Density and specific heat capacity of brick. Thermal storage capacity of materials with high heat capacity is much faster than brick

The choice of brick as a building material for the construction of walls of any premises, stoves or fireplaces is made on the basis of its properties related to the ability to conduct, retain heat or cold, and withstand exposure to high or low temperatures. Most important thermal characteristics: thermal conductivity coefficient, heat capacity and frost resistance.

This name was previously understood only as elements standard size(250x120x65) made of baked clay. Now they produce and sell building products made from any suitable components, having the shape of a regular parallelepiped and dimensions similar to those of the classic ceramic version.

Main varieties:

• ceramic ordinary (construction) - a classic red stone made of baked clay;
• ceramic front - has better external qualities, increased resistance to weathering, usually has cavities inside;
• silicate solid - light gray made of a pressed sand-limestone mixture, inferior to ceramic in all respects (including thermal engineering), except for strength;
• silicate hollow - characterized by the presence of cavities that increase the ability of the walls to retain heat;
• hyperpressed - made of cement with pigments that give shades natural material, the fillers of the mixture are crushed limestone, marble, granules of blast furnace slag;
• fireclay - intended for laying stoves, fireplaces, chimneys;
• clinker - differs from the usual one in that special types of clay and higher firing temperatures are used in its production;
• warm ceramics (porous stone) - its characteristics far exceed the thermal conductivity of red brick, this is achieved due to the presence of air-filled pores in the clay mass and the special design of the element, which has a large number of voids inside.

Coefficient of thermal conductivity

The thermal conductivity of a substance is a quantitative characteristic of its ability to conduct energy (heat). To compare it among different building materials Thermal conductivity coefficient is used - the amount of heat passing through a sample of unit length and area per unit time at a unit temperature difference. It is measured in Watt/meter*Kelvin (W/m*K).

When choosing a brick for building walls, pay attention to the thermal conductivity index, since the minimum permissible thickness of the structure depends on it. How less value, those better wall retains heat and the thinner it can be, more economical consumption. The same parameter is taken into account when selecting the type of insulation, the size of its layer and technology.

Thermal conductivity depends on the following factors:

• material: best performance- for warm porous ceramics, the worst - for hyper-pressed or silicate bricks;
• density - the higher it is, the worse the heat is retained;
• the presence of voids in products - the cavities inside the slotted wall stone after installation are filled with air, due to this, heat or coolness in the room is better retained.

Based on the coefficient of thermal conductivity in the dry state, the following types of masonry are distinguished:

• highly effective - up to 0.20;
• increased efficiency - from 0.21 to 0.24;
• effective - from 0.25 to 0.36;
• conditionally effective - from 0.37 to 0.46;
• ordinary - more than 0.46.

When performing calculations, choosing the front and building bricks and insulation take into account that the ability of a wall to conduct heat depends not only on the properties of the material, but is also characterized by the thermal conductivity coefficient of the solution and the thickness of the seams.

Heat capacity

This is the amount of heat (energy) that must be supplied to a body to increase its temperature by 1 Kelvin. The unit of measurement for this indicator is Joule per Kelvin (J/K). Specific heat capacity is its ratio to the mass of a substance, the unit of measurement is Joule/kg*Kelvin (J/kg*K). For brick, its value is from 700 to 1250 J/kg*K. More precise figures depend on the material from which a particular type is made.

The parameter affects the energy consumption required to heat the house: the lower the value, the faster the room warms up and the less funds will go towards payment. It is especially important if the residence in the house is not permanent, that is, the walls need to be warmed up periodically. The best option- silicate, but accurate calculations It is recommended to have it done by a specialist. It is necessary to take into account not only the heat capacity of the wall, but also its thickness, heat capacity masonry mortar, the width of the seams, the location of the room and the heat transfer coefficient.

Frost resistance

Expressed in the number of freeze-thaw cycles that the element can withstand without significant deterioration in properties. It is not the lower temperature level that matters, but the frequency of freezing of moisture in the pores. Water, turning into ice, expands, which contributes to the destruction of the stone.

Frost resistance is usually indicated by an index, which contains a large Latin letter F and numbers. For example: the F50 marking indicates that this material begins to lose strength no earlier than after 50 freeze-thaw cycles. Possible grades of brick for frost resistance (GOST 530-2012): F25; F35; F50; F100; F200; F300. Based on the indicated figure, you need to understand that the number of cycles does not coincide with the number of seasons.

