in practice W/C = 0.3-0.5 and higher are used.

A common mistake in the artisanal production of concrete is the excessive addition of water, which increases the mobility of concrete, but reduces its strength several times, therefore it is very important to accurately observe the water-cement ratio, which is calculated from tables depending on the brand of cement used.

Types of concrete

Instead of sand, production waste from metallurgical, energy, mining, chemical and other industries can be successfully used.

Laying, compacting, hardening

Laying and compacting concrete.

After preparation and placement, the concrete mixture should be compacted as quickly as possible. During the compaction process, they get rid of air in air pockets, and also redistribute the laitance for closer contact with the solid fractions of concrete. This leads to increased strength of the finished concrete. Vibration is used for compaction. When vibrating compaction in monolithic construction, hand-held vibrators are used, in block construction - vibropresses. Curing temperature - from +5 °C to +30 °C.

Performance properties

Compressive strength

The main indicator that characterizes concrete is compressive strength. The class of concrete is determined according to it.

Concrete class B- this is the cube (prismatic) strength in MPa, accepted with a guaranteed probability (confidence probability) of 0.95. This means that the property set by the class is satisfied in at least 95 cases out of 100, and only in five cases can it be expected to fail.

According to SNiP 2.03.01-84 “Concrete and reinforced concrete structures", the class is designated by the Latin letter "B" and numbers indicating the withstand pressure in megapascals (MPa). For example, the designation B25 means that standard cubes (150×150×150 mm) made from concrete of this class can withstand a pressure of 25 MPa in 95% of cases. To calculate the strength indicator, it is also necessary to take into account coefficients, for example, for concrete of class B25 in terms of compressive strength, the standard resistance Rbn used in the calculations is 18.5 MPa, and the design resistance Rb is 14.5 MPa.

The age of concrete, corresponding to its class in terms of compressive and axial tensile strength, is assigned during design, based on the possible actual timing of loading the structure with design loads, the method of construction, and the conditions of concrete hardening. In the absence of this data, the concrete class is established at the age of 28 days.

Along with classes, the strength of concrete is also specified by grades, designated by the Latin letter “M” and numbers from 50 to 1000, indicating the compressive strength in kgf/cm². GOST 26633-91 “Heavy and fine-grained concrete. Specifications» establishes the following correspondence between grades and classes with a coefficient of variation in concrete strength of 13.5%:

Concrete class in terms of strength	Nearest brand of concrete in terms of strength
B3.5	M50
B5	M75
B7.5	M100
B10	M150
B12.5	M150
B15	M200
B20	M250
B22.5	M300
B25	M350
B27.5	M350
B30	M400
B35	M450
B40	M550
B45	M600
B50	M700
B55	M750
B60	M800
B65	M900
B70	M900
B75	M1000
B80	M1000

From the current version of GOST 26633-2015 this table withdrawn because it was misleading.

Until testing, concrete samples must be stored in normal hardening chambers; the strength of the finished structure can be checked by non-destructive testing methods using Kashkarov, Fizdel or Schmidt hammers, sclerometers of various designs, ultrasonic devices and others.

Workability

According to GOST 7473-2010 “Concrete mixtures. Technical conditions”, according to workability (indicated by the letter “P”), concretes are distinguished:

• super-hard (hardness more than 50 seconds);
• hard (hardness from 5 to 50 seconds);
• movable (hardness less than 4 seconds, divided by cone draft).

GOST establishes the following designations for concrete mixtures for workability:

Workability grade	Hardness standard, s	Cone draft, cm
Super-hard mixtures
SZh3	More than 100	-
SZh2	51-100	-
SZh1	less than 50	-
Hard mixtures
Zh4	31-60	-
Zh3	21-30	-
Zh2	11-20	-
Zh1	5-10	-
Mobile mixtures
P1	4 or less	1-4
P2	-	5-9
P3	-	10-15
P4	-	16-20
P5	-	21 or more

The workability index is critical when concreting with a concrete pump. For pumping, use mixtures with a workability index of at least P2.

Other important indicators

• Flexural strength.
• Frost resistance - indicated by the Latin letter “F” and the numbers 50-1000, indicating the number of freezing-thawing cycles that concrete can withstand.
• Water resistance - indicated by the Latin letter “W” and numbers from 2 to 20, indicating the water pressure that the sample cylinder of this brand must withstand.

Climatic test chambers are used to test concrete for frost resistance and water resistance.

Additives for concrete

The use of additives allows you to significantly influence mixtures, concretes and mortars, giving them specific properties. GOST 24211-2008 offers the following classification of additives:

1. Additives that regulate the properties of concrete and mortar mixtures:
   • plasticizing additives increase the mobility of the concrete mixture, thereby allowing you to obtain the desired consistency with less water consumption;
   • water reducing additives make it possible to obtain highly mobile mixtures with low water content, therefore, with a relatively small volume of cement stone;
   • stabilizing additives ensure consistency consistency, thereby preventing the mixture from separating during laying and compaction;
   • additives regulating mobility retention mixtures are in demand during the hot season, when long-term transportation of the mixture is necessary;
   • additives that increase the air (gas) content of the mixture or air-entraining additives increase frost resistance, water resistance and corrosion resistance, but somewhat reduce the strength of the future structure;
2. Additives that regulate the properties of concrete and mortars:
   • regulating hardening kinetics concrete:
     • retarders used when there is a need to increase the time before the concrete mixture begins to set in case of long-term transportation;
     • accelerators reduce concrete hardening time;
   • increasing the strength of concrete - additives of this type increase the resistance of concrete to abrasion, impact and splitting;
   • reducing permeability- substances that increase the density of the concrete structure;
   • supplements increasing protective properties in relation to steel reinforcement used to prevent corrosion in direct contact of concrete with reinforcement in reinforced concrete structures;
   • supplements increasing frost resistance increase the number of cycles of alternating freezing and thawing of concrete without loss of strength properties;
   • supplements increasing corrosion resistance concrete in an environment that causes deterioration of the properties of the material;
   • expanding additives are used to compensate for the shrinkage of concrete during the operation of the structure;
3. Additives that give concrete and mortars special properties:
   • anti-frost additives, when dissolved in water, greatly lower the freezing point of the mixture, preventing it from freezing during transportation, and also prevent freezing of freshly laid concrete in the cold season;
   • water-repellent additives impart water-repellent properties to the pore walls of concrete, increasing the water resistance of concrete, and also prevent the occurrence of capillary effect;
   • photocatalytic additives give concrete self-cleaning properties; as a result of this reaction, almost any contaminant found on the walls of any structure decomposes - dust, mold, bacteria, exhaust gas particles, etc.
4. Mineral additives for concrete:
   • type I - active mineral:
     • having astringent properties;
     • having pozzolanic activity;
     • possessing both astringent properties and pozzolanic activity.
   • type II - inert mineral.

Designation of concrete mixture

Primary protection measures involve the use of materials that have increased corrosion resistance in an aggressive environment, and also ensure low permeability of concrete. Primary protection measures also include issues of choosing rational geometric shapes and shapes of structures, assigning categories of crack resistance and maximum permissible crack opening width, considering the combination of loads and determining short-term crack opening, assigning the thickness of the protective layer of concrete taking into account its impermeability. Primary protection also includes the use of integral capillary materials - waterproofing with penetrating building mixtures. At the same time, the concrete structure is compacted and water resistance, frost resistance, compressive strength and corrosion resistance increase for the entire service life.

Task secondary protection- prevent or limit the possibility of contact between the aggressive environment and concrete. As secondary protection, dust-removing impregnations, thin-layer coatings, self-leveling floors and highly filled coatings are used. Most often, epoxy, polyurethane and polyester components are used as binders in the production of polymer compositions. Protection mechanism concrete base consists of compacting the surface layer and insulating the surface.

The problem of protecting concrete from chemical and electrical corrosion is especially acute for railway transport facilities, where stray leakage currents are combined with aggressive chemical exposure.

Warming up concrete in winter

A significant disadvantage of concrete is revealed during construction in winter, when due to low temperatures the strength of the concrete structures being erected is at risk. For this reason, there is a need for forced heating of concrete.

Basic and additional methods of heating concrete. Among them are:

• Warming up with wire. Available method, which provides excellent heating of the room.
• Warming up with electrodes. Provides rapid heating due to the spread of the electrode network.

• plate electrodes. They are connected to the concrete mortar from the inside - they are attached to the formwork. Transfer heat directly to concrete.
• strip electrodes. Attached on both sides.
• string electrodes. Most often used in columns and attached to the central part.
• rod electrodes. They are used where it is impossible to use other electrodes.

