MJ Building

MJ-Building Platforme

Publishing House MetalJournal begins to create the MJ-Building Project.

The aim of the Project
is to display in real time the range of services, goods availability and prices of leading manufacturers and traders of building materials; design and construction companies.

The main distinguishing feature of the Project:
for Customers (Buyers) - the ability to quickly complete an order with subsequent shipment / delivery of goods to the destination; finding the optimal solution for the selection of the necessary construction, repair and design company;
for Sellers of goods and services - presence on a specialized Internet platform to promote their products and brand.
The created Internet portal allows users to view the product range, prices and availability, calculate the transport logistics scheme, get acquainted with advertising and news information.

Russian, Ukrainian and English versions are provided.

We are looking forward to fruitful cooperation.

In the process of construction, operation and repair of buildings and structures, building products and structures from which they are erected are exposed to various physical and mechanical, physical, chemical and technological influences. The civil engineer is required to choose the right material that has sufficient strength, reliability and durability for the designed structure.

Building materials and products in accordance with the theory of artificial building conglomerates are classified:

Natural (natural) - without changing the composition and internal structure:

o inorganic (stone materials and products);

o organic (wood materials, straw, fire, reeds, husks, wool, collagen).

Artificial:

o Non-firing (hardening under normal conditions) and autoclave (hardening at a temperature of 175-200 ° C and a water vapor pressure of 0.9-1.6 MPa);

§ inorganic (clinker and clinker-containing cements, gypsum, magnesia, etc.);

    § organic (bituminous and dektevic binders, emulsions, pastes);

    § polymer (thermoplastic and thermosetting);

    § complex:

    § mixed (mixing of several types of minerals);

    § compounded (mixtures and alloys of organic materials);

    § combined (combining mineral with organic or polymer).

o Roasting - hardening from fiery melts:

    § slag (according to the chemical basicity of the slag);

    § ceramic (by nature and type of clay and other components);

    § glass melting (in terms of the alkalinity of the charge);

    § stone casting (by the type of rock);

    § complex (by the type of connected components, for example: slag-ceramic, glass-slag).

 

By application, they are classified into two main categories. The first category includes - structural: brick, concrete, cement, timber, etc. They are used in the construction of various elements of buildings (walls, ceilings, coatings, floors). The second category includes special purposes: waterproofing, thermal insulation, acoustic, finishing, etc.

The main types of building materials and products

· Natural stone building materials and products from them;

· Inorganic and organic binders;

· Forest materials and products from them;

· Metal products.

Depending on the purpose, conditions of construction and operation of buildings and structures, appropriate building materials are selected that have certain qualities and protective properties against the effects of various external environments. Given these features, any building material must have certain construction and technical properties. For example, the material for the outer walls of buildings must have the lowest thermal conductivity with sufficient strength to protect the room from heat loss; the material of the structure for irrigation and drainage purposes is waterproof and resistant to alternating moisture and drying; the material for road paving (asphalt, concrete) must have sufficient strength and low abrasion to withstand traffic loads.

Properties


Materials and products must have good properties and qualities.

Property is a characteristic of a material that manifests itself in the process of its processing, application or operation.

Quality is a set of material properties that determine its ability to meet certain requirements in accordance with its purpose.

The properties of building materials and products are classified into four main groups: physical, mechanical, chemical, technological, etc.

Chemicals include the ability of materials to resist the action of a chemically aggressive environment, causing exchange reactions in them, leading to the destruction of materials, a change in their initial properties: solubility, corrosion resistance, resistance to decay, hardening.

Physical properties: average, bulk, true and relative density; porosity, moisture, moisture yield, thermal conductivity.

Mechanical properties: ultimate strength in compression, tension, bending, shear, elasticity, plasticity, stiffness, hardness.

Technological properties: workability, heat resistance, melting, speed of hardening and drying.

 Physical properties


1. True density ρ is the mass of a unit volume of material in an absolutely dense state. ρ = m / Va, where Va is the volume in a dense state. [ρ] = g / cm³; kg / m³; t / m³. For example, granite, glass and other silicates are almost completely dense materials. Determination of the true density: a pre-dried sample is ground into powder, the volume is determined in a pycnometer (it is equal to the volume of the displaced liquid).

2. Average density ρm = m / Ve is the mass of a unit of volume in its natural state. The average density depends on temperature and humidity: ρm = ρw / (1 + W), where W is the relative humidity, and ρw is the wet density.

3. Bulk density (for bulk materials) - the mass of a unit volume of loosely poured granular or fibrous materials.

4. Porosity P - the degree of filling the volume of the material with pores. P = Vp / Ve, where Vp is the pore volume, Ve is the volume of the material. The porosity is open and closed.

Open porosity Por - the pores communicate with the environment and with each other, are filled with water under normal conditions of saturation (immersion in a bath with water). Open pores increase the permeability and water absorption of the material, and reduce frost resistance.

Closed porosity Pz = P-Po. The increase in closed porosity increases the durability of the material, reduces sound absorption.

The porous material contains both open and closed pores.

Hydrophysical properties


1. The water absorption of porous materials is determined according to the standard method, keeping the samples in water at a temperature of 20 ± 2 ° C. At the same time, water does not penetrate into closed pores, that is, water absorption characterizes only open porosity. When removing samples from the bath, water partially flows out of large pores, therefore, water absorption is always less than porosity. Water absorption by volume Wo (%) - the degree of filling the volume of the material with water: Wo = (mw-mc) / Ve * 100, where mw is the mass of the material sample saturated with water; mc is the dry weight of the sample. Water absorption by weight Wm (%) is determined in relation to the weight of dry material Wm = (mw-mc) / mc * 100. Wo = Wm * γ, γ is the volumetric mass of dry material, expressed in relation to the density of water (dimensionless value). Water absorption is used to assess the structure of the material using the saturation coefficient: kн = Wo / P. It can vary from 0 (all pores in the material are closed) to 1 (all pores are open). A decrease in kн indicates an increase in frost resistance.

2. Water permeability is the property of a material to pass water under pressure. The filtration coefficient kph (m / h is the dimension of velocity) characterizes the water permeability: kph = Vw * a / [S (p1-p2) t], where kf = Vw is the amount of water, m³, passing through a wall with an area of ​​S = 1 m2, thickness a = 1 m for a time t = 1 h with a difference in hydrostatic pressure at the boundaries of the wall p1 - p2 = 1 m of the water column.

3. The waterproofness of the material is characterized by the W2 brand; W4; W8; W10; W12, denoting the one-sided hydrostatic pressure in kgf / cm², at which the concrete sample-cylinder does not pass water under the conditions of a standard test. The lower the kph, the higher the water resistance mark.

4. Water resistance is characterized by the softening coefficient kp = Rw / Rc, where Rw is the strength of the material saturated with water, and Rc is the strength of the dry material. kp ranges from 0 (wet clays) to 1 (metals). If kp is less than 0.8, then such material is not used in building structures in water.

5. Hygroscopicity - the property of a capillary-porous material to absorb water vapor from the air. The process of absorbing moisture from the air is called sorption, it is due to the polymolecular adsorption of water vapor on the inner surface of the pores and capillary condensation. With an increase in the pressure of water vapor (that is, an increase in the relative humidity of the air at a constant temperature), the sorption moisture content of the material increases.

6. Capillary suction is characterized by the height of water rise in the material, the amount of absorbed water and the intensity of suction. A decrease in these indicators reflects an improvement in the structure of the material and an increase in its frost resistance.

7. Moisture deformation. Porous materials change their volume and size when the humidity changes. Shrinkage is a reduction in the size of the material as it dries. Swelling occurs when the material is saturated with water.

Thermophysical properties


1. Thermal conductivity - the property of a material to transfer heat from one surface to another. Nekrasov's formula connects the thermal conductivity λ [W / (m • C)] with the bulk density of the material, expressed in relation to water: λ = 1.16√ (0.0196 + 0.22γ2) -0.16. As the temperature rises, the thermal conductivity of most materials increases. R - thermal resistance, R = 1 / λ.

2. Heat capacity c [kcal / (kg • C)] - the amount of heat that must be communicated to 1 kg of material in order to increase its temperature by 1 ° C. For stone materials, the heat capacity varies from 0.75 to 0.92 kJ / (kg • C). With increasing humidity, the heat capacity of the materials increases.

3. Refractoriness - the property of a material to withstand prolonged exposure to high temperatures (from 1580 ° C and above), without softening or deforming. Refractory materials are used for the inner lining of industrial furnaces. Refractory materials soften at temperatures above 1350 ° C.

4. Fire resistance - the property of a material to resist the action of fire in a fire for a certain time. It depends on the combustibility of the material, that is, on its ability to ignite and burn. Non-combustible materials - concrete, brick, steel, etc. But at temperatures above 600 ° C, some non-combustible materials crack (granite) or strongly deform (metals). Non-combustible materials smolder under the influence of fire or high temperature, but after the fire ceases to burn and smolder (asphalt concrete, wood impregnated with fire retardants, fibrolite, some foam plastics). Combustible materials burn with an open flame, they must be protected from ignition by constructive and other measures, treated with fire retardants.

5. Linear thermal expansion. With a seasonal change in the temperature of the environment and material by 50 ° C, the relative temperature deformation reaches 0.5-1 mm / m. To avoid cracking, long structures are cut with expansion joints.

Frost resistance of building materials: the property of a material saturated with water to withstand alternating freezing and thawing. Frost resistance is quantitatively assessed by the brand. The brand is taken to be the largest number of cycles of alternating freezing to −20 ° C and thawing at a temperature of 12–20 ° C, which material samples can withstand without reducing the compressive strength by more than 15%; after testing, the samples should not have visible damage - cracks, chipping (weight loss no more than 5%).

Mechanical properties


Elasticity - spontaneous restoration of the original shape and size after the termination of the external force.

Plasticity is the property to change shape and size under the influence of external forces without collapsing, and after the cessation of external forces, the body cannot spontaneously restore its shape and size.

Residual deformation is plastic deformation.

Relative deformation - the ratio of the absolute deformation to the initial linear dimension (ε = Δl / l).

Elastic modulus is the ratio of stress to rel. deformation (E = σ / ε).

Strength - the property of a material to resist destruction under the action of internal stresses caused by external forces or others. Strength is estimated by the ultimate strength - the ultimate strength R, determined for a given type of deformation. For brittle (brick, concrete), the main strength characteristic is the compressive strength. For metals, steel - the compressive strength is the same as for tensile and bending. Since the building materials are heterogeneous, the tensile strength is determined as the average result of a series of samples. The test results are influenced by the shape, dimensions of the samples, the state of the supporting surfaces, and the loading rate. Depending on the strength, materials are divided into grades and classes. Stamps are written in kgf / cm², and classes - in MPa. The class characterizes the guaranteed strength. Strength class B is called the ultimate compressive strength of standard samples (concrete cubes with a rib size of 150 mm) tested at the age of 28 days of storage at a temperature of 20 ± 2 ° C, taking into account the static variability of strength.

Structural quality coefficient: KKK = R / γ (strength to relative density), for steel St3 KKK = 51 MPa, for high-strength steel KKK = 127 MPa, heavy concrete KKK = 12.6 MPa, wood KKK = 200 MPa.

Hardness is an indicator characterizing the property of materials to resist the penetration of another, denser material into it. Hardness index: HB = P / F (F is the indent area, P is the force), [HB] = MPa.

Abrasion is the loss of the original mass of the sample when this sample passes a certain path of the abrasive surface. Abrasion: I = (m1-m2) / F, where F is the area of ​​the abraded surface.

Wear is the property of a material to resist both abrasion and shock loads. Wear is measured in a drum with or without steel balls.

 

Source: Wikipedia

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