Concrete is a material that is in great demand in modern construction. Use it in the construction of foundations, walls, walkways, bridges, etc. Moreover, in each case, its composition should be applied. The specific purpose of concrete is determined by its class or brand. The latter are usually indicated on the packaging.
Varieties of concrete
Currently, in the construction of buildings and structures, the following grades of this material can be used:
super light;
lungs;
heavy;
very heavy.
Mix for concrete is made using different types of fillers. By the type of the latter, the brand of the finished solution is determined. As the filler can be used as light materials (for example, expanded clay or sawdust), and heavier (sand, gravel). In industrial construction, special specialized concrete is sometimes used. As filler, they use metal chips. Such a solution is considered very heavy.
Concrete grade
This indicator is determined in specialized laboratories empirically. In order to find out which brand has concrete, a cube made of it with a side length of 15 cm is subjected to a certain pressure. At the same time, they look at compressibility indicators.
At the moment, there are the most commonly used major concrete brands on the market. Both their characteristics (the table below presents them clearly), and methods of application will be considered by us a little later. There are seven such varieties of material. Each of them is indicated by the letter M and a number showing what pressure in kgs per cm² the material can withstand. So, for example, concrete M200 is able to maintain integrity under a load of 200 kgf / cm².
Concrete grade
Strength grade of concrete is directly related to the class of this material. However, the latter is a more accurate and specific meaning. Indeed, the quality of the finished concrete, in addition to the filler and cement grade, can be influenced by many other factors. For example, the variety and purity of the filler, curing agent and binder, as well as filling methods, solidification conditions, etc.
When determining the class of concrete, its brand and correction factors are taken into account. It is calculated by the formula:
B = R * (0.0980655 * (1 - 1.64 * V)),
where R is the average strength of the material (grade),
V is the coefficient of variation.
We found out that there is such a thing as concrete brands. Both their characteristics (the correspondence table will clearly show this) and the scope of use in most cases coincides with the classes. However, the last indicator is indicated not in kgf / cm², but in pascals. The parameter 0.0980655 in the above formula is just the transition coefficient from one unit of measure to another.
So, a certain brand of concrete in strength usually corresponds to its concrete class. However, sometimes the average and actual strengths of this material differ quite significantly. In this case, the brand and class may not coincide. For example, concrete of the M200 brand, due to the not very high quality of the filler or cement, can be designated as B10, and not B15. The number in the class of material shows its ability to withstand certain loads in MPa. So, concrete B25 without any harm to itself tolerates a pressure of 25 MPa.
Of course, its cost depends on the class of material. The solution is usually sold by volume. That is, the unit of measure for which the price of such material is determined is cubic meter. So, 1 m³ of a solution of class M100 costs about 2000 p., M200 will cost about 2200 p., And M300 can be bought for 3500 rubles.
Matching brand and class
When carrying out various kinds of construction work, you often need to know what properties this or that type of solution differs in. Next, let's look at the qualities of concrete grades of concrete. Both their characteristics (the table below will probably be useful to many builders), and the scope, as already mentioned, in most cases correspond to the properties of a particular class.
Class | Mark | Strength (kgf / cm²) | Application |
AT 5 | M75 | 65 | As a plaster |
B7.5 | M100 | 98 | Installation of a curbstone |
B12.5 | M150 | 131 |
B15 | M200 | 196 | Ties, tracks |
B22.5 | M300 | 294 | Foundations |
B25 | M350 | 327 | Monolithic walls, concrete goods |
B30 | M400 | 393 | Bridges, bank vaults |
Concrete M100
Thus, we have considered in general terms what are concrete grades and their characteristics. The table shows that the scope of this material depends mainly on its strength. Next, let's take a closer look at how each class is specifically used. Material of the M100 brand, for example, does not differ in strength too much. Therefore, it is usually used for plastering walls, conducting preparatory work when filling the roadway or erecting a foundation. In the latter case, the so-called concrete block is made of this material - a flat platform on which the reinforcing cage is installed.
Often this concrete is also used in the installation of curbs that are not subject to special loads, pouring sidewalks with low traffic, etc.
The scope of application for concrete M150 is about the same. The material is quite durable for the construction of structures that are not subjected to stress, but not reliable enough for pouring "serious" objects.
Brand M200
Concrete floors and screeds are usually made from class B15 concrete. Also, this brand is well suited for pouring small stairs, walkways, platforms, etc. Sometimes the owners of suburban areas erect with this solution even foundations for houses with walls made of light materials. However, the M200 concrete grade can be used for this purpose only on stable soils. In this case, groundwater should lie deep enough.