• Concrete heating station. It is used in cases where the concrete is planned to be heated with wire. The power of the station directly affects the level of concrete heating. Controlled manually or automatically.
• Heating formwork. It is considered a more profitable and long-term solution for heating concrete than heating with wires.
• Induction method. With this choice, it is important to strictly calculate the number of turns and correlate them with the volume of metal in the structure.
• Infrared method. An effective and simple way to warm up, but quite expensive.
• Concreting in greenhouses and thermomats. A labor-intensive and expensive method that is not suitable for large rooms with columns. In such cases, it is better to protect monolithic columns or walls with canopies, stretch them over scaffolding, and install forced-type thermal generators.
• The set temperature affects the set of strength and timing of formwork removal, for this purpose in winter period It is also necessary to monitor the temperature of the concrete on the surface and inside the core. Therefore, thermal wells are made in the structure or thermocouples are installed. When dismantling the formwork, the temperature difference environment and the core of the concrete structure should not exceed 15 degrees.

For construction, which is obtained as a result of molding and hardening of a properly selected mixture, including a binder, water, as well as small and large fillers. All this undergoes mandatory compaction. In some cases, special additives are used, and if we are talking about asphalt concrete, then water is not used at all.

Components

At its core, concrete is a mixture of cement and water, as a result of the reaction between which a cement stone is formed, which binds the grains of the fillers used into a single monolith. The structure and depend on these substances. They change its degree of porosity, response to loads, hardening time, and also significantly reduce the deformation of concrete during its hardening. Concrete has become the main building material used in all areas due to the fact that it provides ample opportunities for obtaining mixtures with different properties with the addition of various fillers. It is these characteristics that open up such wide possibilities for application.

Concrete is a durable material with a high degree of fire resistance; its density, strength and other characteristics can be changed, giving it some specific properties. With proper processing, the mixture can be used to produce structures of the required shape from the point of view of architecture and structural mechanics.

A little history

Concrete has been known since ancient times as an artificial building material consisting of water, fillers and a binder. More than seven thousand years ago, it was used by the inhabitants of Mesopotamia for the construction of outbuildings and dwellings. It was also used by the builders of the Great Pyramids. The ancient Romans took concrete construction to a new level - they left behind not only the foundations of buildings, but also entire blocks of concrete buildings. The design features of Roman roads, domes, vaults and floors made from this material have not lost their significance even now. However, in the Middle Ages, the technology for making Roman concrete was irretrievably lost.

Of course, ancient concrete is not the same as modern concrete. Its main difference is its composition; at that time there was no cement in it. The materials used were gypsum, lime or clay.

Characteristics

The strength of concrete is its most important characteristic, which has a direct impact on the operational parameters of the material. This concept usually means the ability of concrete to withstand the effects of aggressive environments and external mechanical forces. This value is determined by control methods: ultrasonic and mechanical. GOST 18105-86 specifies the rules for testing the strength of concrete in bending, tension and compression. One of the characteristics is the coefficient of variation, demonstrating the homogeneity of the mixture.

In accordance with GOST 10180-67, the tensile strength of concrete is determined by compressing a control cube with an edge size of 200 millimeters at the age of 28 days. This type It is commonly called cubic strength. In addition to GOSTs, SNiPs are also used to determine strength. For example, the minimum stripping strength of concrete for horizontal unloaded structures with a span length of up to 6 meters should be at least 70% of the design strength, and with a length of more than 6 meters - 80% of the design strength. In this case, it is strength that is the most important property. Like natural stone, this material resists compression better than tension, so the tensile strength for this indicator was chosen as the main criterion.

Properties

Concrete is a material for which strength is a characteristic that increases as a result of physico-chemical processes of interaction between cement and water, which takes place properly in humid and warm conditions. If the material freezes or dries out, this process will end. Early drying or freezing has a negative impact on the final characteristics of the material.

Uniformity

Together with all other factors, uniformity in strength depends on the quality and content of the aggregates used, especially if some properties of the latter do not allow obtaining concrete of the required strength. Therefore, this parameter is associated with the previous one, although experimental data show that such a relationship does not always take place. By increasing the homogeneity of concrete, opportunities arise for its more efficient use.

The homogeneity indicator is determined as a result of tests of control samples made from working concrete with certain specified properties. For example, in the process of calculating this indicator, the test results of material samples of equal dimensions and storage conditions of equal age are taken into account. Uniformity in water resistance is determined by testing samples of the same thickness using the same methods.

