Thermal conductivity of concrete: features, coefficient and table

One of the most important characteristics of concrete, of course, is its thermal conductivity. Change this indicator for different types of material can be significant. Dependsthermal conductivity of concrete,most likely, fromspeciesthe filler used therein. The lighter the material, the better insulator it is from the cold.

What is thermal conductivity?

When erecting buildings and structures,used different materials. Residential and production buildings in the Russian climate are usually warmed. That is, in their construction, special insulators are used, the main purpose of which is to maintain a comfortable temperature inside the premises. When calculating the required amount of mineral wool or expanded polystyrene, the thermal conductivity of the basic material used for the erection of the enclosing structures is necessarily taken into account.

Very often, buildings and structures in our country are built from different types of concrete. Also for this purpose, usingbricksand a tree.Actually the most thermal conductivity is calledThe ability of a substance to transfer energy in its thickness due to the motion of molecules. A similar process can occur, both in solid parts of the material and in its pores. In the first case it is called conduction, in the second case it is called convection.Cooling of the material goes much faster in its solid parts. The air filling the pores delays the heat, of course, better.

thermal conductivity of concrete

What determines the indicator

Conclusions from all of the above can do the following. Depends tConcrete conductivity,wood and brick, as well as any other material,their

  • density;
  • porosity;
  • humidity.

With increasing density of concrete, the degree of its thermal conductivity also increases. The more in the pore material, the better insulator from the cold it is.

Types of concrete

In modern construction, a variety of types of this material can be used. However, all existing concrete on the market can be classified into two large groups:

  • heavy;
  • light foam or with a porous filler.

Thermal conductivity of heavy concrete: indicators

Such materials are also divided into two main groups. Concrete can be used in construction:

  • heavy;
  • especially heavy.

In the production of a second variety of materialsuch fillers as metal scrap, hematite, magnetite, barite are used. Used especially heavy concretes usually only in the construction of facilities, the main purpose of which is protection from radiation. This group includes materials with a density of 2500 kg / m3.

thermal conductivity of cellular concrete

Conventional heavy concretes are manufactured withthe use of such filler types as granite, diabase or limestone, made on the basis of mountain crushed stone. In the construction of buildings and structures, a similar material with a density of 1600-2500 kg / m3.

What can be in this casethermal conductivity of concrete? Table,The information presented below demonstrates the indices characteristic for different types of heavy material.

Thermal conductivity of heavy concrete

Type of concrete

Extremely heavy

Heavy for reinforced concrete structures

On the sand

The heat conductivity index W / (m ° C)

1.28-1.74

With the density2500kg / m3 -

At a density of 1800-2500 kg / m3 - 0.7

Thermal conductivity of cellular lightweight concrete

Such material is also classified into twobasic varieties. Very often in construction, concretes based on a porous filler are used. As the last applied clay, tuff, slag, pumice. In the second group of lightweight concrete filler, the usual one is used. But in the process of kneading such a material foams. As a result, after ripening, many pores remain in it.

Concrete conductivitylung is very low.But at the same time, and in terms of strength characteristics, such a material is inferior to heavy. Use lightweight concretes most often for the erection of various kinds of residential and household buildings that are not subject to serious stress.

coefficient of thermal conductivity of concrete

Classify lightweight concretes not only by the method of manufacture, but also by purpose. In this regard, there are materials:

  • heat-insulating (with a density of up to 800 kg / m3);
  • structural and heat-insulating (up to 1400 kg / m3);
  • structural (up to 1800 kg / m3).

Thermal conductivity of cellular concretedifferent types of lightin the table.

Lightweight concretes: heat conductivity

Type of concrete

Heat-insulating

Structural and heat-insulating

Structural

Maximum allowable thermal conductivity W / (m ° C)

0.29

0.64

Not standardized

Thermal insulation materials

Such concrete blocks are usually used for the lining of walls, assembled from a brick or filled with cement mortar. As can be seen from the table,thermal conductivity concreteThis group can vary in a fairly large range.

Thermal conductivity of lightest concretes

Material

Aerated concrete

Expanded clay concrete

Coefficient of thermal conductivity W / (m ° C)

0.12-0.14

0.23-0.4

Concretes of this variety are often used as insulation materials. But sometimes they are also built of all kinds of insignificant fencing structures.

concrete with low thermal conductivity

Structural and heat-insulating and structural materials

Of this group in construction, foam concrete, slag-pomber-concrete, slag-concrete are most often used. Some types of claydite concrete with a density of more than 0.29W / (m ° C)can also be attributed to this variety.

