Concrete is a modern building material that competes with natural stone in strength. Its high performance properties have made it popular in the production of all types of construction works, including during the construction of the foundation. If light structures can be used, then for capital structures a high-quality strip or pile foundation is required, the characteristics of which directly depend on the choice of concrete brand, skillful mixing and carefully selected composition.
In this article, we will look at what kind of concrete to use for the foundation.
There are two main components in the concrete mix:
The ratio of these substances in the concrete mixture may be different, depending on the moisture content of the filler, the presence of additives. The foundation is the bearing part of the building, therefore, to ensure the resistance to the calculated loads, it is necessary to choose the right composition of the concrete mixture. Concrete works well in compression, which allows the foundation to successfully withstand the pressure of the ground structure. The reinforcing 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 erected. There are various 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 for the foundation of a private house is suitable, consider the main types.
Refers to lightweight concrete, has a 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 the use of non-permanent buildings, such as fences, frame houses, sheds.
According to its characteristics, this brand of concrete does not differ much from M100. The main application is preparatory construction work. From it is possible to pour only the lightest strip foundations of one-story light houses made of wood or hollow blocks, garages and sheds. This brand of concrete for the foundation of a private house is only permissible if the rocky soil acts as a reliable foundation. It is impossible to deepen the foundation because of the danger of groundwater, otherwise the use of waterproofing (liquid rubber) is mandatory.
This concrete is already stronger and is often used in the construction of low-rise (up to two floors) buildings and structures with wooden or metal floors. From concrete grade M200, it is allowed to manufacture reinforced concrete products, for example, piles or floor slabs. The main area of application in residential construction is pouring the foundation for frame-panel houses. Only sandy soil is allowed, and groundwater should not rise to the freezing height, and their seasonal fluctuations should be taken into account.
The content of cement is average. The M250th brand of concrete is used for the foundation of the house (for pouring) up to three floors. Mark M300 - 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 at filling of pools. Concrete of these grades can be used in the arrangement of soils, as well as on gravel or crushed stone soil with relatively high level ground water.
One of the most popular brands of concrete in construction. Significantly surpasses the M300 not only in strength, but also in frost resistance. Differs in the long declared term of operation.
Suitable for construction multi-storey buildings, is used in the construction of consoles, ceilings and other critical structures. When building a foundation, concrete of the M350 brand 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. Freezing, the clay increases in volume, which can lead to deformation of the foundation in case of an incorrectly selected brand of concrete.
This brand is characterized by extremely high strength characteristics due to the high content of cement and specially selected filler.
This brand of concrete is used for the foundation of a private house. Also, the permitted scope is the construction of multi-storey buildings (up to 20 floors in height).
Concrete of a lower grade is cheaper, however, when building a foundation, it is better to provide some margin of safety, especially for those cases when it is planned to make the basement habitable. What brand of concrete is needed for the foundation? Concrete grades M350, M400 is characterized by increased density, and therefore, moisture will penetrate worse through it, and the base will be drier. Sometimes, when building irresponsible structures on poor soil, it makes sense to calculate what is more profitable: use a higher grade of concrete or get cheaper concrete, but treat 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, which brand to choose, is to make a reservation. design and estimate documentation constructor. It defines the appropriate grades of concrete for each type of work, including the foundation, and additional properties that the mortar must satisfy, such as:
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 constructed structure:
Each of the factors listed above affects what kind of concrete is needed for the foundation, the choice of brand of concrete, taking into account its special characteristics, etc.
Multidirectional forces act on a concrete monolithic foundation along the entire perimeter. The foundation should be deepened into the ground so that it is below the freezing level. Specific values for the depth of freezing vary widely, depending on the soil and climatic conditions. In general, for middle latitudes, the level of freezing is 0.9-1.5 m. It is recommended to choose the depth of laying with some margin. Reliance on a soil base that is not subject to freezing saves the strip foundation from frost heaving deformations.
For strip foundation lower grades of concrete will fit, but pile, on the contrary, requires higher and stronger ones. Pile foundations are used in the construction of capital multi-storey buildings. Strip foundations are equipped for
Despite similar designations, the brand of concrete and the brand of cement are completely different concepts. The number in the brand of cement means the strength of the cement mortar.
Since the design of the foundation implies its reinforcement in order to ensure transverse strength, it is optimal to choose crushed stone or gravel of the middle fraction. Chipped granite gravel provides the best grip.
There are no special requirements for water, ordinary tap water is suitable. The cement-water ratio is 2:1.
The preferred method is the use of a concrete mixer, but manual mechanical mixing of the solution is also possible. This will require a volumetric container, in which sand, gravel or crushed stone and cement are added in a certain ratio. Having mixed 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.
An incorrect calculation threatens with a shortage of material or the formation of surpluses, which is also undesirable.
The volumes of the slab, strips of the strip foundation, 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 occupies a certain 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.
Selection instruction:
Monolithic reinforced concrete tape is most often used by individual developers for the construction of one-story and two-story buildings. In this regard, the question often arises - what brand of concrete for the strip foundation of a private house will be optimal? After all, the durability of the base depends on the main operational parameters of the mortar used. In the future, a competent selection of a cement-crushed stone mixture will save the homeowner from carrying out unscheduled repair work requiring large financial investments and strength.
Before ordering mixers with a concrete mix for pouring a monolithic foundation tape, it is necessary to determine its basic parameters:
It depends on their choice how strong the base will be and how long the structure will last, regardless of the operating conditions.
Prior to the adoption in 1986 of SNiP 20301-84, when designing not only strip foundations, but also other reinforced concrete structures, the concrete grade was the basic parameter. This term reflects the average compressive strength of an individual concrete sample. It is expressed as kgf / cm 2 - a kilogram of force exerted per unit area. It is she who is adhered to now in private housing construction.
At present, with the adoption building codes and rules in all calculations of reinforced concrete structures, including strip foundations, it is customary to use not a brand of ready-mixed concrete, but a class of its compressive and tensile strength. This value reflects the guaranteed strength of the material, under the pressure or force exerted on it in MPa. And here it is not the average value that is taken, but the exact value with the minimum permissible error.
The brand and class of concrete are indicated by the letters M and B, respectively, with numerical values. In the first case, the numerical expression for indicates the average value of strength in kgf / cm 2, in the second - the value of guaranteed strength in MPa with a small error (13.5%).
The main range includes the values of classes B7.5 - B40 and grades M100 - M500.
The lowest tensile strength for concrete is 100 kg/cm2. In private construction, cement mixtures used for strip foundations with a value above 400 kg / cm2 are not advisable to use: the highest grades are expensive, which makes their use in this area unjustified waste.
Frost resistance (F) is an indicator that reflects the number of freeze-thaw cycles that a monolithic tape-type foundation can withstand. As a rule, concrete collapses, mainly due to the expansion of water freezing in its pores. The more of them, the lower the F index. Such structures wear out quickly, losing their bearing capacity.
| Characteristics of concrete for frost resistance | |
|---|---|
| Brand | Characteristic |
| Less than F50 - low | Structures made of such concrete quickly crack under the influence of temperature differences. The compositions of this brand are used extremely rarely. |
| F50-F150 - moderate | The most common group. These brands are suitable for many years of operation. This level of frost resistance is typical for mixtures with average compressive strength. |
| F150-F300 - increased | Structures built from concrete of increased frost resistance are able to work for decades in harsh conditions, characterized by significant temperature fluctuations. |
| F300-F500 - high | This level of frost resistance is required in special cases. One example is the fluctuating water level in the life of a facility. Such material is expensive, it is not advisable to use it in private construction. |
| F-500 - extra high | Used in exceptional cases. Such frost resistance is possessed by mixtures of the highest grades. Buildings made of them can last for centuries. |
The numbers indicate the number of freeze-thaw cycles that the monoliths can withstand.
Moisture resistance or hydrophobicity of concrete is its ability to resist the penetration of moisture under a certain pressure. This parameter is marked with a combination of the letter W and an even number - from 2 to 20. The numbers indicate the maximum pressure (MPa x 10-1) at which a test sample with a diameter of 150 mm and the same height will not let moisture through.
| Compliance of concrete grades with moisture resistance class | ||
|---|---|---|
| Waterproof class | Characteristic | Concrete grade |
| W2 | The material is prone to absorption a large number water. Not used without waterproofing. | M100-M200 |
| W4 | Absorbs a moderate amount of water, not recommended for use without waterproofing measures | M250-M300 |
| W6 | Possesses the lowered water permeability. Widely used in construction. | M350 |
| W8 | After absorbing moisture in the amount of 4.2% by weight of the material, the permeability of the brand begins to decrease. | M400 |
| W10-W20 | Resistant to moisture, used in the construction of hydraulic structures, water storage tanks, etc. Does not require waterproofing. The high cost (4.5-5.3 thousand rubles / cubic meter) is the main limiter for use in private construction | Over M400 |
The ideal option for pouring a strip foundation is concrete grade M300. It has sufficient strength, frost resistance falls into the "increased" range and moderately absorbs moisture.
To understand what brand of concrete is needed for a strip foundation, we turn to the requirements of building codes and manufacturers' recommendations:
Grades of higher strength - M350, M400, etc. are used for the production reinforced concrete products- hollow or ceilings of column-and-beam reinforced concrete frames of buildings, for the construction of bridges, bank vaults. AT individual construction these mixtures are practically not used.
Not suitable for strip foundations and brand of concrete M200. However, in the construction of light one-story country houses, its use is quite acceptable - on sandstones with a low level of groundwater.
To determine what brand of concrete is needed for a strip foundation, it is necessary to analyze a series critical factors. These include the weight of the building, the characteristics of the soils on construction site and the location of groundwater relative to the sole of the base of the house.
Mass of all building materials involved in the construction of the house, creates a load on the foundation tape. It is this parameter that is decisive when choosing a brand of concrete. For guidance to private builders, you can use the following rules:
The above recommendations are approximate. In fact, the weight of the above-ground structure is not the only factor taken into account when choosing a concrete grade. It is necessary to take into account wind and snow loads, the magnitude of which depends on the location of the building site.
Data on wind and snow loads can be found in SNiP or building guides. An inexperienced builder is in for a surprise there: these data vary not only depending on the region, but also the design of the roof, the magnitude of its slope, etc.
Without geological research, it is impossible to make a final decision on the choice of concrete brand. Requirements for the strength of the strip foundation of the building depend on the type of soil:
Since clay soils are very common, mixtures of the M300 brand are the most used in private construction.
The location of groundwater makes significant adjustments to previous recommendations for choosing a concrete grade. If they lie below the depth of freezing of the soil, all of the above is quite true. If their level is high, the brand of the working solution must be taken an order of magnitude higher.
And what brand of concrete is used by experienced builders on water-saturated soils to fill the strip base? In this matter, they are guided by the coefficient of water permeability of the material. With a high level of underground water layers the best choice will be brand M350.
In the formulations of concrete solutions, a portion of cement is taken as a unit, other components (sand and crushed stone) are taken in relation to it.
For ease of use in this table, the volume of cement equal to 10 liters is taken as the basis.
Properly selected brand of concrete is a guarantee of the construction of a tape-type foundation of proper strength. But it is equally important to choose best option otherwise you may incur additional costs. The best thing is to order the calculation of the foundation to experienced designers.
Strip foundation - a monolithic reinforced concrete structure located in the ground under the walls or load-bearing structures of the building. The popularity of this type of foundation is due to its technical simplicity and acceptable speed of construction. Its characteristics directly depend on what brand of concrete is needed to fill a strong and durable strip foundation.
When choosing a building mixture, the main criterion is the grade of concrete used for the strip foundation. It shows the mechanical load that the material can withstand in compression. For example, marking M200 means that for every 1 cm² of base area there can be a load of 200 kg. The binder is cement, and sand and gravel are most often used as fillers.
There are other factors to consider when choosing a tape mix. It - climatic conditions the more severe they are, the stronger and more frost-resistant the composition should be. Particular attention is paid to the soil - its density, saturation with moisture.
