Which concrete to choose. Concrete grade and class

7 min

Concrete has been holding the leading position among building materials for many years in a row. It owes such popularity to its unique performance, incl. high strength, frost resistance and moisture resistance. Moreover, varying the ratio of the constituent components of concrete makes it possible to obtain a material with slightly different properties, which makes it possible to use it in almost any conditions. The question of choosing a suitable concrete remains the most important and difficult, because further properties of the structure depend on this.

concreteIt is equally difficult to choose a suitable concrete manufacturer. The growing demand for this building material has led to the emergence of a huge number of proposals, which is quite difficult to navigate. In order for a potential buyer of concrete to be able to quickly find the best offer for himself, the concrete tender system “M350” was developed. It is presented on the page http://m350.ru/price/m350/ and allows the user to quickly familiarize themselves with all offers for the sale of concrete M350 and other brands in the Moscow region and choose the most suitable for themselves, based on the price, location of the plant or the manufacturer’s operating mode. The system saves time and money.

To be able to choose the right concrete mix for specific purposes, you need to know what indicators to pay attention to. Among the most important are the brand and class of concrete, the characteristics of moisture and frost resistance, as well as the mobility of concrete.

Concrete grade

The most important characteristic of concrete is its ability to withstand compressive loads. This parameter is denoted by the letter M, and the index behind it indicates how much load each square centimeter of concrete can withstand. The exact value is determined in vitro by testing concrete hardened for 28 days, and the rounded value is recorded in the marking. For example, concrete that can withstand 98 kgf / m2 is designated M100, and concrete that can withstand 196 kgf / cm2 is M200. Simply put, the digital index indicates the amount of kilogram that can press on 1 cm2 of concrete without destroying it.

concrete 2Today concretes from M50 to M1000 are produced, but concretes of the M100-M500 brands are in the greatest demand. The different level of concrete strength is explained by differences in the composition: the proportions of the components used and their quality affect. Concrete contains sand, cement, crushed stone or gravel. Sand together with crushed stone (the so-called skeleton) are responsible for the bearing capacity of the future structure, and cement, when combined with water, is responsible for the strength of molecular bonds. The higher the proportion of cement in concrete, the higher the strength of the concrete itself.

The quality of the components also plays a role. The sand can be both river and quarry – it is important that it is large and with a minimum amount of clay impurities. The optimal size of crushed stone is 20-25 mm, it should be from hard rocks. The cement grade also affects the strength of the concrete. As a rule, cement M400 and M500 is used, the latter for the preparation of concrete of a given strength will need less.

The least durable concrete grades are used in the construction of the lightest and less critical structures. Foundations of private and multi-storey buildings, industrial buildings are created using more durable compounds (M200 and higher). With the growth of strength, the price of the composition also increases, therefore, there is no need to use excessively strong compositions, as well as to save.

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Concrete class

The class of concrete also indicates the strength of the material; it is a modern derivative of the concrete grade. If, when determining the grade, the average value of the strength of the material is used, then the strength class assumes the determination of strength with guaranteed security. This is a more accurate value and is expressed with a coefficient of variation of 13%. Despite the fact that the class more accurately defines the characteristics of concrete, today most experts use the concept of a brand.

Classes are defined by the letter B and a number from 3.5 to 60: the higher it is, the more durable the composition is in front of you. There is a direct relationship between the classes and brands: for example, the M100 brand corresponds to the B7.5 class, the M200 brand – B15, etc.

The ratio between the class and the grades of concrete in terms of strength

The ratio between the class and the grades of concrete in terms of strength

Water tightness of concrete

The waterproofing of concrete is understood as its ability to keep water out. Previously, this characteristic was denoted by the Russian letter B, now they use W, and the numerical designation next to it can start from 2 and reach 20, equal to the pressure of the water column in kgf / cm2, at which a cylindrical concrete sample of standard height does not allow water to pass through.

concrete 4If a foundation is being erected from concrete under conditions of an increased groundwater level, then it makes sense to choose a composition with a high water resistance value, to which special hydrophobic additives are added. By the way, the use of such material will reduce the cost of full waterproofing of the foundation.

