What is the class of concrete and brand of concrete

For various areas of construction work requires the use of concrete compositions endowed with one or other properties. At the same time, specific characteristics depend on which brand and class the material used belongs to. Our article will help you to deal with these terms and their relationship.

Types of concrete grades

Concrete classification by brand is based on the following product properties:

• compressive strength - this parameter indicates the limit of the load, measured in kg / cm ?, which a sample with a volume of 15 cm can withstand? on day 28 after pouring;
• tensile strength - load limit (kgf / cm?) On a sample of 20 cm? , followed by its destruction;
• frost resistance - the number of freeze-thaw cycles, not leading to a decrease in strength and cracking of the material;
• water tightness - the number of cycles of moisture-drying, in which the properties of the product does not deteriorate.

In accordance with the criteria set out above, the grades are distinguished by their strength, denoted by the letter “M”, by frost resistance - “F”, and by water resistance - by the letter “W”.

The class of concrete and its difference from the brand

Since January 1, 1986, the term “concrete class” has come to replace the concept of “brand” in construction design. This change came into force in connection with the adoption of SNiP number 2.03.01-84.

Before discussing the conformity of the brand and the class of concrete, let's define what is the difference between these two parameters. The fact is that the first value establishes the averaged technical indicators of the product, and the second one guarantees a certain level of strength of the concrete material.

So, for hydraulic structures, the guaranteed security should be 90%, for other objects - 95%. This means that this characteristic is observed, respectively, in 90 and 95 cases out of 100. Denoted by the letter "B".

It is possible to determine which concrete grade corresponds to the concrete class using a special table. It is listed below.

In addition, the ratio of the class and brand of this product can be calculated by the following formula: B = R * (1-t * V), in which:

• B - class of composition, which has guaranteed security equal to 95%;
• R is the average strength of the material. So, for the M250 brand, this parameter is about 250kgs / cm ?;
• t is the student coefficient. It is equal to 1.64. Its use is necessary to ensure guaranteed strength equal to 95%;
• V is the designation of the coefficient of variation of strength. It is necessary in order to carry out the translation of the brand of concrete in the class of concrete. For porous and heavy concrete structures, this figure is 0.135.

Specific types of brands

We considered the classification, as well as the question of how the concrete grade differs from the concrete class. Now let's talk about the individual types of brands.

Grades of concrete strength

They have a range from M50 to M1000. Such marking first of all speaks about the average index of compressive strength, measured in kgf / cm ?. In addition, this designation indicates the type of cement used, the volume ratio of the components of the solution and the time of its hardening. The tables below will help you to make sure of this.

As mentioned earlier, each grade of material has its own strength class. The table of concrete grade and grade of concrete has already been cited earlier, and we will not dwell on it.

Let's discuss another question - how to test the strength. Such verification may be carried out exclusively under laboratory conditions. For this purpose, a prototype is used, placed under a special press. Other methods can be applied, such as a shock pulse or an ultrasonic method.

Tip! Self-made structures should have a margin of safety. The fact is that the concrete mix used, despite the same brand, may have different technical characteristics. This is due to violations of the technology to create a solution.

Grades of concrete for frost resistance

Frost resistance is an important factor on which quality depends. This is especially important in the case of buildings erected in the northern regions.

Влага, попадая на такие изделия, проникает в их структуру. После своего замерзания она увеличивается в объеме, чем наносит повреждения конструкции. Из-за таких циклов замерзания-оттаивания у бетонов, имеющих низкую frost resistance, серьезно уменьшается несущая способность, и появляются внешние разрушения.

This property can be enhanced by adding special chemicals to the solution. These include lignosulfonates, superplasticizers and modifiers, which are poured into the mixture to the extent that is set by the instruction attached to them.

By the named property, a number of categories are distinguished. Their range is from F50 to F1000. The number in the marking indicates the number of thawing-freezing cycles, in which there is no deterioration in the quality of the structure.

Brand concrete for water resistance

Water resistance is the ability of a product to resist the negative effects of water that occurs during moisture-drying cycles. This indicator is calculated based on the change in the strength of the product after a certain number of cyclic effects of moisture. The basis is the ratio between its initial and final strength.

This parameter has a range from W2 to W20. The number in the designation indicates the maximum permissible level of water pressure. The better this property, the higher the price of such material.

Conclusion

Brand of concrete sets the averaged technical indicators of this material. In contrast, the class guarantees at a level of 90-95% compliance with the required properties of the product.

Allocate brand mix for strength, frost resistance and water resistance. This is the main classification of concrete marks in it included are denoted, respectively, by the letters M, F and W and have different ranges of values. More information on these issues can be found in the video in this article.