Concrete M300
A solution of this composition is an excellent answer to the question of which brand of concrete is best suited for the foundation. Also, retaining walls, stairs and fences are often cast from material of this class. This option is also suitable for the construction of monolithic walls of low-rise buildings for residential and household purposes. The M300 brand is by far the most popular type of concrete among owners of suburban areas.
M350
Pouring the foundation and monolithic walls - this is what this brand of concrete (and concrete class) is mainly used for. The table shows that a material of such strength is also used for the manufacture of reinforced concrete products. It can be beams, floor slabs, etc. In addition, M300 concrete is often used for pouring screeds and floors. Sometimes homemade monolithic ceilings in the formwork are also made from it.
Concrete M400
This is a very durable type of material, used mainly in the construction of buildings and structures for special purposes. For example, racks and canvases of bridges are cast from it, bank safes, hydroelectric dams are made. The same concrete is used to fill the runways of airfields.
Other indicators
So, the most important parameters are the grade of concrete and the grade of concrete. The table of their correspondence shows how strong one or another variety can be. Of course, the ability to withstand certain loads is the first thing you need to pay attention to when choosing concrete. However, there are other parameters that are equally important and determine the suitability of the material in a particular case. Therefore, there are brands of concrete not only in strength, but also in indicators such as frost resistance, moisture resistance and ductility.
The ability of concrete to withstand low temperatures
In the middle and northern latitudes, the durability and reliability of finished concrete structures largely depends on such an indicator as frost resistance. Previously, the brand of solutions in this regard was designated as MP3. Now, concrete is classified by frost resistance in terms of frost resistance. The figure following it characterizes the maximum number of freezing and thawing cycles that the material can withstand without loss of quality.
Like strength, frost resistance of concrete of one composition or another is determined empirically. Examine the samples in series. In this case, the concrete strength is pre-measured. Further, it undergoes several freeze / thaw cycles. At the final stage, its strength is again determined.
Concrete of frost resistance grades from F25 to F1000 is currently produced. In private housing construction, concrete for outdoor work should, of course, have the greatest resistance to low temperatures.
However, one should pay attention to this indicator not only during the construction of houses in regions with a cold climate, but also during the construction of such important structures as bridges, dams, airfield coatings, roads.
Moisture resistance marks
This indicator is important to consider when choosing concrete intended for the construction of buildings and structures operated in conditions of high humidity. Water resistance is the ability of a material not to let in moisture under pressure. In this regard, there are different types of concrete. Its main brands for water resistance are only five: W2, W4, W6, W8, W12. Previously, the letter B was used to determine the quality of concrete by this indicator.
The number after W in the marking shows at what pressure of the water column the prototype does not pass water. Testing concrete for moisture resistance is carried out using the "wet spot" method. In practice, two water resistance indicators are usually used:
The maximum water pressure that the sample can withstand without signs of leakage on its surface.
Filtration coefficient. So called the amount of water penetrating into the material at a certain pressure per unit time.
Modern industry produces not only ordinary, but also special, hydraulic concrete. This material is highly resistant to water. In its manufacture, Portland cement of high grades or its plasticized version is used. In this case, special requirements are imposed on the quality of fillers. They should not have any organic residues. The maximum allowable grain size used for the manufacture of hydraulic concrete should be 5 mm.
Plasticity stamps
This parameter primarily affects the workability of the concrete mix. In certain cases, this indicator can be very important. For example, for pumping through pipelines or when pouring structures using equipment, sufficiently fluid concrete should be used.
The plasticity of the solution increases, as you know, with the addition of water. However, if it is too much, concrete will lose strength. Therefore, to increase the mobility of the solution in our time, special additives are used - plasticizers.
This material is marked for fluidity by the letter P. In this regard, the following types of concrete exist:
The ductility is determined as follows:
A cone with a wide side diameter of 200 mm and an apex angle of 30 degrees is made of tin.
In three steps, fill it with concrete mixture with tamping.
Level the concrete and turn the cone onto a flat surface.
- They look how concrete will settle down for a certain period of time.
So, buying a ready-made solution, you should first look at its strength class. If necessary, it is also worth making sure that the brands of its moisture resistance, frost resistance and mobility correspond to certain conditions. In this case, the finished construction will turn out to be reliable and durable.