What kind of concrete for a monolithic foundation. What concrete to use for the foundation? Video: an example of preparing concrete M300 in a concrete mixer

The foundation is the basis of any capital building, and the belt-type foundation of all known is the most durable and reliable in the context of the loads applied to it. Strength determines the grade of concrete for strip foundation, from which the mortar for pouring the base is made. Structurally and technically, a strip foundation is a closed ring of reinforced concrete that runs along the perimeter of the building and falls, as a rule, slightly below the estimated depth of soil freezing in the region.

Several types of concrete are produced in industrial production. Almost all brands can be used for pouring the foundation - it depends on the depth of the foundation, the type of building, the type of soil and regional weather conditions.

Compressive strength is one of the main parameters of concrete. Previously, the strength of concrete was determined by the grade. The concrete grade is designated by the letter “M”: M 100, M 150, M 200, M 300, M 400, M 500, and so on up to 1000. The grade is the ability of concrete to withstand compressive pressure, which is calculated in kg / cm². The concrete grade is checked in the laboratory by the compression method of concrete samples, by the ultrasonic method (non-destructive method) or by the shock pulse method, etc.

Now the defining indicator of strength is the class of concrete. The class is designated by the letter "B" and a number that denotes strength in MPa. That is, the numbers in the strength class from 5 to 60 indicate MPa (Mega Pascal, which is equal to 9.81 kg / cm²). Any indicator of the strength class of concrete guarantees quality in accordance with its class by 95%, and only 5% of the strength of concrete can be underestimated. In the regulatory and project documentation indicate the class of concrete.

Correspondence tables for grade and strength are reflected in and presented below. The letter "B" denotes the class of concrete, "F" - frost resistance, "W" - moisture resistance, "P" - concrete mobility.

Table 1. Conformity of class and grade of concrete.

Concrete class	Average strength concrete class kgf / cm 2	Optimal concrete grade
AT 5	65	M 75
H 7.5	98	M 100
AT 10 O'CLOCK	131	M 150
12.5	164	M 150
T 15	196	M 200
IN 20	262	M 250
T 25	327	M 350
T 30	393	M 400
T 35	458	M 450
T 40	524	M 550
T 45	589	M 600
T 50	655	M 600
T 55	720	M 700
T 60	786	M 800

What is the difference between class and grade of concrete:

The higher the grade of concrete, the stronger the foundation will be. Also, a high number in the marking indicates an increasing rate of concrete hardening. The frost resistance group is designated as "F" and lies in the range of 25-1000. The number in the group is the freeze / thaw cycles.

The table below contains information on the groups of concrete frost resistance during the operation of objects:

Table 2. Use of concrete depending on its frost resistance.

Frost resistance group of concrete	Designation	Additionally
Low	less than F50	Used narrowly
Moderate	F50 - F150	Frost resistance and moisture resistance of groups F50 - F150 are distinguished by optimal parameters.
Increased	F150 - F300	Frost resistance of the F150 - F300 group allows building objects in a harsh climate.
High	F300 - F500	Groups of concrete F300 - F500 are used in conditions of variable humidity.
Especially high	over F500	Frost resistance group F500 and higher is distinguished by special additives. It is used for the construction of especially durable structures.

Concrete water resistance table

Table 3.

Operating mode	Frost resistance grade	Waterproof grade	Suitable brands of ready-mixed concrete, not lower than:
Alternating freezing and thawing under conditions of water saturation (for example, seasonal thawing permafrost or very high groundwater levels) at temperatures
Winter temperature is below 40 0 \u200b\u200bС	F150	W4	BSG V 20 PZ F150 W4 (M-250)
Winter temperature from -20 0 C to -40 0 C	F100	Not standardized	BSG V 15 PZ F100 W4 (M-200)
	F75	Not standardized	BSG V 15 PZ F100 W4 (M-200)
	F50	Not standardized	BSG V 15 PZ F100 W4 (M-200)
Alternating freezing and thawing under conditions of periodic water saturation under the influence of atmospheric factors
Winter temperature is lower - 40 0 \u200b\u200bС	F100	Not standardized	BSG V 15 PZ F100 W4 (M-200)
	F50	Not standardized	BSG V 15 PZ F100 W4 (M-200)
Winter temperature from -5 0 С to -20 0 С	Not standardized	Not standardized	BSG V 15 PZ F100 W4 (M-200)
Winter temperature -5 0 С and above	Not standardized	Not standardized	BSG V 15 PZ F100 W4 (M-200)
Alternating freezing and thawing in the absence of periodic water saturation (concrete protected from precipitation and groundwater)
Winter temperature is below -40 0 С	F75	Not standardized	BSG V 15 PZ F100 W4 (M-200)
Winter temperature from -20 0 С to -40 0 С	Not standardized	Not standardized	BSG V 15 PZ F100 W4 (M-200)
Winter temperature from -5 0 С to -20 0 С	Not standardized	Not standardized	BSG V 1S PZ F100 W4 (M-200)
Winter temperature -5 0 С and above	Not standardized	Not standardized	BSG V 15 PZ F100 W4 (M-200)

The concrete mobility must be selected based on the conditions and construction technology. For example, if access to the formwork for mixers is possible only from one or two sides, it is better to take concrete with a mobility of at least P3, because workers will have to disperse the concrete quite far by hand. With thick concrete, this will be problematic.

If the supply of concrete to the formwork is planned using a concrete pump, then the mobility should be at least P4.

Mobility of concrete solutions for different objects

Table 4. Mobility of concrete solutions for different objects.

p / p	Types of work and objects	Cone draft, cm	Stiffness index
1	Preparatory work for foundations, road bases and floors	0…1	50…60
2	Roads, floors, large structures without reinforcement	1…3	25…35
3	Reinforced objects	2…4	15…25
4	Walls of residential and industrial buildings	2…4	15…25
5	Reinforced concrete structures, poured with concrete on site, with reinforcement up to 1% of the volume of the object	4…6	10…15
6	Reinforcement-rich structures with more than 1% reinforcement	6…8	10…15
7	Objects to be concreted in sliding formwork:
	Sealed by vibrators	6…8	10…15
	Manual seal	8…10	5…10

The most suitable concrete grades for casting strip foundations

• Concrete grade M 200 - designed for the construction of the foundation of a log house, buildings made of foam blocks, gas silicate bricks or expanded clay concrete.
• Concrete grade M 250 is suitable for the construction of foundations for brick private houses with reinforced concrete floors.
• Concrete grade M 300 - construction of foundations for 2-3-storey buildings with large and long-term loads (industrial facilities).
• Concrete of the M 400 grade is optimal for pouring waterproof and frost-resistant foundations in private houses.
• Concrete of the M 500 brand takes the first place for pouring the strip foundation. It can be used for pouring foundations of industrial facilities: multi-storey buildings, warehouses, workshops, hangars, etc. It is used for industrial foundations in conditions of high humidity and changeable climate.

