Concrete mix: properties, composition, types, grades of concrete, characteristics, compliance with GOST standards and application

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Concrete is used today in absolutely all areas of construction. It may have completely different characteristics, which depend on the purpose for which it is made. The mortar is usually mixed at the construction site, but for sufficient strength of the concrete structure, its structure is erected from a factory material called ready-mixed concrete.

Basic Features

Among the most important technological properties of the concrete mix should be highlighted:

• density;
• strength;
• water resistant;
• plasticity;
• flame retardant.

Of these, the main indicator is strength, which is expressed in the ability to resist destruction from loads. The increase in the latter is allowed only up to a certain limit. The strength of the material is determined by its brand. It is understood as the compressive strength of cubes, the side of which is 20 cm. They harden after pouring intoduring the month. Tensile strength is expressed in kg/cm2.

Familiarizing yourself with the concept of brand, you can find out that the following values are set in the documentation. For ordinary concrete, the figure varies from 25 to 600. As for lightweight concrete, the norm here is from 10 to 300. Strength depends on how active the cement is. This parameter is affected by the quality of crushed stone, sand, water and gravel, as well as the conditions of transportation, mixing, age, placement and curing of concrete.

When considering the properties of a concrete mixture, you should definitely pay attention to the density. The described material is not completely dense, because it has air pores that form when water evaporates or air enters. Density is the degree to which a volume is filled with a solid. So, if the density is 0.95, then 95% of the volume is solid materials, and 5% is pores.

In order to obtain dense concrete, the amount of water should be reduced, and the grains of aggregates should be selected in different sizes. This will help reduce the number of voids. Among the properties of the concrete mixture, plasticity should also be distinguished. It is determined by the mobility of the composition, which, when laid, must fill all the bends, voids and shells. Concrete can be:

• cast;
• plastic;
• hard.

The indicator of the plasticity of the mixture is estimated by a device called a cone. This tool is a steel mold without a cone bottom.

An important property is also water permeability. Its degree is characterized by the greatestwater pressure at which liquid percolates through the sample. Water resistance depends on the amount of water pressure, density and structure, as well as curing conditions, density and age of concrete.

Becoming familiar with the properties of the concrete mixture, you will need to pay attention to the fire resistance. This is the ability of the material, which is expressed in resistance to the destructive factors associated with high temperature. Concrete must withstand normal use up to 250 ˚C.

Besides this, it is necessary to pay attention to the shrinkage of the material. When cured in air, concrete shrinks in volume. Outside, this happens faster than inside, cracks become the result of this. Shrinkage, as a rule, is 0.15 mm per 1 m. If you choose the composition of the solution, you can reduce the amount of shrinkage or prevent it altogether.

Feature of the filling is the release of heat during the hardening of the mixture. Therefore, in the structures under construction, one can observe an increase in temperature even at low ambient temperatures. This property allows concreting in winter conditions without heating.

Concrete composition

In order to achieve the desired properties of the concrete mixture, it is necessary to adhere to a certain composition. An ordinary concrete mortar is obtained by mixing the following ingredients in certain proportions:

• cement;
• sand;
• water;
• rubble.

The ratio of components depends on the desired result. Substances are often added to the finished mixture,designed to improve the properties of the material. The mixture in this case will be different, but the main components will remain unchanged.

Cement and water are necessary to ensure the viscosity of the solution and the formation of its integrity. The amount of liquid and cement, as well as the moisture content of sand and aggregates, should be controlled.

Main types of outdoor mortar

The properties of the concrete mixture may vary depending on the purpose of the material. Among the main varieties of concrete that will be used outside, it should be highlighted:

• reinforced concrete;
• silicate concrete;
• asph alt concrete;
• hydrotechnical concrete;
• expanded concrete;
• perlite concrete;
• tuff concrete.

Reinforced concrete is a combination of base material with reinforcement. The mixture is used in all climatic zones, because it does not lose its properties up to -45 ˚С. Operation is possible up to +60 ˚С. Most people are familiar with this type of material from reinforced concrete slabs used in ceilings.

Silicate concrete is a mixture of silicon and lime. The mixture may contain quartz and silica. The filler is sand. This type of concrete is produced by autoclaving. The material is processed with steam at a temperature of 174 to 198 ˚С.

A rather dense mixture is asph alt concrete. It consists of:

• mineral powder;
• sand;
• bitumen;
• rubble.