In some regions, sudden temperature changes can occur many times during one winter. For load-bearing walls It is recommended to use a minimum of F35, for cladding - from F75. Options with lower rates are only suitable for regions with mild climates.

Before answering the main question - is fireclay brick harmful, you need to understand what kind of building material it is, in what areas and structures it is used and from what components it is made.

Most often, fireclay brick is used in the construction of stoves and fireplaces.

Conventional bricks used in construction are not suitable for structures that are constantly exposed to high temperatures. For such conditions, bricks from fireproof materials, the most popular of which is fireclay brick. It is difficult to imagine both private and industrial construction without its use.

The specific sandy-yellow color and coarse-grained structure make fireclay brick easily recognizable. The unusual properties of the material are given by the manufacturing technology, during which the raw material is molded and fired at high temperatures. Moreover, their level at each stage in mandatory strictly controlled.

High performance (heat capacity and fire resistance) are achieved by the special composition of the feedstock. Fireclay bricks are made from special grades of clay (which are called “fireclay”) with the use of certain additives, in particular aluminum oxide. It is he who is “responsible” for the strength and durability of the building material and, most importantly, porosity, on which the heat capacity directly depends fireclay bricks.

It is clear that the more aluminum oxide is added, the higher the porosity of the material and, accordingly, the lower the strength. Finding a balance between these two indicators is the most important thing in the production of fireclay bricks, and the heat capacity also depends on this.

Flaws

Based on the above, we can draw an unambiguous conclusion - the myth about the harmfulness of fireclay bricks has no basis in fact. Moreover, it is difficult to even simply explain the reason for its occurrence. It is quite possible that the material involuntarily “suffered” due to the fact that the very production of fireclay bricks, like most other building materials, especially before the arrival modern technologies, was often not a role model for defenders environment.

Be that as it may, the experience of many years of using the material allows us to unequivocally state that when exposed to high temperatures (even extremely high), absolutely no substances harmful to humans are released. It is difficult to expect otherwise, especially considering that in the production of fireclay bricks a material is used, the environmental purity of which is difficult to doubt, namely clay. One can even draw a parallel with pottery, which accompanies a person for many hundreds of years.

Does this mean that fireclay bricks have no disadvantages? Of course not. Several main ones can be noted:

1. Fireclay brick blocks are difficult to process and cut due to their high strength. This disadvantage is partially offset by the variety of shapes of fireclay brick blocks, which make it possible to achieve almost any design delight without cutting the material.
2. Even in one batch of the product, deviations in the size of the bricks are noticeable, and achieving greater unification of the blocks is problematic due to the peculiarities of the production technology.
3. The material is expensive compared to ordinary brick. It is also impossible to avoid this drawback: operating conditions require the use suitable material. The use of ordinary, non-fire-resistant bricks sharply reduces the service life of the structure or requires the use of additional means of processing it.

Characteristics

Fireclay brick is simply irreplaceable in the field of private construction when constructing stoves and fireplaces. But in order for the structure to be used long years, necessary quality material. This is especially true for private owners, since large industrial enterprises have more opportunities to control the materials used in construction.

And due to its high strength, fireclay bricks are difficult to cut and process.

All indicators of fireclay bricks - from strength to frost resistance, from porosity to density - are strictly regulated state standards. It is worth noting that in last years Some manufacturers in the production of fireclay bricks are guided by their own technical specifications. As a result, some discrepancies are possible on a number of parameters. Therefore, when purchasing material, it is imperative to check the certificate of conformity for product quality.

Should be paid Special attention the weight of bricks. The smaller it is, the higher the thermal conductivity and, accordingly, the lower the heat capacity. The optimal mass of the refractory block is determined by GOST within 3.7 kg.

Types and markings

Modern manufacturing plants offer a large number of a variety of types of fireclay bricks, which differ in weight and shape, production technology and degree of porosity.

The variety of shapes of fireclay bricks does not end with standard-shaped straight and arched blocks.

Trapezoidal and wedge-shaped ones are widely used, capable of satisfying any requirements for structural elements.

Depending on the degree of porosity, fireclay bricks can vary from extremely dense (less than 3% porosity) to ultra-lightweight (porosity 85% or more).

The main characteristics are very easy to determine by the marking of refractory bricks, which must be applied to each block. The following brands are currently produced:

1. SHV, SHUS.

The thermal conductivity of these types of fireclay bricks allows them to be used in industry - for lining the walls of gas ducts of steam generators and convection shafts.

1. SHA, ShB, SHAK.

The most versatile and therefore popular fireproof blocks, used mostly by private owners. They are used especially often when laying fireplaces and stoves. Can be used at temperatures up to 1690 degrees. In addition, they have high strength.

Used in the construction of coke production units.

A lightweight type of material used for lining furnaces with a relatively low heating temperature - no more than 1300 degrees. The low weight of refractory blocks is achieved by increasing the porosity index.

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It is the markings that must be studied first when purchasing a material, which will allow any builder to choose exactly the type of fireclay brick that is most suitable for the design features. And after studying the information provided, anyone can be sure that fireclay bricks do not pose any danger to humans, much less mythical harm.

In construction it is very important characteristic is the heat capacity of building materials. The thermal insulation characteristics of the walls of the building depend on it, and, accordingly, the possibility of a comfortable stay inside the building. Before you start familiarizing yourself with thermal insulation characteristics individual building materials, it is necessary to understand what heat capacity is and how it is determined.

Specific heat capacity of materials

Heat capacity is a physical quantity that describes the ability of a material to accumulate temperature from a heated environment. Quantitatively specific heat equal to the amount of energy, measured in J, required to heat a body weighing 1 kg by 1 degree.
Below is a table of the specific heat capacity of the most common materials in construction.

• type and volume of heated material (V);
• the specific heat capacity of this material (Sud);
• specific gravity (msp);
• initial and final temperatures of the material.

Heat capacity of building materials

The heat capacity of materials, the table for which is given above, depends on the density and thermal conductivity of the material.

And the thermal conductivity coefficient, in turn, depends on the size and closedness of the pores. A fine-porous material, which has a closed pore system, has greater thermal insulation and, accordingly, lower thermal conductivity than a large-porous one.

This is very easy to see using the most common materials in construction as an example. The figure below shows how the thermal conductivity coefficient and the thickness of the material influence the thermal insulation qualities of external fences.

The figure shows that building materials with lower density have a lower thermal conductivity coefficient.
However, this is not always the case. For example, there are fibrous types of thermal insulation for which the opposite pattern applies: the lower the density of the material, the higher the thermal conductivity coefficient will be.

Therefore, you cannot rely solely on the indicator of the relative density of the material, but it is worth taking into account its other characteristics.

Comparative characteristics of the heat capacity of basic building materials

In order to compare the heat capacity of the most popular building materials, such as wood, brick and concrete, it is necessary to calculate the heat capacity for each of them.

First of all, you need to decide on the specific gravity of wood, brick and concrete. It is known that 1 m3 of wood weighs 500 kg, brick - 1700 kg, and concrete - 2300 kg. If we take a wall whose thickness is 35 cm, then through simple calculations we get that specific gravity 1 sq.m of wood will be 175 kg, brick - 595 kg, and concrete - 805 kg.
Next, we will select the temperature value at which thermal energy will accumulate in the walls. For example, this will happen on a hot summer day with an air temperature of 270C. For the selected conditions, we calculate the heat capacity of the selected materials:

1. Wall made of wood: C=SudhmuddhΔT; Sder=2.3x175x27=10867.5 (kJ);
2. Concrete wall: C=SudhmuddhΔT; Cbet = 0.84x805x27 = 18257.4 (kJ);
3. Brick wall: C=SudhmuddhΔT; Skirp = 0.88x595x27 = 14137.2 (kJ).

From the calculations made, it is clear that with the same wall thickness, concrete has the highest heat capacity, and wood has the least. What does this mean? This suggests that on a hot summer day maximum amount heat will accumulate in a house made of concrete, and the least amount of heat will accumulate in a house made of wood.

This explains the fact that in wooden house In hot weather it is cool, and in cold weather it is warm. Brick and concrete easily accumulate a fairly large amount of heat from the environment, but just as easily part with it.

Heat capacity and thermal conductivity of materials

Thermal conductivity is a physical quantity of materials that describes the ability of temperature to penetrate from one wall surface to another.

For creating comfortable conditions In a room, it is necessary that the walls have a high heat capacity and a low thermal conductivity. In this case, the walls of the house will be able to accumulate thermal energy environment, but at the same time prevent the penetration thermal radiation inside the room.

Brick is a popular building material in the construction of buildings and structures. Many people only distinguish between red and white brick, but its types are much more diverse. They differ both in appearance (shape, color, size) and in properties such as density and heat capacity.

Traditionally, a distinction is made between ceramic and silicate bricks, which have different technology manufacturing. It is important to know that the density of brick, its specific heat capacity, and each type can differ significantly.

Ceramic brick is made from various additives and fired. The specific heat capacity of ceramic brick is 700…900 J/(kg deg). The average density of ceramic bricks is 1400 kg/m3. The advantages of this type are: smooth surface, frost and water resistance, as well as resistance to high temperatures. The density of ceramic brick is determined by its porosity and can range from 700 to 2100 kg/m3. The higher the porosity, the lower the density of the brick.

Sand-lime brick has the following varieties: solid, hollow and porous, it has several standard sizes: single, one-and-a-half and double. The average density of sand-lime brick is 1600 kg/m3. The advantages of sand-lime brick are excellent soundproofing. Even if you pave thin layer made of such material, the sound insulation properties will remain at the proper level. The specific heat capacity of sand-lime brick ranges from 750 to 850 J/(kg deg).

Values ​​of the density of bricks of various types and their specific (mass) heat capacity at different temperatures are presented in the table:

One more thing should be noted popular look bricks – facing bricks. He is not afraid of either moisture or cold. The specific heat capacity of the facing brick is 880 J/(kg deg). Facing brick has shades from bright yellow to fiery red. This material can be used for finishing and facing work. The density of this type of brick is 1800 kg/m3.

It is worth noting a separate class of bricks - refractory bricks. This class includes dinas, carborundum, magnesite and fireclay bricks. Fire brick quite heavy - the density of bricks of this class can reach 2700 kg/m 3.

Carborundum brick has the lowest heat capacity at high temperatures - it is 779 J/(kg deg) at a temperature of 1000°C. Masonry made from such bricks warms up much faster than fireclay bricks, but retains heat less well.

Refractory bricks are used in the construction of furnaces, with operating temperature up to 1500°C. The specific heat capacity of refractory bricks depends significantly on temperature. For example, the specific heat capacity of fireclay bricks is 833 J/(kg deg) at 100°C and 1251 J/(kg deg) at 1500°C.

Sources:

1. Franchuk A. U. Tables of thermal technical indicators of building materials, M.: Research Institute of Construction Physics, 1969 - 142 p.
2. Tables physical quantities. Directory. Ed. acad. I. K. Kikoina. M.: Atomizdat, 1976. - 1008 p. construction physics, 1969 - 142 p.

From thermal insulation properties The temperature inside the room depends on the material, which is why the thermal capacity of a brick is an important indicator that shows its ability to accumulate heat. Specific heat capacity is determined during laboratory studies, according to which, the most warm material is a solid brick. It is worth noting that the indicator depends on the type of brick material.

What it is?

The physical characteristic of heat capacity is inherent in any substance. It indicates the amount of heat that is absorbed physical body when heated by 1 degree Celsius or Kelvin. Mistakenly identify general concept with specific, since the latter implies the temperature required to heat one kilogram of a substance. It seems possible to accurately determine its number only in laboratory conditions. The indicator is necessary to determine the thermal resistance of the walls of a building and in the case when construction works carried out at sub-zero temperatures. For the construction of private and multi-storey buildings residential buildings and premises, materials from high performance thermal conductivity, since they accumulate heat and maintain the temperature in the room.

The advantage of brick buildings is that they save on heating costs.

What does the heat capacity of bricks depend on?

The heat capacity coefficient is primarily affected by the temperature of the substance and its state of aggregation, since the heat capacity of the same substance in the liquid and solid states differs in favor of the liquid. In addition, the volume of the material and the density of its structure are important. The more voids there are in it, the less it is able to retain heat inside itself.

Types of bricks and their indicators

Ceramic material used in furnaces.

More than 10 varieties are produced, differing in manufacturing technology. But silicate, ceramic, facing, fireproof and warm are more often used. Standard ceramic brick made from red clay with impurities and fired. Its heat index is 700-900 J/ (kg deg). It is considered quite resistant to high and low temperatures. Sometimes used for display stove heating. Its porosity and density vary and affect the heat capacity coefficient. Sand-lime brick consists of a mixture of sand, clay and additives. It can be full or empty, different sizes and, therefore, its specific heat capacity is equal to values ​​from 754 to 837 J/ (kg deg). The advantage of silicate brickwork- good sound insulation even when laying out the wall in one layer.

Facing bricks used for building facades have quite high density and heat capacity within 880 J/ (kg deg). Refractory brick is ideal for laying a furnace because it can withstand temperatures up to 1500 degrees Celsius. This subspecies includes fireclay, carborundum, magnesite and others. And the heat capacity coefficient (J/kg) is different: