architectural possibilities of bricks
Brick is an artificial stone of the correct shape, made of mineral materials, the main purpose of which is to be used as a building material for a device.
Since ancient times, complex structures have been laid out of bricks, Buildings, structures made of bricks have been performed since the times of ancient Egypt and Rome. Fired brick in Russia began to be used from the end of the 15th century, as evidenced by the walls of temples of past centuries that have been perfectly preserved to our time, as well as other residential and non-residential historically valuable buildings and structures, of which there are a great many throughout the world.
Real works of art have been created from bricks and are still being created, with their own character and uniqueness. An excellent example in our time are the unique cities of Europe, the cultural capitals of most states, which never cease to amaze with the work of architects.
With the development of the construction industry, the technology and quality of bricks as a building material have received enough changes, high quality properties, reliability and durability. Therefore, the demand for this material is always high and it is always in demand.
There are several types of bricks and classification according to different criteria, each of which has its own properties, advantages and disadvantages, each of which we will consider in this section. But there are also general characteristics inherent in each type of brick as a product, we will give them below.
Basic properties and characteristics of bricks:
1.Brick size
2.Strength grade
3. Thermal conductivity of bricks
4. Frost resistance of bricks
5. Water absorption of bricks
Brick size
in the CIS countries are defined as:
- standard brick (single) 250x120x65 mm
- one-and-a-half brick 250x120x88 mm
- double brick 250x120x138 mm
European countries have their own approach to brick size:
- euro brick 250x88x65 mm
- single 288x138x65 mm
In addition, depending on the project and architectural solutions of the building, bricks are made of different sizes, shapes, colors.
facade of a brick house
Brick grade in terms of strength:
Brick strength- this is its ability, without destruction, to withstand mechanical stress in compression, tension and bending. This is one of the main characteristics, denoted by the letter M and the following number: M50, M75, M100, M125, M150, M175, M200, M250, M300, which determines how many kilograms per 1 cm² the product can withstand.
Thermal conductivity of bricks:
Thermal conductivity coefficient of bricks Is the ratio of the amount of thermal energy lost per 1 meter of the structure thickness with a temperature difference of 1 degree between the outer and inner surfaces.
The lower the coefficient, the higher the thermal conductivity, in low temperatures for the construction of residential buildings, a brick with a low thermal conductivity is more suitable if one of the tasks is to keep heat in the room.
- Solid brick - has a thermal conductivity of 0.5-0.6 W / m ° C. And it is characterized by a fairly high thermal conductivity.
- Hollow brick - has a thermal conductivity coefficient of 0.32-0.39 W / m ° C., Since the air in voids has a lower thermal conductivity and it is possible to build walls thinner in comparison with the use of solid bricks.
red brick facade
Frost resistance of bricks:
This is a product parameter that determines the exposure of the material to alternating freezing and thawing, until significant changes in the structure of the material appear. It is denoted by the letter F and the following number, which shows the number of freeze and thaw cycles for this type of brick. For example - F15, F25, F35, F50. The higher the number following the letter F, the more resistant the brick is to temperature extremes. Recommended grade for frost resistance not lower than F35. This indicator is determined when creating extreme conditions for the product, which occur extremely rarely or do not occur at all with a brick.
To determine frost resistance, the brick is completely saturated with water. When frozen, at a temperature of minus 15-20 ° C, part of the water freezes in the pores with the formation of ice. An internal pressure arises in the structure of a brick, associated with the transition of water from a liquid to a solid state with an increase in volume by about 9%, which, with repeated repetition, leads to loosening of the structure with its subsequent destruction.
The less porous the structure of the brick, the more frost-resistant tone, respectively, the most frost-resistant brick is corpulent, withstands more cycles.
Brick water absorption:
The water absorption of a brick is a value that shows as a percentage how much moisture a given type of brick is able to absorb and hold. Water absorption is determined as follows: the brick is kept in an oven at a temperature of 105-110 ° C for a certain time, cooled and weighed. Then, it is placed in water for a certain period of time and weighed again. The difference between these two weightings as a percentage is the water absorption of the brick.
There is an interdependence of such indicators as frost resistance and water absorption. The higher the water absorption, the lower the frost resistance, since more water freezes in the brick structure and, accordingly, the pressure is stronger on the product from the inside.
Bricks with water absorption above 9% have low frost resistance. The recommended water absorption is 6-12%.
Any building material has certain properties that make it suitable or unsuitable for use in a particular area. For example, brick is divided into building and facing, not only in appearance, but also in characteristics. The main ones are the strength, frost resistance and water absorption of the brick.
Bearing structures are erected from ordinary solid stone that can withstand the load from their own weight, the weight of the roof and ceilings. And the facing not only decorates, but also insulates the building. Both species have different functions and are exposed in different ways to the environment, so they are required to have different physical properties.
Basic concepts and definitions
The relationship of the main parameters
The characteristics mentioned above are closely related and dependent on each other. To understand this, it is necessary to define water absorption.
Definition. Water absorption is the ability of a material to absorb and retain water. It is expressed as a percentage of the material's own volume. If we talk about a brick, then its water absorption shows how much water it can absorb during full immersion.
It is clear that the greater the volume of voids in the brick (i.e., the higher its porosity), the more water it will absorb. At the same time, porosity affects the strength of the material, its ability to withstand a certain load. And also for frost resistance, which shows how many freezing and thawing cycles it can withstand without reducing its operational properties.
Norms and requirements
It would seem that in order to improve these indicators, it is enough to maximize the density of the product in order to limit the absorption of moisture into it.
However, this is not done for two reasons:
- If the water absorption of ceramic bricks is very low, the masonry from it will be fragile, since a normal bond with the mortar will not be ensured.
- The absence of pores reduces the thermal insulation properties of the material, making it unsuitable for those operating conditions that exist in our cold climate.
Therefore, there are standards established by GOST, according to which this indicator should be at least 6%. Its upper limit also depends on the conditions in which it will work.
- Private – 12-14%;
- Facial – 8-10%;
- Bricks used in the inner rows of masonry and for the construction of partitions can have a water absorption of up to 16%.
This spread is explained by the fact that the inner layers of the masonry are not directly affected by precipitation and low temperatures, while the outer ones completely take them upon themselves. Therefore, the water absorption of the facing brick should be as low as possible. And to reduce thermal conductivity, special technological voids are made in it.
For reference. The best performance is clinker facing brick. There are practically no foreign inclusions and pores in it, due to which its moisture resistance, frost resistance, strength and durability are very high. But its price is also higher than that of a regular one.
Determination of moisture absorption
To determine this indicator, a technique is used, regulated by GOST 7025-91 “Brick and ceramic and silicate stones. Methods for determining water absorption, density and frost resistance control. "
General requirements of the method
The study is carried out in a laboratory in compliance with the following requirements:
- The air temperature in the room should be within 15-25 degrees;
- Whole products or halves are tested;
- Samples should be dried to constant weight with a specified weighing error. Drying is carried out at a temperature of 1055 degrees in an electrical cabinet;
- Silicate products are tested no earlier than 24 hours after autoclaving.
Testing
For research, at least three samples from one batch are taken. This is required by the instruction for determining the arithmetic mean of moisture absorption.
After drying, they are weighed and immersed in a vessel with water at a temperature of 15-25 degrees, placed on lattices with gaps of at least 2 cm.The water level should be 2-10 cm higher than the upper sample.
Note. Silicate brick is not dried before testing.
After 48 hours, the products are removed from the water and immediately weighed again, including in the mass of the brick and the mass of the water that has flowed out onto the weighing pan.
The results obtained are processed by calculating water absorption using the following formula:
m1 is the mass of the product saturated with water;
m is the mass of the dried product.
That is, the mass of the absorbed water is referred to the mass of the sample itself and the resulting value is expressed as a percentage.
Example. If the dried brick weighed 4000 g, and after the test it began to weigh 4360 g, then its water absorption is (4360 - 4000) / 4000 * 100 = 9%.
Despite the fact that special equipment is required for testing, it can be done with your own hands, but the results will be very close to reality. However, in the case of using a brick, the characteristics of which you do not know, they will be very informative.
Conclusion
The degree of water absorption of a material is the most important characteristic that allows you to determine the scope of its application. For example, sand-lime brick has a high ability to absorb water, and that is why it is not used in the construction of foundations, basements and walls of wet rooms (read also the article). In the video presented in this article, you will find additional information on this topic.
5 samples intended for testing for water absorption are dried to constant weight and, after cooling, weighed with an accuracy of 1 g. After that, the samples are placed in a vessel with water in one row on lining so that the water level in the vessel is at least 2 higher than the top of the samples. cm, and no more than 10 cm. In this position, the samples are kept for 48 hours. After that, it is removed from the vessel, immediately taken with a damp cloth / soft / and each sample is weighed. The mass of water flowing out of the pores of the sample during weighing shall be included in the mass of the water-saturated sample. Weighing of saturated samples should be completed no later than 5 minutes after the samples are removed from the water. Water absorption by weight is calculated by the formula /% /:
where m 1 is the mass of a sample saturated with water, g;
m is the mass of the dried sample, g;
Water absorption is determined as the average of 5 results. The water absorption of the brick must be at least 8%.
1.4. Determination of brick frost resistance
Frost resistance of bricks is the ability of a material or product saturated with water to withstand repeated freezing and thawing in water.
Samples of bricks intended for testing for frost resistance are preliminarily dried to constant weight, and then saturated with water and weighed. In the freezer, the samples are placed in special containers or placed on the racks of the chamber, after the temperature in it drops to -15 0 C. From the beginning to the end of freezing for 4 hours, the temperature in the placement area should not exceed -15 0 below -20 0 С.
After the end of freezing, the samples are taken out of the freezer and immersed in a bath with water at a temperature of 15 - 20 0 C. The duration of one thawing must be at least 2 hours.
Freezing and subsequent thawing of samples is one cycle. According to the number of cycles of alternating freezing and thawing without signs of destruction, a brick grade is established for frost resistance.
To determine the degree of damage, the samples are inspected every 5 cycles after thawing.
The brick is considered to have passed the frost resistance test if, after a specified number of cycles of alternating freezing and thawing, the samples do not break or damage types are not found on the surface of the samples: delamination, peeling, through cracks, spalling. In case of significant chipping of edges and corners, check the loss of mass of the sample, which should not exceed 2%.
To determine the weight loss, the samples are dried after the last test cycle to constant weight.
Weight loss is determined by the formula /% /:
,
where m 1 is the mass of the sample, dried to constant weight before the start of frost resistance tests;
m 2 - the mass of the sample, dried to constant weight for frost resistance.
According to frost resistance, brick is subdivided into four brands: Мрз. 15, Mrz. 25, Mrz. 35, Mrz. 50.
2.Test of ceramic tiles for interior cladding
Tiles used for interior wall cladding are made according to GOST 6141-82 from clay dough by molding, firing and glazing the front surface.
Tiles are produced in rectangular and shaped shapes of various types / square, rectangular, angular, etc. /, for which their sizes are set / for example, square tiles - 150 
150 mm /.
The thickness of all tiles, except for skirting boards, must be no more than 6.0 mm, for baseboards, no more than 10.0 mm. The thickness of tiles from the same batch must be the same.
The permissible deviation in the thickness of tiles of one batch should not exceed 0.5 mm. The deviation of dimensions along the length of the edges of the tile is allowed no more than 
1.5 mm.
Tiles should have a solid or marbled finish. The color of the front surface of the tiles and the tone of their coloring must correspond to the standards.
The water absorption of the tiles should not exceed 16% of the weight of the tiles dried to constant weight.
The dimensions of the tiles are checked with a metal measuring instrument or template with an accuracy of 1 mm. The correctness of the right angles of the tiles will be determined with a metal square.
