Concrete is a modern building material that rivals natural stone in strength. Its high performance properties have made it popular in all types of construction work, including foundation construction. While lightweight structures can be used, capital structures require a high-quality strip or pile foundation, the characteristics of which directly depend on the choice of concrete grade, skillful mixing and carefully selected composition.
In this article we will look at what concrete to use for the foundation.
Mixture composition
There are two main components in a concrete mixture:
- Fractional filler (sand, crushed stone or gravel) is a “power” element that absorbs all loads. The volume fraction in the composition is up to 80%.
- resulting from contact of cement mixture and water. The volume fraction in the composition is up to 30%.
The ratio of the listed substances in the concrete mixture may be different, depending on the moisture content of the filler and the presence of additives. The foundation is the load-bearing part of the building, therefore, to ensure resistance to design loads, it is necessary to correctly select the composition of the concrete mixture. Concrete works well in compression, which allows the foundation to successfully withstand the pressure of the ground structure. The reinforcement cage used in the foundation also provides strength in the transverse direction during soil movements.
The choice of concrete for the foundation depends on the design of the building being constructed. There are different requirements for the foundation, which leads to the use in practice of a wide range of concrete grades.
To answer the question of which brand of concrete is suitable for the foundation of a private house, let’s consider the main types.
Concrete grade M100
Refers to lightweight concrete, characterized by low cement content. The main application is in the preparatory steps of construction work, when pouring concrete preparation. M100 is quite cheap, but its strength characteristics limit its use to non-permanent buildings, such as fences, frame houses, and sheds.
Concrete grade M150
In terms of its characteristics, this brand of concrete is not much different from M100. The main application is preparatory construction work. Only the lightest strip foundations of one-story light houses made of wood or hollow blocks, garages and sheds can be poured from it. This brand of concrete for the foundation of a private house is permissible only if the rocky soil will act as a reliable foundation. The foundation cannot be deepened due to the danger of groundwater; otherwise, the use of waterproofing (liquid rubber) is mandatory.
Concrete grade M200
This concrete is already stronger and is often used in the construction of low-rise (up to two floors in height) buildings and structures with wooden or metal floors. Concrete grade M200 can be used to manufacture reinforced concrete products, for example, piles or floor slabs. The main area of application in residential construction is pouring foundations for frame-panel houses. Only sandy soil is allowed, and groundwater should not rise to the freezing point, and their seasonal fluctuations should be taken into account.
Concrete grades M250 and M300
Cement content is average. M250 grade of concrete is used for the foundation of a house (for pouring) up to three floors. Grade M300 is a more durable concrete; it is used in the foundations of cottages with a height of up to five floors. According to building codes, concrete grade M300 is allowed to be used for the manufacture of monolithic floors. Finds application when filling swimming pools. Concrete of these grades can be used for soil development, as well as on gravel or crushed stone soil with a relatively high groundwater level.
Concrete grade M350
One of the most popular brands of concrete in construction. Significantly superior to M300 not only in strength, but also in frost resistance. It has a long declared service life.
Suitable for the construction of multi-storey buildings, used in the construction of consoles, ceilings and other critical structures. When constructing a foundation, concrete grade M350 can be used for a one-story brick residential building. Suitable for difficult clay soils and places where the groundwater level is high. Loams and clay soils are the most common. When clay freezes, it increases in volume, which can lead to deformation of the foundation if the grade of concrete is incorrectly selected.
Concrete grade M400
This brand is distinguished by extremely high strength characteristics due to its high cement content and specially selected filler.
This brand of concrete is used for the foundation of a private house. Also permitted area of application is the construction of multi-storey buildings (up to 20 floors in height).
What grade of concrete is needed for the foundation?
Concrete of a lower grade is cheaper, but when building the foundation it is better to provide some margin of safety, especially for those cases when it is planned to make the basement residential. What grade of concrete is needed for the foundation? Concrete grades M350, M400 have a higher density, and therefore moisture will penetrate through it less easily, and the base will be drier. Sometimes, when building irresponsible structures on poor soil, it makes sense to consider what is more profitable: using a higher grade of concrete or using cheaper concrete, but treating the foundation with waterproofing to protect it from groundwater.
The easiest way to determine what brand of concrete is needed for the foundation of a house, and which brand to choose, is to pre-order design and estimate documentation to the designer. It defines suitable grades of concrete for each type of work, including foundations, and additional properties that the solution must satisfy, such as:
- density,
- waterproof (protection from groundwater),
- frost resistance (the higher, the more suitable for harsh climates),
- fluidity,
- fire resistance.
However, the brand of concrete for the foundation of a private house can be selected independently. To do this, it is necessary to take into account the following features of the structure being built:
- weight of the structure, number of storeys, presence or absence of a basement,
- geological survey of the site: the type of soil and the depth of groundwater are determined,
- type of foundation: strip, pile or any other.
Each of the factors listed above influences what kind of concrete is needed for the foundation, the choice of concrete grade taking into account its special characteristics, etc.
A concrete monolithic foundation is subject to multidirectional forces along its entire perimeter. The foundation should be deepened into the ground so that it is below the freezing level. Specific freezing depths vary widely, depending on soil and climatic conditions. In general, for middle latitudes the freezing level is 0.9-1.5 m. It is recommended to choose the laying depth with some margin. Reliance on a soil base that is not subject to freezing saves the strip foundation from frost heaving deformations.
For a strip foundation, lower grades of concrete are suitable, but a pile foundation, on the contrary, requires higher and stronger grades. Pile foundations are used in the construction of permanent multi-storey buildings. Strip foundations are equipped for
Selection of concrete mortar composition and mixing
Despite similar designations, the grade of concrete and the grade of cement are completely different concepts. The number in the cement grade indicates the strength of the cement mortar.
Since the design of the foundation involves its reinforcement in order to ensure lateral strength, it is optimal to choose crushed stone or gravel of the middle fraction. Crushed granite gravel provides the best traction.
There are no special requirements for water; ordinary tap water will do. The cement-water ratio is 2:1.
The preferred method is to use a concrete mixer, but manual mechanical mixing of the solution is also possible. To do this, you will need a volumetric container into which sand, gravel or crushed stone and cement are added in a certain ratio. After mixing the dry ingredients well, you can gradually add water, stirring constantly until a homogeneous mass is formed. It is important not to overdo it with the amount of water.
Calculation of the required amount of concrete
Incorrect calculation threatens a shortage of material or the formation of surplus, which is also undesirable.
The volumes of the slab, strip foundation strips, and pillars are calculated separately, which are then summed up. The calculated value is multiplied by the concrete shrinkage coefficient, the value of which is taken from the passport. Since the reinforcement also takes up some volume in the formwork, to take this into account, the volume of concrete should be divided by a factor of 1.05. The resulting value is rounded up.
What kind of concrete is needed for the foundation?
Selection instructions:
- carefully calculate the weight of the structure;
- allocate a margin of safety due to possible errors or unforeseen circumstances;
- determine at what depth groundwater lies;
- determine the interaction of the soil and the future foundation.
A strip foundation is a strip that runs along the perimeter of the house and takes the full load of the structure. The number of tapes depends on the number of load-bearing walls. This type of foundation is characterized by strength and reliability. It is ideal for heaving and difficult soils, high groundwater levels and weak soils. A strip foundation is chosen if you want to build a house with a basement, basement or underground floor.
Installation of a strip foundation involves the installation of removable formwork, reinforcement and pouring concrete. It is labor-intensive and requires a large consumption 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 determining which concrete to choose and use for a strip foundation, you need to understand the principle of installing a strip foundation. Installation of the structure is labor-intensive, but quite easy and understandable. Therefore, you can install a strip foundation with your own hands. Installation includes the following work:
- The land is cleared and leveled;
- Mark the future foundation using pegs and rope. Measure the evenness of the sides using a level along the corners and diagonals;
- They dig a pit 40-50 cm deep. They start digging from the lowest point of the site;
- Sand is placed deep into the resulting trench and covered with gravel in a layer of 15 centimeters, watered with cool water and compacted;
- Ruberoid or a special waterproofing film is laid on the sand cushion;
- Formwork is made from bars, boards or plywood;
- Make a reinforced lattice or mesh at a distance of 50-60 mm from the edges of the pit. To do this, the reinforcement is tied using knitting wire into square cells with a side of 40-50 mm. You cannot use a welding machine for fastening, as corrosion will form at the welding points!;
- Leave openings for pipes and utility networks;
- 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, water 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, strengthen the waterproofing and, if necessary, insulate the foundation.
The tape is perfect for building a country house and cottage. This is a durable and strong structure that can withstand heavy loads and does not require special ground preparation. This 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.
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. The cement contains the following markings:
SS - sulfate resistant;
PL - increased plasticity.
