Concrete brand for the foundation of a private house is an important decision in DIY construction. To do everything right, you need to carefully study the issue before starting work. The choice of material largely depends on the following features:
- type of foundation;
- geological conditions on the site;
- design features of the building (material of walls, floors, number of storeys).
Choosing concrete for the foundation, it is necessary to take into account all of the above factors at the same time.
What is a brand?
Concrete grades are assigned depending on several characteristics:
- strength (brand is indicated by the letter M);
- frost resistance (F);
- mobility (P);
- moisture resistance (W).
The new GOST has replaced the concept of “concrete strength grade” to “concrete strength grade”. Classes are associated with brands, their designation begins with the letter B. In regulatory documents, you can easily find the correspondence of a particular brand to a class. It will be correct to use the designation according to the new GOST, but factories for the manufacture of mixtures and builders often use the outdated concept of “brand”.
The strength grade of concrete shows the bearing capacity of the future structure. The heavier the building, the stronger the material required.
By frost resistance, several types of mixture are distinguished. The number in the marking means the maximum number of thawing and freezing cycles that the structure will be able to withstand. In temperate climates, this number is usually equated to years. For the foundation, it is recommended to use concrete of grades F50 — F150. According to regulatory documents, the frost resistance mark for outdoor structures should not be lower than F35.
Mobility is an important characteristic of concrete. Also, this indicator is called elasticity or workability. The choice depends on the method of performing concrete work. When using a concrete pump, material P4 or P5 is used. In other cases, you can prescribe a mixture of P2 or P3. If the material is selected incorrectly according to the specified indicator, there is a possibility of breakdown of construction equipment (concrete pump).
The moisture resistance index is very important for the foundation. The higher the moisture content of the soil, the less should be the permeability of the material. In normal situations, concrete W4 or W6 is used. With a high level of groundwater, the likelihood of flooding or in marshy areas, it is reasonable to use higher markings (exist before W20).
What concrete is needed for the foundation?
When building a house with your own hands, you need to use the concrete mixture correctly. The foundation mark is especially important because these structures are difficult to replace or repair during operation. Depending on the operating conditions, all types of support elements can be divided into two large groups:
- working only on compression;
- working on compression and bending.
Compression
Concrete accepts loads of this type well, so it is better to use low grades. This will save financial resources. Elements that work only on compressive loads include the following types of foundations:
- bored piles;
- concrete pillars.
In this case, it is sufficient to use material of class B15 — B20 or grades M200 — M250.
Bend
Such types of foundations as bending elements include:
- tape;
- plate.
Subject to the construction technology and good strength characteristics of the base soil, the bending effects in the tape are negligible. But when building with your own hands without a lot of experience, it is better to make a stock and take into account the negative effects of bending on the supporting part of the house.
The concrete grade for the strip foundation can be taken within B15 — B22.5. At the same time, the lower boundary is used only for light small buildings. When erecting a two-story building from massive materials (concrete, brick, etc.), it is recommended to assign the strength of the material for the tape not lower than B20.
Foundation slab - this design, which experiences bending and forcing effects. In order to prevent destruction, it is necessary to treat the choice of material with high responsibility in this case. For the slab type, it will be correct to use concrete not lower than B22.5. The exact class of the material can only be taken into account design features.
Brand selection table
For reference, the table below can be used. It provides recommendations depending on the type of foundation and number of storeys of the building. But you also need to consider the characteristics of the soil at the construction site. For very weak soils, these values may not be relevant.
To make the foundation of a private house with your own hands, it is worth familiarizing yourself with the information in the table.
Type of supporting part of the building | Wall material | Concrete class for a one-story house | Concrete class for a two-story house |
---|---|---|---|
Piles and Pillars | Wood frame | B15 | B15 |
Beam or log | B15 | B15 | |
Foam concrete | B15 | B17.5 | |
Brick | B17.5 | IN 20 | |
Tape | Wood frame | B15 | B17.5 |
Beam or log | B15 | B17.5 | |
Foam concrete | B17.5 | IN 20 | |
Brick | IN 20 | B22.5 | |
Plate | Wood frame | IN 20 | B22.5 |
Beam or log | IN 20 | B22.5 | |
Foam concrete | B22.5 | B25 | |
Brick | B22.5 | B25 and above |
It is especially careful to select material for a two-story brick house with concrete floors. Such a building is distinguished by its high mass and exerts serious loads on the foundations.
How to make a concrete mixture with your own hands
It is worth noting that if you have a choice, it is always better to order material at a specialized factory. In this case, the concrete composition for the foundation will not cause suspicion. When mixing, it is extremely important to strictly observe the proportions: at the slightest deviation, the strength of the material will change. The main problem during operation in this case will be to reduce the bearing capacity of the foundations and the appearance of cracks.
If it is not possible to order the material, you can fill in the mixture made by yourself. For work, you will need to prepare:
- shovels;
- containers for constituent components;
- a concrete mixer (or a mixing tank and a perforator with a special nozzle).
The main components of the concrete mix are cement, sand, gravel (gravel) and water. To improve the operational characteristics of the material, special additives (modifiers) are often introduced into the composition. These include:
- hardening accelerator;
- hardening inhibitors;
- plasticizers;
- superplasticizers;
- antifreeze additives.
The proportions of modifiers must also be strictly observed. Before starting work, you will need to study the manufacturer's instructions on the packaging.
To make the mixture with your own hands, you will need to study the composition of concrete for the foundation (proportion). The number of components is usually determined in parts relative to cement. For each part of the binder, a certain amount of small and large aggregate is taken. Most often, when mixing, the water-cement ratio is assigned equal to 0.6. The value shows that for each part of the cement it is required to take 0.6 parts of the liquid.
Cement for the foundation used grades M400 or M500. When using the latter, it is possible to significantly reduce the volume of the most expensive component in the mixture. This is achieved through the use of cement with higher strength.
When cooking with your own hands, it is extremely important not to add more sand and gravel than is required. The broken concrete composition for the foundation in this case will lead to a decrease in the strength of the material.