Concrete grades for strength: types, features. Stamps of concrete for strength - GOST

The concept of "concrete class" was introduced in 1986. This indicator defines such a characteristic of the material as its standard strength. However, the previously existing concept of the mark is allowed in GOST 26633-91 until now.

How to determine the brand

The concrete grade is the compressive strength of cubes from a solution with a rib length of 15 cm. Before starting the tests, they harden for 28 days under normal conditions. When pouring cubes, concrete must be pierced to remove air bubbles. The obtained results of compressive strength are rounded down. The mark is designated by the letter "M". Next comes a figure showing the strength of the cube in kgf / cm ² . Sometimes, instead of cubes, cylinders with a diameter of 15 cm and a height of 30 cm are taken. GOSTs allow other dimensions of the samples. While the class of concrete reflects the index of minimum strength (with a possible error of 13.5%), the grade shows only the average.

What brands of concrete are found on strength

Currently, the brands are from M50 to M1000. In construction, the material M100-M350 is more often used. In the personal housing construction, the most popular is the M300.

In this way, different grades of concrete can be used for strength:

• M100, as not particularly strong, is used only for the preparatory pouring of pits under the foundation. Sometimes it is used as a binder when laying curb stones.
• M150 can be used for making floor screeds, pouring driveways and pouring foundations for small structures.
• M200 is used in the construction of pile and tape bases under the house. It is also used for making stairs, paths and grounds.
• M250 is used to build more reliable bases under the house.
• M300 - as already mentioned, the most commonly used brand of concrete. Used for pouring foundations, slabs , erecting fences.
• M350. Used for pouring monolithic walls, crossbars, columns and ceilings. The same brand is well suited for the construction of pool basins. It is from such concrete that aerodrome strips are made.
• Of the concrete of the M400 brand, bridges, bank safes, etc. are manufactured. In private housing, such material is practically not used because of the high cost.
• M450-500 is also used in the construction of bridges, dams, tunnels, dams.

Classes of concrete

Concrete grade is a more accurate indicator. It is denoted by the letter "B". The figure behind it shows the pressure that the material in Mpa can withstand to 95% accuracy. The full range of concrete classes used in industry and construction is 3.5-80. Next, we present to your attention a small table of correspondence of the most popular classes and brands:

From what strength of material can depend

The strength class and brand of concrete can depend on various factors. The quality of the mixture is affected by a wide variety of parameters. First of all, this, of course, is the quantitative ratio of cement and filler. The larger the first and less than the second, the stronger the product will be. As a filler, both in private and in industrial construction, sand is usually used. The strength of concrete depends, in part, on its characteristics. The smaller the filler, the lower it is. Of course, the strength of concrete affects the brand of the cement itself. Factors that can lead to a decrease in the brand of concrete can be:

• Presence of organic impurities in the mixture;
• Presence of dust components;
• Impurities of clay.

In addition, the strength of the solution depends on the amount of water added to it. The smaller it is, the greater the load in the subsequent can carry the structure. The thing is that excess water leads to the formation of a large number of pores in the concrete. These bubbles and reduce its strength.

Another factor affecting the ability of concrete to withstand compression and stretching is the degree of uniformity of the mixture. The most durable constructions are obtained if the solution was prepared using special equipment. In private housing, kneading is usually done in a small concrete mixer. The strength of the concrete structure can also be increased by vibrocompression of the stacked mixture.

Ultimate tensile strength of concrete

The ratio of concrete grade and strength is, as mentioned above, the ability of a cube with a face of 15 cm to withstand the compression load, expressed in kgf / cm ² . The fact is that this figure in construction is most significant. After all, concrete structures usually carry some load on top. An example is the seams of wall masonry, pillars and strips of foundations, pillars of support, etc. However, sometimes it is necessary to know the ultimate strength of concrete and the tensile strength. For example, when building tanks, silos or pools. This figure for concrete is usually not very high. This material is torn easily enough. That is why sometimes, when spring whipping, foundations and walls crack, because the pressure on them from below and from the sides is uneven. Increase the strength of expansion reinforcement. The strength of the expansion is the same for almost all concrete grades and is 15 kg / cm ² at a cement consumption of 300 kg / m ³ .

How to choose a brand of concrete

When drafting a design for all structural elements of the structure, the corresponding concrete grades for strength should be indicated. GOST and SNiP - this is what should be guided when choosing. Of course, in case of independent construction, it is rather problematic to determine the concrete grade necessary in this or that case. A good way out of the situation can be a consultation with a specialist. However, masters who construct concrete structures themselves, we have enough in our country. Therefore, the question of how to knead a suitable mixture, in most cases, a special problem is not considered. For example, to build a foundation on a soil with a good bearing capacity on a flat area, a solution of cement M400, river sifted sand and crushed stone in a ratio of 1x3x5 is usually used. Approximately in the same proportion do kneading when using stone rubble instead of rubble .

In construction, a wide range of concrete grades can be used for strength. To choose the right one is to ensure the maximum reliability and durability of the structure being constructed. The cement / sand ratio necessary for obtaining a concrete grade of concrete can be seen in special tables. Find them easily, the information on the network is pretty much.