The highest indicators of water resistance and water resistance are possessed by hydraulic concrete. For its production, use hydrophobic or plasticized Portland cement, sand and crushed stone of a higher quality than for conventional concrete. High levels of water resistance are also achieved through installation with maximum sealing.

Frost resistance of concrete

The frost resistance of concrete is denoted by the letter F with a numerical value from 25 to 1000: the higher it is, the more freezing and thawing cycles the concrete can withstand without losing its strength properties. The choice will depend on the conditions in which the finished structure will be used, on the climate, the number of freezing and thawing periods during the cold period of the year.

For the construction of hydraulic structures, airfield pavements and bridge supports, it is better to choose the most frost-resistant compounds. In private construction, concrete of class F100 or F200 is suitable for the construction of the foundation. You can also focus on density: the higher its value, the more frost-resistant the composition will be.
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Concrete mobility

The mobility of concrete (P) indicates the degree of its fluidity, which directly affects the convenience of working with the composition. The numerical coefficient is expressed in the range from 1 to 5: the higher it is, the more liquid the composition will be. In private construction, when arranging the foundation, concrete P2 and P3 is used. More fluid formulations are used only in cases where it is necessary to pour a tightly reinforced base, or when concrete is supplied using concrete pumps.

It is, of course, more convenient to work with a more fluid composition, but water cannot be added to ready-made concrete to increase the mobility of the composition. In this case, the grade of the mortar immediately decreases, reducing the final strength.
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Areas of use for different grades of concrete

Concrete has become ubiquitous, used to create foundations and many other structures. Depending on the purpose of use, concrete of a particular brand is selected. Here are the main uses for the most common concrete grades:

  • concrete 7M100 is used to create road curbs and before pouring the strip foundation;

  • M150 is suitable for pouring floors, foundations for a fence, as well as for organizing parking for cars;

  • M200 is used in the restoration of buildings, filling paths, as well as for creating blind areas and foundations of light buildings;

  • M250 is suitable for creating different types of foundations, as well as for platforms and paths;

  • M300 is used to create the foundation of brick houses, paving slabs and roads subject to heavy loads;

  • М350 is suitable for creating monolithic foundations and foundations for multi-storey buildings;

  • М400 can be used both for creating foundations of residential buildings and for the construction of bridges and structures on the water;

  • M450 and M500 are suitable for the construction of tunnels, sewers, bridges.

Choosing concrete for the foundation

Since concrete is used in the organization of the absolute majority of foundations, the question of its choice precisely for these purposes requires more detailed consideration. To select the required brand, you need to know the weight that will be assigned to the structure, the conditions of its operation, take into account the type of soil, the level of groundwater, etc. All this should be mentioned in the design documentation, and for those who are building on their own, we will provide information on the use of different grades of concrete.

concrete 8The less the load from the building being erected, the less durable concrete will be needed. If a frame house is being built, then you can get by with M200 concrete, for a wooden house it is better to arrange the foundation of M250 concrete. For two-story wooden houses, houses made of gas silicate and expanded clay concrete blocks, it is better to choose concrete M300. If reinforced concrete wall panels are used or in plans to build a brick house, then concrete M350, M400 and higher are used for the foundation.

Affects the choice of concrete grade and soil type. The more heaving the soil, the greater the load drops on the foundation. So, for clay soils, it is better not to use concrete below M350, and for sandy and rocky soils, M200 is also suitable. If the groundwater level at the place where the house is built is high, then it is better to choose concrete with increased water resistance: even if M250 is suitable for the loads, it is better to use M350, for which W is almost twice as high.

Whatever brand of concrete is used, the characteristics of the finished structure are largely influenced by the correct dilution of the mixture with water, as well as the process of filling the mold with concrete and the uniformity of distribution of concrete.

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