Production of silicate materials. Classification, properties and purpose, raw materials. Typical silicate technology processes, reactor types. Scheme. Ceramics production. Silicate materials and autoclaved products Silicate products

Silicate materials based on building lime with normal conditions hardenings have low strength. Therefore, in order to increase their strength, treatment is carried out with saturated water steam at 70...100°C at atmospheric pressure(steaming) or artificial carbonation.

Contents of the article:

1. Silicate materials autoclave curing.

2. Sand-lime brick.

3. Lime-ash and lime-slag bricks.

4. Silicate concrete

5. Large-sized products made of silicate concrete.

Indicators of strength and durability silicate materials acquire maximum values ​​under conditions of hydrothermal treatment in autoclaves in an environment of saturated water vapor. Hydrothermal treatment (steaming) is carried out under saturated water vapor pressure: 0.8; 1.2 and 1.6 MPa, which corresponds to temperatures of the specified environment of 174.5; 190.7 and 203.3°C.

Autoclave building materials are produced in the form of bricks, blocks and panels for external and interior walls, floor panels, columns, flights of stairs and platforms, beams and other products. Their properties are close to those of cement concrete, but they are characterized by lower consumption of binders, widespread use of cheap local aggregates and, therefore, lower cost.

However, autoclaves are required for their production.

♣ Sand-lime brick

Large-size silicate concrete products

Silicate concrete is a compacted mixture hardened in an autoclave, consisting of quartz sand (70...80%),
ground sand (8..15%) and ground quicklime (6... 10%). Dense silicate concrete is a type of heavy concrete.
Silicate concrete, like cement concrete, can be heavy (dense aggregates - sand and crushed stone or sand-gravel mixture), light (porous aggregates - expanded clay, expanded perlite, agloporite, etc.) and cellular (the aggregate is air bubbles, evenly distributed in product volume).

The binder in silicate concrete is a finely ground lime-silica mixture - a lime-siliceous binder capable of forming a high-strength compound when mixed with water during heat and humidity treatment in an autoclave. fake diamond. Ground silica component is used as a silica component. quartz sand, metallurgical (mainly blast furnace) slags, thermal power plant ash. The siliceous component (finely ground sand) has big influence on the formation of the properties of silicate concrete.

Thus, with increasing dispersion of ground sand particles, the strength, frost resistance and other properties of silicate materials increase.
With increasing fineness of sand grinding, the relative content of CaO in the binder mixture increases until the content of active CaO allows it to be bound during autoclave processing by the existing sand into low-basic calcium hydrosilicates.

According to VNIIstrom, with a specific surface area of ​​ground sand of 2000...2500 cm²/g, the lime content in the mixture (in terms of CaO) is
20...28% by weight of the calcareous-siliceous binder, and with a specific surface area of ​​sand of more than 2500 cm2/g, the optimal CaO content in the mixed binder can be increased to 33%.

Autoclave processing is the last and most important stage in the production of silicate products. Occur in the autoclave complex processes transformation of the original, laid and compacted silicate concrete mixture into durable products of different densities, shapes and purposes. Currently, autoclaves are produced with a diameter of 2.6 and 3.6 m, a length of 20...30 and 40 m. As stated above, an autoclave is a cylindrical horizontal welded vessel (boiler) with hermetically sealed spherical lids at the ends.

The boiler has a pressure gauge indicating steam pressure and a safety valve that automatically opens when the pressure in the boiler rises above the limit. At the bottom of the autoclave there are rails along which trolleys with products loaded into the autoclave move. Autoclaves are equipped with traverse tracks with transfer trolleys - electric bridges for loading and unloading trolleys and devices for automatic monitoring and control of the autoclave processing mode.

To reduce heat loss into the surrounding space, the surface of the autoclave and all steam lines are covered with a layer of thermal insulation. Dead-end or through-flow autoclaves are used. Autoclaves are equipped with lines for releasing saturated steam, bypassing spent steam into another autoclave, into the atmosphere, a recovery unit, and for condensate removal.