Density

This characteristic of concrete is quite complex, since it changes depending on which components are added to the mixture. To increase the size, you can use pozzolanic Portland cement, which expands or does not form voids when hardening. This parameter is also influenced by plasticizer additives, which often improve the characteristics of already ready mixture. If it complies with GOST, then its density will be a known value.

Classes

At the moment there are several types. Lightweight concrete is a material whose density is 500-1800 kg/m3. This class includes: foam concrete, expanded clay concrete, aerated concrete, cellular concrete, wood concrete, perlite and vermiculite concrete. This mixture has a rather low load-bearing capacity after hardening. Ordinary, or heavy concrete, is characterized by a density of 1800-2500 kg/m 3. Crushed stone and gravel are used as filler here. This type is used in industrial construction, which is ensured by its increased resistance to wear. A particularly heavy class of concrete is a material characterized by a density of more than 2500 kg/m3. Such mixtures are used for the construction of nuclear power plants, as they have properties of protection against ionizing radiation.

Concrete grade

This is another important characteristic of this material. The compressive strength indicator shows the resistance to axial compression. relative to tension shows the resistance to axial tension of control samples. The frost resistance indicator shows the number of cycles of alternating thawing and freezing. The waterproof grade of concrete shows at what one-sided hydraulic pressure concrete will not allow water to pass through during standard testing.

conclusions

When constructing an object for any purpose the right decision will be the purchase of ready-made concrete, manufactured in full compliance with GOSTs, since it is difficult to achieve the desired result when producing it yourself and without special equipment.

Select rating Rating 1/5 Rating 2/5 Rating 3/5 Rating 4/5 Rating 5/5

Average: 1 (1 rating)

Any of us can confidently say that he knows what concrete is. After all, everyone has encountered it at some point. And this is not surprising. After all, concrete is the most common modern building material. But not everything is so simple - it turns out that concrete can be very different...

History, composition, types of concrete

So what is concrete?

Concrete is an artificial stone material made from cement, aggregates and special additives and water. Today, concrete is one of the main building materials.

In addition to ordinary concrete, from which slabs, beams and panels of residential buildings are made, there is also, for example, concrete that is impenetrable to X-rays, concrete that is resistant to sea water - embankments and piers are made from it. There is also steel concrete - steel filings are added to it and especially durable floors are made in factories. There are pumice concrete and tuff concrete. Their fillers are pumice and tuff - porous and lightweight building materials. Therefore, concrete becomes, firstly, lighter, and secondly, it transmits heat worse, which means it protects from heat in summer and from cold in winter. Frost-resistant concrete is being prepared for the northern regions, which can be frozen and thawed five thousand times, and it remains just as strong. There is concrete with metal reinforcement - reinforced concrete; concrete with wood reinforcement - wood concrete; polymer concrete is concrete with synthetic resins inside. By the way, the word “concrete” in Latin means “mountain resin.” Indeed, thousands of years ago stones were sometimes held together with resin.

In short, modern concrete- This is an artificial stone. But why make stones? Really natural stones lacks? Nature has worked for millions of years to create mountains. But all these millions of years, wind, sun, water, frost and heat also worked on the stone blocks. And inside most natural stones there are cracks and flaws. Stones are difficult to cut, but much easier to split. A scientist would say that the stone has a heterogeneous structure. And therefore it is not as durable as it seems. That is why for many years people have been taking small pebbles - crushed stone and gravel, mixing them with cement and water and getting a universal and durable artificial stone - concrete.

So, if sand, crushed stone and gravel are mixed with cement and water, you get a concrete mixture. Let it harden and it will turn into concrete. But this concrete will be fragile. Even if steel rods or wires are laid inside a beam made of such concrete, that is, concrete is reinforced, it will still be bad. It is dangerous even to hang a children's swing on such a beam. It might not last. The whole point is that the concrete mixture must be compacted before it hardens. Fresh concrete is most often compacted with a vibrator; in other words, it is shaken thoroughly. For this purpose, all house-building plants and all reinforced concrete factories have vibration platforms - durable slabs on springs. 2 eccentrics rotate under them - unbalanced weights. The loads jump up and down, the slab bounces on springs, and the reinforced concrete panel that lies on the slab becomes compacted.

From the history of concrete

Concrete is one of the oldest building materials. When constructing massive structures and structures such as vaults, domes, triumphal arches, the ancient Romans used concrete and used clay, gypsum, lime, and asphalt as binding materials.