Structural concretes: thermal conductivity

Material

Foam Concrete

Slag-pomber-concrete

Slag Concrete

Coefficient of thermal conductivity

0.3W / (m ° C)

Up to 0,63W / (m ° C)

0.6W / (m ° C)

Very often suchConcrete with low thermal conductivity is used directly as abuilding material. But sometimes it is also used as an insulator that does not let the cold pass.

How does the thermal conductivity of moisture

Everyone knows that almost any dry material isolates from the cold much better than the wet one. This is primarily due to the very low degree of thermal conductivity of the water.Protectconcrete walls, floors and ceilingspremises from low street temperatures, as we found out, mainly due to the presence of pores filled with air in the material. When wet, the latter is displaced by water. And, consequently, and significantly increasescoefficient of thermal conductivity of concrete.In the cold season, the water that gets into the pores of the material freezes.The result is thatheat-retaining qualities of walls, floors and ceilings are reduced even more.

The degree of moisture permeability in different types of concrete may not be the same. For this indicator, the material is classified into several grades.

Water permeability of concrete

Concrete grade

W4

W6

W8

W10-W14

W16-W20

Water-cement ratio (not more)

0.6

0.55

0.45

0.35

0.30

Tree as an insulator

And "cold" heavy, and lightweight concrete, thermal conductivitylow is low,of course,highlypopularand popular typebuildermaterial. In any case, the foundations of most buildings and structures are built exactly fromcement mortar mixed with rubble or rubble stone

lightweight concrete heat conductivity

Applyan etonite mixture or blocks made from it andfor the erection of enclosing structures. But often enough for the assembly of floors, ceilings and walls, and other materials, for example, wood. The beam and the board differ, of course, much less durable than concrete. However, the degree of thermal conductivity of a tree is, of course, much lower. In concrete, this figure, as we found, is 0.12-1.74W / (m ° C).In a tree, the coefficient of thermal conductivity depends, in particular, on a given concrete breed.

Thermal conductivity of different types of wood

Type of wood

Pine

Lime, fir

Spruce

Poplar, oak, maple

Coefficient of thermal conductivity W / (m ° C)

0.1

0,15

0.17-0.2

In other breeds, this indicator may be different.It is believed that, on average, the thermal conductivity of the wood across the fibers is 0.14W / (m ° C). It is best to isolate the space from the cold cedar. Its heat conductivity is only 0.095 W / (m C).

Brick as an insulator

Next, for comparison, consider the characteristics in terms of thermal conductivity and this popular building material.On strength propertiesbricknot only not inferior to concrete, but often exceeds it.The same applies to the density of this building stone. All brick used today for the erection of buildings and structuresis classified for ceramic and silicate.

thermal conductivity of heavy concrete

Both of these varieties of stone can in turn be:

  • full-bodied;
  • with voids;
  • slotted

Of course, solid bricks retain heat worse than hollow and crevice.

Thermal conductivity of bricks

Brick

Full silicate / ceramic

Silicate / ceramic with voids

Slotted silicate / ceramic

Coefficient of thermal conductivity W / (m ° C)

0.7-0.8 / 0.5-0.8

0.66 / 0.57

0.4 / 0.34-0.43

Thermal conductivity of concrete and brick, tThus, almost the same. Both silicate and ceramic stone isolate the rooms from the cold is rather weak. Therefore, houses built from such material should be additionally insulated. As insulation during the plating of brick walls, as well as those filled from ordinary heavy concrete, polystyrene or mineral wool is most often used. You can also use porous blocks for this purpose.

How is the coefficient of thermal conductivity calculated?

This indicator is determined for different materials,including concrete, according to special formulas. In total, two methods can be used. The thermal conductivity of concrete is determined by Kaufman's formula. It looks like this:

  • 0.0935x (m) 0.5x2.28m + 0.025, where m is the mass of the solution.

For wet (more than 3%) solutions, Nekrasov's formula is used:(0.196 + 0.22 m2) 0.5 to 0.14

thermal conductivity of concrete and brick

Erazitobeton density of 1000 kg / m3 has a mass of 1 kg. Respectively,for example,according to Kaufman, in this case we get a coefficient of 0.238.The thermal conductivity of concrete is determined at a mixture temperature of +25 ° C. Its cold and heated materials may change slightly.

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