When operating autoclaves, it is necessary to strictly observe the “Rules for the design and safety of operation of pressure vessels.”
After loading the autoclave, close the lid and slowly and evenly introduce saturated steam into the autoclave. Autoclaving is the most effective means acceleration of concrete hardening. High temperatures in the presence of water in a drop-liquid state in the treated concrete create favorable conditions for the chemical interaction between calcium oxide hydrate and silica to form the main cementitious substance - calcium hydrosilicates.

The entire cycle of autoclave processing (according to Prof. P. I. Bozhenov) is conventionally divided into five stages: 1 - from the beginning of steam intake until the temperature in the autoclave reaches 100 ° C; 2 - increase in medium temperature and steam pressure to the designated minimum; 3 - isothermal exposure at maximum pressure and temperature; 4 - reduction of pressure to atmospheric, temperature to 100 °C; 5 - period of gradual cooling of products from 100 to 18...20 °C either in an autoclave or after unloading them from the autoclave.

The quality of autoclaved silicate products depends not only on the composition and structure of the new formations, but also on proper management physical phenomena, arising on various stages autoclave processing. During autoclave processing, in addition to the physicochemical processes that ensure the synthesis of calcium hydrosilicates, there are physical processes associated with temperature and humidity gradients, determined by the thermodynamic properties of water vapor and changes physical characteristics in the raw material mixture, and then in the resulting artificial silicate stone.

Included silicate stone Low-basic calcium hydrosilicates, having a fine-needle or scaly microcrystalline structure of the CSH(B) type, and tobermorite predominate. However, along with low-basic ones, there can also be coarse-crystalline highly basic calcium hydrosilicates of the C2SH(A) type.

In 1880, the German scientist W. Michaelis invented a method that was used to produce silicate (lime-sand) bricks. By the beginning of the twentieth century, there were already five factories in Russia producing sand-lime brick.

Until the 50s, the only type of silicate autoclave products there were sand-lime bricks and small stones made of cellular silicate concrete. However, thanks to the work of Russian scientists, for the first time in the world, the production of large-sized silicate concrete autoclaved products for prefabricated construction was created. At present, almost all elements of buildings and structures (panels, floor slabs, staircase elements, etc.) can be made of reinforced silicate concrete, which in its properties is almost not inferior to reinforced concrete, and thanks to the use of local raw materials and industrial waste costs 15 ...20% cheaper than similar reinforced concrete elements using Portland cement.

Raw materials for silicate materials and products

One of the main components of the raw material mixture from which products are formed is lime, which is highly chemically reactive to silica during thermal and moisture treatment. That is why the second main component of the raw mixture is quartz sand or other minerals containing silica, for example slag, ashes, etc. In order for the chemical interaction to take place quite intensively, the silica component is finely ground. The finer the sand is ground, the higher the relative lime content in the mixture should be. Fillers in the form of unground quartz sand, slag, expanded clay, expanded perlite, etc. can also be introduced as other components.

For modern production When making sand-lime bricks, a raw material mixture is used, which includes 90...95% sand, 5...10% ground quicklime and a certain amount of water.

3. General technology obtaining silicate materials

The technology for producing silicate products usually consists of the following steps:
1. Obtaining the raw material mixture.
2. Pressing of products.
3. Autoclave processing of products.
4. Aging of finished products.

Production of silicate building materials is based on the hydrothermal synthesis of calcium hydrosilicates, which is carried out in an autoclave reactor in an environment of saturated water vapor at a pressure of 0.8-1.3 MPa and a temperature of 175-200°C. For hydrothermal synthesis, with proper justification, other autoclave parameters can be used; treatment can be used not only with steam, but also with a steam-air or steam-gas mixture, or water.

IN this production A large amount of work involves the process of obtaining lime for the raw material mixture. IN technological process lime production includes the following operations: extraction limestone in quarries, crushing and sorting it into fractions, firing in shaft rotary and other kilns, crushing or grinding lump lime (producing quicklime).
The raw material mixture is produced in two ways: drum and silo, which differ from each other in the preparation of the lime-sand mixture.

The autoclave is a horizontally located steel cylinder with hermetically sealed lids at the ends. In an autoclave in an atmosphere of saturated steam at a pressure of 0.8-1.3 MPa and a temperature of 175-200°C, the brick hardens in 8...14 hours.