The curvature of the tiles is determined in the following ways: in the case of a concave surface, by measuring the largest gap between the tile surface and the edge of a metal ruler set diagonally to the tile; in the case of a convex surface, by measuring the gap between the surface of the tile and the edge of a metal ruler set diagonally to the tile and resting at one end on a caliber equal to the permissible amount of curvature.
To determine the thermal resistance of the tiles, the selected three tiles are placed in an air bath and gradually heated. Upon reaching a temperature of 100 0 C, the tiles are quickly immersed in water having a temperature of 18-20 0 C, and left in it until completely cooled; then they are taken out and examined. In order to more accurately detect the presence of a counter / roughness /, a few drops of liquid paint or ink are applied to the surface of the tiles and wiped with a soft cloth.
Tiles are considered thermally resistant if, as a result of the test, no cracks, notches, or flakes are found on their glazed surface.
To analyze the uniformity of the color of the front surfaces of square and rectangular tiles, they are placed on the shield close to an area of 1 m 2, and shaped tiles - in a row at least 1 m long. The shield is installed in an upright position in an open place.
The color of the surface of the tiles at a distance of 3 m from the eye of the observer should appear uniform in accordance with the standard.
● Brick dimensions, produced in other countries, differ significantly from the sizes adopted in the main part of the space of the former USSR.
| in Germany | 240x115x71 | in the USA | 203x102x57 |
| in England | 215x102.5x65 | in Australia | 230x110x76 |
| in Sweden | 250x120x62 | in South Africa | 222x106x73 |
| in Romania | 240x115x63 | in India | 228x107x69 |
Brick strength grade |
● An important characteristic of a brick is its ability to transfer heat at different temperatures outside and inside the structure. There is such a concept - the coefficient of thermal conductivity. In numerical terms, this looks like the ratio of the amount of thermal energy lost per 1 meter of structure thickness with a temperature difference of 1 degree between the outer and inner surfaces. For example, solid brick has a thermal conductivity of 0.5-0.6 W / m ° C. Solid brick has a fairly high thermal conductivity and therefore it is much more profitable to use hollow brick - its coefficient is 0.32-0.39 W / m ° C. Air in voids has a lower thermal conductivity and walls can be built less thick. Although in connection with the use of more and more thermal insulation materials in modern construction, the relevance of thermal conductivity has somewhat dropped, you should not underestimate the importance of this quality in bricks, just as you should not overpay extra money and neglect such an indicator as a decrease in labor intensity when performing construction work.
Frost resistance of bricks |
● Water absorption of bricks- a percentage value that shows how much moisture a given type of brick is able to absorb and hold. To find out the water absorption, the brick is kept in an oven at a temperature of 105-110 ° C for a certain time, cooled and weighed. After that, the brick is placed in water for a certain period of time and weighed again. The difference between these two weightings as a percentage is the water absorption of the brick.
Water absorption greatly affects the frost resistance of a brick - for example, a product with water absorption above 9% has low frost resistance.
In silicate bricks, water absorption can reach 15%, therefore it is not recommended to use it in places with high humidity (basement rooms, foundations), as well as ceramic bricks produced by the method of semi-dry pressing.
The quality of the brick is a defining parameter when choosing this material. Durability, warmth, environmental friendliness, and the appearance of the future house directly depend on the quality of the selected brick. The document confirming the quality of the product is the certificate of conformity. To confirm the compliance of a batch of bricks with quality standards prescribed in GOST 530-2012, quality tests of finished products are carried out at each manufacturing plant.
Test methods for incoming quality control of raw materials and materials are indicated in the technological documentation for the manufacture of products, taking into account the requirements of regulatory documents for these raw materials and materials.
Test methods during production operational control are established in the technological documentation for the manufacture of products.
