MAIN PROPERTIES OF MATERIALS: PHYSICAL, MECHANICAL, CHEMICAL
Physical properties
These properties characterize its structure or relation to the physical processes of the environment. These include mass, true and average density, porosity, water absorption and water loss, humidity, hygroscopicity, water permeability, frost resistance, air-, gas- and vapor permeability, heat conductivity and heat capacity, fire resistance and fire resistance.
Weight - a collection of material particles (atoms, molecules, ions) contained in a given body. The mass has a certain volume, i.e. occupies part of the space. It is constant for a given substance and does not depend on its speed and position in space. Bodies of the same volume, consisting of various substances, have an unequal mass. To characterize the differences in the mass of substances having the same volume, the concept of density is introduced. The latter is divided into true and average.
True density - the ratio of mass to volume of the material in an absolutely dense state, i.e. without pores and voids. To determine the true density r (kg / m 3, g / cm 3), it is necessary to divide the mass of the material (sample) m (kg, g) by the absolute volume V (m 3, cm 3) occupied by the material itself (without pores):
Often the true density of the material is attributed to the true density of water at 4 ° C, which is equal to 1 g / cm 3, then the determined true density becomes a dimensionless quantity, as it were.
However, most materials have pores, so their average density is always lower than the true density:
Only in dense materials (steel, glass, bitumen, and some others) are the true and average densities equal, because their internal pore volume is very small.
Average density - this is a physical quantity determined by the ratio of the mass of the material sample to the entire volume occupied by it, including the pores and voids present in it. The average density r (kg / m 3, g / cm 3) is calculated by the formula:
where m is the mass of the material in its natural state; V is the volume of material in its natural state.
The average density is not a constant value - it varies depending on the porosity of the material. For example, artificial materials can be obtained with different porosities (heavy concrete has a density of up to 2900 kg / m 3, and lightweight - up to 1800 kg / m 3). Density is influenced by material moisture.
For bulk materials, an important characteristic is bulk density - this includes not only the porosity of the material itself, but also the voids between grains or pieces of material.
Porositymaterial - this is the degree of filling it with pores. Porosity complements the density up to 1 or up to 100%. The porosity of various materials:
· Glass, metal 0%;
· Heavy concrete 5 - 10%;
Brick 25 - 35%;
Aerated concrete 55 - 85%;
Polyfoam 95%,
those. it varies significantly.
The properties of the material are also affected by the size of the pores and their nature (small or large, closed or interconnected).
Density and porosity directly affect such characteristics of materials as water absorption, water permeability, frost resistance, strength, thermal conductivity, etc.
Water absorption- the ability of the material to absorb water and retain it. The amount of water absorption is determined by the difference in the mass of the sample in water saturated and absolutely dry. Volumetric water absorption is distinguished when the difference is related to the volume of the sample and mass water absorption is when the difference is attributed to the mass of the dry sample. Mass water absorption for some materials:
Granite 0.5 - 0.8%
· Heavy concrete 2 - 3%
· Ceramic brick 8 - 20%
· Porous heat-insulating materials, for example, peat cookers\u003e 100%.
The saturation of materials with water adversely affects their basic properties: it increases density and thermal conductivity, reduces strength.
Humidity - moisture content, referred to the mass of the material in a dry state. The moisture content of the material depends both on its ability to absorb moisture in the material itself and on the environment in which the material is located.
Moisture return- the property of the material to give moisture to the surrounding atmosphere. It is determined by the amount of water (in percent by weight or volume of a standard sample) lost by the material per day at an ambient humidity of 60% and a temperature of 20 0 C. The water evaporates until an equilibrium is established between the moisture of the material and the humidity of the surrounding air.
Hygroscopicity - the property of materials to absorb a certain amount of water with increasing ambient humidity. This property is typical, for example, for wood - to avoid this, apply protective coatings.
Water permeability - the property of a material to pass water under pressure. It is characterized by the amount of water passed in 1 hour through 1 cm 2 the area of \u200b\u200bthe test material at constant pressure. Especially dense materials (steel, glass, bitumen) and dense materials with closed pores (for example, concrete of a specially selected composition) are waterproof.
Frost resistance - the property of water-saturated material to withstand multiple alternate freezing and thawing without signs of destruction and a significant decrease in strength.
Water freezing increases in volume by 9%, and if it completely fills the pores, the ice will destroy the pore walls, but usually the pores are not completely filled, therefore, destruction can occur with repeated freezing and thawing.
Dense materials that do not have pores, or materials with insignificant open porosity, the water absorption of which does not exceed 0.5%, have high frost resistance. Frost resistance is of great importance for wall, foundation and roofing materials that are systematically subjected to alternate freezing and thawing.
Materials are tested for frost resistance in freezers. Water-saturated samples are cooled to a temperature of –15–17 ° C and then thawed at a temperature of + 20 ° C. A material is considered frost-resistant if, after a given number of cycles, the loss in mass of the samples as a result of chipping and delamination does not exceed 5%, and the strength reduced by no more than 25%. According to the number of withstanding cycles of freezing and thawing (degree of frost resistance), materials are divided into brands М Мрз 10, 15, 25, 35, 50, 100, 150, 200 and more.
If the samples in the test process do not have traces of destruction, then the degree of frost resistance is established by determining the coefficient of frost resistance:
To mrz \u003d R mrz / R us,
where R mrz - ultimate compressive strength of the material after testing for frost resistance, MPa; R us is the compressive strength of a material saturated with water, MPa. For frost-resistant materials, K mrz should be at least 0.75.
Steam and gas permeability - the property of a material to pass water vapor or gases, including air, through its thickness under pressure. All porous materials in the presence of open pores are able to pass steam or gas.
Steam and gas permeability is characterized by a coefficient that is determined by the amount of steam or gas in liters passing through a layer of material 1 m thick and 1 m 2 in area for one hour with a partial pressure difference of 133.3 Pa on the opposite walls.
Thermal conductivity - the property of the material to transfer heat through the thickness in the presence of a temperature difference on the surfaces that bound the material. the thermal conductivity of the material is estimated by the amount of heat passing through the wall of the test material 1 m thick, 1 m 2 in 1 hour at a temperature difference of the opposite surfaces of the wall 1 0 C. The thermal conductivity is measured in W / (m · K).
The thermal conductivity of a material depends on many factors: the nature of the material, its structure, porosity, humidity, and the average temperature at which heat transfer occurs. The material of the crystalline structure is usually more thermally conductive than the material of the amorphous structure. If the material has a layered or fibrous structure, then its thermal conductivity depends on the direction of the heat flux with respect to the fibers, for example, the thermal conductivity of wood along the fibers is two times greater than across the fibers.
Fine-porous materials are less heat-conducting than large-porous materials, even if their porosity is the same. Closed cell materials have lower thermal conductivity than interconnected cell materials.
The thermal conductivity of a homogeneous material depends on its average density. So, with a decrease in the density of the material, thermal conductivity decreases and vice versa.
The moisture conductivity significantly affects the material’s thermal conductivity: wet materials are more heat-conducting than dry materials, since the thermal conductivity of water is 25 times greater than the thermal conductivity of air.
With increasing temperature, thermal conductivity increases.
Heat capacity - the property of a material to absorb a certain amount of heat when heated and to release it when cooled. The heat capacity indicator is the specific heat capacity equal to the amount of heat (J) required to heat 1 kg of material per 1 0 C.
Specific heat, KJ / (kg · 0 C):
· Artificial stone materials 0.75 - 0.92;
· Wood 2.4 - 2.7;
0.48 steel
Water 4,187.
The heat capacity is taken into account when calculating the heat resistance of walls and ceilings of heated buildings, as well as when calculating furnaces.
Fire resistance - the ability of the material to withstand the effects of high temperatures and water in a fire. According to the degree of fire resistance, the materials are divided into: non-combustible, difficult to combust and combustible.
Fireproof materials under the influence of fire or high temperature do not ignite, do not smolder and do not char (steel, concrete, brick).
Hardly combustible materials under the influence of fire are difficult to ignite, smolder, or char, but after removing the source of fire, their burning and decay cease (wood-cement material fiberboard, asphalt concrete, some types of polymeric materials).
Combustible materials under the influence of fire or high temperature ignite and continue to burn after removing the source of fire (wood, felt, roofing, roofing material).
Fire resistance- the property of the material to withstand prolonged exposure to high temperature, without melting and without deformation. According to the degree of refractoriness, the materials are divided into refractory (they withstand temperatures over 1580 0 С for a long time), refractory (1350 - 1580 0 С) and low-melting, softening at temperatures below 1350 0 С (ordinary clay brick is also referred to them).
Physical properties of materials
The main properties of materials
In order to choose the right material, design and build a structure, you need to know the properties of the materials used. Highlight the basic properties that are important for all building materials.
Classification of basic properties.Given the dependence on the nature of the work of the material in the structures and its interaction with the environment, they distinguish: a) physical properties (specific and structural characteristics, hydrophysical, thermophysical, acoustic, electrical); b) mechanical properties (deformative and strength); c) chemical properties; d) biological properties; e) integral properties - durability and reliability. Material properties are always evaluated by numerical indicators, which are established by testing.
Specific and structural characteristics- ϶ᴛᴏ true, average and bulk density of the material, as well as various types of porosity.
True density r (g / cm 3) - mass tvolume units V and material in an absolutely dense state without pores and voids:
Average density r o (kg / m 3) - mass t volume units V about the material in its natural state along with pores and voids:
True density, in contrast to average density, is a fairly constant characteristic that should not be changed, like the average density of a material, until its chemical composition or molecular structure changes. Most building materials have pores; therefore, their true density is always higher than average. Only in dense materials (steel, glass, bitumen), the true and average density are equal, since the pore volumes are very small.
Often the average density of the material is referred to the density of water, at 4 ° C equal to 1 g / cm 3, and then the determined density becomes a dimensionless quantity, which is called the relative density.
Bulk density r n (kg / m 3) is the ratio of the mass of the material in bulk to its volume. Bulk density is determined for bulk materials (sand, gravel, cement, etc.). Its value reflects the influence of not only pores in each grain, but also intergranular voids in a loose bulk material.
The values \u200b\u200bof the average and bulk density of materials are necessary characteristics when calculating the strength of a building, taking into account its own weight, to determine the volumes, method and cost of transporting materials, etc.
In many ways, the properties of the material determine the amount, size and nature of the pores.
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Porosity - a relative value (usually in percent), showing how much of the volume of material is occupied by internal pores or voids (voidness). Pores are cells that are not filled with solid matter (up to several millimeters in size). Larger pores, for example, between grains of bulk materials, or cavities that are present in some products (hollow bricks, panels made of yellow concrete), are called voids.
There are general, open and closed porosity. Total porosity calculated by the formula
.
Open porosityP about is determined by water absorption (see below). Closed porosity P s equal to the difference P and P about.
The total porosity varies widely: from 0.2-0.8% for granite and marble, up to 75-85% for heat-insulating bricks and cellular concrete, and over 90% for foams and mineral wool.
Hydrophysical properties - ϶ᴛᴏ properties of building materials with respect to the action of water (hygroscopicity, humidity, water absorption, moisture deformation, water permeability, water resistance, and also frost resistance - with the simultaneous action of water and frost).
Hygroscopicity called the property of a porous material to absorb water vapor from air.
Humidity characterizes the relative water content in the material as a percentage.
Water absorption - the ability of the material to absorb and retain water in direct contact with it. The amount of water absorption depends on the structure of the material, and first of all, on open (capillary) porosity. Distinguish water absorption by mass In m (%),
,
and water absorption by volume In about (%),
,
where m us - mass of sample saturated with water, g; m dry - dry sample weight, g; V o - sample volume, cm 3; r in - the density of water, 1 g / cm 3.
Water absorption by mass varies over a wide range, for example, for granite it is 0.02-0.7%, for heavy concrete - 2-4%, brick - 8-15%, for thermal insulation material should be more than 100%. Water absorption by volume characterizes mainly the open porosity of the material. Knowing water absorption by mass V m and density ρ о, we can calculate water absorption by volume:
Moisture strain - ϶ᴛᴏ shrinkage and swelling. Shrinkage(shrinkage) - a decrease in the volume and size of the material when it dries. It is caused by a decrease in the thickness of the layers of water surrounding the particles of the material, and by the action of capillary forces striving to bring them closer. Swelling (swelling) - an increase in the volume and size of the material when it is moistened. It occurs due to the wedging effect of water and a decrease in capillary forces.
Water permeability - the ability of a material to pass water through its thickness. It is characterized by the value of the filtration coefficient K f (m 2 / h), which is determined by the amount of water passing through 1 m 2 area for 1 h at constant pressure.
Water resistant - the ability of the material not to pass water, and it is associated with a filtering coefficient inverse relationship. For concrete, water resistance is characterized by brands W2, W 4, … W20, denoting excess pressure (0.2; 0.4; ... 2.0 MPa), at which the sample does not pass water during a standard test (method of "wet spot"). Water resistance increases with the compaction of the material and the reduction of capillary pores.
Water resistance characterized by a softening coefficient K p, which is calculated by the formula
where R us - ultimate compressive strength in a water-saturated state, MPa; R dry - ultimate compressive strength in the dry state, MPa.
Materials with K p less than 0.6 are classified as non-waterproof materials, materials with K p not lower than 0.6 are water-resistant materials, and materials with K p not lower than 0.7 are waterproof (0.8 - for hydraulic structures and foundations )
Frost resistance - the ability of the material to withstand repeated and alternate freezing and thawing in a water-saturated state. The destruction of the material when it is frozen in a state saturated with water is associated with the formation of ice in the pores, the volume of which is about 9% more than the volume of water. Frost resistance is quantified by the brand for frost resistance. The largest number of cycles of alternate freezing and thawing is taken as a frost resistance brand, образцы samples of the material are held without visible signs of destruction and a definite decrease in strength and weight loss. Installed frost resistance grades: heavy concrete - F25- F1000, ceramic and silicate bricks - F15- F50 etc.
Thermophysical Properties characterize the ratio of the material to the action of heat.
Thermal conductivity - the ability of a material to transfer heat from a body with a higher temperature to a less warm one. It is characterized by the coefficient of thermal conductivity l (W / (m × ° С), which is equal to
,
where Q - the amount of heat, J; d is the thickness of the material, m; BUT - cross-sectional area, m 2; ( t 1 _ t 2) - temperature difference, ° C; T - the duration of the passage of heat, s.
Thermal conductivity depends on the structure of the material, its humidity and temperature. There is an empirical formula for Nekrasov to determine the thermal conductivity of a material by its average density
where d - the relative density of the material (the density of the material relative to the density of water is 1 g / cm 3), dimensionless quantity.
Thermal conductivity depends on the humidity of the material, since water has a higher thermal conductivity (25 times) compared with the thermal conductivity of air.
Thermal resistance R, (m 2 × ° С) / W, structures of thickness d equal
Heat capacity determined by the amount of heat, ĸᴏᴛᴏᴩᴏᴇ it is extremely important to report 1 kg of this material in order to increase its temperature by 1 ° C. With increasing humidity of materials, their heat capacity increases, since water has a heat capacity of 4.19 kJ / (kg × ° C).
Fire resistance - the ability of the material to withstand the long influence of high temperatures under load.
Fire resistance - the ability of the material to withstand short-term exposure to open flame. Distinguish materials: fireproof, ᴛ.ᴇ. which do not burn and do not support combustion (concrete, metal, ceramics); incombustible, ᴛ.ᴇ. which, when exposed to fire, burn (smolder), and when the fire is removed, they stop burning (asphalt concrete, wood impregnated with flame retardants); combustible (wood, polymeric materials).
Physical properties of materials - concept and types. Classification and features of the category "Physical Properties of Materials" 2014, 2015.
The main properties of materials
Physical properties of materials - characterize the physical state of materials or the relationship of a given material to the course of any physical processes. 1. The true density of the material is the ratio of the mass of the material to its volume in an absolutely dense state, without pores.2. Average density - a value determined by the ratio of mass to volume of material in its natural state.
For example: we take conditionally a brick - - - 
For porous materials, true density is always greater than average. For dense materials, the true and average density will be equal to ρ=ρ
SR True density is a constant value, and average density is a variable value and it depends on external factors, on the porosity of the material, on the nature of the pores, water absorption, etc. 3. Porosity - the degree of filling the volume of material with pores. P - porosity 
It is important to know not a quantitative indicator of porosity, but also the nature of the pores, i.e., large pores or small ones, open or closed, communicating or not.
4. Hygroscopicity - the ability of a material to absorb water vapor from air.
Materials that attract vapors from the air are called hydrophilic. And repulsive are called hydrophobic. The hygroscopicity of the material depends on the porosity and on the nature of the pores, on external conditions, and depends on the nature of the substance (for example: wood, foam). 5. Frost resistance - the property of a material saturated with water to withstand multiple alternate freezing and thawing without signs of destruction and a significant decrease in strength. A material is considered frost-resistant if its mass loss is not more than 5%, and the loss of strength is not less than 25%. TO SIZE - softening coefficient. If TO SIZE\u003e 75%, then the material is considered frost-resistant. The most frost-resistant are dense materials. A characteristic of frost resistance is a brand that shows the number of seasoned cycles of freezing and thawing. 6. Water absorption - the ability of a material to absorb and retain water. Materials with non-communicating pores will be minimal. Water absorption is calculated by weight and volume. By weight: 
m - mass of water-saturated material m 1 - mass of dry material By volume: 
V is the volume in its natural state. Water absorption depends on the quantitative indicator of porosity, on the size of the pores, on whether they are closed or open, reported or not. 7. Thermal conductivity - the ability of a material to transmit heat through its thickness. The main indicator is the coefficient of thermal conductivity, which is numerically equal to the amount of heat passing through the material with a thickness of one meter, an area of \u200b\u200bone square meter with a temperature difference of t 2 and t 1 on parallel planes of 1 ° and a time of one hour. λ - lambda Q - amount of heat f - area b - thickness t 1 and t 2 - temperature difference Z - time 
Dense materials have high thermal conductivity. The coefficient of thermal conductivity, as well as the coefficient of heat capacity, are necessary when conducting thermotechnical calculations of building envelopes. 8. Heat capacity - the ability of a material to absorb heat when heated and to emit when it cools. Mechanical properties
- characterize the ability of the material to resist the destructive action or deformation of external forces. 1. Strength - the ability of a material to resist destruction under the action of internal stresses arising from external forces. 
In structures under the action of external forces, internal stresses arise (σ - sigma). When calculating building structures, an indicator such as tensile strength (R - er) is used. The tensile strength corresponds to the internal stresses that occur in the structure under the action of a destructive force. (P - action of destructive force). In case of unexpected loads, safety margins are created. Strength indicator for different materials, as a rule, is the strength grade, which is numerically equal to the compressive strength of this material. (Grade is equal to tensile strength) 2. Hardness - the ability of a material to resist the penetration of another harder material into it. For plastic materials, hardness is determined by the indentation of a metal ball (Brinell hardness). For natural stone materials, hardness is determined by the Mohs scale of hardness. Elastoplastic properties.
Elasticity - the ability of a material to deform under load and restore its shape and size after its removal. Plasticity is the ability of a material to deform under load without rupture and cracks and maintain its changed shape and size after unloading. Fragility - a property of a material will instantly collapse under the influence of external forces, without preliminary visible deformation. Abrasion - the property of the material will change in volume and mass under the influence of external abrasive forces. Chemical properties
- characterize the ability of the material to resist the effects of acids, salts, gases, etc. They are characterized by the chemical and corrosion resistance of materials.
Forest materials
The true density for all rocks is 1.55g / m 3. The average density will range from 0.37 - 0.7g / m 3. The main property of wood is moisture. Humidity is the mass amount of water currently contained in wood. According to the degree of humidity, wood can be divided into three groups:
- wet or freshly chopped wood with a moisture content of ≥35%. air-dry wood with humidity ≥15 ... 20% room-dry wood ≥8 ... 12%.
Standard humidity is 12%.
Hygroscopicity is very high for wood. Depends on the type of wood and environmental conditions. High hygroscopicity and water absorption of wood lead to shrinkage or swelling. The resistance of wood to mechanical stress is not the same, depending on the direction of the fibers. (this is called anisotropy). Well perceives compression along the fibers and bending. Protection of wood from destruction and fire.
Destruction.
Two groups of measures:
1. constructive measures.
A) organizational water drainage from wooden structures
B) house cladding
C) coloring
2. chemical measures.
Impregnation with antiseptics.
Antiseptics are substances that protect wood from destruction, they must be harmless to humans and animals, should not have color and smell. They are divided into three groups: 1. water-soluble 2. oil 3. pastes Ignition. Two groups of measures: 1. constructive measures Removal of wooden structures from sources of ignition. Protection of wooden structures with metal or asbestos-cement sheets. Painting with paints based on liquid glass. 2. chemical measures. Impregnation with flame retardants. Fire retardants are substances that prevent burning and wood, impregnated with these compounds, does not burn in the fire, but smolders.
The use of wood.
Wood is widely used in construction, for indoor and outdoor decoration. And also for the construction of houses, baths, etc.
Rocks
Natural stone materials are construction materials obtained from rocks by mechanical processing. Minerals are called bodies that are products of natural reactions and possess in each part of their mass, a certain chemical composition and characteristic chemical properties.
Rock application
Clay - Ceramics
Shell rock - for blocks
Penza - for warming
Limestone - for additives in solutions
Ceramic materials
Ceramic materials are called artificial stone materials obtained from clay masses by molding and subsequent firing.
Properties and structure of ceramic products.
Ceramic products are characterized by high strength (with proper manufacture), durability, resistance to aggressive environments and resistance to abrasion. The technical properties of ceramic products are completely dependent on the composition and structure of the ceramic crock, i.e. from the properties of the material of which the products consist. By the water absorption of the products, one can judge the nature of the porosity of their shard. All ceramic materials, depending on porosity, are divided into two groups:
- dense - with water absorption less than 5%; porous - with water absorption more than 5%
products can be glazed and unglazed
Raw materials for ceramics .
It is divided into two types, plastic and non-plastic materials. Plastic - clay, kaolin. To reduce the ductility of highly plastic clays, low-plastic clays or scrubbers (ash, lime, sawdust, metallurgical slag) are added to them. To increase the plasticity of clays, highly plastic clays, organic plasticizing additives are added, steaming and vacuumization are also used. Manufacture of ceramic products.
1. mining of raw materials
2. drawing up the ceramic mass and preparing it for molding. The preparation of ceramic mass, depending on the properties of the feedstock and the type of manufactured products is carried out in the following ways:
A) semi-dry method (moisture content of raw materials 8 ... 12%)
B) the plastic method (moisture content of raw materials 20 ... 25%)
C) wet or slinky method (moisture content of raw materials up to 68%)
3. molding products in one of the following ways.
Plastic and dry pressing, casting in cold or hot pressing.
4. drying of the semi-finished product + additional finish.
5. product glazing
The use of ceramic products
Brick - wall material
Tile - Finish
Plumbing Faience
Roof Tiles - Roof
Expanded clay warming
Wall materials.
Clay ordinary brick. Available in accordance with GOST
250/120/65 - ordinary red
250/120/88 - modular
With proper manufacture, the brick is characterized by a porous structure, significant strength and durability. In case of violation of brick manufacturing technology, unbaked or burnt products can be obtained.
Brick is produced in the following grades in strength: 75, 100, 125, 150, 200, 250, 300. Brick is made in two ways: plastic and semi-dry.
Metals
Metals are simple substances with characteristic properties under ordinary conditions. (high strength, electrical conductivity, weldability, etc.) Alloys are solid or liquid systems formed by alloying two or more metals.
Ferrous metals are an alloy of iron and carbon.
Cast iron is an alloy of iron and carbon. Where the carbon content ranges from 2 ... 4.3%, and in special cast irons - ferroalloys of 5% or more. In cast iron, there are elements such as silicon, phosphorus, etc. that affect the properties of cast iron. Sulfur and phosphorus are harmful impurities (increase fragility). Depending on the form in which carbon is contained in cast iron, gray (foundry) and white (limit) cast irons are distinguished. In construction, gray cast irons are used (pipes, bathtubs, supports, column shoes - (it works well for compression)). Steel is an alloy of iron with carbon, where carbon is contained up to 2%. Unlike cast iron (brittle metal), steel is ductile, elastic and has high technological properties.
They are classified: