Brand of concrete for the strip foundation of a private house: which type is best to choose and use + composition and mixing proportions

The strip foundation is one of the most developed and studied types of supporting structures.

It is reliable, durable and capable of long-term service in any, even very difficult conditions.

At the same time, it is difficult to avoid mistakes without careful and professional calculations.

This especially applies to monolithic strips cast from reinforced concrete.

They are designed for the most difficult conditions and heavy loads, so it is necessary to exclude any possibility of miscalculations and errors that could cause irreparable damage.

To do this, first of all, you should have a sufficient understanding of the properties and parameters of the material used.

What brands and strength classes of concrete exist?

There are two quality indicators that characterize concrete:

Class.
Brand.

Concrete class means tensile strength in Megapascals.

Distinguish:

Compressive strength class (denoted by Latin B).
Axial tensile strength class (Bt).

Concrete class is a guaranteed strength value corresponding to GOST 26633-91. Depending on production conditions, technological features and other factors, the permissible error level is 13.5%.

There are classes from B3.5 to B80, but under normal conditions concrete with a class from B7.5 to B40 is used. This is due to the fact that extreme values are needed very rarely, low values are needed due to their weakness, and high values are used only on special structures and are redundant in normal construction.

The grade of concrete indicates the average strength value for a particular indicator. In construction practice, the brand is more often used, since the class value is not maintained by all manufacturers.

Taking into account the coefficient of variability, the quality of concrete of the same grade can belong to different classes that have close values to the real indicators of this material.

What factors influence the choice of brand of composition.

Unfortunately, there are no universal recipes; price is not always a fundamental factor. After all, even expensive formulations have their own recommendations and restrictions on use.

Scheme of formwork option for strip foundation.

Dependence on the weight of the building.

If you want to build a house with your own hands, but you do not have a ready-made project with prescribed recommendations, then, first of all, you should pay attention to the total weight of the building. This is the first indicator from which to start when selecting a brand of composition.

Here are some general recommendations:

A prefabricated panel house with a height of 2 floors, in most of our country, will comfortably stand on a reinforced concrete foundation poured with the M200 grade.
For 2 - 3 storey log buildings, as well as for houses built from foam concrete, gas silicate blocks or other cellular concrete, grades M200 - M300 are recommended.
For heavy, permanent buildings built from brick, solid concrete structures or other heavy materials, it is recommended to use a grade of M300 and higher.

Brand of concrete for the strip foundation of a private house.
Reinforced blank for pouring the structure.

Soil characteristics.

Much depends on the geology of the soil in a given area, its composition and how deep the groundwater lies.

Sandstones and rocks are considered the most favorable. They can be poured with concrete M200 - M250.

Clay soils and loams pose quite a big problem. The fact is that these soils are susceptible to heaving when they freeze. That is, they do not freeze evenly and are capable of squeezing out the shallowly buried strip foundation in some places, which leads to general deformation. In this case, you can do it in two ways.
First, deepen the structure to a level exceeding the average rate of general soil freezing in a given region.
Secondly, you can build a strip-column, well-reinforced foundation. This is when concrete support pillars are poured to a considerable depth at key points, which stabilize the entire structure.

If we talk about what brand of concrete is needed for a strip foundation laid on clay, then experts recommend taking a grade that is an order of magnitude higher, approximately M250 - M300.

Diagram of a strip-column structure.

Important: it should also be taken into account that starting from grade M200, if necessary, cutting of reinforced concrete with diamond wheels is already used, and for deepening, diamond drilling of holes in concrete is used.

Waterproofing on the foundation of the house.

Common grades of concrete.

When producing different grades of concrete for foundations, M 400 cement is most often used, but in different proportions.

M100 - used as an underlayment when building roads, laying deep foundations or pouring floor screeds.
M200 – suitable for shallow foundations based on stable soils. It is used to fill basements and various open areas.
M250 – used for casting fences, various kinds of stairs and strip-column structures.
M300 is considered the most popular brand for pouring foundations. It can be successfully poured into the vast majority of known foundation structures and can be used in damp environments.
M400 - used for pouring underwater structures, bridges and other permanent structures. Used for building houses in extreme conditions.
M500 - used for pouring vertical structures, repairing roads and structures, or as an additive.

Important: the quality and strength of concrete is greatly influenced by the so-called shrinkage coefficient - the lower it is, the stronger the structure will be. It can be reduced using special additives. When using vibrating machines, harder and drier compounds can be poured.

Detailed table of proportions of concrete grade.

What else is worth paying attention to?

There is also a marking characterizing the strength class of the hardened composition. It is designated by the letter “B”, characterizes the compressive strength margin and is measured in megapascals.

Important: the strength of concrete can change over time. Active strength gain occurs within 28 days from the moment of pouring. Further, these processes slow down significantly, but do not stop.

Classification of concrete for grade 500 cement.
Classification of concrete for M500 cement.

The strength level and grade of concrete are related indicators. According to GOST, each grade of concrete corresponds to its own level of concrete strength. Here are some key indicators:

B7.5 corresponds to M100
B15 corresponds to M200
B20 corresponds to M250
B22.5 corresponds to M300
B25, B27.5 correspond to M350
B30 corresponds to M400
B35 corresponds to M450

For our country, the frost resistance indicator is also relevant; it is marked with the letter “F” and a certain number after it. The number indicates how many times the structure can freeze. For a larger area of the country, F200 is sufficient; the more thaws in winter, the higher this figure.
It is also worth paying attention to the indicator of resistance to high humidity. It is indicated by the letter “W” and the number after it.

Technical characteristics according to GOST.
It is worth considering the fact that the higher the class, quality and of course the price of concrete, the faster it will set. Experts advise pouring high-quality compounds within 1 day. Accordingly, quickly pouring such a foundation with your own hands will be problematic, so here it is better to resort to the services of construction companies. You can find more information in the video posted in this article.

Brand of concrete for the strip foundation of a private house.

Recommendation: Good review article. He will bring you up to date and help you understand in general terms what grade of concrete is needed for the strip foundation of a private house. But you should not relax prematurely, never forget, the foundation is the foundation of the house, errors in the grade of concrete can lead to huge losses and damages.

Scope of application of various types

The scope of concrete is determined by its strength and resistance to external loads. The main criterion for the quality of a material is its ability to withstand pressure.

This indicator determines the area of use:

Concrete grades from M5 to M35 are intended for filling voids in auxiliary elements or footings.
M50-M100 are used for the preparatory layer before pouring concrete bases (the so-called footing).
M150 is used for the manufacture of non-critical structures in low-rise construction.
M200-M300 is the most common material in private or low-rise construction and is capable of solving most problems in this area. Used for foundations, wall structures and other elements.
M400 is used for monolithic foundations of large multi-storey buildings, structural elements, floors, etc.
M550 and higher grades are used for the manufacture of critical elements of special structures, used in the construction of subways, hydroelectric power stations, etc.

In private construction, the M200 and M250 brands predominate, the quality of which is quite sufficient to solve existing problems.

NOTE!

Brand is an old classification system inherited from Soviet times. Today's standards operate with the concept of “class,” but most builders have not yet adapted to the change in units of measurement, so the concept of “grade of concrete” is still relevant.

Additional markings

The letter “M” is usually indicated on the packaging of the mortar, but there is also a class “B”, which characterizes the level of strength that must correspond to “its” brand of concrete.

Strength factors influence the calculation of the ratio of sand, cement and crushed stone. Based on this, in order to build a strip concrete foundation, it is necessary to maintain certain proportions of the mixture components.

In addition, there is an “F” indicator, which determines the level of frost resistance. The number after the letter shows how many times the composition can freeze. Based on this, there is the following frost resistance range:

F50 is the lowest degree.
F50 – 150 is a normal degree of frost resistance, allowing concrete to withstand temperature changes for 100 years.
F150 - 300 - an increased degree, which is suitable for more severe regions of the Russian Federation (for example, Western Siberia), where the soil freezes to a depth of more than 1.5 meters.
F300 - 500 - used only if there is a threat of increased soil moisture with simultaneous freezing.

When determining what kind of concrete is needed for the construction of a strip foundation on the territory of the Russian Federation, it is best to choose a composition with a normal degree of frost resistance, for example, F150 - 200.

You can make the desired grade of concrete for a specific project on your own.

What requirements must it meet?

The main requirement for concrete is high strength and the ability to withstand external loads. The greatest forces acting on the belt are the weight of the building, the loads of frost heaving of the soil, acting on the sole (from bottom to top) and on the side surfaces.

The monolithic concrete strip must withstand all emerging loads and impacts, including the possibility of moisture saturation and freezing. Most of them manifest themselves in winter at low temperatures when interacting with groundwater.

The criterion is the predicted loads, taking into account the weight of the house, the effects of frost heaving, soil movement in the off-season, etc. The choice of material is made based on the totality of these indicators, which are subject to specialized calculations or determination using tables in the appendices of SNiP.

Useful tips and tricks

When choosing materials and components for the foundation of a building, pay attention to the following nuances:

Even if the grade of concrete corresponds to high reliability, reinforcement will give the greatest strength to the structure, for which it is best to use corrugated reinforcement with a cross-section of at least 12 mm. In addition, this way you can compensate for ground movements.
It is recommended to lay the strip foundation in one go, especially if we are talking about low grade concrete.
If the weather is hot, then you should throw sawdust on the poured formwork or cover it with burlap.
During the first week after pouring, it is recommended to water the hardening mixture several times a day.

Frost resistance

Frost resistance is an indicator characterizing the ability of a material to withstand a certain number of freezing-thawing cycles without changing its performance. It is designated by the letter F and has a range of values from 50 to 2000 cycles.

Frost resistance increases with increasing grade of concrete. For example, if concrete M250 has an F value of 100, then M350 has an F value of 200. At the same time, there is no direct relationship, which is due to the high coefficient of variability of the material.

This means that concrete of relatively weak grades can have high F values, but the probability of such a combination is very low. With a full guarantee, the expected F value can only be obtained with higher grades (or classes) of concrete.

Calculation of concrete for the foundation

The ratio of materials in different grades of concrete (cement M-400)

Concrete grade	Material ratio (Cement x Sand x Crushed stone)	Cement consumption per 1m3 of concrete (kg)
M-100	1 x 4.6 x 7.0	170
M-150	1 x 3.5 x 5.7	200
M-200	1 x 2.8 x 4.8	240
M-250	1 x 2.1 x 3.9	300
M-300	1 x 1.9 x 3.7	320

How to calculate the load

The load on a strip foundation is calculated by adding up all the impacts on the strip.

Are taken into account:

Self-weight of the base.
The weight of the house, the total weight of the walls, ceilings, roof, structural elements, increased by a special coefficient (taking into account the weight of furniture, property and other interior items).
Loads from the weight of snow in winter.
Wind loads.
Impact of frost heaving.

It is strongly not recommended to perform independent calculations of these impacts. Without experience in such calculations, errors are inevitable, the consequences of which can be fatal for the foundation or the entire structure.

It is necessary to contact a specialized organization and order a qualified calculation of the loads and load-bearing capacity of the belt.

IMPORTANT!

Alternatively, you can use an online calculator that is available on the Internet. They are able to provide fairly accurate data; this is usually sufficient for the construction of a private house. For greater reliability, you should duplicate the calculation on several calculators to protect yourself from miscalculations.

The ratio of components in the solution.

Before preparing concrete for the strip foundation of a house, you will have to study the required proportions of mixing crushed stone, sand and cement. The properties of the building mixture are affected by each of the listed ingredients that are included in its composition.

What brand of concrete is needed for a strip foundation.

The main binding component is cement, which forms a plastic mixture. After hardening, it becomes a strong monolithic structure, and the load-bearing capacity of the foundation of buildings depends on the strength indicator.

Thick concrete is considered the ideal option, however, it is difficult to achieve the desired consistency on your own. In industrial settings, vibrators are used to distribute the ingredients throughout the mixture.

Kawabanga! All about plasticizers for concrete

You can prepare concrete for a strip foundation when laying a house using a concrete mixer. You can achieve a thick consistency by tamping with a stick and a vibrator.

How ingredients affect the quality of concrete.

If suddenly the concrete cracks after pouring, the cracks must be repaired immediately with fresh mortar.

Brand of concrete for the strip foundation of a house.

Durable crushed stone plays an important role in the formation of a strip foundation. It needs to be selected only in a single large fraction of 20-25 mm so that the mixture is homogeneous.

Which brand is suitable for the strip foundation of a private house?

The grade of concrete that best suits the existing conditions can be determined using the following criteria::

Design load on the base.
Qualitative indicators of the soil on the site, its type and composition.
Depth of groundwater (GWL).

The main indicator is the load on the belt, the impact of soil and soil water - additional parameters that allow you to clarify and supplement the data obtained. It is noteworthy that detailed and detailed calculations are necessary for heavy and large buildings.

Private houses are predominantly lightweight and practically do not require too detailed calculations. In most cases, concrete grade M200 is used; for more difficult conditions, M250 or M300 is chosen.

The need to use heavier material arises extremely rarely, since the weight of a private house is not too large, and in the presence of very problematic soils, the solution to the problem is to change the foundation design from strip to pile-strip or pile-grillage.

It is not advisable to use concrete of stronger grades in these cases, since the soil pressure becomes too high and unstable, and relying on the strength of the tape becomes dangerous.

Which one is needed for private construction?

The brand is selected taking into account:

soil quality,
wall materials for the future home,
its architectural features,
number of storeys,
purpose of the building (temporary building, summer cottage, year-round country house).

The heavier the building and the weaker the soil, the stronger the concrete should be. For areas with high underground flows, concrete with a high moisture resistance is needed.

Provided that the construction will be carried out on dense soil, you can select the material simply by number of floors and material in accordance with this table:

Wall material	Concrete for a one-story building	Concrete for a two-story building
Brick or stone	IN 20	B22.5
Tree	B15	B17.5
Porous concrete	B17.5	IN 20

Concrete proportions

The composition of concrete includes:

Cement.
Sand.
Water.
Filler (crushed stone of different fractions depending on the brand of concrete).

If it is necessary to produce concrete grade M200, per 1 m3 of material you will need:

Cement M400 - 325 kg.
Crushed stone - 1300 kg.
Sand - 1300 kg.
Water - 205 l.

For concrete M250:

Cement M500 - 320 kg.
Crushed stone - 1280 kg.
Sand - 1280 kg.
Water - 205 l.

Attention! The amount of crushed stone is indicated for a fraction of 10 mm. From different manufacturers, the composition of the material may vary slightly, which is due to different quality of the components.

Main components of homemade concrete mixture

If the mixture will be produced directly on the construction site on your own, you must adhere to the concrete manufacturing technology so that it obtains the necessary characteristics.

Cement

There are several types of cement suitable for making concrete for foundations:

quick-hardening Portland cement;
pozzolanic cement;
Portland slag cement;
Portland cement.

The most commonly used option is Portland cement. It is quite economical and has satisfactory properties. Other options are used for special requirements. Portland cement is purchased grade M400 or M500.

Sand

The sand must be homogeneous, without impurities and debris . It is better to use river sand - it is cleaner. An important parameter of sand is grain size.

When using M300 cement, you need to purchase fine sand with a particle size of about 2.5 mm. For a mixture based on stronger cement, coarser sand is needed - with a grain size of 3.5 mm or more.

Gravel or crushed stone

The base filler can be gravel or crushed stone . It is better to use gravel, as it has an optimal strength-to-price ratio. The size of the filler fractions depends on the dimensions of the foundation.

Large foundation strips are filled with concrete with a filler fraction of 10-20 mm. When arranging a shallow foundation, the gravel should be finer.

Water

Much depends on the quality of the water. It must meet the requirements of GOST. It should contain less than 5000 mg of salts per liter, no more than 2700 mg of sulfates, low acidity is needed.

You can use technical or drinking water . With an optimal salt composition, sea water is suitable. Sewage and swamp water cannot be used to create a foundation.

How to mix it correctly

Making concrete with your own hands is advisable only for small buildings with a shallow immersion depth of the tape and, accordingly, a small amount of material. The technology requires pouring the entire tape at one time, so for large bases it is better to order ready-made concrete delivered in a mixer directly to the site.

This option will allow you to avoid delays in pouring, which can be dangerous due to the appearance of poorly connected areas. A tape with such flaws will not be able to withstand operational loads.

If you decide to make concrete yourself, you will need to prepare all the necessary components and a concrete mixer. It is not necessary to purchase it; you can rent it for a couple of days.

You will need a sieve to sift sand, which may contain various clogging elements . In private construction, it is customary to use an armored mesh from a bed, which is installed obliquely above the receiving container.

Sand is thrown with a shovel through it into a container (box or trough), debris and foreign elements remain on the mesh. The best option is washed river sand without clay inclusions.

A gravity concrete mixer is capable of producing from 60 to 500 liters of solution per batch, depending on the volume. The volume must be known in order to be able to ensure the correct ratio of components.

The required amount of sand, crushed stone and cement is placed in a concrete mixer and mixed until a homogeneous mass is obtained, after which water is gradually poured in. Ready-made concrete is a plastic mixture with evenly distributed filler and the absence of lumps of sand or cement.

NOTE!

When mixing concrete in small batches, you should start laying with sand, to which cement is gradually added and then filler. This will allow the sand to be mixed with cement better and will eliminate lumps from the solution.

Self-cooking

During the preparation process, it is necessary to mix the components in the correct proportions, taking into account the brand of cement used:

Cement brand	Cement	Sand	Gravel	Water
M100	1	4,1	6,1	1,1
M200	1	2,5	4,2	0,9
M300	1	1,7	3,2	0,65
M400	1	1,1	2,4	0,5
M500	1	0,8	1,5	0,4

Mixing in a concrete mixer

If you need to mix more than 50 liters of concrete at once, you need to use a concrete mixer.
First, use a measuring bucket to pour dry components into a concrete mixer , maintaining the correct order - cement, sand, crushed stone.

All this is mixed dry for several minutes. Next, water is poured in and everything is mixed together for 12-16 minutes. The finished concrete mixture is moved into special containers and supplied to the pouring site.

How to calculate quantity

Calculating the amount of concrete is necessary in order to stock up on all components in the required volumes. Experts recommend calculating each straight section of the tape separately and then summing up the obtained values.

In this case, it turns out that the corners are counted twice, but this is good, since it allows you to get a small supply of material.

The calculation begins with calculating the cross-sectional area of the tape. To do this, its height is multiplied by its width.

All calculations must be made in the same units, preferably in meters . Then the volume of material will be expressed in cubic meters, which allows you to simply and without errors calculate the number of components.

The cross-section of the tape is sequentially multiplied by the length of all straight sections of the tape, measured along the outer perimeter. Areas located under internal walls are calculated according to the length of the center lines.

The volumes of all sections are added up, the resulting value will represent the required amount of concrete with some margin.

Proportions for self-production of popular brands of cement

It is not at all necessary to buy ready-made, expensive solutions that do not always meet the stated characteristics. You can make the material according to the following recommendations:

To get M 100, you need to mix 220 kg of cement, 0.8 m3 of crushed stone, 0.6 m3 of sand and 180 liters of water.
For M 200 you will need 280 kg of cement, 0.8 m3 of crushed stone, 0.5 m3 of sand and 180 liters of water.
M 250 will require 330 kg of cement, 0.5 cubic meters of crushed stone, 0.6 m3 of sand and 180 liters of water.
For M 300, mix 380 kg of cement, 0.8 m3 of crushed stone, 0.45 m3 of sand and 180 liters of water.

To obtain a high-quality composition, the grade of Portland cement used must be 2 times higher than the grade of the finished composition. This means that if you want to get an output of M 200, then the Portland cement must be at least 400.

Healthy! It is worth remembering that if we are talking about obtaining a more durable grade (for example, M 300 or M 500), then the ratio of cement to the final mortar can be reduced to 1.5.

In addition, it is important to take into account the characteristics of the suburban area and the weight of the future building, as this will affect the calculation of the mixture.

Advice from professionals

It is important to take into account several observations from professionals who will help with the selection or preparation of a concrete mixture:

At high temperatures, proper curing of concrete may be compromised. It is necessary to sprinkle it with sawdust, which will need to be moistened from time to time. Then there will be no cracks in the foundation.
If possible, the strip foundation should be poured in one go, and not in several. Then its maximum strength and uniformity will be guaranteed.
Never neglect waterproofing your foundation. If this procedure is not carried out properly, the concrete may lose some of its strength characteristics.

For information on how to prepare concrete for pouring a foundation, see below.

Types of foundations

Columnar. It consists of free-standing pillars made of rubble stone, brick, and concrete blocks.
Pile. It is made of a pillar immersed in the ground, which consists of a wooden log, a steel pipe, and a concrete pile.
Monolithic. It is produced by pouring concrete onto a surface to obtain a solid slab of a certain thickness reinforced with reinforcement.
Tape. To create such a foundation, wooden beams or logs, metal channels or concrete beams are used. Power support elements are located horizontally in trenches or at ground level and tied together by means of wedges, welding or pouring concrete at the joints of the beams.

For the foundation of a private house, columnar or pile foundations in combination with a strip type are most suitable. The latter can be used independently, as a separate structure.

Requirements for pouring the foundation

Efforts to select the correct grade of concrete can be negated by errors in preparing and pouring concrete:

Insufficient mixing time - the composition of the concrete mixture will be heterogeneous, with a loss of strength after setting. Most often this happens when kneading by hand. To avoid such a mistake, it is advisable to order factory-made concrete or prepare the concrete mixture in a concrete mixer.
A hard, high-viscosity solution can sometimes cause incomplete filling of the foundation volume, which leads to a malfunction of the structure as a whole. Conclusion: before laying concrete, it is necessary to check its viscosity properties.
Insufficient compaction of the mixture leads to the formation of voids inside the foundation. This occurs when there is insufficient manual influence on the mixture using a shovel or metal rod. The solution is to use a deep construction vibrator.
Interruptions in laying the foundation lead to the formation of weak embedment between the previously laid batch of concrete and the next one. To avoid this, it is necessary to lay the concrete mixture in one go. Breaks should not exceed 2…3 hours.

Stamps

The classification of concrete itself is very ramified. But for the foundation, heavy mortars based on Portland cement are used, to which dense fillers are added. And if you make a choice of mixture for the construction of foundations, then you need to choose according to only four criteria.

The grade strength of concrete also determines the class of the material. Denoted by the letters "M" or "B".
Frost resistance, designated by the letter “F”.
Mass mobility is the letter “P”.
Water resistance, designated "W".

The class indicator and brand of mixture for constructing foundations, plus frost resistance are the main ones on this list. The other two indicators are secondary. Although experts say that it is easier to work with plastic concrete.

Which concrete to choose depending on the foundation of the building

The cement for the foundation, the brand, as is clear, is taken into account and selected according to other parameters. It is imperative to take into account what type of foundation is planned for the structure. For example, a strip foundation is more suitable for buildings made of stone, wood, brick or concrete. To compensate for the load, it is better to make the walls in the shape of trapezoids. Rectangular or stepped shapes are also suitable.

The strip type of foundation is created monolithic or prefabricated

Because of this, you need to pay attention to the brand of concrete for the foundation of the house. For hand masonry, M100, M200, M250 and M300 are suitable

Before preparing the solution, you need to take into account that there are many special additives, there is frost-resistant, waterproof, instantly hardening and standardized concrete. There are also separate types of cement that are resistant to aggressive conditions.

M300 is best suited for foundations, but builders recognized the M500 brand as optimal. In addition, you need to take into account that the composition of concrete and the brand of cement for a wooden house will differ from the materials for a brick house. This is due to the fact that wooden buildings are lighter. An M150 cent is suitable for them. For brick buildings you need to choose M300 cement. And for cottages made of monolithic slabs it is better to prepare M250

How is cement marked?

Not only the operational life of the structure, but also its tensile and bending strength indicators - those types of loads that the concrete strip experiences most of all - depend on the cement used to fill the foundation base. To know what brand of cement is needed for the foundation of a house, it is recommended to understand its differences.

NOT so long ago, a concrete mixture was prepared on the basis of one of the binding components - PC (Portland cement) or ShPC (slag Portland cement). The main difference was the powder composition and strength characteristics. The grades of cement for the foundation complied with current GOST standards.

In addition to the name, the brand of cement material for constructing foundations and other works contains a designation with numbers that indicate the maximum strength under load until complete destruction.

Now let's see what grades of cement there are, how the marking is applied and what its meaning is.

According to the old designation system, several brands were distinguished:

M 300 - withstands loads of up to three hundred kilograms per square centimeter of surface;
M 400 – corresponds to a pressure of 400 kg;
M 500 - withstands impacts of at least five hundred kilograms per unit of area;
M 600 - carries a load of six hundred kilograms.

The characteristics given here are not able to give unambiguous advice on what brand of cement to use for constructing the foundation of a house, and what to use when building lighter structures. Naturally, for large structures it is necessary to take material with a greater load. But you can prepare a concrete solution with the required characteristics by changing the amount of cement composition of a lower grade, increasing its quantity.

This criterion is present in the labeling of the material, and its presence is indicated by the corresponding letters and numbers D0 or D20. Before making the final choice in cement, it is recommended to clarify how mineral components influence the quality of the binder. For example, D0 does not contain any components, and the solution is of the highest quality. But the brand with the designation D20 contains up to twenty percent of impurities, which reduce not only strength, but also cost. When choosing a cement material, for example, to construct a fence foundation, you can use a powder with a lower strength index, thereby reducing the overall cost of construction work.

When deciding which material is best to use for pouring a strip foundation, you should study the remaining characteristics of the component indicated in the labeling. The most common designations are:

PL – cement contains plasticizer additives. This type of foundation material is used when the region experiences low temperatures in winter;
VRC - this abbreviation denotes the moisture resistance of the mixture and the increase in volume during hardening. If you are in doubt which cement is best for a foundation in a swampy area, then you will not find another option;
B - such material requires less time before final hardening. If you have a choice about what to use for the foundation of a house, when the time frame for work is limited, choose this particular cement material;

SS – sulfate-resistant cement. It is rarely used by private developers, because its main purpose is considered to be concreting hydraulic structures. When plugging oil and gas wells, plugging cement is used - a mixture of clinker powder, gypsum and other components;
N – cement with this marking has undergone additional rationing using clinker. This additive ensures high strength of the material;
BC – “white cement”. A distinctive feature is that it becomes lighter after hardening. It is rarely used, mainly for finishing work.

Other characteristics

In addition to the main characteristic - strength, concrete has a number of other indicators that can affect the choice of brand under special construction or operating conditions.

Frost resistance, water resistance and workability of concrete grades

Frost resistance - indicated by the letter F. Shows how many freezing-thawing cycles a given solution can withstand without loss of strength. It is clear that the higher this indicator, the better (see table). The grade of concrete for frost resistance for the foundation is taken into account when constructing unheated premises (baths, periodic dachas). When building permanent residences, this indicator can be ignored, especially if the foundation is insulated and an insulated blind area is made around the perimeter of the house.
Waterproof. Denoted by the letter W. This indicator determines how much moisture the concrete will absorb. After the letter W there are numbers from 2 to 10 (actually there are also W20 grades, but they are not used in private construction). W2 and W4 - high and normal absorbency. Concrete grades with such water resistance can only be used on well-drained soils (sands and sandy loams) with deep groundwater. With W6, moisture absorption is already reduced, and a solution with such characteristics can be used for foundations on soils that do not drain water well. When waterproof, the W8 absorbs only 4.2% of the total weight of water, and the W10 absorbs even less.

One of the parameters is fluidity
Comfortability. It is designated by the letter P, followed by numbers from 1 to 5. P1 - cone settlement of 1-4 cm, semi-rigid or low-plasticity solution (almost does not slide off an inclined shovel);
P2 - cone draft 5-9 cm, medium-plastic - slides off an inclined shovel;
P3 - sediment 10-15 cm, semi-cast - when it flows off a level shovel;
P4 - draft 16-20 cm - cast - practically fluid.
P5 - the cone settles more than 21 cm, the solution flows.

As for workability, it affects how comfortable you will be working with the solution. For foundations, concrete with characteristic P2 is most often used (for frequent reinforcement, P3 is used). It is permissible to use P1 when it is necessary to process concrete with a vibrator - it settles the solution well, making it more homogeneous.

Taking into account all these characteristics, we can recommend the following grades of concrete for the foundation of one-story houses.

Type of one-story house	Slightly heaving soil	Heaving soil
Panel, frame house	M-200 (P3 F100 W4)	M-250 (P3 F150 W4)
House made of timber and logs	M-250 (P3 F150 W4)	M-300 (P3 F150 W6)
House made of aerated concrete, foam concrete, expanded clay concrete	M-300 (P3 F150 W6)	M-350 (P3 F200 W8)
Brick, monolithic house	M-350 (P3 F200 W8)	M-400 (P3 F200 W8)

Remember that when building a two-story house, the grade of concrete increases by one step from those given in the table.

Classification of concrete solutions

First of all, what exactly is concrete? This term is usually understood as a stone of artificial origin, which is obtained as a result of hardening of a mixture poured into a mold, consisting of correctly selected components, which include:

— binder (most often cement plays this role);

— aggregates (usually sand, gravel or crushed stone, but some concretes require the use of other materials).

- water, which acts both as a diluent and as a necessary component for the chemical reaction of the formation and maturation of concrete stone.

Brands and strength classes of concrete

This is perhaps the main indicator that must be taken into account when choosing a specific solution.

The grade indicates what compressive load fully matured concrete can withstand, expressed in kgf/cm².

There are quite a few grades of concrete in terms of strength, from M50 to M800. However, in the field of private construction, and specifically when constructing foundations, developers, as a rule, will have to deal with grades from M100 to M300, less often - M400.

The grade of concrete indicates its ability to withstand compressive loads, expressed in kgf/cm²

In reference literature and in construction technological instructions, very often, instead of the concepts of brand strength, they operate with an indicator of the class of concrete. These quantities are, to a certain extent, interconnected, and differ, rather, in their “coordinate system”.

The class is denoted by the letter B and a numerical indicator that corresponds to the load (expressed in megaPascals), which with a 95% probability will be withstood by the prototype - a cube with sides of 150 mm.

However, in conditions of independent private construction, knowledge of such subtleties is unlikely to be needed. It is important to understand the grades of concrete and how they roughly relate to classes. The following table will help with this.

Table 1. Correlation between grades and classes of concrete

Compressive strength of concrete, kg/cm2	Concrete strength class	The closest concrete grade in terms of strength
65.5	AT 5	M 75
98.2	B 7.5	M 100
131.0	B 10	M 150
163.7	B 12.5	M 150
196.5	B 15	M 200
261.9	B 20	M 250
294.4	B 22.5	M 300
327.4	B 25	M 350
392.9	B 30	M 400
458.4	B 35	M 450

Having such a “cheat sheet” at hand, it is easy to navigate both systems for assessing the strength of concrete.

Frost resistance of concrete

The frost resistance grade is designated by the letter symbol “F” and a number, which indicates the number of freezing and thawing cycles of material samples without any significant changes in its physical, mechanical and operational characteristics.

The method for determining frost resistance is established by GOST 10060.0-95. The same standard also provides for the classification of materials according to this indicator - markings vary from F25 to F1000.

When assessing frost resistance, unnecessary extremes are often taken:

Whatever concrete the foundation is poured from, its waterproofing is a must!

If we think sensibly, then the frost resistance class indicator in private construction is important only in two typical places where concrete products are used and there is no way to protect them from direct exposure to water.

Practice shows that for foundations (of course, with their waterproofing) the F150 indicator is quite sufficient, and for walls - even less, about F50÷F100

Cement prices

Concrete waterproof class

This indicator is indicated by the letter symbol W and a number (from W2 to W12). The numerical indicator indicates the maximum pressure, expressed in megaPascals, at which the prototype (cylinder 150 mm high) does not allow water to pass through.

Table 2. Approximate correspondence of concrete indicators with standard optimal combinations of components and compliance with the technology of mixing solutions

Class (closest grade) of concrete by strength	Frost resistance	Waterproof
V-7.5 (M100)	F50	W2
V-12.5 (M150)	F50	W2
V-15 (M200)	F100	W4
V-20 (M250)	F100	W4
V-22.5 (M300)	F200	W6
V-25 (M350)	F200	W8
V-30 (M400)	F300	W10

Indicators of workability of the solution

There are several criteria for assessing workability, but in everyday construction practice the most commonly used indicator is the workability indicator, denoted by the letter symbol P and a digital value. Where does everything come from?

Measuring how much the formed experimental mortar cone sank helps determine the mobility indicator of the finished concrete

The measured amount of subsidence of the cone from the initial horizontal level (from the top of the mold) will lead to the desired indicator of the mobility of the solution.

Table 3. Indicators of concrete mobility and features of the use of solutions