The galleries of the Egyptian labyrinth (3600 BC), part of the Great Chinese wall(III century BC), a number of buildings in India, Ancient Rome and other places.

With the fall of the Roman Empire, the use of concrete ceased and was resumed only in the 18th century in Western European countries.

The use of concrete and reinforced concrete for mass construction began only in the second half of the 19th century, after the production and organization of industrial production of Portland cement, which became the main binder for concrete and reinforced concrete structures. Initially, concrete was used to build monolithic structures and structures. Rigid and slow-moving concrete mixtures were used, compacted by compaction. With the advent of reinforced concrete reinforced with frames connected from steel rods, more flexible and even cast concrete mixtures are being used to ensure their proper distribution and compaction in the concrete structure.

However, the use of such mixtures made it difficult to obtain high-strength concrete and required increased cement consumption. Therefore, a great achievement was the emergence in the 30s of a method for compacting concrete mixtures by vibration, which made it possible to ensure good compaction of low-moving and rigid concrete mixtures, reduce cement consumption in concrete, and increase its strength and durability.

During these same years, a method was proposed for prestressing reinforcement in concrete, which helped reduce the consumption of reinforcement in reinforced concrete structures and increase their durability and crack resistance.

Concrete in Russia

The development and improvement of concrete technology in Russia, as in other countries, was associated with the production of cement, which appeared in our country at the beginning of the 18th century.

According to archival evidence, during the construction of the Ladoga Canal in 1728-29, cement was used that was produced at a cement plant that existed in the Konorsky district of the St. Petersburg province.

In St. Petersburg in 1822, the book “Treatise on the art of preparing good food” was published. mortars" A few years later, its author, Russian builder Egor Cheliev, published a book on how to prepare cement and concrete, and how to use these amazing materials in the construction of embankments, foundations and for other various construction needs. Since then, not a single large structure in Russia can do without cement and concrete.

Concrete technology has been widely developed in the USSR since the time of the first large hydraulic engineering constructions - Volkhovstroy (1924) and Dneprostroy (1930).

In the 1930s, Soviet scientists and engineers developed methods winter concreting and thereby ensured the year-round construction of concrete and reinforced concrete structures, created a number of new types of concrete, developed ways to increase the durability of concrete, and the basics of prefabricated reinforced concrete technology.

In the post-war years, new types of binders and concretes were created, chemical additives began to be widely used to improve the properties of concrete, and methods for designing the composition of concrete and its technology were improved.

Every year, approximately 250 million m 3 of concrete and reinforced concrete are used in construction, including about 125 million m 3 of precast reinforced concrete. The enterprises operate over 25,000 technological lines for the production of precast reinforced concrete.

Concrete composition

Concretes are artificial stone materials obtained as a result of hardening of a thoroughly mixed and compacted mixture of mineral or organic binder with water, fine and coarse aggregates, taken in certain proportions. Before hardening, this mixture is called concrete mix.

Concrete prepared with cement or other inorganic binders is widely used in construction. These concretes are usually mixed with water. Cement and water are active ingredients concrete; as a result of the reaction between them, a cement stone is formed, which binds the grains of aggregates into a single monolith.

There is usually no chemical interaction between cement and aggregate (with the exception of silicate concretes obtained by autoclave processing), therefore aggregates are often called inert materials.

However, they significantly affect the structure and properties, changing its porosity, hardening time, behavior when exposed to load and the external environment. Fillers significantly reduce the deformation of concrete during hardening and thereby ensure the production of large-sized products and structures.

As fillers They use mainly local rocks and industrial waste (slag, etc.). The use of these cheap aggregates reduces the cost of concrete, since aggregates and water make up 85-90%, and cement – ​​10-15% of the concrete weight.

In recent years, they have been widely used in construction lightweight concrete, obtained on artificial porous fillers. Porous aggregates reduce the density of concrete and improve its thermal properties.

To regulate the properties of concrete and concrete mixtures, various chemicals are introduced into their composition. supplements, which accelerate or slow down the setting of the concrete mixture, make it more plastic and workable, accelerate the hardening of concrete, increase its strength and frost resistance, and also, if necessary, change other properties of concrete.

Concrete on mineral binders are capillary-porous bodies, the structure and properties of which are noticeably influenced by both internal processes of interaction between the components of concrete and environmental influences.

Over a long period of time, the pore structure of concrete changes, structure-forming and sometimes destructive processes occur and, as a result, the properties of the material change. As the age of concrete increases, its strength, density, and resistance to environmental influences increase. The properties of concrete are determined not only by its composition and the quality of the starting materials, but also by the technology of preparation and placement of the concrete mixture into the structure, and the conditions of concrete hardening. All these factors are taken into account when designing concrete and producing structures based on it.

On organic binders(bitumen, synthetic resins, etc.) the concrete mixture is obtained without introducing water, which ensures high density and impermeability of concrete. The variety of binders, fillers, additives and technological methods makes it possible to obtain concrete with a wide variety of properties.

Concrete is a brittle material: its compressive strength is several times higher than its tensile strength. To absorb tensile stresses, concrete is reinforced with steel rods, obtaining reinforced concrete. In reinforced concrete, the reinforcement is placed so that it absorbs tensile stresses, and compressive stresses are transferred to the concrete. The joint work of reinforcement and concrete is determined by good adhesion between them and approximately equal temperature coefficients of linear expansion. Concrete protects reinforcement from corrosion.

Concrete and reinforced concrete structures are manufactured either directly at the construction site - monolithic concrete and reinforced concrete, or at factories and landfills with subsequent installation at the construction site - precast concrete and reinforced concrete.

Types of concrete

Concrete is classified according to the type of material used binder material: concrete on inorganic binding materials (cement concrete, gypsum concrete, silicate concrete, acid-resistant concrete, heat-resistant concrete, special concrete and others) and concrete on organic binding materials (asphalt concrete, plastic concrete).

Cement concrete, depending on the volumetric mass (in kg/m 3), are divided into especially heavy (more than 2500), heavy (from 1800 to 2500), light (from 500 to 1800) and especially light (less than 500).

Extra heavy concrete intended for special protective structures (from radioactive influences); they are made primarily using Portland cement and natural or artificial fillers (magnetite, limonite, barite, cast iron scrap, rebar scraps). To improve the protective properties against neutron radiation, boron carbide or other additives containing light elements - hydrogen, lithium, cadmium - are usually added to especially heavy concrete.

Most common heavy concrete, used in reinforced concrete and concrete structures of industrial and civil buildings, in hydraulic structures, in the construction of canals, transport and other structures. Of particular importance in hydraulic engineering is the durability of concrete exposed to sea and fresh water and atmosphere. There are special requirements for aggregates for heavy concrete. The harsh climatic conditions of a number of regions of our country have led to the need to develop and implement winter concreting methods. In areas with temperate climate The processes of accelerating the hardening of concrete are of great importance, which is achieved by using quick-hardening cements, heat treatment (electric heating, steaming, autoclave treatment), introducing chemical additives and other methods. Heavy concrete also includes silicate concrete, in which calcium lime is the binder.

Lightweight concrete made from hydraulic binder and porous artificial or natural fillers. There are many varieties of lightweight concrete; they are named depending on the type of aggregate used - vermiculite concrete, expanded clay concrete, pumice concrete, perlite concrete, tuff concrete, etc.

The scope of application of lightweight concrete is external walls and coatings of buildings where low thermal conductivity and low weight are required. High-strength lightweight concrete is used in load-bearing structures of industrial and civil buildings (in order to reduce their own weight). Lightweight concrete also includes structural-thermal-insulating and structural cellular concrete. Based on the method of formation of the porous structure and the type of binder, cellular concrete is divided into aerated concrete and foam concrete.

Extra lightweight concrete used mainly as thermal insulation materials.

Application areas of concrete in modern construction are constantly expanding. In the future it is planned to use high-strength concrete (heavy and light), as well as concrete with specified physical and technical properties: low shrinkage and creep, frost resistance, durability, crack resistance, thermal conductivity, heat resistance and protective properties against radioactive influences. To achieve this, it will be necessary to conduct a wide range of studies involving the development of the most important theoretical issues of the technology of heavy, light and cellular concrete: macro- and microstructural theories of concrete strength taking into account internal stresses and microcrack formation, theories of short-term and long-term deformations of concrete, etc.

Concrete, the oldest, but always modern material, belongs to a great future.

"Construction Rules", No. 46 /1, July 2014

The copyright holder of all materials on the site is Construction Rules LLC. Full or partial reprinting of materials in any sources is prohibited.