Each part is dried separately, and then heated to 150 ˚С. ByAt the paving temperature, asph alt concrete can be hot or viscous, cold or liquid. The working temperature of the former reaches 120 ˚С, and the latter should not be lower than 10 ˚С. Roofs of houses and road surfaces are made from such concrete.

Among the main properties of the concrete mixture, which is also called hydrotechnical concrete, it is necessary to highlight the increased water resistance. Buildings are being built from this material, which will be used in swampy areas or in regions that are often subject to floods.

Expanded concrete is one of the types of lightweight concrete. The filler here is expanded clay. This allows you to reduce the cost of work, and the mass of structures is less.

Perlite acts as a filler in perlite concrete. This material belongs to the class of light, concrete fences are made from it. The filler in tuff concrete is volcanic tuff. Walls and floor slabs are made from this material.

The main types of concrete for interior work

The properties of concrete and concrete mixture can be such that the material can only be used for interior work. This applies to gypsum concrete. Instead of cement, building gypsum is used here, to which stone aggregates are added. Straw and wood are additional components.

Instead of cement, an organic polymer is also used as a binder in plastic concrete. Any sand can be used as a filler. This material is used for filling floors in public and industrial premises. The filler in concrete can also be pumice. This is aboutpumice stone, which acts as a heat-insulating material.

Aerated concrete is divided into several subspecies. This should include gas and foam concrete. Both of these types are used as thermal insulation components in construction. The cellular material is inferior to the heat insulator. A separate type is heat-resistant concrete, which is used in the metallurgical industry as the foundation of open-hearth furnaces.

Types by strength class

Considering the basic properties of the concrete mixture, you should pay attention to strength. The material is divided into concrete strength classes:

• light;
• heavy;
• especially heavy.

For the former, the strength does not exceed 1,800 kg/m³, for the latter, it varies from 1,800 to 2,500, and for the third, the value exceeds 2,500 kg/m 3^.

Concrete grades and their applications

The properties of the concrete mix and how to evaluate them are subject to study if you are going to build a building structure yourself. Evaluation methods include placing the cone in the mixture and determining the water permeability of the material.

And the quality of concrete can be determined by paying attention to its brand. The most common are grades from M100 to M550.

Concrete B7, 5 (M100) is a lightweight material that is used at the foundation pouring stage. With this solution, you can prepare the surface andlay reinforcement. In road construction, such a composition is used in the arrangement of curbs.

One of the varieties of lightweight concrete, which is also called lean, is concrete B12, 5 (M150). The area of use is the pouring of monolithic slabs and foundations. These materials are used very widely, for example, for the formation of screeds when pouring floors, footpaths, as well as when installing curbs. The mixture can also be used in the construction of foundations for small structures.

A fairly wide area of construction work covers concrete B15 (M200). It has high compressive strength and is used in the construction of various retaining walls, foundations, paths and in the arrangement of sites. The material can also be used in the manufacture of stairs, as well as in the construction of concrete cushions for curbs and roads.

Concrete B20 (M250) in terms of use and characteristics can be compared with B15, however, the composition can be used in the manufacture of slabs that will be subjected to a small load. This material is much stronger than previous samples. A fairly popular brand, which is used in the construction of pile-grillage and other monolithic structures, is B22, 5 concrete, better known under the M300 brand. It is customary to use it when pouring blind areas, making stairs and fences, as well as platforms.

In the construction of high-rise buildings for foundations, concrete B25 (M350) is usually used. The composition is characterized by high strength, it can be used in the production of hollow core slabs and beams. The material has become widespread in monolithic housing construction, as well as in the manufacture of road slabs, bowls for pools, load-bearing columns and much more. This concrete can withstand high loads, making it widely used in the construction of commercial and public buildings.

The average brand of concrete is B30 (M400). The composition is more expensive and quick setting, so it is not so popular. It is characterized by high strength and reliability, therefore it is an indispensable material in the construction of hydraulic structures and reinforced concrete products, as well as bank vaults, which are subject to special requirements. This brand of concrete is recommended for facilities with high safety requirements. These should include:

• indoor pools;
• entertainment and shopping malls;
• water parks.

A large percentage of cement in its composition has concrete B40 (M500) and B45 (M550), which has high strength and is used in reinforced concrete products for special purposes, as well as hydraulic engineering. For the construction of buildings, it is usually not used.

