Concrete brand for the foundation: selection criteria and

The brand of concrete for the foundation of a private house must comply with the operating conditions and design parameters. And since monolithic foundations are gradually crowding out other types of supporting structures, therefore the question of choosing concrete becomes relevant for many consumers.

The brand of concrete for pouring the foundation is selected in accordance with the design data, but there are also general selection criteria. We will tell about them.

Concrete for foundation casting

Marking and classification features

First you need to understand what these symbols or other names indicated in the marking of ready-mixed concrete mean. We are talking precisely about the commercial material produced at the factory in accordance with the standard recipe, since it is difficult to discuss the solution made with our own hands, because we know nothing about its real characteristics.

So, there are several basic indicators of the quality and design features of concrete:

1. Compressive strength. The main parameter on the basis of which the material is assigned to a particular brand. If you see a product with the marking M250 - this means that before you is concrete that can withstand a compressive force equal to 250 (more precisely - 262) kgf / cm2;
2. Water resistant. Also refers to the most significant indicators of product quality, indicated by the letter W and numbers from 2 to 20, this or that watertightness class is assigned on the basis of testing with pressure water in a special chamber;
3. Frost resistance. This characteristic is also important, especially for our climate, indicated by the letter F and a numerical value from 50 to 1000, which indicates the number of freezing / thawing cycles that the sample withstood during the test in the climatic chamber;
4. Mobility. This indicator speaks about the fluidity of the solution, it is important when mechanized methods of supplying the mixture (concrete pump) and laying in narrow formwork, columns, etc. It is indicated by the letter P and numbers from 1 to 5, for the use of a concrete pump mobility must be at least P4.

In addition to these basic characteristics, there are a great many other parameters, such as bulk density, water-cement ratio, purpose, type of binders and aggregates, structure and conditions of hardening.

Note! There is no need to delve into all the details. It is enough to remember that for laying in foundations, heavy construction concrete of dense structure, natural hardening, prepared on dense aggregates is necessary.

In addition to the brand, there is such a parameter as a class. It was introduced somewhat later in compression marking and is a more accurate and broad indicator that indicates not only the strength of concrete, but also other characteristics.

This parameter is standardized according to St SEV 1406-78 and SNiP 2.03.01-84 and is indicated by the letter B and a number from 3.5 to 80. The class indicates a certain set of basic parameters that give us the opportunity to expect certain known properties in 95% of cases.

There is a definite correlation between classes and brands, which makes it possible to compare them.

Note! First of all, we need to know the class and brand of concrete, as well as its water resistance and frost resistance. The remaining parameters have no significant effect on the choice.

Choosing a brand for the foundation

Although, according to the rules, the choice of a particular material grade should be made on the basis of calculated data and expected loads, as well as operating conditions, construction and geological data, you can specify the main classes of concrete used and simplify the task.

The fact is that the calculation will give us the values ​​by which we will determine the nearest suitable brand. But practice shows that there are only a few brands that can be used in civil engineering when laying mortar into the foundation.

So, the lowest is the concrete grade for the foundation slab. It can correspond to M200, and in dry, strong soils with weak heaving and M100. This refers to the sole design, which does not bear special loads, except for vertical compression and bending.

For pouring slabs of the strip foundation and the main structure of the monolithic structure, as well as for concrete posts, piles, grillages and reinforcement belts, concrete of classes B20 - B25 is used, which corresponds to the grades М250 - М350. The most popular is the brand M300, but in most cases it can be easily replaced with M250.

Of course, you can take the material with a margin of safety, so as not to be mistaken. However, it should be remembered that the price of high-class concrete will be significantly higher, and work with it will have to be faster and more organized.

In addition, if you need to make an opening or hole in it, you will need professional cutting of reinforced concrete with diamond circles or diamond drilling of holes in concrete.

If you live in a region with heaving soils, high groundwater levels and cold winters (North-West District of Russia), then it makes sense to pay attention to such an indicator as the frost resistance of concrete for the foundation. It should be at least F150, and better than F200.

Also important here is such a parameter as waterproof. It should be at least W4, but it is better to raise it to W8. Here we are dealing with the case when it is advisable to apply a solution of a higher class, that is, M350, which has F200 and W8.

In addition, it is a material of increased strength, which is useful during the movement of the soil during freezing.

Note! The most acceptable in most cases is concrete grades M250 and M300, the quality of which is quite enough for the purposes of civil engineering.

Conclusion

The choice of brand and class of concrete is made on the basis of the project and load calculations taking into account the design features, the presence of a basement and geological details of the terrain.

At the same time, knowledge of the basic parameters of brands and classes will help you to make the right choice, and the video in this article will allow you to better understand the styling process.