For the foundation, choose cement marked M. Keep in mind that from M200 cement you can get maximum M100 concrete for a strip foundation, 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 index, concrete will withstand 100 frosts and defrosts).
Concrete marking indicates how much load one square meter of base can withstand. For example, M250 concrete 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, timber and even brick.
What concrete to use
Concrete grade below M200 is used for pouring paths, sidewalks or blind areas. This material is not suitable for the foundation of a residential building! For a lightweight structure, for example, for a gazebo, a bathhouse or a small prefabricated panel house, choose M200. By the way, it is also suitable for pouring a concrete staircase, if one is planned for a summer cottage. And for a small garden house made of timber or logs, use M250.
For a large, spacious wooden cottage, the grade of concrete for a strip foundation is M300 or M350. This is a very durable composition, since in addition to standard components it includes granite. Such concrete is characterized by resistance to temperature changes and severe frosts, and increased water resistance. It will allow you to build a high-quality, solid and durable country house 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.
Grades M400 and M450 are the most reliable, durable and strong concrete compositions that guarantee durability of the most complex and heaviest structures with heavy loads. Such materials are chosen for the construction of multi-story concrete buildings. In addition, there is M500 concrete. This composition is used for the construction of special objects, such as a bank vault.
If you have not yet decided on a country house project, the “MariSrub” catalog will help you. Here you will find ready-made options for luxurious wooden cottages, cozy and compact country houses made of logs and timber. Projects vary in number of floors, functionality, design and external style. In the catalog you will find two-story and one-story houses, cottages with an attic, balcony or terrace and many other projects.
How to make concrete for a foundation with your own hands
Before preparation, it is important to correctly calculate the foundation to find out how much concrete will be needed. To do this, each tape is counted separately and the results are added up. 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 it will be approximately 40-45 liters).
To prepare the mixture, use only dry sand and fine crushed stone or gravel. Combine the ingredients and mix the mass 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 or two weeks before preparing the solution. Because over time it absorbs moisture and deteriorates.
It is better to pour concrete in the warm season. Otherwise, at sub-zero temperatures down to -10 degrees, add table salt to the mixture at the rate of 1.5% of the volume of cement. In severe frosts, calcium chloride is used in the same proportion as salt. In addition, various useful substances can be added to the concrete mixture to enhance the strength and durability of the material, improve quality and speed up construction time.
Useful additives for concrete mix
How to pour concrete for a foundation correctly
When the concrete mixture is ready, pouring into the formwork begins. Do this slowly or smoothly in layers. In this case, each layer is compacted with a vibrator or by tapping with a hammer and the air is released. To do this, reinforcement is slowly pierced into the concrete every two to three meters along the foundation. After this, the surface is leveled using a flat board.
After preparation, the concrete mixture can be left for 2-3 hours. If it is not possible to continue work, you can pour the composition over the surface of the future foundation and cover it with plastic film. You can leave concrete in this state for no more than 12 hours! After this time, the resulting white coating 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 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 waterproofing materials, after which construction work can continue.
What concrete to use for a strip foundation
Concrete for strip foundations: construction installation technology, composition and types, material selection criteria, do-it-yourself mixture preparation, useful additives,
To build a reliable house, you need to build a solid foundation. Concrete, as the main component of any structure, provides the required resistance to mechanical stress, water resistance, and therefore increases the durability of the building and its foundation. Therefore, correct calculation and selection of brand allows you to build a high-quality foundation. Below are the main points of selecting a category for constructing the foundation of a residential building.
What does a concrete foundation consist of?
The composition of the ingredients in concrete for the base in a private house includes water, cement, sand, crushed stone or gravel. The fractional content of sand should consist of particles measuring 1.2-3.5 millimeters, but not smaller. The component must be free of silt and clay. However, impurity content up to 5% is allowed. Otherwise, the strength of concrete will decrease.
The size of gravel or crushed stone varies between 1 and 8 centimeters. The material must also be clean. Cement is selected from the following categories:
- Portland cement, suitable for the construction of any buildings on a monolithic foundation;
- slag Portland cement, characterized by increased moisture resistance, but instability at low temperatures and low speed;
- pozzolanic Portland cement, intended for the construction of foundations with close groundwater or in conditions of high humidity, for the construction of underwater and underground buildings, but in the air it loses its properties and causes severe shrinkage;
- quick-hardening derivatives of the categories of mixtures listed above, which shorten the maturation period of ready-made concrete.