The foundation must serve as a reliable foundation for the entire life of the structure. It is almost impossible to repair it, so miscalculations made during construction will lead to irreversible consequences. And here the question of what brand of concrete is used for the strip foundation is the key.
You can choose the brand of mixture for the base of this type only after calculating the load. It depends on the weight of the walls and ceilings, for which it will serve as a support. Less pressure is provided by panel-panel or small wooden structures, such as gazebos, baths or country houses. Brick or monolithic walls require grades with a strength index of M250.
Before starting work, it is necessary to perform geo-prospecting of the land plot, which will help to calculate the depth of the foundation, strength, and take into account other features of the foundation. Exploration will allow to find out the composition of soils, characteristics, depth of groundwater. When choosing which brand of concrete is needed for a strip foundation, it is necessary to take into account the type of foundation on which it will be laid - clay, rock or sand.
Studying the properties of soils, pay attention to the depth of their freezing in the selected region. The sole of the foundation must be below the freezing level of the soil, otherwise it will collapse. Depending on soil moisture, the degree of reinforcement with metal elements is calculated. On unstable soils, at the corners of the tape, where the load is maximum, reinforced concrete pillars are buried.
The most “convenient” soils include rocky and sandy ones with high density. They can use cheaper mixtures, with less cement. Clays and loams swell when freezing, so trenches are dug deeper, more durable material is taken. On unstable marshy wet soils, concrete with increased water resistance is used, special piles or poles are used.
The characteristics of the solution also depend on other factors. One of them is the quality of the aggregates used to make the mortar. Sand is used without foreign inclusions such as clay or organic elements. Water must be clean and free of impurities and salts dissolved in it.
The grade of cement must be higher than that of concrete, for example, to make the M250 composition, M400 cement is used.
The crushed stone fraction affects the strength, it is advisable to choose as large as possible. It is also important what this filler is made of - crushed granite is the best option, but gravel with similar strength indicators can be used in the tape.
Concrete for strip foundations, as a rule, is selected from the M200-M400 range, depending on the main and related factors. The brand of the mixture depends on the number of ingredients for preparation and calculation of the required proportions. For example, for M400, 1 part of M500 cement, 1.2 parts of sand, 2.7 parts of crushed stone are taken. Each type is intended for a specific type of building:
Sometimes mortar characterized by an indicator of the concrete strength class, denoted by the letter "B", which also shows the material's resistance to compressive loads. These values are interrelated, their correspondence can be found in the tables. For example, B20 corresponds to M250. It is the classes and brands that are the main characteristic by which the material for the construction of this type of foundation is selected.
Competent reinforcement will give greater strength to the foundation. For this, 12 mm corrugated reinforcement is used, and in case of large loads, other diameters are selected. The minimum cross-sectional area of the reinforcement should be 0.1% of the cross-section of the foundation where it is laid.
If the work is carried out in the heat, the concrete is covered with a heat-insulating material (rags, films, cloth, sawdust, etc.). It is advisable to water the surface several times. With increased GWL, the water resistance of concrete should be at least W4. In this case, it will not lose strength throughout its entire service life.
When building a foundation, you can not save on concrete. An incorrectly made foundation will cause constant problems both at the stage of building a structure and during operation.
The strip foundation in modern construction is considered the most popular concrete base.
Before proceeding with the construction of the facility, experts recommend finding out what brand of mortar is needed for the construction of the strip base.
The strip foundation is externally presented in the form of a closed contour - a reinforced concrete trench, which is laid under each load-bearing wall of the object in order to distribute the weight of the building along its perimeter. With the help of such a foundation, subsidence and distortion of buildings are prevented. The main advantages of this design are strength, reliability and durability.
To do this, it is recommended to use in each case when pouring concrete of the appropriate brand and class. These quality criteria are considered the most significant when choosing a mixture. The difference between these concepts is as follows:
What kind of concrete is required for pouring is determined in each case individually. In this regard, experienced builders identify several aspects that must be considered when choosing the most suitable solution. For a strip foundation, this material of low grades is usually used. For objects being built without a project, it is recommended to use concrete class B15 grade M200. If the groundwater is shallow, then the grade should not be lower than M300.
Often, under the strip foundation, it is necessary to make a pillow 10 cm thick. Such a structural element performs important functions:
In this regard, the M100 grade or higher is considered the most suitable for laying the pillow. When carrying out such work, you should know the proportions of mixing sand, crushed stone and cement.
Taking into account European standards for unreinforced construction, it is recommended to use a similar mixture of the following proportions:
This composition of the mixture is as close as possible to M150.
For reinforced structures, the following composition is used:
The M350 brand is the most consistent with this composition.
A mark for pouring a strip foundation during the construction of heavy buildings, for example, prefabricated panel houses, should be presented in the form of M200. If it is planned to build small houses from beams, then the foundation is poured using the M250 or M300 brand. For pouring the foundations of heavier massive houses, it is recommended to use the M350.
The brand directly depends on the type of soil on which it is planned to fill the strip foundation. In such a situation, it is recommended to lay the base on sandy or rocky soil. To do this, you can use the brands M200 and M250. Otherwise, the brand used must be higher than indicated. If the foundation is poured higher in class, then the foundation will be frost-resistant, which is very important for regions with severe winters.
A serious mistake made by households in the construction of personal facilities is the purchase of concrete below the recommended class. Naturally, such a step is justified from the point of view of economy. But in this situation, the tape base will not be considered a reliable design of the object being built.
Another mistake that amateur builders make is ignorance of concrete grades, class and other characteristics. In this regard, experienced builders are advised not to rely on managers of specialized stores, but to choose on their own. The data of the most suitable material can be as follows:
In any case, the brand of concrete is selected for a tape-type foundation, taking into account the strength, frost resistance, and water permeability of this material.
The foundation tape is not the main criterion for choosing a brand of concrete. The total weight of the object, the condition of the soil are the main aspects that should be taken into account in this matter. Based on this, it is recommended to use M200 for light buildings, and for sandy or rocky soil, the strip foundation is poured with low grades - M150-M200.
An important criterion for choosing concrete is the weather conditions typical at the time of construction work, as well as the proximity to the object under construction of rivers and reservoirs. If you use a heavy solution of B15-B25 for the strip base, then you will need to purchase crushed stone 20-30 mm. As for the size of sand particles, concrete is prepared from river coarse-grained bulk material.
The foundation of any building is the foundation. It perceives significant loads, compensates for the reaction of the soil, ensures the stability and safe operation of the building. To ensure the reliability of the foundation, it is necessary to know which concrete for the foundation is best used. After all, the strength characteristics of the foundation must correspond to the mass of the building being erected, the characteristics of the soil, and for a long period of time protect the structure from destruction. Let's figure out which brand of mixture it is advisable to use to fill the solid foundation of a private building.
For concreting foundations, various types of compositions are used, differing in strength characteristics. Depending on the brand of mixture used, its strength changes. It increases from the minimum value, which is 7.5 MPa for the M100 solution, to maximum indicator, equal to 50 MPa for a mixture of M700.
Having settled on one of the foundation laying structures, it is necessary to choose a brand of concrete for the foundation
For the implementation of activities related to concreting, various grades of concrete mortar are used. When choosing the optimal concrete mix option, the following factors are taken into account:
In the construction industry, concrete compositions are used, which are marked with the capital letter M and a digital index characterizing strength. Depending on the marking, the percentage of Portland cement in the solution and strength characteristics change.
Consider the purpose of various concrete mixtures:
If we proceed only from the load, then in most cases concrete M200 class B15 is suitable for 1-2 storey buildings
When deciding which concrete to use for the foundation of a house, it is advisable to give preference to solutions that have increased strength, frost resistance and water resistance. They will provide a high margin of safety and allow you to safely operate the building for a long time.
It is important to choose the right type of composition used for specific construction activities. Concrete mortar, which has increased strength, has an increased price. Lightweight concretes with low strength characteristics are not able to withstand real loads.
In the case of sandy or rocky soils, for a strip foundation and a building of 1-2 floors, you can safely choose low grades of concrete M150 - M200
It is necessary to find the best option, focusing on the following parameters:
