Lamination of autoclaved aerated concrete. What is non-autoclaved aerated concrete. The difference between aerated concrete and autoclaved aerated concrete according to technical characteristics
Due to the increased interest in aerated concrete blocks, many are interested in what is the difference between aerated concrete and autoclaved aerated concrete. And although they receive new material from the same components, there are differences in the use of material, quality, strength and density of the block. Depending on the curing conditions, autoclaved and non-autoclaved aerated concrete differ in performance. Non-autoclaved products are characterized by large shrinkage, while autoclaved products are characterized by dimensional stability.
The difference between autoclaved aerated concrete and non-autoclaved aerated concrete in terms of production technology and application
Despite the popularity of aerated concrete products, not everyone knows how autoclaved and non-autoclaved aerated concrete is made. Many people not associated with construction industry, cellular concrete is associated with non-autoclave technology. However, aerated concrete products are also produced by the autoclave method. Depending on the chosen production method, necessary equipment for the manufacture and solidification of blocks.
Performance characteristics differ between autoclaved and non-autoclaved aerated concrete
Aerated concrete composites, depending on the method of solidification, are divided into the following varieties:
Autoclave materials
Portland cement mixed with quartz sand, lime and water is used as the feedstock. Aluminum powder is introduced into the working mixture, which, interacting with lime, promotes the formation of air pores.
In the process of a gas-forming reaction, the volume increases due to the uniform formation of many pores inside the aerated concrete mass round shape no more than 3 mm in diameter. After filling according to the molds, the products are placed in autoclave chambers. At a temperature exceeding 200 degrees Celsius and a pressure of 10-12 atmospheres, the material hardens, acquiring working properties;
Non-autoclave products
It is made from the same components as autoclave blocks. In the manufacture of aerated concrete by a non-autoclave method, there is no need to use autoclaves. A simple technology allows the production of aerated concrete in small enterprises or in the conditions of a construction site.
After preparation of the working solution, molding containers are filled. Aerated concrete mix hardens in natural conditions. By reducing the energy intensity of production, the cost of non-autoclave blocks is significantly reduced. However, at ambient temperature, the drying time increases to a month.
Features of manufacturing technology affect the structure and properties of the material. Autoclave blocks with evenly distributed cells inside the array have increased strength. Non-autoclaved products also have a porous structure, however, the air cavities are unevenly located inside the blocks. This negatively affects strength.
The structure and properties of the material are influenced by the features of manufacturing technology The use of non-autoclaved and autoclaved aerated concrete is different:
- blocks obtained by autoclave technology are used to build residential buildings of various heights, cottages and summer cottages;
- non-autoclave material is used to build utility rooms and technical facilities.
The strength of buildings built from non-autoclaved aerated concrete is lower than that of buildings made from autoclaved building materials. A different production technology that determines the performance characteristics of the material is the main difference between autoclaved aerated concrete and non-autoclaved aerated concrete.
Main properties of non-autoclaved and autoclaved aerated concrete
Consider the properties of heat-treated and naturally hardened aerated concrete. The main characteristics of the materials:
- improved thermal insulation properties. Thanks to the air cells located inside the aerated concrete mass, the material retains heat well. The energy-saving properties of gas blocks make it possible to maintain a favorable temperature in the building all year round, as well as reduce the cost of space heating;
- soundproof characteristics. Aerated concrete walls make it difficult for street noise to enter the living quarters. Effective sound insulation is provided due to the saturation of the array with air pores that absorb extraneous sounds. Noise-absorbing properties provide comfortable living conditions;
The material retains heat well due to air cells located inside the aerated concrete mass - resistance to negative temperatures. The frost resistance of aerated concrete depends on the concentration of moisture accumulating inside the air cells. Under the influence of negative temperatures, the liquid crystallizes and, increasing its volume, tries to destroy the gas block. Plastering the surface of the blocks increases frost resistance;
- light weight. Block aerated concrete, characterized by reduced mass and increased volume, is quickly erected different kinds buildings. For transportation of light gas blocks, vehicles with increased carrying capacity are not required. Products for masonry are fed manually, and aerated concrete walls do not exert an increased load on the foundation;
- workability. To change the size of gas blocks during masonry, there is no need to use special equipment. The material is easily cut with a hand saw or grinder. If it is necessary to make a hole or cavity inside the aerated concrete block, this operation can be easily performed using an electric drill.
Aerated concrete blocks are also characterized by:
- the correctness of the form;
- exact dimensions;
- rough surface;
- environmental cleanliness;
- fire safety;
- affordable price.
When planning to build a box of your own house or cottage from aerated concrete blocks, you should choose the right material and figure out how autoclaved aerated concrete differs from non-autoclaved aerated concrete. Let us dwell on this point in more detail and compare the properties of materials produced using different technologies.
The frost resistance of aerated concrete depends on the concentration of moisture accumulating inside the air cells. The difference between aerated concrete and autoclaved aerated concrete according to technical characteristics
For the construction of buildings, autoclaved and non-autoclaved aerated concrete is used. What is better to use for the construction of a particular structure? To answer this question, you should compare the characteristics.