Characteristics of M200 concrete according to GOST

The pouring of a concrete mixture, the main technological properties of which are important, must be controlled from start to finish. At large construction sites, this is done by the foreman. His experience allows you to judge the quality of concrete. For example, he knows that the M200 material is classified as light, and hisvolumetric weight and density depend on the type of filler. This parameter ranges from 500 to 1800 kg / m3,material mobility varies from P2 to P4, the frost resistance index is F100, the water resistance is W4.

The composition corresponds to GOST 10181-2000, according to which the ingredients must include:

• large aggregates in the form of crushed stone;
• sand;
• cement;
• water.

Sometimes a plasticizer is added. The most commonly used crushed stone fraction for this type of concrete is 10-20 mm. If crushed stone with finer or coarser grains is present in the composition, its volume should not exceed 5%.

When considering the composition and properties of the concrete mixture, you should pay attention to the following. In the manufacture of M200 materials, crushed granite, which has high strength characteristics, will be the best component. The brand of stone in terms of strength should not be less than M800. The quality of the final product is influenced not only by the properties of the materials for the manufacture of the concrete mix, but also by the purity of the coarse aggregate. If the presence of clay and dust inclusions is noticed, this will become an obstacle to the adhesion of crushed stone to cement, as a result of which the concrete strength may decrease by up to 30%.

Characteristics of M450 concrete and its compliance with state standards

Among the main properties of heavy concrete and concrete mix there is mobility. For the mentioned brand, this parameter is equal to the limit P3- P5. The thermal insulation properties decrease when the concrete hardens, and there is also an increase in frost resistance and water resistance. Therefore, it is possible to build hydraulic structures where the water level periodically changes.

This material has a high level of strength and is resistant to frost. Compliance with the class according to the latest characteristic - F300. With regard to water resistance, the mixture belongs to the class W8 - W12. This indicates that there is no need to use additional sealing additives.

Solution corresponds to GOST-7473. The most commonly used samples of the category P2, P3, P4, P5. It is possible to make M450 concrete from one share of M400 brand cement, 1.1 parts of sand and 2.5 parts of crushed stone. If cement grade M500 is used, then the proportions should be observed: 2.9 parts of crushed stone, part of cement, 1.4 parts of sand.

Property persistence

Assessment of the persistence of the properties of a concrete mixture over time is to obtain data on the change in characteristics over a certain period. From the moment of sampling to the moment of testing the concrete mixture, it is necessary to observe the correct storage conditions for the sample.

Determination of the properties of the concrete mixture will allow you to understand how well the material will be preserved over time. The product can belong to one of three classes, each of which determines the level of preservation. Separate low, medium and high levels.

If the mortar was made on the basis of quick-setting cement, then the finished material can be attributed to class C-1, which is characterized byincredibly low shelf life of only 20 percent.

If the material is made of normally setting cement, then it can already be attributed to class C-2, which is characterized by an average shelf life. It can vary from 20 to 60%.

If the composition contains slow-setting cements and components with a low temperature, then the finished material can be classified as C-3 with a high level of persistence - more than 60%. This material is more likely to not break down over time.

Special properties of concrete

Under the influence of external factors, the structure is loosened, after which the bonds between the elements are weakened. As a result, the ability to deform increases, mobility increases. The ability of systems to change their rheological properties of the concrete mixture under the influence of mechanical influences and recover after the termination of the impact is called thixotropy.

The thixotropic properties of the concrete mixture are one of the main ones. They determine the ability of the material to liquefy, namely: to acquire the properties of a liquid body. This happens with periodically repeated mechanical influences.

A special characteristic of the viscoplastic properties of concrete is its workability. It is understood as the ability of the composition under the action of techniques and mechanisms to fit into the shape and compact.

According to GOST 7473-2010, in terms of workability, concretes can be:

• super hard;
• hard;
• movable.

The former have a stiffness of more than 50 seconds, the latterit varies from 5 to 50 seconds, the third hardness is less than 4 seconds.

Rheological properties of the concrete mixture are used to describe the behavior of concrete under different conditions. Among them should be highlighted:

• viscosity;
• ultimate shear stress;
• relaxation period.

Thus, knowledge of the composition and special properties of concrete mixtures will help in the future to use mortars without the risk of destruction of erected structures.