Thermal conductivity and heat capacity of bricks
The thermal conductivity and heat capacity of bricks are important parameters that make it possible to determine the choice of material for the construction of residential buildings, while maintaining the required level of heat in them. Specific indicators are calculated and are given in special tables.
What is it and what influences them?
Thermal conductivity is the process that occurs inside the material during the transfer of thermal energy between particles or molecules. At the same time, the colder part receives heat from the more heated one. Energy losses and emissions of heat occur in materials not only as a result of the heat transfer process, but also during radiation. It depends on the structure of the substance.
Each building component has a specific indicator of heat conductivity, obtained experimentally in the laboratory. The process of heat distribution is uneven, so it looks like a curve on the graph. Thermal conductivity is a physical quantity that is traditionally characterized by a coefficient. If you look at the table, you can easily notice the dependence of the indicator on the operating conditions of this material. Extended reference books contain up to several hundred kinds of coefficients that determine the properties of building materials of different structure.
For reference, the choice in the table indicates three conditions: normal - for a temperate climate and medium humidity in the room, the "dry" state of the material, and "wet" - that is, operation under conditions of increased moisture in the atmosphere. It is easy to see that for most materials the coefficient increases with increasing humidity of the environment. The “dry” state is determined at temperatures from 20 to 50 degrees above zero and normal atmospheric pressure.
If the substance is used as a heat insulator, indicators are chosen especially carefully. Porous structures retain heat better, and more dense materials give it away to the environment. Therefore, traditional insulation have the lowest coefficient of thermal conductivity.
As a rule, glass wool, foam concrete and aerated concrete with a particularly porous structure are optimally suitable for construction. The denser the material, the greater the thermal conductivity it possesses, therefore, transfers energy to the environment.
Types of materials and their characteristics
Brick, produced today in many species, is used in the construction of ubiquitous. Not a single object - a large industrial building, a residential apartment building or a small private house, is built without a brick foundation. The construction of cottages, popular and relatively inexpensive, is based solely on the brickwork. Brick has long been the main building material.
This is due to its universal properties:
- reliability and durability;
- environmental friendliness;
- excellent sound and noise insulation characteristics.
Allocate the following types of bricks.
- Red. It is made of baked clay and additives.Differs in reliability, durability and frost resistance. Suitable for wall construction and foundation construction. Usually placed in one or two rows. Thermal conductivity depends on the presence of gaps in the product.
- Clinker. The strongest and dense facing brick. Full-bodied, solid and reliable furnace material due to its high density has the most significant thermal conductivity coefficient. And therefore it is senseless to use it for the walls - it will be cold in the house, you will need a significant warming of the walls. But brick clinker is indispensable in road construction and when laying the floor in industrial buildings.
- Silicate. Inexpensive material from a mixture of lime with sand, often products are combined into blocks to improve performance properties. In the construction of buildings is used not only full-bodied, but also silicate with voids. The durability of the sand block is average, and the thermal conductivity depends on the size of the connection, but still remains quite high, so the house will require additional insulation.
Lower figure for a slotted briquette compared to the analog without internal gaps.It should also be noted that the product absorbs excess moisture.
- Ceramic. Modern and beautiful material, produced in a significant range. If we talk about thermal conductivity, it is significantly lower than that of ordinary red brick.
There is a full ceramic briquette, fireproof and slotted, with voids. The conductivity coefficient of heat depends on the weight of the brick, the type and number of slots in it. Warm ceramics are externally beautiful, besides inside it has a lot of thin gaps, which makes it very warm and therefore ideal for construction. If there are also weight-reducing pores in the ceramic, the brick is called porous.
The disadvantages of such a brick should include the fact that the individual units are small and fragile. Therefore, warm ceramics is not suitable for all designs. In addition, it is an expensive material.
As for refractory ceramics, this so-called fireclay brick is a burnt block of clay with a high thermal conductivity, almost the same as that of an ordinary full-bodied material. However, refractoriness is a valuable property that is always taken into account during construction.
Fireplaces are built from such a “stove” brick, it has an aesthetic appearance, it retains heat in the house due to its high thermal conductivity, it is frost-resistant and is not affected by acids and alkalis.
The specific heat capacity is the energy that is consumed to heat one kilogram of material by one degree. This indicator is needed to determine the resistance to heat of the walls of a building, especially at low temperatures.
For products from clay and ceramics, this indicator ranges from 0.7-0.9 kJ / kg. The silicate brick gives indicators of 0.75-0.8 kJ / kg. Chamotte is capable, when heated, to increase the heat capacity from 0.85 to 1.25.
Comparison with other materials
Among the materials that are able to compete with bricks, there are both natural and traditional - wood and concrete, and modern synthetic - penoplex and aerated concrete.
Wooden buildings have long been erected in the northern and other areas characterized by low winter temperatures, and this is no accident. The specific heat of a tree is much lower than that of a brick. Houses in this area are built of solid oak, coniferous trees, and also used chipboard.
If the tree is cut across the fibers, the thermal conductivity of the material does not exceed 0.25 W / M * K. The low rate and chipboard - 0.15. And the most optimal factor for construction is wood, cut along the fibers - no more than 0.11. Obviously, in the houses of this tree is achieved excellent heat preservation.
The table clearly demonstrates the variation in the value of the coefficient of thermal conductivity of a brick (expressed in W / M * K):
- clinker - up to 0.9;
- silicate - up to 0.8 (with voids and gaps - 0.5-0.65);
- ceramic - from 0.45 to 0.75;
- slotted ceramics - 0.3-0.4;
- porous - 0.22;
- warm ceramics and blocks - 0.12-0.2.
At the same time, only warm ceramics and porous bricks, which are also fragile, can argue with the tree in terms of the level of heat preservation in the house. However, brickwork is used more often in the construction of walls, and not only because of the high cost of solid wood. Wooden walls are afraid of atmospheric precipitation, fade in the sun. Does not like wood and chemical influences, besides, wood is capable of rotting and drying out, and mold is formed on it. Therefore, this material requires special treatment prior to construction.
In addition, the fire can quickly destroy the wooden structure, as the wood burns well.In contrast, most types of bricks are quite resistant to fire, especially fireclay bricks.
As for other modern materials, for comparison with a brick, foam block and aerated concrete are usually chosen. Foam blocks are concrete with pores consisting of water and cement, a foaming composition and hardeners, as well as plasticizers and other components. The composite does not absorb moisture, is highly frost resistant, retains heat. Used in the construction of low (in two or three floors) private buildings. Thermal conductivity is 0.2-0.3 W / M * K.
Aerated concrete - very strong compounds of similar structure. They contain up to 80% of pores providing excellent thermal and sound insulation. The material is eco-friendly and convenient to use, as well as inexpensive. Thermal insulation properties of aerated concrete is 5 times higher than that of red brick, and 8 times higher than that of silicate (thermal conductivity does not exceed 0.15).
However, gas block structures are afraid of water. Moreover, in terms of density and durability, they are inferior to red brick. Extruded polystyrene extruded, or penoplex is called one of the most popular building materials on the market.These are the plates intended for thermal insulation. The material is fireproof, does not absorb moisture and does not rot.
According to experts, the comparison with a brick this composite can withstand only thermal conductivity. Insulation has a figure of 0.037-0.038. Penoplex is not dense enough, it does not have the necessary carrying capacity. Therefore, it is best to combine it with brick in the construction of walls, with the addition of penoplex masonry and a half hollow bricks will ensure compliance with building codes for thermal insulation of residential premises. Penoplex is also used for foundations of houses and pavilions.
Frost resistance is determined by freezing and thawing cycles. This parameter is important when choosing the type of brick for laying bearing walls. The brand depends on the number of cycles and is indicated on the products. The highest frost resistance is possessed by facing and red bricks, which can withstand temperatures well to -50 degrees Celsius and below. If you use silicate brick, its properties are worse, so the laying will have to be done in two layers. Silicate is not suitable for the construction of the foundation.
In winter weather conditions, heat in the house is maintained by the heating boiler of the heating system. But in order to avoid heat dissipation, we need walls, floor and ceiling of the appropriate material, which maintains the desired temperature well. The type of brickwork plays an important role during construction. Material should be chosen, taking into account all parameters and weather conditions.
In the next video you will find a review of the thermal conductivity of the brick SB 8.