Concrete grades below M 200 and above M 500 are generally not used for casting strip foundations.

How to choose the right grade of concrete for a strip foundation

The composition of the soil (clay, rocky, sandy, black earth, etc.) and the depth of groundwater are the main determining factors when choosing concrete for the foundation of any construction site. For example, on sandy and rocky rocks, concrete of grades M 200 - M 250 can be used. Such a foundation will cost less, but will not be weaker.

On clay and loamy soils, the heaving of the soil is strongly manifested during freezing - the foundation can simply be squeezed out to a certain height, which will lead to a general deformation of the building and cracks in the walls. On such soil, proceed as follows:

• The foundation is deepened below the level of soil freezing in the region.
• They equip a strip-columnar reinforced foundation, as mentioned above.

For clay soil, it is recommended to take a grade an order of magnitude higher than for other soils. So, if concrete grade M200 - M250 is suitable for sandy soil, then for clay soil - M300 - M400. Concrete is made from various brands with different proportions of fillers (cement, sand, crushed stone, respectively):

• M 100 - 1: 4.6: 7.
• M 150 - 1: 3.5: 5.7.
• M 200 - 1: 2.8: 4.8.
• M 250 - 1: 2.1: 3.9.
• M 300 - 1: 1.9: 3.7.
• M 400 - 1: 1.2: 2.7.
• M 500 - 1: 1.1: 2.5.

Even if all proportions of the constituent components of concrete are strictly observed, the strength of concrete continues to depend on other factors. There may be deviations in the technology for preparing the solution, poor quality of sand or water, unsuitable weather or technological conditions during the formation of the concrete composition, as well as the peculiarities of its solidification. Therefore, concrete made from a solution of the same brand can be of different strength.

When preparing concrete mortar big role the fraction of crushed stone plays - it is important that the crushed stone is of the same size. Crushed stone of different fractions in one batch will lead to the formation of a low-quality concrete solution. Large crushed stone is a guarantee of durable concrete.

What else to consider

The temperature regime also affects the strength of the foundation. In the heat, it is necessary to pour sawdust on the poured foundation or cover it with rags, burlap, etc. For the first week, it is recommended to water the foundation surface with water several times a day: this technique will allow the foundation to solidify evenly and save it from the appearance of deep and superficial small cracks.

If the groundwater is located too close to the soil surface, it is recommended to use a concrete mortar using grade M300 and higher with a water permeability of at least W4. Concrete made from high grades of cement does not lose strength with constant contact with moisture. It is recommended to fill the strip foundation in one pass.

- another condition for the reliability of the structure. Usually corrugated reinforcement with a diameter of 12 mm and more is used. If the foundation is reinforced with segments with a length shorter than the length of the straight segment of the foundation, then these segments must overlap each other by 15 or more of their diameters. The reinforcement is connected at a distance of at least a meter. total area the section of the reinforcing rods should be 0.1% of the cross-sectional area of \u200b\u200bthe strip foundation.

When pouring a strip foundation, you can not save on the price of concrete, or on its quality. The foundation is the foundation of the building, the guarantee of reliability and durability. And concrete is the main component of the foundation, its quality affects the result construction works... Therefore, buy quality building materials.

The strip foundation is a strip that runs along the perimeter of the house and takes the full load of the building. The number of tapes depends on the number of load-bearing walls. This type of base is characterized by strength and reliability. It is perfect for heaving and difficult soils, high water tables and soft soils. A strip foundation is chosen if you want to build a house with a basement, basement or underground floor.

The installation of the strip foundation provides for the arrangement of removable formwork, reinforcement and concrete pouring. It is labor intensive and requires a lot of building materials. The quality of concrete has a great influence on the reliability and strength of the structure. In this article, we will take a closer look at what grade of concrete is needed for a strip foundation.

Strip foundation installation technology

Before deciding which concrete to choose and use for a strip foundation, you need to understand the installation principle strip base... Installation of the structure is laborious, but quite easy and straightforward. Therefore, you can install the strip foundation with your own hands. The installation includes the following works:

• The land plot is cleared and leveled;
• They mark the future foundation with pegs and a rope. Measure the evenness of the sides with a level at the corners and diagonals;
• They dig a pit 40-50 cm deep. Digging begins from the lowest point of the site;
• Sand is laid deep into the resulting trench and covered with gravel with a layer of 15 centimeters, poured with cool water and tamped;
• Roofing material or a special waterproofing film is placed on a sand cushion;
• Formwork is made from bars, boards or plywood;
• A reinforced grating or mesh is made at a distance of 50-60 mm from the edges of the pit. For this, the reinforcement is tied with knitting wire into square cells with a side of 40-50 mm. Do not use a welding machine for fastening, as corrosion forms in the welding places !;
• Leave holes for pipes and utilities;
• After reinforcement, concrete is poured into the formwork and left to dry. It is advisable to cover the surface with plastic wrap, and in hot or dry weather, pour it with cool water;
• After about a week, the formwork is removed and the concrete is left to dry further. Typically, this will take another two to three weeks;
• When the concrete hardens, the waterproofing is reinforced and, if necessary, the foundation is insulated.

The tape is perfect for building a country house and a summer residence. It is a durable and robust structure that can withstand heavy loads and does not require special ground preparation. It is an indispensable option for heterogeneous soil and heaving soil... The main advantage of such a foundation is the possibility of arranging a basement floor. Now let's find out what brand of concrete is needed for a strip foundation.

The composition and types of concrete

The traditional composition of concrete used for foundation construction includes water, cement and sand. In addition, it may contain gravel, crushed stone and various additives that give the composition certain properties. Cement contains the following markings:

SS - sulfate resistant;

PL - increased plasticity.

For the foundation, choose cement marked M. At the same time, keep in mind that concrete can be obtained from M200 cement for a strip foundation, a maximum of M100, M400 cement will give M250 concrete, and with M500 - M350.

Concrete marking differs from cement marking and includes the following indicators:

W - water resistance (varies between 2-12);

F - frost resistance, shows how many frosts and defrosts the foundation will withstand (for example, with an F100 indicator, concrete will withstand 100 frosts and defrosts).

Concrete marking means how much load one square meter grounds. For example, concrete M250 means that 1 cm2 of the foundation can withstand 250 kg of static load. By the way, this is very high strength and is suitable for almost every private house made of logs, beams and even bricks.