Autoclaved and non-autoclaved aerated concrete - which is better in quality
Technology plays a decisive role in product quality:
- autoclave materials are produced in industrial environment on modern technological equipment with a high degree of automation. The influence of the human factor in manufacturing process minimized. Quality control is carried out in special laboratories;
- Not autoclaved aerated concrete It is manufactured using a simplified technology that does not require special equipment. Using a concrete mixer, formwork and auxiliary workers, it is easy to make blocks in an artisanal way. Under such manufacturing conditions, it is difficult to talk about the stability of product quality.
Thinking about the durability of the future structure, give preference to industrial products manufactured in accordance with the requirements of the current standard.
Differences in strength of aerated concrete
The strength properties of aerated concrete are related to its density. With equal specific gravity the load capacity of autoclaved concrete and non-autoclaved composite is significantly different:
It is easy to cut material with a hand saw or grinder - heat-insulating aerated concrete with a specific gravity of 0.4 t/m3, made by the autoclave method, has a strength class up to B2.5;
- a similar material that has undergone hardening at natural temperature and pressure has a strength class reduced to B0.75.
The popular D600 gas block, steamed in autoclaves, has a compressive strength of B3.5. The strength of the same non-autoclaved block is B2. The heterogeneity of the structure of handicraft blocks adversely affects their strength.
Shrinkage of non-autoclaved and autoclaved building materials
Aerated concrete blocks have different shrinkage. For this indicator, the value is regulated by the standard:
- shrinkage of autoclaved materials per meter of masonry does not exceed 0.5 mm;
- the same indicator for non-autoclaved blocks reaches 3 mm.
To prevent cracking of the walls, a reinforcing mesh should be used and the surface of aerated concrete should be plastered.
How does the technology of creating aerated concrete affect the porous structure?
Depending on the production method, the homogeneity of aerated concrete changes:
- air cavities in autoclave products are evenly distributed throughout the volume;
- cells inside non-autoclave blocks are concentrated at the outer surface.
The production of non-autoclaved aerated concrete without compaction of the material causes uneven structure, which negatively affects performance.
The homogeneity of aerated concrete varies depending on the production method Block manufacturing accuracy
Aerated concrete products manufactured by various methods are characterized by geometric accuracy and dimensional stability:
- due to the use of precise equipment for the production of autoclaved products, the error of the blocks does not exceed 1 mm;
- the use of inexpensive equipment and different forms for the manufacture of non-autoclaved blocks increases the dimensional tolerance to 5 mm.
With stable dimensions and precise tolerances, the consumption of glue is reduced, which can be laid in a layer of 1-2 mm.
Comparing the properties of materials in terms of thermal conductivity
Both types of aerated concrete have increased thermal insulation characteristics, but there are certain differences:
- autoclaved aerated concrete provides thermal protection with a reduced thickness of products;
- to ensure the thermal insulation of the structure of non-autoclave blocks, an increased thickness of the walls is necessary.
Autoclaved blocks are superior to non-autoclaved building materials in terms of thermal insulation properties.
We compare the frost resistance of aerated concrete blocks
The durability of buildings depends on the frost resistance of the blocks:
- walls erected from non-autoclaved aerated concrete can withstand no more than 50 freezing cycles;
- structures made of autoclave gas blocks are not subject to destruction for 100 cycles.
When choosing a material for a residential building, it is important to consider its frost resistance.
We evaluate the fire resistance of aerated concrete
Both types of aerated concrete are equally fireproof. When the material is heated, toxic substances are not released. Aerated concrete is used for the construction of fire-resistant structures, where there is a high probability of exposure to elevated temperatures.
Conclusion
After analyzing the difference between autoclaved aerated concrete and non-autoclaved aerated concrete, it is easy to choose a building material for solving specific problems. It is important to comprehensively assess the properties of the material. It is preferable to use high-quality aerated concrete, characterized by increased strength.
To understand how autoclaved concrete differs from non-autoclaved concrete, it is necessary to consider the main features of both types of aerated concrete. The popularity of aerated concrete in construction is growing every day, which is explained by its positive properties: good strength, low density, high quality, low weight (which generally reduces the cost of foundation and flooring), the possibility of laying thin, but warm and reliable walls.
Autoclaved and non-autoclaved concretes differ in the method of production and, accordingly, performance characteristics. Initially, they were created exclusively in industrial production, but soon they found a way to make a cellular material without additional heat and moisture treatment.
Autoclaved aerated concrete is more stable, but non-autoclaved aerated concrete involves shrinkage. But if we consider their differences in more detail, it becomes clear: both types of aerated concrete are relevant for repair work. construction works, it is important to know their characteristics and choose the right one for the implementation of specific tasks.
Aerated concrete production technology
Autoclaved and non-autoclaved aerated concrete are produced using the same technology, the differences are only in the accuracy of following the technology and in the final stages of material processing. Raw materials are used identical and in a single proportion.
