Strength grade concrete: types, features. Strength grade concrete - GOST

The concept of “concrete class” was introduced in 1986. This indicator defines such a characteristic of a material as its standard strength. However, the previously existing concept of the brand is allowed by GOST26633-91 so far.

How is the brand determined

The brand of concrete is the compressive strength of cubes from a solution with a rib length of 15 cm. Before the start of testing, they harden for 28 days under normal conditions. When pouring cubes, concrete is necessarily bayoneted to remove air bubbles. The results of compressive strength are rounded down. Mark is marked with the letter "M". Next is 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 also allow other sizes of samples. While the concrete class reflects the minimum strength indicator (with a possible error of 13.5%), the brand shows only the average.

What brands of concrete are found in strength

At the moment, stamps from M50 to M1000 are produced. In construction, the material M100-M350 is often used. In personal housing construction, the M300 is considered the most popular.

This is how different grades of concrete can be used in terms of strength:

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

Concrete classes

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

What may depend on the strength of the material

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

• the presence of organic impurities in the mixture;
• the presence of dust components;
• clay admixtures.

Among other things, the strength of the solution depends on the amount of water added to it. The smaller it is, the greater loads can subsequently be transferred to the structure. The thing is that excess water leads to the formation of a large number of pores in concrete. These bubbles and reduce its strength.

Another factor affecting the ability of concrete to withstand compression and tension is the degree of homogeneity of the mixture. The most durable structures are obtained if the solution was prepared using special equipment. In private housing construction, mixing is usually done in a small concrete mixer. The strength of the concrete structure can also be increased by vibropressing the laid mixture.

Concrete tensile strength

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 compressive load, expressed in kgf / cm ² . The fact is that this indicator in construction is the most significant. After all, concrete structures usually carry some kind of load from above. An example is the seams of masonry walls, pillars and foundation tapes, support columns, etc. However, sometimes you need to know the tensile strength of concrete. For example, in the construction of tanks, silos or pools. This indicator in concrete is usually not very high. This material is torn quite easily. That is why sometimes under spring heaving foundations and walls crack, since the pressure on them from below and from the sides is uneven. Increase reinforcement expansion strength. The tensile strength for expansion is the same for almost all concrete grades and is 15 kg / cm ² with a cement consumption of 300 kg / m ³ .

How to choose a concrete brand

When drawing up a project for all structural elements of the structure, the corresponding concrete grades should be indicated in strength. GOST and SNiP - this is what you need to be guided by when choosing. Of course, with independent construction it is quite problematic to precisely determine the concrete grade necessary in a particular case. A good way out of the situation can be a consultation with a specialist. However, there are enough masters in our country who build concrete structures on their own. Therefore, the question of how to knead a suitable mixture, in most cases, is not considered a special problem. For example, to build a foundation on soil with good bearing capacity on a flat area, a solution of cement M400, river sifted sand and crushed stone is usually used in a ratio of 1x3x5. Around the same proportion, they knead when using rubble stone instead of crushed stone.

In construction, a variety of concrete grades can be used in strength. Choosing the right one means ensuring maximum reliability and durability of the structure under construction. The cement / sand ratio required to obtain a particular brand of concrete can be found in special tables. It is not difficult to find them, there is a lot of information on the network.