Determination of geometric dimensions
The dimensions of the products, the thickness of the outer walls, the diameter of the cylindrical voids, the dimensions of the square and the width of the slot-like voids, the length of the cuts, the length of the ribs, the radius of curvature of the adjacent edges and the depth of the chamfer on the edges are measured with a metal ruler in accordance with GOST 427 or with a caliper in accordance with GOST 166. Measurement error - ± 1 mm:
- The length, width and thickness of each product are measured along the edges (at a distance of 15 mm from the corner) and in the middle of the ribs of the opposite edges. The arithmetic mean of three measurements is taken as the measurement result.
- The thickness of the outer walls is measured in at least three places - in the middle of each face of the product. The smallest value is taken as the measurement result.
- The dimensions of the voids are measured within the voids in at least three voids. The largest value is taken as the measurement result.
- The crack opening width is measured using a measuring magnifier in accordance with GOST 25706, after which the product is checked for compliance with the requirements. Measurement accuracy 0.1 mm.
- The depth of the beating of corners and edges is measured using a square in accordance with GOST 3749 and a ruler in accordance with GOST 427 along the perpendicular from the apex of the corner or edge formed by the square to the damaged surface. Measurement error - ± 1 mm.
Determining the correctness of the form
- The deviation from the perpendicularity of the edges is determined by applying a square to the adjacent edges of the product and measuring the largest gap between the square and the edge with a metal ruler in accordance with GOST 427. Measurement error - ± 1 mm.
The largest of all the obtained measurement results is taken as the measurement result. - The deviation from the flatness of the product is determined by applying one side of the metal square to the edge of the product, and the other along each diagonal of the face and measuring with a feeler gauge, calibrated in the prescribed manner, or a metal ruler in accordance with GOST 427, the largest gap between the surface and the edge of the square. Measurement error - ± 1 mm.
The largest of all the obtained measurement results is taken as the measurement result.
Determination of the presence of lime inclusions
The presence of lime inclusions is determined after steaming the products in the vessel.
Samples that have not previously been exposed to moisture are placed on a lattice placed in a vessel with a lid. The water poured under the wire rack is heated to a boil. Steaming is continued for 1 hour. The samples are then cooled in a closed vessel for 4 hours, after which they are checked for compliance.
Determination of the voidness of products
The voidness of the products is defined as the ratio of the volume of sand filling the voids of the product to the volume of the product.
The voids of the product lying on a sheet of paper on a flat surface with the holes upward are filled with dry quartz sand of fraction 0.5-1.0 mm. The product is removed, the sand is poured into a glass measuring cylinder and its volume is fixed. The voidness of the product P,%, is calculated by the formula:
where V dog - the volume of sand, mm 3;
l- product length, mm;
d- product width, mm;
h- product thickness, mm.
The arithmetic mean of three parallel determinations is taken as the measurement result and rounded to 1%.
Determination of the rate of initial water absorption
Sample preparation
The sample is a complete product, from the surface of which dust and excess material has been removed. The samples are dried to constant weight at a temperature of (105 ± 5) ° С and cooled to room temperature.
Equipment
- A container for water with a base area larger than the bed of the product and at least 20 mm high, with a grate or ribs at the bottom to create a distance between the bottom and the surface of the product. The water level in the tank must be kept constant.
- Stopwatch with 1 second division.
- Drying cabinet with automatic temperature maintenance (105 ± 5) ° С.
- Balance providing measurement accuracy of not less than 0.1% of the dry sample mass.
Testing
The sample is weighed, the length and width of the supporting surface of the sample immersed in a container with water are measured and its area is calculated. The product is immersed with a supporting surface in a container with water at a temperature of (20 ± 5) ° С to a depth of (5 ± 1) mm and kept for (60 ± 2) s. Then the test piece is removed from the water, excess water is removed and weighed.
Processing of results
The initial absorption rate is calculated for each sample with an accuracy of 0.1 kg / (m 2 min) using the formula:
where WITH abs is the rate of initial absorption of water, kg / (m 2 · min.);
m 1 - weight of dry sample, g;
m 2 - mass of the sample after immersion, g;
S- submerged surface area, mm 2;
t is the holding time of the sample in water (constant value t= 1 min).
The initial water absorption rate is calculated as the arithmetic mean of the results of five parallel determinations.