What concrete to use

Concrete grade below M200 is used for filling paths, sidewalks or blind areas. This material is not suitable for the foundation for a residential building! For a light construction, for example, for a gazebo, a bathhouse or a small panel board, choose the M200. By the way, it is also suitable for pouring a concrete staircase, if such is planned for summer cottage... And for a small garden house made of a bar or log, use the M250.

For a large, spacious wooden cottage, a concrete grade for strip foundations M300 or M350 is suitable. It is a very durable composition, as it includes granite in addition to standard components. Such concrete is characterized by resistance to temperature extremes and severe frosts, increased water resistance. It will allow you to build a high-quality, solid and durable vacation home for year-round use. In addition, it is recommended to choose a grade higher than M300 for construction in regions with a cold harsh climate.

M400 and M450 brands are the most reliable, durable and strong concrete compositions, which guarantee durability of the most complex and heavy structures with serious loads. Such materials are chosen for the construction of multi-storey concrete buildings. In addition, there is concrete M500. This composition is used for the construction of special facilities, such as a bank vault.

If you have not yet decided on the project of a country house, the catalog "MariSrub" will help you. Here you will find ready options luxurious wooden cottages, cozy and compact country houses from a log and a bar. Projects vary in number of storeys, functionality, design and exterior style. In the catalog you will find two-story and one-story houses, summer cottages with an attic, balcony or terrace and many other projects.

How to make concrete for the foundation with your own hands

Before preparing, it is important to correctly calculate the foundation in order to find out how much concrete is needed. For this, each tape is counted separately and the results are added. To prepare a concrete mixture, the components are taken in the following proportions:

Crushed stone or gravel - 50 kg;

Water - ½ part of the volume of the remaining components (in this case, you get about 40-45 liters).

To prepare the mixture, use only dry sand and fine crushed stone or gravel. Combine the ingredients and mix thoroughly. By the way, the cleaner the sand, the faster it sets. If the solution is too thick or hard, add more water. Buy cement no earlier than one to two weeks before preparing the solution. Since over time it absorbs moisture and deteriorates.

It is better to pour concrete in the warm season. Otherwise, at sub-zero temperatures up to -10 degrees, add table salt to the mixture at the rate of 1.5% of the volume of cement. In more severe frosts, calcium chloride is used in the same proportion as salt. In addition, various useful substances can be added to the concrete mixture in order to enhance the strength and durability of the material, improve the quality and speed up the construction time.

Useful additives for concrete mix

How to properly pour concrete for the foundation

When the concrete mix is \u200b\u200bready, pouring into the formwork begins. Do it slowly or smoothly in layers. In this case, each layer is rammed with a vibrator or by tapping with a hammer and air is released. To do this, along the foundation, reinforcement is slowly pierced into concrete every two to three meters. After that, the surface is leveled with a flat board.

After preparation, the concrete mixture is allowed to be left for 2-3 hours. If there is no way to continue working, you can pour the composition over the surface of the future foundation, cover with plastic wrap. You can leave the concrete in this state for no more than 12 hours! After this time, the formed white plaque is removed from the surface and work continues.

The poured concrete is left for 4-7 days and then the formwork is removed and left for another two to four weeks until it is completely dry. Remember that the foundation gains about 90% of its strength in the first month after pouring! Cover the surface with plastic wrap. In hot and dry weather, water the concrete with cool water. After hardening, the foundation is covered with heat and waterproof materials, after which construction work can be continued.

What concrete to use for a strip foundation

Concrete for strip foundations: construction installation technology, composition and types, material selection criteria, do-it-yourself mix preparation, useful additives,

Monolithic foundation slabs belong to the class of non-recessed bases. Concrete is poured into a pit, along the perimeter of which a formwork is exposed, with an installed reinforcing cage, on a compacted sand-crushed stone pillow. The height of the slab is from 0.2 m. A base of this type can be used on various soils. This is a great option on unstable soils. In order for the erected base to serve as long as possible, to be strong and reliable, it is necessary to select a suitable grade of concrete for the slab foundation. There are a number of factors to consider when choosing. Material and labor costs will depend on its correctness.

Features of the slab foundation

The foundation slab is used mainly in areas with problematic, unstable soils, in places close to the surface of groundwater. Also, such a foundation is used when there is a likelihood of landslides or on bulk soils.

The technology for creating a monolithic slab is implemented in several stages:

• carry out a geodetic survey of the construction site;
• dig a pit of the required depth;
• expose the formwork;
• the bottom of the excavation is covered with a crushed-sand cushion, the thickness of which varies from 0.1 to 0.3 m;
• knit in two rows of reinforcement;
• pour the form with concrete.

The slab-type foundation is also called "floating", because it can withstand sufficiently significant ground movements without consequences for the construction. Also, such a foundation allows the construction of multi-storey, heavy buildings.

Large consumption of building material, and accordingly money, for the implementation of the project in practice is considered the main disadvantage monolithic foundation... Construction work is also accompanied by high labor costs, in comparison with the creation of other types of foundations.

The choice of the highest grade concrete will provide a result of high quality in terms of reliability, strength and durability, but the financial costs will increase significantly. In most cases, this will not be justified from the point of view of the existing loads, therefore, in each specific case, the choice of the grade of concrete should be approached taking into account the factors acting on the foundation being erected.

Classification of concrete

The main components of concrete are cement, water, filler and various additives. The first serves as a binding agent, with the help of which other constituent elements are connected.

Scheme of concrete varieties

The following materials can be used as fillers:

• gravel;
• sand;
• crushed stone;
• various bulk materials.

Fillers are designed to reduce the internal stress in concrete when it gains strength (hardening).

The final strength of the monolith depends on the presence of water in the right proportion in the solution. An excessive amount of liquid leads to mechanical weakening of the created structure.

The concrete is classified according to the criteria given in the table below.

Classification criterion	Letter designation	Characteristics of the indicator
brand	M	is the most important characteristic of the material that determines its performance
class	IN	shows the guaranteed strength of the composition, gives an idea of \u200b\u200bthe compression of concrete during hardening
mobility	P	determines the optimal water content in the solution, its fluidity
waterproofness	W	shows the degree of water permeability of the monolith

The material class ranges from B3.5 to B60. In practice, B7.5 - B35 have become widespread. Guaranteed strength means the load that the monolith can withstand in 95% of cases.

It is recommended to use compounds with an increased degree of frost resistance in order to avoid the appearance of cracks after a few years due to the effect of temperature extremes. The parameter range is F25 to F1000. Frost resistance is an important parameter in very wet soils, where there is constant contact of the support structure with the soil.

The value of the water resistance coefficient is from 2 to 20. When erecting the base, choose W2 - W12, focusing on the level of occurrence of groundwater.

The final fill quality is determined by many factors. One of the main is the correct ratio of the incoming components. The material should be of high quality.

Concrete grades

The concrete grade defines the construction area in which it can be used. It shows how a foundation that has gained full strength will resist the impact of operational loads. The brand is the main characteristic when choosing a building material, its strength is shown in kgf / cm2. In this case, water resistance and mobility are lowered.

Among the existing grades of concrete (from M50 to M1000), M100-M450 are widely used.

The table below shows the grades of the material and their characteristics.

№	Brand	Material characteristic
1	M100	is not suitable for the construction of foundations, but is used for the construction of blind areas, car sites, sidewalk paths
2	M200	suitable for the construction of foundation strips with low masses, structures erected on them, and also used for the construction of monolithic, reinforced belts and floor slabs
3	M300	supporting structures based on this material can withstand heavy loads, so it is used for construction different types grounds and houses
4	M400	it is used to create the supporting structures of buildings and industrial facilities
5	M500	structures created from this brand are distinguished by the maximum level of strength, reliability, therefore they are used in the construction of dams for hydroelectric power plants, metro, bank safes, bunkers

Due to its high cost, the M500 is not popular. The most widespread among private developers was the concrete grade M350. It is the best option in terms of the ratio of the price of the material to its quality.

Factors determining the choice of concrete for a monolithic slab

When building lightweight structures on a slab, such as a garage, a gazebo, a shed, a small frame or wooden house, the foundation material can be selected with an approximate consideration of the existing loads. Concrete grades M200 and M250 are suitable. Very rarely, a slab base is made for light structures. Often they dispense with pile or columnar types of foundation.

In order to choose which concrete is better suited for creating a reinforced monolithic slab in a particular case when erecting heavier buildings, it is necessary to analyze a number of factors:

• geological conditions at the construction site: type of soil, its structure, level of soil water;
• climatic features of the region: temperature regime and degree of air humidity;
• the weight of the building to be erected and related loads from snow, furniture, residents, household appliances and equipment.

All the factors considered should be taken into account in order to correctly determine the appropriate grade of concrete. Independent construction of the foundation (completely of the entire structure) requires certain knowledge and practical skills in performing work.

If the necessary experience is not available, then it is better to use the services of specialists who will not only competently build the object, but also choose the material suitable for specific conditions.

Concrete grades for creating a monolithic slab

In hard, rocky and sandy soil types, the entire load from the structure is evenly distributed. To build lightweight buildings on them, you can use concrete of the M150 or M200 brands. Heavier buildings will require an M300 or M350.

Clay soil is characterized by a high degree of heaving, its volume greatly increases when freezing unevenly in different directions. In this case, only the M350 - M450 varieties are suitable.

On any soil, even the heavier the building to be erected, the higher the grade of concrete used to build the foundation for it should be.

In most cases, to fill a monolithic slab foundation, you can use concrete with the following performance characteristics:

• from F200 by the degree of frost resistance;
• mobility P-3;
• the value of the coefficient of water resistance, starting from W8;
• m300 brand;
• class B22.5.

If the soil moisture is increased on the building site or the groundwater is close to the surface, then special attention should be paid to the water resistance of the concrete. Correct waterproofing of the base from below and to the sides will also help to cope with the problem. When choosing a method for protecting a foundation from water, economic feasibility is often a decisive factor. It is often cheaper to use waterproofing materials than waterproof concrete types.

Ready-made mixes offered by construction trade networks contain ingredients in the required proportional proportions. It is enough to simply mix them in the right ratio with water. The marking of the finished mixture is determined by the quality of the materials included in its composition: the brand of cement, the size and strength of the particles of crushed stone and sand.

If you mix M400 cement, crushed stone and sand in a ratio of 1: 4: 2 with water (50%), you get concrete with the M250 marking. If you add the binding component M500, then the grade of the final material will already be M350.

During the manufacture of the mixture in the factory, many related factors are taken into account when labeling products. At home, the best option is often the use of M300 compounds, which have the recommended parameters of frost resistance, mobility, and water resistance.

Calculation of the required volume of material for pouring the foundation

To determine the amount of concrete required for the construction of a slab, you need to know its volume. It is found by multiplying the height by the width and the length, or by the area of \u200b\u200bthe base.

The table below, according to GOST 7473-94, shows the compliance of the concrete class with its brand and the consumption of cement (M400) with a certain frost resistance, water resistance, mobility per 1 cubic meter of mortar together with crushed stone, sand and water.

Knowing the volume of the slab, according to the table, you can determine the required amount of sand, gravel and cement for pouring the foundation with the required strength. The working mixture in the indicated proportions can be easily prepared by yourself.

The technology for building a slab foundation is presented in the video below.

Recommendations for choosing crushed stone, sand and concrete grade for the construction of the base are given in the video below.

The operating time, reliability and strength of the entire building will depend on the correct choice of the grade of concrete used for the construction of the slab foundation. The choice of material is determined by the geology of the site and the mass of the future building. Products with the required parameters can be purchased in the form of ready-made mixtures or prepared independently.

In the construction of any building object, the construction of the base - the foundation - plays an important role. IN recent times the foundation blocks were replaced by pile and pile-strip foundations. Such foundations are made on site, and concrete will be required to fill pre-prepared structures.

Due to the violation of the technology for the construction of the foundation, often built houses crack over time, doors and windows warp, brickwork collapses, the frame of the house is deformed.

The result of the correct construction of the foundation is the high stability of the house, its long service life, as well as the ability to avoid time-consuming and costly repairs of an already constructed building. Everyone knows that fixing and rebuilding is always harder than building quality at once.

The strength and reliability of the foundation part depends on the type of soil, its level of freezing. The quality of the building is influenced by groundwater, the severity of the triple room, the type of shape of the building itself, the quality of the material and the influence of external action - digging a trench, foundation pit, the location of the construction site.

One of the important parts of any foundation is concrete. What grade of concrete and when is it needed?

Materials for making concrete

The main materials used for the manufacture of concrete mix include water, varieties of sand, all kinds of additional fillers and cement brands. Clean coarse sand and crushed stone are required as fillers. The use of fine sand with an admixture of clay, soil, other impurities, as well as the use of limestone or broken brick instead of high-quality crushed stone, significantly reduce the quality of concrete, even when a higher grade of cement is added to it.

Concrete grades and their application

There are different grades of concrete for different purposes. What brand do they use for building foundations? There are such grades of concrete:

• M100 is used at the beginning of construction to create a foundation cushion (foundation) for the construction of a wooden house, other small buildings, and is also used when installing fences.
• M150 is suitable for making strip foundations for the construction of small residential buildings built from cinder block materials, foam concrete and aerated concrete, as well as for the construction of small outbuildings.
• M200 is added to the mix for the construction of residential one-story and low-rise buildings that have light floors. Having high strength properties, such a mixture is used in factories for the manufacture of reinforced concrete blocks, which in some cases are also an integral part in the construction of the foundation.
• M250-300 is best suited for making foundations for large and multi-storey residential buildings and cottages that have a height of up to 5 floors.
• The M400 grade is used for the manufacture of foundations that can withstand large vertical loads. Such a concrete solution is used in the construction of multi-storey residential and industrial buildings.

What is the best solution to use for building the foundation of a house? For the correct choice, you need a lot of information about the site and the future building.

Which concrete to choose for a strip foundation?

When erecting small structures, especially on personal plots, the concrete mixture is prepared directly on the construction site, manually or using a small concrete mixer.

For large-scale construction, both residential and industrial buildings, the mortar can be ordered directly from the factory. Typically, a commercial solution will perform better than one made on its own.

In one case or another, when choosing a brand of concrete, you need to take into account the weight of the building being built and the load that the foundation will withstand. The characteristics of the soil and the degree of its moisture are also required.

The type of the foundation itself (tape, pile or pile-tape) also plays a role. To select the required concrete solution, you must first calculate the load from the building on the support itself. If we take into account only the loads, then for the construction of 1-2 storey buildings, concrete M200 of class B15 is needed.

If the building is made of bricks, aerated blocks, expanded clay concrete blocks, and a reinforced concrete slab is used as a floor, then concrete of a grade not lower than B20 is needed. When erecting multi-storey buildings with reinforced concrete elements, concrete M300 is used for the foundation - concrete B25 and higher.

The choice of concrete depending on the characteristics of the soil

Before starting the construction of the foundation monolith, you need to have a clear idea of \u200b\u200bwhat kind of soil prevails on the site. On solid soils, during the construction of low buildings, it is better to use concrete M150-200 for the construction of the strip part of the foundation. For construction on weaker soils, greater strength is needed, therefore high grade concrete is used.

The main reasons that affect the increase in the degree of soil moisture are the level of groundwater and the location to water bodies, as well as the presence of a basement.

To determine the required grade required for soil with high humidity, there is a coefficient of water resistance of the concrete mixture - W, its ability to prevent water from passing under pressure from the outside. It can be from W2 to W20. The numbers indicate the pressure in kgf / sq. cm.

For this type of soil, it is desirable to use B20-25. To increase the degree of impermeability, elements of external waterproofing of the foundation are used. Also, additives are used, which increase the stability of the concrete solution and make it more impervious to moisture.

It is better if all the components of the concrete material are calculated by a specialist. After all, only a person who knows the properties of concrete and soil will be able to tie everything together.

Subscripts for designating concrete for foundation structures

• M and number - denotes the grade of concrete;
• B and the number is the class of the material;
• F and number - indicates the number of times of freezing and defrosting;
• W and the number - the degree of resistance to moisture;
• P and number - indicates the degree of mobility of the resulting solution.

Characteristics of concrete mortar

In order for the concrete base to reliably support the house built on it for many years, it is necessary to choose the right material, taking into account its parameters:

1. Fluidity (P) depends on the amount of water injected. This parameter characterizes the mobility of the solution. This indicator is indicated by a number from 2 to 5. During the construction of a residential building, a concrete mixture marked 2-3 is used. Liquid concrete is intended for pumping it to a height or a long distance, as well as for pouring it into a formwork with a fine mesh.
2. Resistance to moisture penetration - W. Selection of concrete with this characteristic is intended for use in an area with high humidity soil. The maximum number of the index is 20, which means the maximum resistance to moisture. What is the permeability of the material, so will the durability of the foundation.
3. Frost resistance- F. The number after the index indicates the number of permissible frosts and defrosts. The maximum number is 1 thousand. For the construction of a residential building, concrete is suitable that can withstand 200 freeze cycles.

The strip foundation can be safely attributed to the category of the most popular - it is he who is preferred in the vast majority of cases when building their own housing outside the city. The scheme of such a foundation, an algorithm for its calculation, reinforcement drawings and pouring technology - all these issues have been worked out in practice to the smallest detail, and therefore many site owners very often prefer to take on its construction

But competently conducted size calculations will cost nothing. foundation tape, neatly dug trenches and firmly put together, reliable waterproofing and perfectly coordinated according to the drawings reinforcement cage, if the pouring is used not corresponding to the conditions of future operation or poorly prepared concrete. Therefore, we invite the reader who is interested in the topic of the strip foundation to take a short excursion into the theory and practice of preparing the solution necessary for such purposes. It is useful to know this both when planning the order of ready-made concrete, and for self-preparation of the mortar at the construction site.

So, what brand of concrete is needed for a strip foundation, and how it can be made on our own.

Classification of concrete solutions

First of all, what exactly is concrete? By this term it is customary to understand 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:

- an astringent (most often cement acts in this role);

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

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

If you read the construction literature, you can be convinced that the classification of concretes is quite ramified, and includes many of their varieties for very different purposes. However, in this case we will not delve into it - we are only interested in those types that are suitable for the construction of foundations. This means that from the whole variety we will single out only heavy solutions based on Portland cement and on dense aggregates.

If you look at it, then four main indicators of the solution give an almost complete picture of the performance of concrete: this is the brand strength or class (can be indicated by the symbol M or B), frost resistance (F), water resistance (W) and mobility or workability (P). Some indicators are of decisive importance for the construction of the foundation, others, say, indirect, but you need to get to know everyone.

Concrete grades and strength classes

This is perhaps the main indicator that must be considered when choosing a specific solution.

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

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

In the reference literature and in building technological instructions, very often, instead of the concepts of brand strength, they operate with an indicator of the class of concrete. These values \u200b\u200bare interrelated to a certain extent, and differ, rather, by the "coordinate system".

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

Thus, if the brand speaks about the average value of strength, then the class is already about the actual one. An example is a solution of the same component composition, corresponding to a certain brand, but solidified and gaining strength under different conditions, can show a different strength class according to the test results.

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

Table 1. The ratio of grades and classes of concrete

Compressive strength of concrete, kg / cm2	Concrete strength class	The closest concrete grade by 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

With 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 mark is designated by the letter symbol "F" and a number that 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 - the marking varies from F25 to F1000.

When assessing frost resistance, unnecessary extremes are often allowed:

• The number of freezing cycles does not mean the number of years, that is, the alternation of winter and summer. During one cold season, there can be several such freeze-thaw cycles, and sometimes even several dozen - remember winters with an abundance of thaws.
• Frost resistance class, for example, F50 - this does not mean at all that after 50 cycles the concrete becomes completely unusable.

In principle, such an assessment of frost resistance applies to concrete that is saturated with water. So, for example, a dry wall structure made of, say, concrete with a frost resistance grade F50 or F100, over the period of its many years of operation, is able to withstand thousands of freeze-thaw cycles, while remaining completely unharmed. That is, if the foundation is provided with the proper quality of waterproofing (and this is one of the key requirements for ensuring the durability of your own home), then the frost resistance brand will not be a critical indicator. Moreover, if the technology for preparing concrete is observed, this indicator, even if desired, cannot be underestimated - to make a smaller F100.

From whatever concrete the foundation is poured, its waterproofing is a must!

A big mistake is made by those owners who ignore this issue when building their home. Even the use of unjustifiably expensive brands of concrete in the absence of reliable waterproofing does not guarantee the durability of the building foundation. But it's not so difficult to execute. About this - in a separate publication of our portal.

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

• This is the paving of paths and the filling of blind areas: here a frost resistance class of at least F300 is desirable.
• The second case is a cement roof tile, when released, responsible manufacturers achieve frost resistance F600 ÷ F800.

Practice shows that for foundations (naturally, with their waterproofing), the F150 indicator is quite enough, and even less for walls, of the order of F50 ÷ F100

Cement prices

Concrete water resistance 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 (a cylinder with a height of 150 mm) does not allow water to pass through itself.

From the point of view of practical application in the conditions of individual construction (in particular, when erecting a strip foundation), the significance of this indicator is small. By analogy with the frost resistance class, if you follow the requirements of the technology for preparing a high-quality concrete solution of the required grade (class) of strength, then the optimal water resistance parameters will be achieved by themselves.

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

Strength class (closest grade) of concrete	Frost resistance	Water resistance
B-7.5 (M100)	F50	W2
B-12.5 (M150)	F50	W2
B-15 (M200)	F100	W4
B-20 (M250)	F100	W4
B-22.5 (M300)	F200	W6
B-25 (M350)	F200	W8
B-30 (M400)	F300	W10

Even if it seems to the owners that the soil at the construction site is oversaturated with moisture, it will still be much cheaper, faster and more reliable to perform high-quality waterproofing than to order expensive concrete with an increased waterproof grade (W12 or even higher).

Workability indicators of the solution

But this parameter is extremely important for ensuring the quality of work on the construction of the foundation. Moreover, in the conditions of an ordinary construction site, when the means of mechanization for placing concrete in the formwork may not be available. In fact, this indicator hides how plastic the solution is, amenable to pouring, distribution with full filling of all cavities, and leveling at a given level.

There are several criteria for assessing workability, but in everyday building practice, the mobility indicator is most often used, denoted by the letter P and a numerical value. Where does that come from?

The indicator of the mobility of the solution shows how much it can spread under the influence of its own weight. This parameter is checked by a simple experiment - a special form in the form of a truncated cone is tightly filled with a ready-made solution (base diameter - 200 mm, upper hole diameter - 100 mm, height - 300 mm. Filling is carried out in three steps - layers equal in height, with mandatory multiple Then, the excess solution is removed from above, and the form is carefully, progressively removed upward (this should take 3 to 7 seconds). The form is installed next to the cone formed from the solution, which sags under own weight.

The measured value of the cone subsidence from the initial horizontal level (from the top of the form) will lead to the desired indicator of the fluid mobility.

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

The amount of subsidence of the cone	Mobility indicator	Note
0	Not regulated	Rigid concrete is a special area of \u200b\u200bapplication.
- from 1 to 4 cm	P1	Inactive, semi-rigid concrete. Held on a vertically positioned shovel bayonet. In the practice of private construction, it is practically not used.
- from 5 to 9 cm	P2	A solution of medium mobility - smoothly slides off the spade bayonet. It can be used when pouring a foundation, but with a rather sparse arrangement of reinforcement rods and with mandatory deep vibration.
- from 10 to 15 cm	P3	Movable mortar - drains from a vertically located shovel bayonet. It can be considered, probably, optimal for pouring a strip foundation with any frequency of arrangement of reinforcing rods. Requires the mandatory use of a vibrator.
- from 16 to 20 cm	P4	Concrete mortar with increased mobility, practically fluid. Excellent for working with concrete pumping units. A good option for strip foundations. The use of vibro-laying is desirable.
- over 20 cm	P5	Completely fluid solution. More suitable for pouring monolithic walls and ceilings. For a strip foundation, it will still be too mobile, and for such purposes it is usually not used.

What kind of concrete to order for a strip foundation?

So, the main criteria for evaluating concrete solutions used for individual construction were considered. It remains to find out: what composition will be optimal for pouring the strip foundation.

Table 4. Fields of application of ready-mixed concrete of various brands

Strength class (grade) of concrete	Concrete brand	Concrete application
B7.5 (M100)	BSG V 7.5 P3 F50 W2	Foundation preparation
B10 (M150)	BSG V 10 P3 F50 W2	Preparation for the foundation, pouring the strip foundation for irresponsible structures
B12.5 (M150)	BSG V 12.5 P3 F100 W2	Preparation for the foundation, pouring the strip foundation for irresponsible structures (light farm buildings)
B15 (M200)	BSG V 15 P3 F100 W4	Monolithic tape and slab foundations, screeds, grillages.
B20 (M250)	BSG V 20 P3 F150 W4	Monolithic foundations - tapes and slabs, crossbars, insulated Swedish slabs, underfloor heating screeds
B22.5 (M300)	BSG V 22.5 P3 F150 W6	Monolithic foundations of any type, monolithic reinforced concrete supporting structures, thin high-strength screeds of warm floors.
B25 (M350)	BSG V 25 P3 F200 W8	All of the above applications - in particularly difficult operating conditions
B30 (M400)	BSG V 30 P3 F200 W8	Monolithic foundations and supporting structures for heavy multi-storey buildings, including those in difficult construction areas. Stronger brands are not used in individual construction.

Let's pay special attention - for the time being we are talking about ready-mixed concrete, which are ordered from the relevant companies with delivery to the construction site. In this case, the unloading of the mixture should be made no later than 90 minutes after the initial mixing of the components with water - during transportation in special concrete mixer trucks, and no more than 45 minutes - if the solution is transported in a dump truck, that is, without constant mixing. This means that it is necessary to assess in advance the fundamental possibility of such delivery, to provide access roads to the place of pouring the foundation.

