Composition - the totality of something that forms something whole. According to its composition, the material can be characterized from the standpoint of its chemical, mineralogical, morphological, particle-size and other features.
Phase - a thermodynamically equilibrium state of a substance, characterized by an aggregative state, atomic (molecular) composition and structure, as well as separated by spatial boundaries from other possible equilibrium states (phases) of the same substance. The phase composition of the material characterizes the content of solid, liquid and gas phases. In this sense, all building materials are composed of solid matter forming the pore walls, i.e. "frame" of the material, and pores filled with air (this is the gas phase) and water (liquid phase). The content of these phases affect all properties and behavior of the material during operation.
The chemical composition of building materials reflects the content of chemical elements, oxides, compounds. By chemical composition of the materials are divided into organic and inorganic.
Organic materials consist primarily of hydrocarbons and their derivatives. Accordingly, they are characterized by flammability, aging under the influence of sunlight and atmospheric oxygen, etc. Examples of organic materials: polymers (linoleum), tar, roofing felt, plastics (plastic windows).
Inorganic building materials can be divided into metal and mineral (non-metallic). Metallic materials are characterized by high density, strength, but they have low heat resistance and are susceptible to corrosion. The construction uses steel and aluminum structures, steel fittings, cast iron products.
The chemical composition of almost all mineral building materials can be represented as a combination of acid and alkali oxides. The overwhelming majority of construction inorganic materials belong to the class of silicates - compounds formed by SiO2 and oxides of other elements. They are non-flammable, heat resistant, durable. These are ceramic materials, glass, concretes on mineral binders.
For mineral materials, the most important characteristic is the mineralogical composition , which shows which minerals and in what quantity are contained in the binder or in the stone material. Minerals are chemical compounds of crystalline structure. 1/3 of all minerals on Earth are natural silicates. All minerals differ from each other in composition, structure and properties, therefore the predominance of certain minerals in the material determines its construction properties. The more durable minerals, the stronger the material.
Morphological characterizes the form of structural components in terms of their geometry: fibrous, lamellar, prismatic forms of formations in the composition of the material.
The particle size (dispersion) reflects the size of the particles entering the material.
Structure - structure - is the spatial volumetric interposition of phases (components) in the material and their connection with each other. With the same composition, but different structure, the material will have different properties. All materials are characterized by polystructurality - their structure is a “structure in structure” system. Traditionally, the structure of materials is studied at three scale levels: 1) the macrostructure of the material - the structure visible to the naked eye; 2) the microstructure of the material - the structure visible in the optical microscope; 3) the internal structure of the substances that make up the material, at the molecular-ion level, studied by X-ray structural analysis, electron microscopy, etc.
With the same composition, the same structure of the material, one can speak of its different state . State - a category of scientific knowledge, which characterizes the ability of moving matter to manifest in various forms with their inherent essential properties and relationships. With the help of this category, the process of change and development of things and phenomena is expressed, which ultimately leads to a change in their properties and relationships. The combination of such properties and relationships determines the state of a thing or phenomenon. The same material can be in the dry and moistened state, in the unstressed and stress-deformed state, in the heated and cooled state. Accordingly, he will show different properties.
The composition, structure, state of the material are systemically interrelated, interdependent, interdependent concepts.
Density reflects the amount of material in a unit of its volume, i.e. condensation of a substance. Distinguish between true density, average density and bulk density.
Porosity P is the degree of filling the volume of material with pores. With few exceptions (metals, glass, monominerals) building materials are porous. The structure of the porous material is characterized by total, open and closed porosity, the distribution of pores along their radii, the average pore radius and the specific inner surface of the pores.
Porosity is expressed in fractions of the volume of material taken as 1, or as a percentage of the volume.
Humidity is the content of moisture in the material, that is, the liquid phase.
Properties - internal, inherent in this material features that determine
its difference or generality with other materials and manifested as a response to the effects of external fields or environments. A simpler definition: properties is the ability of a material to respond in a certain way to individual or aggregate external or internal influences. Impacts or loads may be:
- physical (heat, moisture, radiation, light, etc.);
- mechanical (power loads);
- chemical (precipitation, exhaust gases, alkalis, acids);
- climatic or natural (frost, thaw, wind); - biological (biogenic) , etc.
Construction materials must have a set of properties that can withstand these loads. From here there are physical, mechanical, chemical and other properties . The level of these properties is set for the material in accordance with its purpose in the design.
1.3.1. Physical properties (the ability of a material to respond to the effects of physical factors — thermal, aquatic, acoustic, electrical, radiation, etc.). Are divided into:
Hydrophysical properties (reaction of the material to the action of the aquatic environment):
- hydrophilicity (hydrophobicity) - the ability (inability) of the material to be wetted with water. Hydrophilic materials - clays, silicates; hydrophobic - metals, organic compounds (bitumen, some plastics). Depend on the chemical composition of materials and affect many properties;
- water absorption - the ability of the material to absorb and retain water, being completely placed in it. Unlike moisture, water absorption is the maximum degree of filling the open pores of a material with water. Water absorption of various materials varies widely: granite - 0.02 - 0.7%, heavy concrete -2-4%, brick - 8-15%, porous insulation materials - 100% and more;
- hygroscopicity refers to the property of capillary-porous material to absorb water vapor from humid air. The absorption of moisture from the air is due to the polymolecular adsorption of water vapor on the inner surface of pores and capillary condensation. Wood, heat-insulating, wall and other porous materials possess a developed inner surface of pores and, therefore, high sorption capacity;
- capillary absorption - absorption of moisture partially immersed in the material;
- water, gas and vapor permeability (impermeability) - the ability of the material to pass (not pass) water, steam or gas under pressure;
- moisture deformations - the ability of materials to change their volume and size with changes in humidity;
- water resistance - the ability of a material to retain its strength properties when wetted. It is characterized by the softening coefficient Kp - the ratio of the strength of a material saturated with water to the strength of a dry material;
- frost resistance - the ability of a material saturated with water to withstand alternate freezing and thawing without destruction.
Thermophysical properties (reaction of the material to the action of heat):
- thermal conductivity is the ability of a material to conduct heat flux through its thickness under the action of temperature gradients. Estimated by thermal conductivity λ , W / (m · ° С), is the amount of heat (J) passing through a wall 1 m thick and 1 m2 in 1 h with a temperature difference of 1 КК;
- refractoriness - the ability of a material to withstand prolonged exposure to high temperature, without softening or deforming;
- fire resistance - the ability of a material to resist the action of an open fire for a certain time)
- heat capacity - the ability of a material to accumulate heat when heated and to release heat during cooling. Estimated by the coefficient of heat capacity - the amount of heat that must be given to 1 kg of this material in order to increase its temperature by 1 ° C;
- temperature - or heat resistance - the ability to withstand repeated sudden temperature changes;
- temperature deformations - the ability of a material to change its size and volume with temperature. Estimated by the coefficient of linear or volumetric thermal expansion - elongation of 1 m of the material when it is heated by 1 ° C
Physical also include acoustic (sound absorption and sound conductivity), optical (light transmission), electrical (electrical conductivity), radiation (radiation resistance, absorption of nuclear and X-ray radiation), etc. properties.
1.3.2. Mechanical properties (the ability of a material to resist deformation and destruction from internal stresses arising in materials under the action of external force static and dynamic loads) are divided into deformative and strength properties . Deformative properties :
- elasticity - the ability of a solid body to spontaneously restore the original shape and size after the termination of the external force;
- plasticity - the ability of a solid body to change shape or size under the action of external forces, not collapsing, and after the cessation of the force, the body cannot spontaneously restore its size and shape;
- fragility - the ability of a solid to collapse without the formation of noticeable residual deformations;
These properties are evaluated using the modulus of elasticity E (Young's modulus), which depends on the energy of interatomic bonds and characterizes the measure of the rigidity of the material, that is, its ability to resist the elastic shape change under the action of external forces; Poisson's ratio (transverse compression ratio) - the ratio of the transverse relative deformations to the longitudinal and shear modulus associated with the elastic modulus by the Poisson's ratio. Strength properties:
- compressive strength - the ability of a material to resist destruction from internal tensile stresses arising in it under compressive loads (scheme). Estimated by compressive strength Rсж (MPa, kgf / cm2), which is equal to the quotient of the breaking force (load) Рр per initial cross-sectional area of the sample (cube, cylinder, prism) S :
P p
R SG = 
S
- tensile strength - the ability of a material to resist destruction from internal tensile stresses arising in it during tensile loads. Estimated by tensile strength at axial tension Rp (MPa, kgf / cm2):
P p
R p =
S
or indirect methods of tensile strength when splitting a cylinder:
2 P p
R pp = 
,
n d l
where d and l is the diameter and length of the cylinder, cm; or ultimate tensile strength in bending:
where Рр - breaking load, kgf or N; l is the distance between the supports, cm; b and h is the width of the beam height, cm; and - the distance between the axes of the load, see
- Flexural strength - the ability of a material to resist destruction from internal tensile stresses arising in it under bending loads. Estimated by the flexural strength Ri (MPa, kgf / cm2), defined as the maximum tensile stress in the lower stretched layer of the beam (beam):
Depending on the ratio Rp / Rsc, it is possible to conditionally divide the materials into three groups: materials in which Rp> Rсж (fibrous - wood, etc.); Rp = Rssh (steel); Rр (fragile materials - natural stones, concrete, brick). For the latter, the value of Rр is more important than Rсж , since these materials in most of the designs work exactly for bending.
- critical stress intensity factor (fracture toughness) KIc, kN / m3 / 2 - characterizes the stress state of the end zone of the fracture at the moment of its cracking, is a material constant.
- hardness (the ability of the material to resist the penetration of another more solid body into it);
- abrasion - the ability of the material to decrease in mass or volume under the action of abrasive forces;
- wear - the ability of the material to resist the simultaneous effects of abrasion and shock;
- impact strength (dynamic or impact strength) - the ability of a material to resist fracture under impact loads.
Strength properties of materials depend on the strength of internal bonds, their quantity per unit volume of material and the uniform distribution of the volume of the material. Depending on the strength, building materials are divided into grades or classes of compressive strength, axial tension, and flexural tension. The strength mark is the standardized value of the unified compressive strength of the material in kgf / cm2, taken by its average value. The concrete class is the value of the unified strength at the design age in MPa, taken with a guaranteed security of 0.95.
1.3.3. Chemical properties:
Chemical (corrosion) resistance - the ability of a material to resist chemical effects of the environment: air and vapors and gases contained in it (weather resistance), water and substances dissolved in it (water resistance), chemically aggressive substances - acids, alkalis (acid and alkali resistance), with interactions with which destruction of the material may occur (corrosion). Corrosion resistance of a material depends on its chemical composition. With a high silica content, for example, high acid resistance is observed. If the composition of many basic (alkaline) oxides, then this material is usually not resistant to acids, but not destroyed by alkali. Organic materials (wood, bitumen, plastic) at ordinary temperatures are usually resistant to the action of weak acids and alkaline conditions. A significant part of building materials, especially on the basis of mineral binders, has a low corrosion resistance, so they must be protected from corrosion.
1.3.4. Biological properties
Bio - resistance is the ability of a material to resist the aggressive action of a biological environment (macro-, microorganisms, etc.).
1.3.5. Technological properties - grindability ;
- sawing, splitting ;
- formability (for example, workability b. mixture); - persistence (eg, stratification b. a mixture);
- boring, nailed , etc.
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