Determination of the presence of efflorescence
To determine the presence of efflorescence, a half of the product is immersed with a broken end in a container filled with distilled water to a depth of 1 - 2 cm and kept for 7 days (the water level in the vessel must be kept constant). After 7 days, the samples are dried in a drying oven at a temperature of (105 ± 5) ºС to constant weight, and then compared with the second part of the sample that has not been tested and checked for compliance.
Flexural and compressive strength
- The ultimate bending strength of a brick is determined in accordance with GOST 8462.
- The compressive strength of products is determined according to GOST 8462 with the following additions.
Sample preparation
Samples are tested in an air-dry state. The test piece consists of: two whole bricks laid on top of each other, or of one stone.
Preparation of the supporting surfaces of products for acceptance tests is carried out by grinding, for samples from clinker bricks - leveling with cement mortar is used; in arbitration tests of brick and stone, grinding is used, clinker brick - leveling with cement mortar prepared in accordance with 2.6 GOST 8462. It is allowed to use other methods of leveling the supporting surfaces of the samples during acceptance tests, provided there is a correlation between the results obtained in different ways, as well as the availability of verification information that is the basis for such communication.
The deviation from flatness of the supporting surfaces of the test specimens shall not exceed 0.1 mm for every 100 mm of length. The non-parallelism of the supporting surfaces of the test specimens (the difference in height values measured along the four vertical ribs) should be no more than 2 mm.
The test piece is measured along the center lines of the bearing surfaces with an error of up to ± 1 mm.
Axial lines are drawn on the lateral surfaces of the sample.
Testing
The specimen is positioned in the center of the compression tester, aligning the geometric axes of the specimen and plate, and pressed against the top plate of the machine. During testing, the load on the sample should increase as follows: until approximately half the expected value of the breaking load is reached, arbitrarily, then the loading rate is maintained so that the destruction of the sample occurs no earlier than after 1 min. The breaking load value is recorded.
Compressive strength value of products R compressed, MPa (kgf / cm 2) is calculated by the formula:
R sr = P / F, (3)
where R- the greatest load established during the test of the sample, N (kgf);
F- cross-sectional area of the sample (without deducting the area of voids); calculated as the arithmetic mean of the areas of the upper and lower surfaces, mm 2 (cm 2).
The value of the ultimate compressive strength of the samples is calculated with an accuracy of 0.1 MPa (1 kgf) as the arithmetic mean of the test results of the established number of samples.
Density, water absorption, frost and acid resistance of bricks
The average density, water absorption and frost resistance (volumetric freezing method) of products are determined in accordance with GOST 7025.
The result of determining the average density of products is rounded up to 10 kg / m 3.
- Water absorption is determined when samples are saturated with water at a temperature of (20 ± 5) ºС at atmospheric pressure.
- Frost resistance is determined by the method of volumetric freezing. The assessment of the degree of damage to all samples is carried out every five cycles of freezing and thawing.
- Acid resistance of clinker bricks is determined in accordance with GOST 473.1.
- The specific effective activity of natural radionuclides Aeff is determined according to GOST 30108.
Thermal conductivity coefficient of masonry
The thermal conductivity coefficient of the masonry is determined according to GOST 26254 with the following additions.
The thermal conductivity coefficient is determined experimentally on a fragment of the masonry, which, taking into account the mortar joints, is made with a thickness of one butt and one spoon rows of bricks or stones. The masonry of enlarged stones is made with a thickness of one stone. The length and height of the masonry must be at least 1.5 m (see Figure 2). The masonry is carried out on a complex solution of grade 50, with an average density of 1800 kg / m 3, composition 1.0: 0.9: 8.0 (cement: lime: sand) by volume, on Portland cement grade 400 with a cone draft for solid products 12- 13 cm, for hollow - 9 cm. It is allowed to perform a piece of masonry other than the above, using other solutions, the composition of which is indicated in the test report.
δ is the thickness of the masonry; 1 - single brick masonry; 2 -; thick brick masonry; 3 - stone masonry
Figure 2 - A fragment of the masonry to determine the coefficient of thermal conductivity
A fragment of masonry from products with through voids should be performed using a technology that excludes filling the voids with masonry mortar or filling the voids with a solution, which is recorded in the test report. The masonry is carried out in the opening of the climatic chamber with a device along the contour of thermal insulation made of plate insulation; thermal resistance of thermal insulation must be at least 1.0 m 2 · ° C / W. After making a fragment of masonry, its outer and inner surfaces are rubbed with plaster mortar with a thickness of not more than 5 mm and a density corresponding to the density of the tested products, but not more than 1400 kg / m 3 and not less than 800 kg / m 3.
A piece of masonry is tested in two stages:
- stage 1 - the masonry is kept and dried for at least two weeks to a moisture content of no more than 6%;
- stage 2 - additional drying of the masonry is carried out to a moisture content of 1% - 3%.
The moisture content of products in the masonry is determined by non-destructive testing devices. Tests in the chamber are carried out with a temperature difference between the inner and outer surfaces of the masonry Δt = (tv - tn) ≥ 40 ° C, temperature in the warm zone of the chamber tv = 18 ° C - 20 ° C, relative air humidity (40 ± 5)%. It is allowed to reduce the holding time of the masonry provided that the outer surface is blown and the inner surface of the fragment is heated with tubular electric heaters (heating elements), soffits, etc. to a temperature of 35 ° C - 40 ° C.
Before testing, at least five thermocouples are installed on the outer and inner surfaces of the masonry in the central zone according to the current regulatory document. Additionally, heat meters are installed on the inner surface of the masonry in accordance with the current regulatory document. Thermocouples and heat meters are installed so that they cover the surface areas of the spoon and butt rows of masonry, as well as horizontal and vertical mortar joints. Thermal parameters are recorded after the onset of a stationary thermal state of the masonry not earlier than 72 hours after turning on the climatic chamber. The parameters are measured at least three times with an interval of 2-3 hours.
For each heat meter and thermocouple, the arithmetic mean of the readings for the observation period is determined q i and t i. Based on the test results, the weighted average values of the temperature of the outer and inner surfaces of the masonry are calculated t n wed, t in Wed, taking into account the area of the spoon and butt measured sections, as well as the vertical and horizontal sections of mortar joints according to the formula
t h (s) cf = (Σ t i F i) / (Σ t i F i), (4)
where t i is the surface temperature at the point i, ° С;
F i - area i-th plot, m 2.
According to the test results, the thermal resistance of the masonry is determined R to pr, m 2 ° C / W, taking into account the actual humidity during testing according to the formula
R to pr = Δ t/q Wed, (5)
where Δ t = t on Wednesday - t n Wed, ° C;
q cf is the average value of the heat flux density through the test piece of masonry, W / m 2.
By value R to pr calculate the equivalent coefficient of thermal conductivity of the masonry λ eq (ω), W / (m ° C), according to the formula
λ eq (ω) = δ / R to pr, (6)
where δ is the thickness of the masonry, m.
A graph of the dependence of the equivalent coefficient of thermal conductivity on the moisture content of the masonry is plotted (see Figure 3) and the change in the value of λ eq is determined by one percent of humidity Δλ eq, W / (m ° C), according to the formula
Δλ eq = (λ eq1 - λ eq2) / (ω 1 - ω 2). (7)
Figure 3 - Graph of the dependence of the equivalent coefficient of thermal conductivity on the moisture content of the masonry
The coefficient of thermal conductivity of masonry in a dry state λ 0, W / (m ° С), is calculated by the formulas:
λ 0 II = λ eq2 - ω 2 Δλ eq (8)
or λ 0 I = λ eq1 - ω 1 · Δλ eq. (nine)
The test result is taken as the arithmetic mean value of the coefficient of thermal conductivity of the masonry in a dry state λ 0, W / (m ° С), calculated by the formula
λ 0 = (λ 0 I + λ 0 II) / 2. (ten)