When ordering ready-mixed concrete (BSG), some more nuances must be taken into account. Unfortunately, the appearance of a considerable number small firmspracticing the production of mortars does not mean that they all work in compliance with standards or established technical conditions... Alas, the realities are such that not everyone can be trusted - you should familiarize yourself with the reputation of similar organizations located nearby. Very often you have to deal with the fact that, according to the results of concrete maturation, its final actual strength significantly differs from that declared when purchasing a solution, and it is very difficult to check this at the stage of purchase. The desire of manufacturers to “save on cement” is understandable, but not at the expense of quality!

Which exit?

• The first is to trust only yourself, and, with strict observance of all necessary proportions (we will approach this issue a little later).
• Second, for insurance purposes, when ordering ready-mixed concrete, deliberately overestimate its strength class by one or two steps and all other relevant characteristics. By the way, they do the same if the construction has to be carried out on a site with pronounced heaving of the soil.

Therefore, we can give one more table based on the practice of construction in the usual conditions of the "Russian hinterland". The indicators given in it do not have any theoretical justification - these are only generalized average statistical data on the use of ready-made ready-mixed concrete specifically for pouring strip foundations.

Type of one-storey house	Soils with good load-bearing capacity, slightly loose	Heaving soils
Lightweight wooden panel or frame houses	BSG V 15 P3 F100 W4 (M-200)	BSG V 20 P3 F150 W4 (M-250)
Log houses, log cabins	BSG V 20 P3 F150 W4 (M-250)
Houses made of gas silicate blocks, expanded clay concrete, sawdust concrete (wood concrete) and other similar materials	BSG V 22.5 P3 F150 W6 (M-300)	BSG V 25 P3 F200 W8 \u200b\u200b(M-350)
Houses made of brick, stone or monolithic reinforced concrete	BSG V 25 P3 F200 W8 \u200b\u200b(M-350)	BSG V 30 P3 F200 W8 \u200b\u200b(M-400)

Note to table 5. In the event that it is planned to build a building with more than one floor, it is recommended to order BSG for a higher brand. But in any case - not higher than B30 (M400).

We prepare concrete for the strip foundation ourselves

If there is no opportunity to use the services of manufacturers of ready-mixed concrete, or there is no trust at all in the local "shabashniki", you can assign this very laborious function to "your own shoulders".

We must be prepared for the fact that the work to be done is considerable and almost continuous, since it is recommended to fill the strip foundation during one shift. Therefore, it is necessary to prepare in advance all the necessary components for the preparation of the desired grade of concrete, to provide for the procedure for their correct dosage (by volume or by weight). Perhaps you should consider whether there will be enough working hands to carry out almost continuous loading and unloading of the concrete mixer.

Concrete mixer prices

concrete mixer

So, for self-preparation of concrete solution for the foundation, the previously mentioned components will be required - cement, sand, crushed stone or gravel, water. The use of special additives that improve certain qualities of the finished solution is not excluded. But about additives - this is a special conversation, and they will be discussed in a separate publication of our portal. In the meantime - the basic components of concrete.

The main components of the concrete solution

Cement

The cement in concrete acts as a binder. Most often, for these purposes, Portland cement (PC) is used, obtained by fine grinding of grains of special clay (clinker) and limestone sintered at a high temperature, with a dosed addition (from 1.3 to 3%) of gypsum.

The cement produced by the industry is subdivided into grades - from 300 to 600. The brand itself indicates the approximate compressive strength of a solution prepared from cement and sand (in a ratio of 1: 3), with an optimal water-cement ratio and full maturation (28 days). For the preparation of concrete solutions used for pouring strip foundations, cement PC-400 is most often used, as the most accessible and quite universal for such purposes. Cement PC-500 can also be used - it's only a matter of changing the initial proportions, but it's just that PC-400 is, as a rule, easier to purchase because of its widespread availability, and the price-quality ratio speaks in its favor.

Some more information can be gleaned from the cement labeling.

• So, the symbol D indicates the presence of modifying additives: "DO" - there are no additives, another number is the percentage of additives from the mass of cement;
• Symbol "B" - fast-setting cement;
• - "PL" - plasticized cement;
• - "GF" - cement with hydrophobic qualities.

You should always pay attention to the date of cement production. Even under normal storage conditions, cement in the first three months is able to lose up to 20% of its brand strength, in six months this loss will already be 30%, and up to 40% - within a year. The way out is either to use only fresh cement, in accordance with the proportions of the solution, or to make the appropriate adjustments for the amount of cement applied (in proportion to the loss of strength) and an increase in the time for preparing the solution (almost fourfold). Much better, of course, is to try to get by with fresh cement.

Sand

Sand is used as an obligatory fine aggregate in concrete. The best option is open-pit mine, with a fineness modulus from 2 to 3.25 mm, but with a voidness of no more than 30%, that is, with the content of all fractions.

In private construction, when preparing concretes of grade up to M300, it is allowed to use sand. With a fine fraction (less than 1.6 mm) not more than 20% of the total volume., And with an impurity (clay) content of up to 3% by weight. The content of dusty sand fractions (less than 0.6 mm) should also not exceed 3%.

It is better to use dry sand for the correct water-cement ratio. The average density of the sand is about 1500 kg / m³.

Crushed stone prices

Gravel or crushed stone

Crushed stone or gravel is used as a coarse aggregate for concrete. The difference between these materials mainly lies in the fact that crushed stone is a derivative of forced crushing of rocks, and its edges are usually sharp. Gravel, on the other hand, is a product of natural destruction (weathering or water erosion) of rocks, and therefore its elements often have rounded outlines and smooth edges.

Crushed stone and gravel can also differ in the size of the fraction - usually this indicator can vary in the range from 5 to 70 mm (four fractions are subdivided: 5 ÷ 10 mm, 10 ÷ 20 mm; 20 ÷ 40 mm and 40 ÷ 70 mm). According to existing standards, for the high-quality preparation of concrete, crushed stone or gravel of at least two different fractions should be included in its composition - with a maximum of up to 40 mm, or three - with a maximum of 70 mm.

Wherein maximum size grains of crushed stone or gravel should not exceed two thirds of the distance between the rods of longitudinal reinforcement. In addition, the maximum size should not be more than 1/3 (or better - even 1/5) of any minimum size a poured building structure. since we have in question about a strip foundation, then, for example, with a belt width of 200 mm, the size of the fraction of crushed stone or gravel should not be higher than 40 mm.

In fact, when pouring strip foundations for small buildings, private developers often use a large aggregate of one fraction - 20 mm. This, in principle, is quite enough, but working on small ones with larger crushed stone or gravel, and when pouring narrow belts with a rather frequent arrangement of reinforcing rods, it is very difficult.

Crushed stone or gravel must also be clean - even small clay contamination can dramatically, up to 30%, reduce the final actual strength of the finished concrete solution. So if you purchased a material with clear signs of strong contamination with clay or soil, before starting work, you must in advance flush with directed jets of water from the hoses.

Water

It would seem - but what is difficult here: pour yourself water into the mixed solution until you get the desired consistency ...

It turns out that things are not so simple.

• First of all, certain requirements are also imposed on water in terms of its purity and chemical composition. All of them are listed in detail in the TU established by GOST 23732-79 - this is the absence of traces of oil products, acids, phenols, sugars, regulatory oxidizability, maximum salt content, etc. True, in most cases, clean tap or well water is fine for mixing.
• The second and, perhaps, the most important thing is the optimal ratio of water and cement. Excessive moisture never benefits the resulting "cement stone". Just look at the following diagram for an example.

Curved lines in the diagram indicate changes in the grade strength of the resulting concrete from cement (in proportion with sand 1: 3) of the corresponding grade. Let's take, for example, PC-400 cement. With a water-cement ratio of 0.4, the strength at full maturation reaches an indicator of over M400. But with an increase in the amount of water, there is a sharp decrease, and with a ratio of 1.0, the strength of concrete is already estimated at only M100, that is, the loss in this indicator is four times !!!

This, however, is easy to explain. Water that is not involved in the chemical reaction with cement has only two paths:

- or it gradually evaporates, leaving behind large pores, which sharply reduce the strength properties of the material.

- or it remains unbound in the pores - and this is even worse, as with the onset of frost, this moisture begins its destructive effect.

So, when mixing concrete, it is necessary to strictly observe the optimal water-cement ratio. For reference, the average values \u200b\u200bfor different grades of concrete and the cement used for their manufacture are given in the table:

Concrete grade (class) planned for production	Portland cement PC 400	Portland cement PC 500
M100 (B7.5)	1.03	does not apply
M150 (B12.5)	0.85	does not apply
M200 (B15)	0.69	0.79
M250 (B20)	0.57	0.65
M300 (B22.5)	0.53	0.61

But what if the construction took place in the winter?

"Recipes" of concrete for pouring strip foundations and the procedure for batching

Dosage of components for concrete preparation

So, it remains to consider what proportions must be observed for the preparation of a particular grade of concrete.

If desired, it would be possible to give the entire methodology for calculating and theoretically substantiating the ratio of the initial ingredients - by weight and by volume. But, probably, the reader is more interested in the practical side. Well, the preparation of this type of concrete suitable for pouring strip foundations is a question that has been worked out in everyday practice, that you can simply give tables of proportions.

Table 7. Dosage of components for preparing concrete based on PC-400 cement

M100 (B7.5)	1: 4.6: 7.0	10: 41: 61	7.8: 1
M150 (B10 ÷ B12.5)	1: 3.5: 5.7	10: 32: 50	6.4: 1
M200 (B15)	1: 2.8: 4.8	10: 25: 42	5.4: 1
M250 (B20)	1: 2.1: 3.9	10: 19: 34	4.3: 1
M300 (B22.5)	1: 1.9: 3,7	10: 17: 32	4.1: 1
M400 (B30)	1: 1.2: 2.7	10: 11: 24	3.1: 1

Table 8 Dosage of components for the preparation of concrete based on PC-500 cement

Brand (class) of strength of the concrete produced	Weight ratio (cement: sand: crushed stone)	Volume ratio (cement: sand: crushed stone)	Volume ratio of ready-mixed concrete to cement
M100 (B7.5)	1: 5.8: 8.1	10: 53: 71	9.0: 1
M150 (B10 ÷ B12.5)	1: 4.5: 6.6	10: 40: 58	7.3: 1
M200 (B15)	1: 23.5: 5.6	10: 32: 49	6.2: 1
M250 (B20)	1: 2.6: 4.5	10: 24: 39	5.0: 1
M300 (B22.5)	1: 2.4: 4.3	10: 22: 37	4.7: 1
M400 (B30)	1: 1.6: 3.2	10: 14: 28	3.6: 1

The amount of water is easy to determine for each specific case according to the recommendations of the table of water-cement ratio located above.

Mixing ingredients in a concrete mixer

The main task is to create an enveloping layer of their cement "paste" for all aggregate granules, regardless of their fraction. It is practically impossible to do such an operation manually - the use of mechanical mixers makes it possible to increase the strength of the resulting solutions up to 40% compared to mixing with a shovel in a container.

When preparing a solution in a concrete mixer, adhere to next order performing operations:

• At the very beginning of work, the container of the concrete mixer must, so to speak, "lubricate". To do this, a thin solution of cement, sand and water is mixed for several minutes - it is then drained - you can find it used at an ongoing construction site.
• Then, in a working large-volume concrete mixer (0.5 m³ or more), add in succession:

- 15 ÷ 20% of the planned amount of water;

- the amount of sand and cement required for dosage;

- after mixing this load, a coarse aggregate (crushed stone, gravel) and the remaining amount of water are added.

• If a small-volume concrete mixer is used, then it is better to do this:

- the required proportion of dry sand is mixed with about half of the crushed stone;

- then added, also on dry, cement;

- after thorough mixing on dry - add water, and at the very end, in order to finally break up all possible lumps - the rest of the crushed stone (gravel).

• You should never assume that the longer you stir, the better the solution. There should be a measure in everything, since it can turn out exactly "the opposite": the longer the cycle, the more water will simply evaporate, and the plasticity of concrete will decrease.

The minimum mixing time is usually estimated at one and a half minute. (Interestingly, German standards have their own opinion on this - the duration of mixing is generally estimated at 30 seconds).

Video: an example of preparing concrete M300 in a concrete mixer

Application: Fast and accurate calculation of components for self-preparation of concrete for pouring strip foundations

Below is a calculator that will allow you to quickly calculate the required amount of ingredients to prepare the required amount of concrete.

The calculator allows you to calculate in two ways:

• The first is determining the amount of ingredients for preparing a specific volume of solution - this can be useful, say, for planning the loading of a concrete mixer of known one-time productivity.
• The second option - allows you to determine the total amount of concrete for pouring the entire strip foundation. In this case, we will rather talk about the volumes of ingredients that must be purchased or prepared on the job site for self-preparation of the solution.

The calculator calculates the two most commonly used brands of mortar - M200 and M300, which are made from PC-400 cement.

The "folk" unit of measurement - a bucket - appears in the calculations. This refers to a bucket with a capacity of 10 liters.