Concrete is a modern building material, competing in strength with natural stone. Its high operational properties ensured its popularity in the production of all types of construction works, including the construction of the foundation. If lightweight constructions can use columnar foundations, then for capital constructions a high-quality strip or pile foundation is required, the characteristics of which directly depend on the choice of concrete grade, skillful mixing and carefully selected composition.
In this article we will consider which concrete to use for the foundation.
Mixture composition
In the concrete mixture, two main components can be distinguished:
- Fractional filler (sand, crushed stone or gravel) is a “power” element that accepts all loads. The volume fraction in the composition is up to 80%.
- An astringent resulting from the contact of a cement mixture and water. The volume fraction in the composition is up to 30%.
The ratio of the listed substances in the concrete mixture can be different, depending on the brand of cement, the moisture content of the filler, and the presence of additives. The foundation is the bearing part of the building, therefore, to ensure resistance to the calculated loads, it is necessary to choose the composition of the concrete mix correctly. Concrete works excellently in compression, which allows the foundation to successfully withstand the pressure of the ground structure. The reinforcing cage, used in the foundation, provides strength in the transverse direction when moving the soil.
The choice of concrete for the foundation depends on the design of the building being built. There are various requirements for the foundation, which leads to the practical use of a wide range of concrete grades.
To answer the question, what brand of concrete is suitable for the foundation of a private house, consider the main types.
M100 brand concrete
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-capital buildings, such as fences, frame houses, sheds.
M150 concrete
According to its characteristics, this concrete brand is not very different from M100. The main application is preparatory construction work. Only the lightest strip foundations of single-storey light houses made of wood or hollow blocks, garages and sheds can be poured from M150 concrete . 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 because of the danger of groundwater, otherwise the use of waterproofing (liquid rubber) is mandatory.
Concrete brand M200
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 ceilings. Reinforced concrete, for example, piles or floor slabs, is allowed from concrete of the M200 brand. The main field of application in residential construction is the pouring of the foundation under frame-panel houses. Soil is allowed only sandy, and groundwater should not rise to the freezing height, while seasonal fluctuations should be taken into account.
Concrete brands M250 and M300
Cement content is average. The M250th concrete grade is used for the foundation of the house (for pouring) up to three floors. The M300 brand is more durable concrete, it is used in the foundations of cottages with a height of up to five floors. According to building codes, M300 concrete is allowed to be used for the manufacture of monolithic ceilings. Finds application when filling pools. Concrete of these grades can be used in the construction of foundations on sandy soils, as well as on gravel or crushed stone soil with a relatively high groundwater level.
M350 concrete
One of the most popular concrete brands in construction. Significantly surpasses M300 not only in strength, but also in frost resistance. It features a long declared life.
Suitable for the construction of multi-story buildings, used in the construction of consoles, ceilings and other critical structures. When constructing the foundation, concrete of the M350 brand can be used for a one-story residential building made of brick. Suitable for difficult clay soils and places where there is a high level of groundwater. Loams and clay soils are the most common. When freezing, clay increases in volume, which can lead to deformation of the foundation in the case of an incorrectly selected concrete grade.
M400 brand 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 area of application is the construction of multi-storey buildings (up to 20 floors in height).
What brand of concrete is needed for the foundation?
Concrete of a lower grade is cheaper, but 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 residential. What brand of concrete is needed for the foundation? Concrete grades M350, M400 are characterized by increased density, and therefore, moisture will penetrate through it worse, and the base will be drier. Sometimes, when building non-responsible structures on poor soil, it makes sense to consider which is more profitable: use a higher grade of concrete or 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 the house, which brand to choose is to pre-order design and estimate documentation for the designer. It defines the appropriate concrete grades for each type of work, including the foundation, and additional properties that the mortar must satisfy, such as:
- density,
- water resistance (protection against groundwater),
- frost resistance (the higher, the more suitable for harsh climate),
- fluidity
- fire resistance.
However, the concrete brand for the foundation of a private house can be selected independently. For this, it is necessary to take into account the following features of the constructed structure:
- construction weight, number of floors, presence or absence of a basement,
- geological surveys of the site: the type of soil and the depth of groundwater are determined,
- type of foundation: tape, pile or any other.
Each of the above factors affects what concrete is needed for the foundation, the choice of concrete grade, taking into account its special characteristics, etc.
Multidirectional forces on the entire perimeter act on the concrete monolithic foundation. The foundation should be deepened into the ground so that it is below the freezing level. Specific freezing depths vary widely, depending on the soil and climatic conditions. In general, for mid-latitudes, the freezing level is 0.9-1.5 m. It is recommended to choose a depth of laying with some margin. Reliance on a soil foundation that is not susceptible to freezing saves the strip foundation from deformation of frost heaving.
For a 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 low-rise construction.
Selection of the composition of the concrete mortar and mixing
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 slurry.
Since the construction of the foundation implies its reinforcement in order to ensure lateral strength, it is optimal to choose gravel or gravel of medium fraction. Chipped granite gravel provides the best grip.
As for the sand, in theory it is recommended that the sea, but the usual one from the sand pit is also suitable. It is important to note that sand should be filtered beforehand to eliminate clay and other undesirable inclusions.
There are no special requirements for water, an ordinary tap water will do. 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. For this, a volumetric capacity is required, in which sand, gravel or crushed stone and cement are added in a certain ratio. Mixing the dry components 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 with a shortage of material or the formation of surplus, which is also undesirable.
The volumes of the slab, strip footing, columns, which are then summed up, are calculated separately. The calculated value is multiplied by the coefficient of shrinkage of concrete, the value of which is taken from the passport. Since the reinforcement also occupies a certain volume in the formwork, to account for this, it is necessary to divide the concrete volume by a factor of 1.05. The resulting value is rounded up.
What concrete is needed for the foundation
Selection Instructions:
- carefully calculate the weight of the structure;
- to allocate a margin of safety due to a possible error or unforeseen circumstances;
- determine at what depth groundwater lies;
- determine the interaction of the soil and the future foundation.