Thermal conductivity of concrete. characteristics of heavy

Another 30-40 years ago, in our country, great importance was not attached to the preservation of heat. The houses were built from structures based on heavy types of concrete, and in the first place was the number of buildings being erected, and the thermal conductivity of concrete was considered a concomitant parameter. But times have changed, energy has risen in price, so energy efficient materials are now valued on the market.

What is thermal conductivity

Thermal conductivity is currently called the amount of heat that can pass in 1 hour after 1 m? material (in this case, concrete) when the ambient temperature changes by 1? C.

• This value is called the coefficient of thermal conductivity and is measured in watts per meter-kelvin..
• The coefficient is measured and calculated in laboratory conditions using specialized equipment.. For wide use there is a table of heat conductivity of concrete, thanks to which you can learn the characteristics of any type of concrete used in construction.

Important: this factor is most influenced by the material used as a filler in the monolith. For wet material during tempering, GOST 20024-76 is applied. Dry materials are regulated according to GOST 7076-78.

Characteristics of materials

Currently on the construction market there are several types of concrete. In addition to the well-known heavy compounds, the so-called light types of concrete are widely used, each of which has its own unique characteristics.

Heavy compounds

Heavy compounds are called monoliths, which are based on cement-sand mixture, the so-called peskobeton.

Or solutions, which include, in addition to the cement-sand mixture, heavy filler in the form of crushed stone of various fractions.

• In addition, most of the structures of this kind come with internal metal reinforcement, which gives the product additional strength and resistance to mechanical stress.
• Compared with new types of material, thermal conductivity of reinforced concrete is considered to be the highest, it can reach up to 1.5 - 1.7 W / mK. This is because heavy compounds have the highest density and specific gravity.
• The air, which in most cases acts as a heat insulator, should be removed as much as possible during the filling process. As a rule, vibropressing is used for this. Plus, the presence of metal reinforcement frame additionally increases the already considerable coefficient.
• This material is now more used for the construction of supporting structures. But even if the project provides for the use of wall reinforced concrete panels, they are necessarily insulated with an additional layer of thermal insulation.
• Single-layer panels can be used in the construction of industrial buildings, which do not provide internal heating. For the most part these are factory workshops of metallurgical plants or covered storage pavilions.

Next, we will talk exclusively about light types of concrete, they all appeared relatively recently and are the product of modern technology. Most of these materials have been specifically designed to save energy. They differ in small weight and rather low heat conductivity.

Aerated concrete blocks

This material has a porous structure, low thermal conductivity of aerated concrete blocks due to the fact that air acts as a heat insulator.

In addition, the production technology does not provide for the use of such traditional materials as sand and crushed stone for concrete.

• If you move away from engineering terms, the aerated concrete is made on the principle of yeast dough. The composition is mixed on the basis of special types of cement and additives, after which baking powder is added to it, as a rule, aluminum powder. The resulting mixture is poured into the form and "rises." As a result, we obtain a monolith, the air pores with a diameter of from 1 to 3 mm are evenly distributed throughout the volume.
• Compared to other porous materials, the thermal conductivity of aerated concrete can be called almost the highest, on average, about 0.12 - 0.14 W / mK.

Important: despite such high rates this material has a high hygroscopicity. That is, he is able to soak up moisture, so if you decide to build a house of aerated concrete blocks, you will need to seriously think about the quality of the lining.

On the video in this article you can follow the construction of a house of aerated concrete.

Claydite monolith

• First of all, let us dwell on what exactly clay is. This material has been known for a long time, it is a specially burned special clay, which contains additives. After firing, we obtain a porous material in the form of granules.
• The industry produces ready-made blocks of 2 types, light hollow and solid-cast. The first type is more used as a heat insulator or for the construction of light, one-story buildings. The second is designed for installation of supporting structures, it has greater density and increased strength.
• The thermal conductivity of the expanded clay block intended for warming is certainly higher, but the difference is not great. On average, the thermal conductivity of claydite-concrete is 0.23 - 0.4 W / mK.

Tip: claydite concrete is best suited for arranging screed or pouring blocks with your own hands. Instructions for kneading and pouring the mortar are traditional, proportions 1 part cement, 2 parts sand and 3 parts expanded clay. In this case, the price of the composition will be quite affordable.

The video in this article shows the principles of claydite construction.

Foam concrete

• The production technology of this material is akin to the production of aerated concrete. But it still contains sand, plus, thanks to special additives, foam concrete blocks practically do not absorb moisture.
• The price of these blocks is somewhat lower than that of aerated concrete, although the strength of foam concrete also leaves much to be desired. It is more used for arranging additional thermal insulation or building cottages no higher than 12 m. The thermal conductivity of foam concrete is also slightly higher than that of a gas silicate, it is about 0.3 W / mK.

Polystyrene concrete

• The heat insulator in this building material is pellets of foamed polystyrene foam, otherwise everything is traditional, cement, sand and additives. As a result, the design is more dense and durable.
• These blocks are produced with different density, as a result they can also be used as insulation and as a supporting structure. In view of such a wide range of thermal conductivity of polystyrene concrete can also vary depending on the purpose of products.
• So for insulating concrete blocks, it is 0.05 W / mK, then as the density increases, it can reach up to 0.14 W / mK.

The video in this article shows some moments of construction from polystyrene concrete.

Conclusion

In this article, we presented the averaged, standard thermal conductivity data for common concretes. But they can vary significantly depending on the level of moisture of the material and the presence of a reinforcing cage.