The classic solution for the foundation of a private house consists of 80% fractional filler (sand, crushed stone or gravel) and 30% binder (cement with water).
Selecting a concrete grade based on strength characteristics
Concrete strength table. In the presence of groundwater, solutions M350 and higher are taken for laying foundations from slabs and strips. It is recommended to use only chalked gravel as filler. For the construction of bored piles, the 200th and . It is suitable for small private houses and cottages. Their strength is sufficient if the mixing proportions are maintained exactly as required. This should result in a homogeneous solution that requires high-quality tamping by vibration. This will increase not only the strength of these brands, but also frost resistance and moisture resistance.
Other characteristics
To choose concrete, in addition to strength, soil quality, wall materials, other characteristics should be taken into account:
- Conditions of construction and operation.
- Frost resistance. The parameter is taken into account if the foundation is poured in an unheated house, for example, in private summer cottages for temporary residence. This value is also taken into account when constructing foundations and insulation around the perimeter of the house.
- . Compositions with this parameter, equal to W2, W4, are recommended for laying foundations on well-drained soils in the absence of groundwater. Class W6 is suitable for foundations on leaking soils. The remaining water resistance categories (W8, W10) are practically not used for private homes.
- Workability. This value determines the comfort of working with concrete. For pouring the foundation, a material with parameter P2 is recommended. If frequent reinforcement is carried out, the use of grade P3 is allowed. Category P1 concrete is also allowed for use, but this will require high-quality vibration of the masonry to settle it and achieve high homogeneity.
To build a reliable foundation for a private house, you need to pay special attention to the material used for manufacturing. It’s easy to get lost in the types of concrete, but if you prepare carefully, determining what kind of concrete is needed to pour the foundation will not be a problem.
The grade of concrete provides information about its main characteristics when designing and purchasing, it is necessary to find out the following characteristics:
- class or grade (outdated designation) of concrete in terms of compressive strength;
- frost resistance grade;
- moisture resistance grade;
- mobility grade.
All these characteristics are indicated by the manufacturer of the concrete mixture. Each of these points must be taken seriously, since they together and individually affect the durability and reliability of the structure. Next in order.
Selection by material strength
For the non-professional, there is a lot of confusion due to the presence of two ways to classify concrete by strength. Because of this, it is difficult to determine what kind of solution is needed to build the foundation of a private house. Here the case is similar to steel reinforcement. Builders of the “old school” use one designation, while young specialists in educational institutions are taught another. This is where misunderstanding arises. To determine which mixture is best to use for the foundation, you need to understand the concepts of class and brand.
The grade of concrete is designated by the letter M. The number after the marking is the average compressive strength of the finished structure in kgf/cm². Strength tests are carried out on concrete cubes with an edge of 15 cm. Experiments can be carried out 28 days after manufacturing the sample, provided that its hardening occurred at an average daily temperature of 20ᵒC. The cubes are pressed under pressure and determine the average strength. It is necessary to know the brand of concrete in order to order it at the factory, since outdated designations are still often used there.
The concrete class is designated by the letter B. After the marking, the value of the guaranteed strength in MPa is indicated. The guarantee is 95%. This means that if you take 100 samples, 95 or more of them will withstand the load specified on the brand. It is the class of concrete that is given as a characteristic of compressive strength in new (updated) regulatory documents.
A comparison of various designations is given in GOST “Heavy and fine-grained concrete. Technical specifications" table 6, appendix 1.
| Strength class | Nearest brand in terms of strength | Deviation of strength characteristics for a brand compared to a class |
| B 7.5 | M 100 | +1,8% |
| AT 10 | M 150 | +14,5% |
| At 12.5 | M 150 | -8,4% |
| At 15 | M 200 | +1,8% |
| IN 20 | M 250 | -4,5% |
| At 22.5 | M 300 | +1,8% |
| At 25 | M 350 | +6,9% |
| At 27.5 | M 350 | -2,8% |
If calculations are carried out using the markings from the first column, and the order at the factory is carried out according to the second, then a deviation with a plus sign means that concrete of greater strength than necessary is ordered (will ensure greater reliability).
The table shows only those values that are best used for pouring the foundation. The use of higher classes is acceptable, but economically unjustified. Classes below B 7.5 are not used for load-bearing structures. The foundation is an element that works primarily in compression. In this case, the strength of concrete under vertical load is high, so there is no reason to use particularly strong concrete; the tension is compensated by the reinforcement.
Purpose of each brand
Classes B 7.5, B 10, B 12.5 (M 100, M 150) classified as “lean” concrete. They are used for the manufacture of concrete screeds or preparations. B 12.5 can be used for light, small utility buildings or porch foundations; lower classes are not designed for significant loads. The main role played by such mixtures during construction is leveling and preparation.
Class B 15 (M 200) has great strength. Can be used for retaining walls, concrete preparations for foundations, foundations of small buildings and structures with low mass.
Class B 20 (M 250) one of the most common for pouring support structures of an individual house. Can be used for the manufacture of foundation slabs for wooden or frame houses, as foundations for porches and entrance groups. The soil characteristics must be quite good.
Class B 25 (M 350) ranks first in popularity. Suitable for pouring any type of foundation for a two-story house made of massive materials (brick, concrete). The class is highly durable. It is also used for constructing floors or steps of porches. Suitable for foundations on weak heaving soils.
If you plan to build a particularly important facility with high loads, the answer to the question of what kind of concrete is needed for the foundation will be At 27.5 and higher. For private housing construction, the use of these brands is not recommended due to the high load-bearing capacity margin and a strong increase in financial costs for materials.
Choice by frost resistance
What brand of foundation is needed for frost resistance depends on the climatic conditions of the area and the area of application. Frost resistance is the ability to withstand a certain number of cycles of alternating thawing and freezing. Marking is done with the letter F. The number after it means the minimum number of cycles. On average, the number of freeze-thaw cycles is equal to the number of years. That is, F50 concrete is designed for 50 seasonal changes from warm to cold (50 years). Determination of the frost resistance number is carried out according to GOST “Concrete. Methods for determining frost resistance".
The scope of concrete application, depending on the number of freeze-thaw cycles, can be summarized in a table.
| Frost resistance | Area of use |
| Limited area of application: for structures protected from contact with the external environment |
|
| F50-F150 | The best option for private and mass housing construction. It is better to choose the average value F100 |
| F150-F300 | Used in harsh climatic conditions (for example, regions of the Far North) |
| F300-F500 | Used for the construction of structures operated in damp conditions; unpopular for private housing construction |
| >F500 | Not used for the construction of private houses, suitable for particularly critical structures with a long expected service life |
Important! For any structures in contact with the external environment, according to regulatory documents, frost resistance must be at least F50.
Choice by water resistance
This characteristic is determined according to GOST “Concrete. Methods for determining water resistance". According to GOST “Heavy and fine-grained concrete. Technical Specifications" there are 10 grades of concrete mixture for the foundation of a house from W2 to W20 in increments of 2 (W4, W6 and so on).
The letter in the marking indicates the waterproof classification. The number characterizes resistance to water pressure. For example, brand W4 can withstand water pressure up to 4 atmospheres, which is 0.4 MPa.
To answer what kind of solution is needed for the foundation of a house, it is necessary to consider the climatic features of the area and the water saturation of the soil. A universal option would be the composition designated W4.
Mixture mobility
Depends on the technology for performing foundation work. There are three options for the development of events:
- The concrete mixer's access to the foundation area is limited. If access is completely limited, the solution is supplied in buckets (for small objects), after pouring it into prepared containers. In this case, it is better to choose a solution with a mobility of at least P3.
- If the concrete solution is supplied to the formwork by a pump, then the mobility of the mixture is chosen to be at least P4.
- If access for mixers is free from all sides, P2 is sufficient.
Remember that you need to place concrete in the formwork no later than 2 hours from the moment the solution is prepared at the factory. And it’s better within 1.5 hours, so as not to ask questions on the forum later -.
Knowing the grade (class) and other characteristics of concrete (frost resistance, water resistance, mobility), you can safely contact the plant and order a concrete solution for monolithic work.
The foundation is the basis on which the strength and durability of any building depends. Typically, for individual construction, strip structures are erected (a reinforced concrete strip that is buried in the ground and runs in a closed circle under the load-bearing elements of the building). Since the grade of concrete for the strip foundation of a private house determines the hardness of the future building, before starting construction work, it is recommended to familiarize yourself with all the classifications and features of this material.
Concrete grade
To figure out which brand of concrete to use for a strip foundation, let's consider the main classifications of this material:
- M 50 and M 75 are the most brittle concrete, used exclusively for filling voids. It is not suitable for load-bearing structures.
- M 100 - suitable for preparatory work, for example, when pouring a cushion under the main foundation.
- M 150 - can be used both for a cushion under the base and during the construction of a light one-story building.
- M 200 - suitable if the concrete for the strip foundation is made on stable soil and provided that the load on the base is small.
- M 250 - more often used in the manufacture of strip-column structures.
- M 300 is the most popular brand of concrete for strip foundations, which has a good ratio of cost and strength.
- M 350 – for “serious” projects that involve a large load on the base. For example, if we are talking about column-transom reinforced concrete frames.
- M 400 is not the most successful brand of concrete for constructing a strip foundation for a private house, since this expensive composition is usually poured into underwater structures or the foundations of houses located in seismic zones.
- M 500 - it is recommended to use it when pouring vertical structures or use it as an additive to give the structure greater strength.
From all of the above, it follows that composition M 300 is optimal for strip structures. However, in addition to the main marking of the mixture, it is worth taking into account other indicators.
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.
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 m 3 of crushed stone, 0.6 m 3 of sand and 180 liters of water.
- For M 200 you will need 280 kg of cement, 0.8 m 3 of crushed stone, 0.5 m 3 of sand and 180 liters of water.
- M 250 will require 330 kg of cement, 0.5 cubic meters of crushed stone, 0.6 m 3 of sand and 180 liters of water.
- For M 300, mix 380 kg of cement, 0.8 m 3 of crushed stone, 0.45 m 3 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.
Building weight and soil characteristics
If we are not talking about a finished project that contains all the recommendations for construction work, then before deciding what grade of concrete is needed for a strip foundation, check the total weight of the structure.
Let's look at the most common building options and the types of mixtures suitable for them:
- For a prefabricated panel house with a height of no more than two floors, it is enough to prepare the foundation using M 200 cement.
- For a two- and three-story log building, as well as for a house made of foam concrete or gas silicate blocks, choose grades M 200/250/300.
- A heavy, permanent brick building will require concrete M 300 or higher.
If we talk about the characteristics of the soil, then a lot depends on the geology of your site and the level of groundwater. Based on this:
- A composition based on M 200-250 will work well on sandstone and rocks.
- To lay a foundation on clay, choose grades 250-300.
- If the groundwater is located quite close to the base of the foundation, then the concrete should be no lower than M 300. The fact is that the higher the strength of the concrete, the lower the moisture absorption rate will be.
The most problematic areas are those in which clay soil or loam predominates. The problem is that this type of soil, when frozen, “heaves,” that is, it does not freeze evenly, which is why the shallow foundation can be squeezed out. Ultimately, this leads to its deformation. There are no “special” grades of concrete for this case, so it’s best to:
- Check the level of soil freezing and bury the structure below it.
- Make a rubble concrete strip foundation reinforced with reinforcement. Only in this case, the role of the load-bearing frame is not a metal rod, but a coarse filler (rubble stone).
Having decided what grade of concrete is needed for the strip foundation, it is necessary to calculate the material that will be required for the foundation.
How to calculate the amount of concrete for a strip foundation
To independently determine how much concrete you will need to create a foundation for a house or bathhouse, you need to determine the total values of the future tape, namely:
- Length. The length of the tape passing under the internal walls of the building.
- Height. Depth of laying (including the length that will rise above ground level).
- Width.
In the construction industry, there is a standard formula that can easily be used to calculate the volume of concrete in cubic meters:
V (required volume of concrete) =S (cross-sectional area)xL (tape length)xH (belt height)
Let's say we plan to build a bathhouse, for this we estimate approximate parameters:
- The uniform cross-section of the tape will be 0.20 “squares”.
- The total length of the tape will be about 30 meters.
- The height will be about 0.6 meters.
We multiply 0.20 by 30 and by 0.6, we get 3.6 cubic meters (0.6 m = 3.6 m 3). This will be the cubic capacity of concrete we need for the foundation for the bathhouse.
If the section of the tape is non-uniform in the same area:
- the length will be 10 meters (0.16 m2);
- the length of the section is 20 meters, the cross-section will be 0.24 m 2;
Then the calculation will look like: V = (10 x 0.16) + (20 x 0.24) x 0.6. As a result, we will get 3.84 cubic meters of composition.
Healthy! If you plan to order a mixer for kneading, it is better to take a small supply of solution (about 10-15% more).
In addition, there are a number of tips that may be useful when constructing a fundamental strip-type foundation.
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.
In custody
Knowing the characteristics of different brands of concrete and taking into account the characteristics of a suburban area, you can easily independently prepare the fundamental foundation of a future house, bathhouse, garage and many other objects.