- Fine sand 2-2.5 mm
- Portland cement grades M300 and M400
- Lime
- Aluminum powder or paste with an active metal content of 90-95%
- A variety of additives and modifiers (not necessarily introduced, they are needed to improve various performance properties)
- Water
First, an ordinary cement-sand mortar is kneaded, poured into a special mold, then aluminum powder is poured. As a result of the reaction of powder and lime, carbon dioxide appears, due to which the mass increases in volume, swelling and forming a porous structure. The gas evolution reaction must be completed before the cement sets; to intensify the process, the mold is processed on a vibrating platform. But this process is relevant only for large plants.
In small workshops, foam concrete is created, which is a variety. Indeed, according to the method of foam formation, concrete is divided into gas and foam concrete. And if in the first case the foam is created by gas, then in the second - due to chemicals.
The cellular structure is created by adding and whipping special chemical foaming agents. Workshops are usually small, with a small number of employees, a predominance of manual labor. The production of aerated concrete is more expensive, but such a material is also more stable, with better properties.
Further, the technology for the production of autoclaved and non-autoclaved aerated concrete suggests differences. If autoclaved aerated concrete is produced, after pouring the mixture into the mold and starting the reaction, they wait a certain time, allowing the mixture to partially harden and gain sufficient strength to remove the array from the formwork and cut into blocks.
The cut blocks are sent to an autoclave and fired at a temperature of + 190-200 degrees, the pressure is 8-10 bar (so that moisture is completely removed from the material). Processing aerated concrete by autoclave allows you to: accelerate the hardening of the material, increase its strength characteristics, reduce shrinkage in the future, make the structure homogeneous, improve the geometry of the finished blocks.
Non-autoclaved aerated concrete gains strength not in the oven, but in the natural environment - without the influence of temperature and pressure to evaporate moisture. Moreover, often for the production of this type of material, not large molds are used with further cutting of gas blocks, but molds for casting individual elements.
Autoclaved and non-autoclaved aerated concrete are produced in accordance with the following regulatory documents: GOST 21520 "", GOST 25485 "Aerated concrete", as well as GOST 31360 and GOST 32359.
Properties of non-autoclaved and autoclaved aerated concrete
Autoclaved and non-autoclaved aerated concrete - completely different materials at the exit. They differ as appearance(therefore, you can immediately determine by eye which concrete is in front of you), and performance characteristics.
External indicators
The honeycomb blocks, cut from the array, are usually characterized by greater compliance with the design dimensions. Of these, it is easier to perform masonry, less time, effort and materials are spent on sealing joints, the thickness of the masonry joints is much less (and cold bridges, respectively, too), building decoration is easier.
Non-autoclaved aerated concrete is gray, autoclaved - almost white. If the shade is not uniform and various inclusions are visible in the structure, most likely the quality of such material is not very good.
The production of non-autoclaved aerated concrete is often carried out practically in artisanal conditions - concrete is simply mixed, formwork is used for pouring, after hardening in natural conditions, the material is supplied for construction. All this negatively affects the quality of the final material and its basic properties.
Physical and mechanical properties
Autoclaved aerated concrete shows a density of D400-800, compressive strength is in the range of B1.5-B5, but non-autoclaved aerated concrete gives a maximum strength of B3. Shelves and cabinets, air conditioners, speakers and other devices that non-autoclaved aerated concrete is far from always able to withstand can be fixed on walls made of fired blocks.
One of the main differences between materials is shrinkage - there is moisture in unbaked aerated concrete, which provokes the appearance of cracks on the walls. Yes, and the density plays an important role - with its decrease, the shrinkage coefficient increases during the residual curing. The process takes about 5-10 years. Autoclaved aerated concrete shrinks by about 0.5m/mm, unfired - by 2-3mm/m.
Thermal conductivity indicators also vary - the property depends on the density: the lower the density, the more heat-consuming material. To reduce the thermal conductivity of walls, it is best to choose aerated concrete with high strength and lower density.
Differences: pros and cons of materials
Autoclaves aerated concrete blocks quite significantly differ in various indicators from the material that has not been fired. Due to their different properties, blocks are used to perform different tasks and are relevant for certain types of construction. Before using this or that material in your work, you first need to study all the specifications, advantages and disadvantages.
Strength
Aerated concrete of natural hardening is less durable, especially if it is completely fresh. It takes a lot of time to build strength. But the autoclave for aerated concrete contributes to the speedy passage of the process of curing (accelerates hundreds of times), therefore, after steam treatment at high temperature, the strength of autoclaved concrete is one and a half to two times higher than that of an analogue without firing.
So, for example, autoclave grades D500 and D600 demonstrate a strength index of B2.0-B3.5, a non-autoclave of a similar brand will at best give class B2.
Block geometry
During the construction process, the evenness of the blocks and their compliance with the specified parameters are very important. Regardless of which object is being built (bathhouse, garage or residential building), the quality of the masonry is the higher, the more accurately the blocks are made. After all, in which case the difference in level is leveled with glue or mortar, cold bridges are created, and thermal insulation properties are reduced.
Thick seams negatively affect shrinkage in the process, cracks may appear. To avoid this, the difference in levels is removed, the usual hand saw. But the time and labor costs in this case are simply huge. It is much easier and cheaper to immediately buy even autoclaved aerated concrete and build a building out of it.
Structure homogeneity
The homogeneity of the structure is determined by the number of bubbles in the material and the uniformity of their distribution. The more homogeneous the material, the better it is - this has a positive effect on quality. Autoclaved aerated concrete blocks have a more uniform structure, as they are created quickly, harden immediately, and then the arrays are cut into individual blocks.
Non-autoclaved aerated concrete is produced differently - foam and blowing agents may not be distributed evenly: bubbles often float up, heavy elements fall down. This has a bad effect on construction - strength decreases in places with a large accumulation of bubbles, cold bridges appear in places with a small number of bubbles. Characteristics are unstable.
Possibility of fastening
Autoclaved aerated concrete is a durable material on which even very heavy devices and elements can be fixed. It is possible to fasten facades made of lightweight expanded clay or even heavy porcelain stoneware. So, the anchor 10x100 freely withstands the axle pull-out load of about 700 kilograms. That is, you can mount shelves, cabinets, boilers, air conditioners, without fear that all this will fall with a piece of wall and fasteners.
Non-autoclaved aerated concrete is much less durable - sometimes you can even push screws or nails into it with your hands. Mechanical fasteners are not used, light objects are attached to an expensive two-component chemical anchor.
Dry shrinkage
When choosing autoclaved blocks for masonry, one can hope for minimal shrinkage in the process. Under firing conditions, concrete has already gained strength and gives a shrinkage rate of a maximum of 0.5 mm / m, while non-autoclaved aerated concrete gives about 5 mm / m - a significant difference.
Strong shrinkage of non-autoclaved aerated concrete buildings can cause a lot of trouble - masonry cracking, cracking, peeling of finishes, plasters. All this can continue for several years until the concrete takes on all the strength.
Environmental friendliness
Autoclaved aerated concrete is absolutely environmentally friendly, it passes air well, allows the building to breathe and contributes to the creation of an optimal microclimate. Aerated concrete is created from mineral raw materials, so it is not afraid of decay, moisture and mold.
In the case of the production of non-autoclaved aerated concrete, chemical additives are used to form foam, which already reduces the level of safety of its operation. Often, chemical components are introduced into a fiber block impregnated with special thiocyanates, chlorides and acids, which is even more dangerous, since these substances can be released and accumulate in the air over time.
Thermal insulation properties
The heat retention characteristics are directly dependent on the density. Here, foam concrete demonstrates the best performance, the disadvantage of using it in construction is low strength. For masonry walls, denser materials are used - the density kg / m3 should be at least 700 kilograms per cubic meter. And if you use non-autoclaved aerated concrete of such a density, then due to the cold bridges of thick joints, the characteristics are further reduced.
Autoclaved aerated concrete gives the same properties, but with a smaller wall thickness and with less cold bridges, which ultimately provides better performance.
It can be concluded that autoclaved aerated concrete is superior to non-autoclaved blocks in many areas and indicators. We are talking about both geometry and physical and mechanical properties. Autoclave blocks are created in a factory, with strict adherence to regulations and standards. It is easier and easier to build from such concrete, the buildings are more durable and of high quality. Completely safe and environmentally friendly material withstands any load and guarantees the best performance properties of the building.
Refers to artificial building materials. It has a porous structure and is highly popular in the construction of residential and industrial buildings. Depending on the method of production, aerated concrete is divided into autoclaved and non-autoclaved. This article will help you understand the production technology of autoclaved aerated concrete, its advantages and disadvantages.
Compound
Autoclaved aerated concrete is obtained by firing blocks in special autoclave kilns, where they are subjected to high pressure up to 12 atm. and a temperature of 191 °C. This allows not only to accelerate the curing process of the material, but also to obtain a material with improved strength characteristics compared to conventional non-autoclaved blocks. During the firing process, the molecular structure of the material changes and as a result, aerated concrete is obtained, resembling the volcanic rock tobermorite.
Autoclaved aerated concrete is obtained by firing the material in special kilns in which it is exposed to high pressure and temperature
Aerated concrete obtained by autoclave firing is often called gas silicate. Its composition includes:
- Portland cement.
- Quartz sand.
- Lime.
- aluminum powder.
- Gypsum.
- Water.
In the manufacture of gas silicate, the exact proportions of these materials are observed. Gypsum is added so that the mass does not immediately thicken, and aluminum powder helps the process of formation of many bubbles.
Material advantages
Convenient autoclave dimensions make the job easier. They allow you to complete the laying of building elements faster, in comparison with the laying of ordinary bricks. Gas silicate meets the standards fire safety, since it does not distinguish harmful substances during combustion and does not quickly catch fire.
Aerated concrete blocks are resistant to harmful microorganisms and mold, as they are made from mineral raw materials Aerated concrete - pros and cons
Advantages
- High thermal insulation performance. Houses made of gas silicate blocks reliably retain heat. With their help, the owners can significantly save on additional heating.
- Lightweight blocks. This makes it easier to work with the material and reduces the load on the foundation of the building.
- High soundproofing material. Is good advantage when choosing an apartment in a multi-storey building.
Flaws
- Poor compressive and tear strength. During construction, it is used, which reduces the likelihood of cracks in the walls of the building.
- The high cost of blocks. Gas silicate is practically not produced in small industries due to the need for autoclave ovens. Large production involves the production of quality products and compliance with production standards, but such work will have to pay a lot.
- Low moisture resistance. Due to the porous structure of the blocks, moisture quickly penetrates into them, which does not allow them to be used in bathrooms.
- Increased brittleness of blocks. Air bubbles create a porous structure, and the material is easily subjected to mechanical damage.
Mortar joints and armored belt reduce the thermal insulation of autoclaved aerated concrete blocks Areas of use
The environmental friendliness of the composition made autoclave blocks publicly available both in mass and in individual construction. They are used in many areas, and because of their good thermal insulation properties, such blocks are used in the construction of schools, government agencies and hospitals. The large dimensions of the block allow you to quickly erect a building, which is very convenient in the design of multi-storey buildings. They are often used in the construction of the walls of the premises, as well as in the restoration of old buildings. Aerated concrete blocks are often used in the construction of cottages, country houses, garages and extensions to the house.
Production
Non-autoclaved blocks require about a month of curing before use. Processing with an autoclave oven allows you to reduce the setting time of the material. The production of firing blocks is often carried out by large manufacturers (autoclave gas blocks are produced only at factories), since this requires expensive equipment and large premises. The production technology complies with GOST, therefore, when firing in autoclaves, specialists strictly observe certain temperatures and pressure in the furnace.
Preparing the Components
All Consumables are delivered to the plant by trucks and stored in special bunkers. Before use, quartz sand and other components undergo special treatment. Quartz sand is fed by belt conveyors into a ball mill, where it is finely ground into a powder-like mass. The mass is stored in large sludge pools equipped with a stirrer, which brings the raw material to the desired consistency. The prepared material is fed into machines that form the necessary proportions of each component.
All work at plants for the production of autoclaved aerated concrete is automated Dosing and mixing
The dosage of the components is carried out according to a proven and proven recipe. With the help of automation, each component is accurately weighed and fed into the mixer. Before feeding aluminum powder, it also undergoes pre-treatment. This material is explosive, therefore, all the required fire safety standards are observed in the room.
Mixing of components takes place on special conveyors. The components are mixed with water until the consistency of sour cream is formed. Automated mixing is carried out at high speed for 4-5 minutes. After kneading, the mixer is cleaned with water and filled with the next portion.
Slicing into blocks
After mixing, the mass is poured into large steel molds to half its volume, since after swelling of the material it will fill the mold to the brim and become porous. Before cutting into blocks, the material is left for 2.5 hours to mature and gain the necessary strength. The maturation time of the mixture is determined by the recipe and external conditions created indoors. After that, the material is fed for cutting. Cutting aerated concrete is carried out on automated lines with special strings. In a given sequence aerated concrete material amenable to vertical, horizontal cutting with a trimmer.
Aerated concrete is cut into blocks on special lines with wire strings Autoclaving
Autoclaving changes the molecular structure of the blocks, allowing them to fully mature. Products are placed in an autoclave oven for an average of 12 hours. After the oven is closed, the temperature rises automatically up to 190 °C. With the created vacuum inside the furnace, the pressure gradually increases to 12 bar. On modern factories autoclaves are installed in which excess steam is automatically transferred from one furnace to another.
Maintaining the created temperature is maintained in the oven for 6 hours Sorting and packaging
After processing the blocks in furnaces, they are unloaded using special equipment. The blocks move out on the gratings one after another, the crane removes them from the gratings to load the next batch of blocks onto them.
The removed blocks are placed on wooden pallets and packed in a film. Finished pallets are transported by a forklift to the finished product warehouse. So they are stored, protected from moisture. From the warehouse, the goods are delivered to specialized stores.
Finished aerated concrete blocks are stacked on pallets and packed with a special film. Reinforce or not?
During the construction of residential and public buildings from gas blocks, it is necessary to perform reinforcement. This eliminates the longitudinal deformation of the walls, which occurs due to temperature differences and shrinkage of the material. The installed reinforcement will take on additional loads and increase the durability of the erected building.
The need for reinforcement is foreseen by specialists during the design of the building. Most often, reinforcement is used:
- on structures with increased load;
- under window openings;
- after the construction of the foundation during the laying of the first row of blocks;
- in each 3-4 row of masonry walls.
Reinforcement of aerated concrete walls takes on tensile loads many non-professional builders worries about:
- "How ?" The rods are laid on both sides of the block in specially made strobes (grooves), they do not increase the thickness of the masonry joints and do not reduce the thermal insulation characteristics of aerated concrete blocks. Such grooves are cut with a manual wall chaser and, before laying the rods, they are cleaned of dust with a building hair dryer. It is best to use periodic reinforcement with a diameter of 8 mm.