The strength of autoclave materials is formed as a result of the interaction of two processes: structure formation, caused by the synthesis of calcium hydrosilicates, and destruction, caused by internal stresses.

To reduce internal stresses, autoclave treatment is carried out according to a certain regime, including a gradual increase in steam pressure for 1.5-2 hours, isothermal exposure of products in an autoclave at a temperature of 175-200 ° C and a pressure of 0.8-1.3 MPa for 4 -8 hours and a decrease in steam pressure for 2-4 hours. After autoclave treatment for 8-14 hours, silicate products are obtained.

Almost finished products are unloaded from the autoclave, which are kept for 10...15 days for carbonation of unreacted lime with carbon dioxide air, resulting in increased water resistance and strength of products. The processing temperature and total energy consumption in the production of sand-lime bricks are significantly lower than in the production of ceramic bricks, therefore sand-lime bricks are economically more efficient.

Autoclaved silicate products include sand-lime bricks, large silicate blocks, slabs of heavy silicate concrete, floor and wall panels, columns, beams, etc. Lightweight aggregates help reduce weight wall panels and other elements. Silicate products They are produced solid or lightweight with through or semi-closed voids. Of particular importance are silicate cellular concrete, filled with evenly distributed air cells, or bubbles. They can have a structural and thermal insulation purpose, which determines the shape and size of the products and their quality indicators.

Silicate materials and autoclave-hardening products are artificial building conglomerates based on calcareous-siliceous (silicate) stone, synthesized during autoclave processing under the influence of steam at high temperature and high blood pressure. One of the main components of the raw material mixture from which products are formed is lime, which is highly chemically reactive to silica during thermal and moisture treatment.

That is why the second main component of the raw material mixture is quartz sand or other mineral substances containing silica, such as slag, thermal power plant ash, etc. In order for the chemical interaction to take place quite intensively, the silica component is finely ground. The finer the crushed sand, the higher the relative lime content in the mixture should be. Other components can also include fillers in the form of unground quartz sand, slag, expanded clay, expanded perlite, etc. An indispensable component in all mixtures is water.

The possibility of formation of a stone-like product in an autoclave was established in late XIX century, but mass production of silicate products, parts and structures, especially such as concrete, was organized for the first time in our country. The technology for their production is mechanized and largely automated, which ensures cheaper products compared to cement materials and products. Effective research in this direction was carried out by P.I. Bozhenov, A.V. Volzhensky, P.P. Budnikov, Yu.M. Buttom et al. It was shown that autoclave treatment produces the most stable low-basic hydrosilicates with a CaOiSiCh ratio in the range of 0.8-1.2, although more highly basic chemical compounds are also possible at intermediate stages of solidification.

P.I. Bozhenov, noting the “technical synthesis” of a cementitious binder in an autoclaved conglomerate consisting of a mixture of hydrosilicates, believes that chemical raw materials must meet certain requirements. It should be highly dispersed with a specific surface area of ​​the powder in the range of 2000-4000 cm2/g, if possible amorphous, glassy.

Chemically active raw materials provide not only the formation of a cementing binder in an autoclaved conglomerate, but also a number of technological properties of the raw material mixture (formability of products, evenness of their surface, transportability, etc.). But not only chemical and physicochemical processes influence the formation of the structure and properties of silicate materials during autoclave processing. A.V. Volzhensky was the first to draw attention to the change in heat and humidity conditions during autoclave processing and their impact on the quality of products. In this regard, it was decided to distinguish three stages in autoclave processing: filling the autoclave and products with steam to a given maximum pressure; steam release; removing products from the autoclave.

Products acquire the properties necessary for building materials after autoclave treatment, during which a new calcareous-siliceous cement is formed with its characteristic new formations of calcium and magnesium hydrosilicates, as well as anhydrous silicates.

The formation of the micro- and macrostructure of a silicate product in an autoclave occurs at various stages of processing. The mechanism of hardening of lime-sand raw material to a stone-like state is expressed in the fact that first a calcareous-siliceous cementing substance is formed as a product of the chemical interaction of the main components in the mixture under conditions of elevated pressures and temperatures.

According to one of the theories (P.P. Budnikova, Yu.M. Butta, etc.), the formation of a cementitious substance occurs through the preliminary dissolution of lime in water. Since the solubility of lime decreases with increasing temperature, the solution gradually becomes saturated. But with increasing temperature, the solubility of finely dispersed silica increases. For example, with an increase in temperature from 80 to 120°C, the solubility of silica increases (according to Kennedy) by almost 3 times. Therefore, at a temperature of 120-130°C, lime and silica, while in solution, interact to form gel-like calcium hydrosilicates. As the temperature rises further, the new formations become larger with the appearance of nuclei and a crystalline phase, and then crystalline intergrowths.

With an excess of lime, relatively coarse-crystalline dibasic calcium hydrosilicates of the C2SH and C2SH2 type appear, and after complete binding of lime and in the process of recrystallization, more stable microcrystalline low-basic calcium hydrosilicates of the CSH and C5S6H5 type (that is, bermorite) appear. Crystallization occurs around quartz grains and in the intergranular space; is accompanied by the fusion of crystalline new formations into a framework with its further strengthening and fouling.

The full cycle of autoclave treatment, according to P.I. Bozhenov, consists of five stages:

• steam inlet and temperature setting at 100°C;
• further increase in the medium temperature and steam pressure to the designated maximum; isothermal holding at constant pressure (the higher the pressure, the shorter the autoclave mode);
• a slow and gradual increase in the rate of reduction of steam pressure to atmospheric, and temperature - to 100°C;
• final cooling of products in an autoclave or after unloading them from the autoclave.

Optimal mode, i.e. best conditions in terms of steam pressure, temperature and duration of all stages of processing, it is determined by the type of raw material, although for economic reasons they always strive for a rapid increase and slow decrease in pressure.

Of great benefit in shaping the structure and properties of silicate stones and materials are the additives introduced into mixtures, which act as accelerators for the formation of calcium or magnesium hydrosilicates, crystallization of new formations, and modifiers of properties and structure. In general, the composition of silicate stone is dominated by low-basic calcium hydrosilicates, which have a fine-needle or scaly microcrystalline structure CSH and tobermorite C5S6H. In high-calcareous mixtures, the synthesis results in the formation of hillebrandite 2CaO Si02 H20 (i.e. C2SH).

According to another theory, the formation of the microstructure of the binder occurs not through the dissolution of lime and silica, but in the solid phase under the influence of the process of self-diffusion of molecules under conditions 1 aquatic environment and elevated temperature. There is a third theory (A.V. Satalkin, P.G. Komokhov, etc.), which allows for the formation of a binder microstructure as a result of reactions in the liquid and solid phases.

The studies of silicate stone and silicate conglomerate using the examples of fine- and coarse-grained concrete showed that with optimal structures their properties are completely subject to the general laws of ISC.

The optimal structure of silicate material is formed with a certain amount of calcareous-silica cement and a minimum ratio of its phase components. In a freshly prepared conglomerate, the dispersion medium (c) is lime paste (It), and the ground siliceous (sand) component (PM) acts as the solid dispersed phase (f). The activity (strength) of a calc-siliceous binder of optimal structure after autoclave treatment, like other properties of the silicate material, depends on the value of the Th: Pm ratio (by weight).

In addition to siliceous raw materials, common low-quartz raw materials can be used in the production of autoclave products - feldspathic, clayey, carbonate sands, as well as slags and other industrial by-products. Minerals of low-quartz raw materials, having dissolved under autoclaving conditions, become active components that are not inferior in solubility to quartz. Their activity depends on the size of the radii of the anions and cations included in their composition. In the autoclave, a new binder is formed (non-firing salt-slag binder), which has properties superior to calcareous-siliceous autoclave hardening. It consists of low-basic, weakly crystallized calcium hydrosilicates, and in the presence of aluminum ions - of highly basic calcium hydrosilicates.

Classification and types of silicate materials

Silicate materials belong to the group of artificial stone materials based on binders.

General information about artificial stone materials based on binders

Classification criteria by which cementitious materials are distinguished:

1. Depending on the type of binder, products based on cement, lime, gypsum, etc. are distinguished.
2. Depending on the production method, the conditions for hardening of such materials are determined: natural hardening, steaming, autoclave processing.

A variety of materials are used as fillers to produce artificial stone products: sand, expanded clay, and other porous fillers, sawdust and shavings, and a specific reinforcing filler - asbestos.

To the main artificial stone materials and products include:
1. Sand-lime brick
2. Silica concrete products:
2.1. Heavy silicate concrete products similar to conventional concrete
2.2. Light silicate concrete products based on porous aggregates or cellular (foam and gas silicates)
3. Gypsum and gypsum concrete products
4. Wall stones made of lightweight and cellular concrete
5. Wood concrete
6. Cement particle boards and asbestos-cement products

Unlike ceramics, materials based on mineral binders are obtained through natural hardening or heat treatment at temperatures up to 200 °C. Thus, the energy consumption for the production of products using mineral binders, even taking into account the energy consumption for obtaining the binder itself, is less than for the production of ceramics. However ceramic materials more durable and resistant to water, aggressive solutions and high temperatures.

Types of hollow products made of silicate materials according to GOST 379-95 Silicate bricks and stones

Figure A1 - Stone (brick) 14-hollow (hole diameter 30 - 32 mm, hollowness 28 - 31%)

Figure A2 - Stone (brick) 11-hollow (hole diameter 27 - 32 mm, hollowness 22 - 25%)

Figure A3 - 3-hollow brick (hole diameter 52 mm, hollowness 15%)

LIST OF MATERIALS USED IN PRODUCTION
SILICATE PRODUCTS

Silicate materials and autoclaved products are artificial building conglomerates based on calcareous-siliceous (silicate) stone, synthesized during autoclave treatment under the action of steam at high temperature and elevated pressure.

One of the main components of the raw material mixture from which products are formed is lime, which has a high chemical reactivity to silica during thermal and moisture treatment; the second main component of the raw material mixture is quartz sand or mineral substances containing silica. In order for the chemical interaction to occur sufficiently intensively, the silica component is subjected to fine grinding. Water is an essential component in all mixtures.

Autoclaved silicate products include sand-lime bricks, large silicate blocks, slabs of heavy silicate concrete, floor and wall panels, columns, beams, etc.

Lightweight aggregates make it possible to reduce the weight of wall panels and other elements.

Silicate products are produced solid or lightweight with through or semi-closed voids.

7.6.1. Sand-lime brick

Lime-sand silicate brick is no different in shape, size and main purpose from clay brick.

The brick is pressed from a moistened lime-sand mixture: pure quartz sand 92-95%, airy lime 6-8%, water - approximately 7%.

Brick molding is carried out on presses under a pressure of 15-20 MPa.

To harden, the raw brick is sent to an autoclave for steaming. The autoclave is a steel cylinder, its ends are hermetically sealed with lids. Hardening occurs not only at high temperatures, but also at high humidity, for which steam under pressure is supplied to the autoclave. The steam pressure is gradually increased. The steaming cycle continues for 10-14 hours.

Steaming raw meat in an autoclave conventionally consists of five stages:

From the start of steam release until the temperature in the autoclave reaches 100 °C;
from the beginning of the rise in steam pressure until the maximum set point is established
nogo;

Holding the product at constant temperature and pressure;

From the moment the pressure and temperature drop to 100 °C;

Cooling of products to a temperature of 18-20 °C.

Sand-lime brick is produced in sizes 250><120 х 65 мм как пустоте­лым, так и сплошным. По механической прочности различают марки кирпича 75, 100, 150. Водопоглощение кирпича составляет 8-16 %; значение теплопро­водности 0,71-0,75 Вт/(м-°С); объемная масса 1800-1900 кг/м 3 , т. е. больше, чем у глиняного кирпича, морозостойкость F15. Теплоизоляционные качества стен из силикатного и глиняного кирпича практически равны.

The cost of sand-lime brick is 25-35% lower than clay brick, since fuel consumption is two times less, electricity consumption is three times less, and the labor intensity of production is lower.

Sand-lime brick is used in the same way as clay brick for laying load-bearing walls of residential, industrial and civil buildings, for pillars, supports, etc. It cannot be used for laying foundations and plinths and in products and

structures exposed to prolonged exposure to temperatures above 500 °C.

Lime-slag and lime-ash bricks is a type of sand-lime brick, characterized by a lower volumetric mass and better thermal insulation properties, since in them quartz sand is replaced by porous light slag in lime-slag brick and ash in lime-ash brick.

Dimensions, physical and mechanical properties and manufacturing method are similar to sand-lime brick.

Lime-ash and lime-slag bricks are used for laying the walls of low-rise buildings, as well as for laying the walls of the upper floors of multi-story buildings.

7.6.2. Silicate concrete

Silicate concrete is a heavy concrete.

Large wall blocks of internal load-bearing walls, floor panels and load-bearing partitions, steps, slabs, beams are made from silicate concrete of at least grade 150 using heat treatment in an autoclave.

Bending elements are reinforced with steel rods and meshes.

Large-sized silicate products have a compressive strength of 15-40 MPa, a bulk density of 1800-2100 kg/m 3, and frost resistance of 50 cycles or more.

Cellular silicate products They are characterized by low volumetric mass and low thermal conductivity. There are foam silicate and gas silicate products.

Foam silicate products are made from a mixture of lime (up to 25%) and ground sand, a foaming agent. A mixture of aluminum powder is added to gas silicate ones.

Cellular silicate products are hardened in autoclaves.

They are manufactured both reinforced and non-reinforced.

In reinforced ones, steel reinforcement and embedded parts are more susceptible to corrosion, so steel reinforcement is coated with protective compounds.

Silicate products made from cellular concrete are divided into:

Thermal insulation;

Structural and thermal insulation;

Constructive.

The thermal conductivity value is 0.1-0.2 W/(m-°C), they are quite frost-resistant.

They are used for external walls of buildings, partitions, and for coverings of industrial buildings, while the load-bearing and thermal insulation properties of cellular concrete are effectively used.

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SILICATE MATERIALS AND PRODUCTS. Asbestos-cement PRODUCTS

Mineral binders are not yet ready-made building materials. The main property of binders is the ability to harden after mixing with a certain amount of water.

The reaction that occurs during hardening of binders is mainly the reaction of hydration, the addition of part of the water.

Along with cements, they are used to make mortars. lime: air and hydraulic in the form of hydrated fluff, lime paste or milk, as well as in the form of quicklime ground lime. Lime dough must have a density of at least 1200 kg/m3 and contain at least 30% lime by weight. Lime for plastering and facing mortars should not contain unextinguished particles that can cause spalls (dubs) in the hardened layer. Therefore, freshly slaked lime is passed through a sieve with cells of 0.315 - 0.25 mm.

Construction air lime CaO– a product of moderate firing of natural carbonate rocks at 900-1300°C CaCO3 containing up to 8% clay impurities (limestone, dolomite, chalk). Firing is carried out in shafts and rotary kilns. Shaft furnaces are the most widely used. When calcining limestone in a shaft kiln, the material moving in the shaft from top to bottom passes through three zones in succession: a heating zone (drying of raw materials and the release of volatile substances), a firing zone (decomposition of substances) and a cooling zone. In the heating zone, the limestone is heated to 900°C due to the heat coming from the combustion zone from gaseous combustion products. In the firing zone, fuel combustion and limestone decomposition occur. CaCO3 on lime CaO and carbon dioxide CO2 at 1000-1200°C. In the cooling zone, the burnt limestone is cooled to 80-100°C by cold air moving from bottom to top.

As a result of firing, carbon dioxide is completely lost and lumpy, quicklime is obtained in the form of white or gray pieces. Lump quicklime is a product from which different types of building aerial lime are obtained: ground powdered quicklime, lime paste.

Construction aerated lime of various types is used in the preparation of masonry and plaster mortars, low-grade concrete (working in air-dry conditions), the manufacture of dense silicate products (bricks, large blocks, panels), and the production of mixed cements. Adding lime to a cement mortar increases plasticity and strength and coverage time.

The hardening process of air lime occurs largely as a result of carbonization under the influence of carbon dioxide in the air. When airy lime hardens, compounds are formed that are soluble in water.

Hydraulic lime obtained by moderate firing of natural marls and marly limestones at 900-1100°C. Marl and marly limestone used for the production of hydraulic lime contain from 6 to 25% clay and sand impurities. Its hydraulic properties are characterized by the hydraulic (or main) module ( m), representing the percentage ratio of the content of calcium oxides to the content of the sum of oxides of silicon, aluminum and iron. Hydraulic lime is a slow-setting and slow-hardening substance. It is used for the preparation of mortars, low-quality concrete, lightweight concrete, and for the production of mixed concrete.

Hydraulic lime hardens and maintains strength in both air and water. Hydraulic lime is not used in its pure form, but is used in a mixture. The raw material for producing hydraulic lime is darker in color than air lime, as it contains clay as an impurity.

Sand-lime brick. Lime-sand mortars based on air lime are low-strength, slow-hardening and non-waterproof materials.

The first to obtain a sufficiently waterproof and durable material based on lime and sand was the German scientist W. Michaelis, who in 1880 proposed processing the lime-sand mixture in an atmosphere of saturated steam at a temperature of 150...200°C.

Michaelis's discovery was used to produce so-called silicate (lime-sand) bricks. Modern production of sand-lime brick is as follows. The raw material mixture, which includes 90...92% pure quartz sand, 8...10% ground quicklime and a certain amount of water, is thoroughly mixed and kept until the lime is completely slaked. Then brick is pressed from this mixture under high pressure (15...20 MPa), which is placed on trolleys and sent for hardening in autoclaves- thick-walled steel cylinders with a diameter of up to 2 m and a length of up to 20 m with hermetically sealed lids. In an autoclave in an atmosphere of saturated steam at a pressure of 0.8 MPa and a temperature of 180 ° C, the brick hardens in 8... 14 hours. Almost finished brick is unloaded from the autoclave, which is kept for 10... 15 days, as a result of which the water resistance and strength of the brick increase.

Air lime is widely used in the production of autoclaved dense cellular materials at a pressure of 0.8-1.6 MPa and T = 200° products in the form of panels, blocks, floor elements, and flights of stairs.

The processing temperature and total energy consumption in the production of sand-lime bricks are significantly lower than in the production of ceramic bricks, therefore sand-lime bricks are economically more efficient than ceramic ones.

The density of ordinary sand-lime brick is slightly higher than that of solid ceramic brick. Reducing the density of bricks and stones is achieved by molding voids into them or introducing porous aggregates into the raw material mass.

Sand-lime brick, like ceramic brick, depending on the size, can be:

single(solid or with porous fillers) 250x120 x 65 mm;

thickened(hollow or with porous fillers) 250x120x88 mm (the weight of thickened bricks should not be more than 4.3 kg);

silicate stone(hollow) 250x120x138 mm. The sand-lime brick production technology ensures greater dimensional accuracy.

The color of the brick ranges from milky white to light gray. They produce facing bricks with increased physical and mechanical properties. It can be colored with alkali-resistant pigments painted in the mass or on the front edges in blue, greenish, yellow and other light colors.

Depending on the compressive and bending strength, sand-lime bricks and stones are divided into eight grades: 300; 250; 200; 175; 150; 125; 100 and 75, having average compressive strength values ​​of at least 30...7.5 MPa, respectively. Water absorption of sand-lime brick is at least 6 %. Frost resistance grades for bricks and stones - F50; 35; 25 and 15; For facial products, frost resistance should be at least 25.

A significant disadvantage of sand-lime brick compared to ceramic brick is its reduced water resistance and heat resistance.

Sand-lime brick is used for laying external and internal walls of above-ground parts of buildings and structures. It is prohibited to use it in structures exposed to water (foundations, basement, sewer wells, etc.) and high temperatures (furnaces, chimneys, etc.).

Currently, large-sized silicate concrete autoclaved products are produced for almost all elements of buildings and structures for prefabricated construction (panels, floor slabs, staircase elements, etc.). Structures that are not inferior to reinforced concrete are made from reinforced silicate concrete.

Silica concrete products can be heavy (similar to conventional concrete) and light (based on porous aggregates) or cellular (foam and gas silicates). This unfired brick is made by dry pressing a mixture of air lime (5-10%) and quartz sand (90-95%) at a humidity of 6-7%. To increase strength, lime-silica mixtures are used. Brick grades M - 75, 100, 125,150,200,250.

Dimensions 65x120x250 - single and one-and-a-half or modular 88x120x250 hollow weighing no more than 4.3 kg. Average density 1700-2000kg/m3. frost resistance Mrz-15, 25 and 50. Sand-lime brick is not water-resistant, and not resistant to aggressive water, not fire-resistant. Cannot be used for laying stoves and pipes. Produced in autoclaves at a temperature of 170°C and a pressure of 4-6 atm.

Lime-based materials are used to prepare lime-sand, lime-clay and lime-ash materials. Such products are called: cement-free or based on silicate concrete. Lime is used in pure form or mixed with chalk for whitewashing.

Sand-lime brick accounts for a significant portion of the total volume of wall materials. The given costs for constructing walls made of sand-lime bricks are approximately 84% compared to the required costs when using ceramic bricks. The consumption of equivalent fuel and electricity for the production of sand-lime brick is 2 times lower than that of ceramic brick. To receive 1 thousand pieces. sand-lime brick consumes an average of 4.9 GJ of heat, half of which is heat for lime burning, and the other half for autoclave processing and other technological operations.

In the production of this material, ash and slag from thermal power plants are used as a component of the binder or filler. In the first case, ash consumption reaches 500 kg per 1 thousand pieces. bricks, in the second - 1.5-3.5 tons. The optimal ratio of lime and ash in the binder composition depends on the activity of the ash, the content of active calcium oxide in the lime, the size and granulometric composition of the sand and other technological factors. With the introduction of coal ash, lime consumption is reduced by 10-50%, and shale ash with a content of (CaO + MgO) up to 40-50% can completely replace lime in the silicate mass. Ash in lime-ash binder is not only an active siliceous additive, but also contributes to the plasticization of the mixture and increases the strength of the raw material by 1.3-1.5 times, which is especially important for ensuring the normal operation of automatic stackers.

In addition to lime-sand silicate bricks, they produce lime-slag and lime-ash, in which instead of sand, industrial waste is partially or completely used: slag and ash from thermal power plants. The properties of these types of bricks are similar to those of lime-sand.

Calcareous-siliceous binder in the production of sand-lime bricks is obtained by joint grinding of lump quicklime with ash and quartz sand. The total content of active CaO and MgO in the binder is 30-40%, the specific surface is 4000-5000 cm2/g, the residue on sieve No. 02 is no more than 2%. The optimal content of ash and slag in a silicate mixture depends on the grain composition and the molding method, increasing with the particle size modulus and the pressing cycle.

Sand-lime brick with the addition of ash and fuel slag hardens in autoclaves at a saturated steam pressure of 0.8-1.6 MPa. Recommended exposure is 4-8 hours. The resulting material is superior in water and frost resistance to ordinary sand-lime brick, has lower water absorption and permeability values, and has a better presentation. The advantage of bricks made from an ash-silicate mixture of optimal composition is its lower average density than that of a conventional one (A = 700-1800 kg/m3 versus 1900-2000 kg/m3).

Using thermal power plant ash, porous sand-lime brick with the following properties was obtained: density 1250-1400 kg/m3; strength 10-17.5 MPa, porosity 27-28%, frost resistance 15-35 cycles.

Its use makes it possible to reduce the thickness of external walls by 20 and the weight by 40% and significantly reduce heat consumption for heating buildings.

Therefore, building materials based on gypsum and airy lime must be protected from moisture, operated in a dry environment, or components must be added to increase water resistance.

Water consumption of mineral binders affects the properties of the resulting materials. Water requirement is determined by the amount of water required to obtain a workable mixture. If there is not enough water, the mixture will be loose; too much water will cause the mass to spread. A significant increase in water affects the properties of artificial stone - it can cause the formation of large pores, severe shrinkage, and reduces strength.