- "?" There are many advantages and disadvantages when building a bath from aerated concrete. Such blocks have high thermal insulation properties, are economical, easy to work with, they do not rot and are completely environmentally friendly. Unlike wooden bath, such a bath during the construction process requires additional costs for waterproofing and interior decoration, as this material is characterized by low moisture resistance. For reliable waterproofing of aerated concrete, fiberglass can be used, and walls and floors can be insulated with mineral wool.
- "What is the difference between aerated concrete and gas silicate?" Gas silicate is autoclaved aerated concrete, which includes lime, and it matures in autoclaves. The main material of conventional non-autoclaved aerated concrete is and it hardens by natural exposure to fresh air for a month. The production technology and the different composition of materials also affect the differences between these blocks in color (gas silicate has White color, aerated concrete - gray shade).
conclusions
Autoclaved aerated concrete has high quality indicators and is used for the construction of various types of buildings. Like all materials, it has its advantages and disadvantages, which you need to familiarize yourself with before carrying out construction work. The advantage of autoclave blocks over non-autoclave ones is that the former are produced at large automated factories and more often comply with state standards and quality standards.
Comments:
Autoclaved aerated concrete is prominent representative porous concrete and has proven itself quite well in many countries of the world. Such materials in our time are widely used in the construction of residential and industrial facilities.
The main components of autoclaved aerated concrete are cement, quartz sand and special blowing agents.
Currently, many companies are engaged in the manufacture and sale of the material. Autoclaved aerated concrete in the building materials market is presented in a wide range: different forms, size and color. One thing is invariable - high performance characteristics, which favorably distinguish it from other products.
Material structure
Aerated concrete is a kind of cellular concrete, in which air pores of 1-3 mm in size are located throughout the volume. It is based on a concrete mixture of a binder, filler and water.
In general, the class of aerated concrete includes (with separation according to the type of binder composition) cement-based aerated concrete, aerated concrete with lime as a binder, slag-based gas-slag concrete and gas-gypsum. As autoclaved aerated concrete, the most widely used material is based on cement with the addition of lime.
Air pores in the structure are created by a chemical reaction with the release of gas. To initiate such a reaction, aluminum powder or paste is added to the mixture. Thus, the composition of aerated concrete, in the general case, is a mixture of cement, lime, sand, water and aluminum powder residues. Additives may be added as needed to impart specific properties. Accordingly, the structure of autoclaved concrete is a hardened concrete mass with numerous small pores evenly distributed throughout the volume.
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Manufacturing features
Autoclaved aerated concrete got its name from the method of hardening of the concrete mass, after the implementation of a chemical reaction with the release of gas. The scheme of the complete material manufacturing cycle is shown in fig. 1.
The manufacture of such aerated concrete is carried out in an autoclave in the following order. The concrete mixture is mixed to the consistency of sour cream and poured into molds by half the volume, while the mixture is subjected to shock loading, at which the lime is quenched with heat release. Since all this happens in an autoclave, the temperature rises to 80 degrees.
Figure 1. Scheme of the full cycle of manufacturing autoclaved aerated concrete.
An active reaction of aluminum and lime begins with the release of hydrogen. The concrete mass increases in volume and fills the entire form. The pressure rises in the autoclave. Under the influence of temperature and pressure, the cement hardens, clogging the pores within its volume. During the reaction, air displaces hydrogen from the pores, filling them. Thus, a concrete structure is formed, in which air pores occupy up to 80% of the total volume. By changing the mode and amount of aluminum powder introduced, the pore concentration can be changed over a wide range.
Autoclave curing of the mass is carried out within 1-2 hours. Then the autoclave cover is removed and the aerated concrete is cut into blocks of the desired size, while complete curing of the concrete is not yet achieved. When cutting, the end elements of the engagement of the blocks are formed (if necessary). After cutting, the blocks are again placed in an autoclave, where they are moistened at a temperature of about 190 degrees and a pressure of up to 1.2 MPa. Under such influence, the mass finally crystallizes with the formation of a durable mineral. Final hardening and crystallization occur within 12 hours. Typically, the concrete mixture is prepared in the following proportion: cement (more often Portland cement) - 20%, quartz sand - 60%, lime - up to 20%. Aluminum residues - no more than 1%.
The main advantage of the autoclave curing method is that when exposed to high temperature and pressure, cellular aerated concrete forms a special mineral formation - tobermorite, which has increased mechanical strength and is not subject to shrinkage. In addition, such artificial conditions significantly accelerate the process of mass hardening, which is very important in industrial production.
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Basic material properties
Due to its porous structure, aerated concrete has a low specific gravity (from 300 to 700 kg / m³) and high thermal insulation properties. The autoclave production method also provides high compressive strength, up to 50 kg/cm².
By varying the pore volume, the density of aerated concrete changes; strength and thermal conductivity change simultaneously. At the same time, the change in the main parameters goes in different directions. A decrease in density (an increase in porosity) leads to an increase in thermal insulation properties and a decrease in strength, while an increase in density leads to the opposite effect.
Based on this dependence, autoclaved aerated concrete is divided into 3 categories: heat-insulating, structural and structural-heat-insulating. Autoclaved concrete with a density of up to 400 kg / m³ belongs to the heat-insulating type and is intended for private low houses in areas with a fairly cold climate. Aerated concrete with a density of 700 kg / m³ is structural and is used in load-bearing structures and houses with several floors, but it will have to be additionally covered with thermal insulation. Optimal properties have structural and heat-insulating concretes with a density of 500 kg / m³, which, with a sufficiently high strength, provide good thermal insulation.
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What are the block sizes?
The low weight of porous concrete makes it possible to use building elements with increased dimensions. Building blocks made of aerated concrete have a length of 625 mm, a height of 200 and 250 mm, a width of 100-400 mm. Such dimensions make it possible to significantly speed up and simplify the laying of walls, while the weight of the block remains within reasonable limits for its manual movement and installation.
An important advantage of autoclaved concrete is the accuracy and stability of the geometry of building elements (blocks). Autoclave curing of the concrete mass in the form allows to provide well-defined ribs and corners, an even smooth surface of the edges, very high dimensional stability, which almost do not change over a long production time. If we take blocks from different release batches, then the deviation is only possible within 1.5 mm in all directions (the first category of accuracy) or up to 3 mm for the third category. Very strict standards are set for the stability of ribs and corners.
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Other properties of aerated concrete
Autoclaved aerated concrete has a high vapor permeability. According to its breathability, it belongs to "breathable" building materials, i.e. able to bring steam out of the room. This property eliminates the formation of mold or fungi in places of steam condensate.
The porous structure provides increased soundproofing properties.
The material will receive wide popularity in Europe due to its environmental friendliness. The composition of aerated concrete does not contain any harmful impurities (even aluminum is in a small amount and in a bound state), which eliminates harmful emissions, both during construction and during operation. The environmental friendliness of the composition does not violate even the effects of high temperatures and other climatic factors. In terms of its fire safety and fire resistance, aerated concrete can be considered unique. Even prolonged exposure to open flame and thermal stress does not ignite or destroy the material.
The primary task of every builder is to right choice building material. Of all the variety on the market, it has proven itself well fake diamond- autoclaved aerated concrete, which is a kind of cellular concrete (foam concrete, aerated concrete). Considering that the material is gaining popularity in private construction, it is worth understanding what it is and what properties it has. Also, you need to know how non-autoclaved aerated concrete differs.
Characteristics
Blocks of cellular concrete have a porous structure, which is formed due to the presence of spherical pores. The size of air particles is from 1 to 3 mm. The quality of the building material directly depends on the uniformity of the distribution of pores throughout the volume of the stone and their closeness.
The raw material composition of aerated concrete produced by autoclave and non-autoclave methods is completely identical. The mixture contains the following components:
The pore-forming reaction does not occur at the mixing stage, but directly in the moulds. Hydrogen released as a result of a chemical reaction permeates the entire filled mass and ensures the formation of air particles of almost the same size with their uniform distribution. Despite the identity of the components, there is a difference: the physical and chemical composition of the artificial stone changes under the influence of high pressure and humidity. Inside the stone there are global changes in strength. When hardening in natural conditions, the strength of the blocks is much lower.
Types and scope
Aerated concrete blocks are divided into 3 categories:
- heat insulating,
- Structural.
- Structural and thermal insulation.
The autoclaved gas block with a density of up to 400 kg/m2 is heat-insulating and is used for construction low-rise buildings in areas with very cold climates. Artificial stone with a density of 700 kg/m2 belongs to the structural type and is designed to create load-bearing structures and buildings no higher than 3 floors. Such material requires additional thermal insulation. Structural and heat-insulating blocks with a density of 500 kg/m2 are universal: they have sufficiently high strength and good thermal insulation.
Thanks to the low weight building blocks available in larger sizes. Length is 625 mm, height - 200, 250 mm, width - 100-400 mm. Large parameters contribute to a significant acceleration of the construction of buildings, and simplify the laying of walls.
Differences
What are the main differences between the two types of aerated concrete blocks? It is most convenient to compare materials using a table.
| Characteristics of autoclaved aerated concrete | Characteristics of non-autoclaved aerated concrete |
| Artificial synthesized stone. | Solidified mortar with pores naturally or using steam at normal atmospheric pressure. |
| The structure of the finished block is the same in terms of characteristics and properties at any point. | Properties and characteristics differ within the same batch. |
| There are no shrinkage deformations. The necessary strength is achieved at the stage of production and autoclaving. The shrinkage index does not exceed 0.4 mm/m. |
The shrinkage rate is 10 times greater - up to 5 mm / m. |
| Cutting into blocks is carried out on specialized equipment using strings. As a result, such machining wall material of an ideal geometric shape is obtained. Dimensions are regulated by GOST. Permissible deviations are up to 3 mm in length, up to 2 mm in width, and up to 1 mm in thickness. The laying of artificial stone is carried out on an adhesive solution, which creates a thinner layer compared to the cement-sand version. The adhesive composition gives the structure solidity, increases thermal insulation properties and eliminates the formation of "cold bridges". The minimum deviation rate contributes to saving masonry adhesive composition. |
For the manufacture of blocks, collapsible formwork with limited cycles of use is used. Significant deviations of geometric dimensions are allowed - in thickness up to 5 mm (GOST 1989). Due to the large run-up in geometry:
|
| Blocks with a thickness of only 40 cm and a density of D400-D500 have the necessary requirements for thermal protection and strength. | To ensure the necessary thermal insulation without the use of insulation, the thickness of the stone should be about 65-70 cm. The density of cellular concrete is at least D700. |
| Frost resistance, (cycles) - F20 | Frost resistance index - F15 – F35 |
| The period of operation is 200 years. | Operational period - 50 years. |
| Strength according to GOST - B2.5-B5 | Strength according to GOST - B1.5-B2.5 |
| High environmental performance. | Environmentally friendly material. |
By autoclavingaerated concretehas improved physical and technical properties and appearance.
Technology
The high quality of the building material can only be guaranteed by an enterprise with specialized equipment, where production takes place in strict observance technological processes at all stages. Autoclaving production technology involves the use of a hermetic chamber, where the solidified solution with pores is given to heat treatment under high pressure. This technology makes it possible to construction material with improved properties and characteristics that cannot be achieved in normal conditions. Changes in the structure of artificial stone are carried out at the molecular level. At modern autoclaved aerated concrete plants, products comply with European quality standards.
The proportions of non-autoclaved and autoclaved products are regulated and recommended in the following ratio of components:
- Portland cement - from 35 to 49%.
- Quicklime - from 12 to 26%.
- Calcium silicates - approximately 2.6%.
- Calcium chloride - from 0.18 to 0.25%.
- Aluminum powder - from 0.06 to 0.1%.
- The water is unsalted until 100% by volume is obtained.
The percentage of components and composition is established empirically. Depending on the strength and hardening conditions, the indicators vary over a wide range. When autoclaving is used, excess moisture is removed from the product and the curing process is completed.
Production
The production of autoclaved aerated concrete takes place in a certain sequence:
- Sand and water are combined, after which the particles are crushed into sand slurry.
- Further, the remaining components are gradually introduced - cement, lime, table salt. Mixing time lasts 5 minutes and ready solution poured into the prepared formwork, the surface of which is lubricated with oil.
- In the form, the main cycle of a chemical reaction occurs with the participation of highly dispersed aluminum. As a result of the hydrogen reaction, bubbles are formed, foaming the solution and creating a porous structure, which occupies up to 80% of the total volume. The concrete mass increases in volume, filling the entire form.
- The ripening and hardening time lasts approximately 2-3 hours.
- The frozen mass is cut by industrial strings into blocks of appropriate sizes.
- The final processing stage includes steaming the workpieces in an autoclave at a temperature of 180-200°C and under a pressure not exceeding 1.2 MPa. The crystallization process continues for 12 hours.
In order to make a non-autoclaved gas block at home, you will definitely need a concrete mixer. Before cooking, the components are weighed in separate containers: 50 parts of water are taken for one part of aluminum powder and washing powder is added. The resulting mixture is thoroughly mixed until no metal particles remain on the surface. When filling out the forms, the features of the geometry of non-autoclaved concrete should be taken into account. When the foaming process begins inside the product, surfaces not limited by the formwork heave. Therefore, in the upper plane, the so-called “hump” is formed, the dimensions of which can reach 7% of the total volume of the block. Such swelling must be removed.
The increased demand for artificial stone led to the formation of a national association of manufacturers of autoclaved aerated concrete. The problems of the industry related to the production of aerated concrete are solved at a professional level. Are being developed modern requirements to the quality of the building material.
Advantages
The main advantages of autoclaved aerated concrete are:
- environmental friendliness - there are no harmful impurities in the composition;
- increased refractoriness and the ability to keep the combustion process for 7 hours or more;
- low thermal conductivity;
- accurate and stable geometry of blocks, which allows you to create even and smooth surfaces of faces, make out the outer and inner corners;
- increased vapor and air permeability, due to which the walls of buildings "breathe" and the formation of condensate is excluded;
- light weight - as a result of low density;
- resistance to moisture, the effects of microorganisms and decay processes;
- ensuring an optimal microclimate in the premises, regardless of the season.
The advantages of autoclaved aerated concrete include the presence in the composition of a mineral formation - tobermorite. Under the influence of high temperature and pressure, the stone acquires increased mechanical strength and non-shrinkage. Thanks to the created conditions, the hardening of the mass is significantly accelerated, which is important point in large scale production.
Mounting in walls attachments, furniture is carried out using special anchors that can withstand up to 350 kg.
Application
Autoclave production has significantly expanded the scope of cellular concrete products. The material is in high demand among individual developers. Cottages and low-rise houses are being built from autoclaved aerated concrete, buildings for industrial and commercial purposes.
