Gas silicate block of autoclave curing. What is better non-autoclaved or autoclaved aerated concrete? How properties are improved

Aerated concrete happens autoclave and non-autoclave, and many builders are wondering what are the differences between them.

Let's figure it out together, but looking ahead, let's say that autoclaved aerated concrete is a much better material, and we will explain why below.

What is Autoclaved Aerated Concrete?

Autoclaving – the stage of processing aerated concrete with high temperature (190°C) under high pressure during 12 hours. Autoclaves are metal containers in which cut gas blocks are placed.

Autoclaving is done for the following purposes:

1. acceleration of hardening of aerated concrete;
2. increase in strength;
3. shrinkage reduction;
4. improving the uniformity of the structure;
5. block geometry improvement.

Also, the autoclave changes the structure of aerated concrete at the molecular level, forming new material – tobermorite. This synthesized stone has properties that cannot be obtained in normal conditions at standard pressure and temperature.

We repeat that non-autoclaved aerated concrete hardens in natural conditions, and for its production it is expensive and modern equipment not required. In other words, many manufacturers stamp gas blocks in their garages, which does not inspire much confidence.

And now we will understand in more detail the differences in aerated concrete, and we will start with strength.

Comparison of autoclaved and non-autoclaved aerated concrete

It is important to note that non-autoclaved aerated concrete is tested in the video, to which fiber was added, it significantly increases the strength of the blocks. But we note that in reality, far from everyone uses fiber in the production of non-autoclaved aerated concrete, since it is quite expensive.

Strength

Aerated concrete without an autoclave is less durable, especially when fresh. After all, like ordinary concrete, it still needs time to gain strength, while autoclaved hardening accelerated hundreds of times due to high-temperature steam treatment. But even with complete hardening of both materials, the strength of the autoclave is higher by half or more.

For example, autoclaved aerated concrete grades D500 and D600 have a strength class of B2.5 - B3.5, while a non-autoclaved analogue of the same brand is gaining class B2 at best.

Shrinkage

Large shrinkage of blocks can create multiple cracks in the masonry, moreover, cracks can appear for a year or more. To minimize such processes, block shrinkage should be minimal.

Shrinkage of non-autoclaved aerated concrete is from 3 to 5 mm per meter, autoclaved - ten times less. That is, autoclaved aerated concrete practically does not give shrinkage cracks, with proper masonry.

Block geometry

The geometry of the blocks is also very important, and the more even the blocks are, the better. After all, if the blocks differ by 5 mm, then the difference in level must be leveled with glue, and these are cold bridges that greatly worsen the thermal insulation characteristics of the masonry.

Moreover, thick seams give a lot of shrinkage, which again can cause cracks. Experienced builders will say that the difference in levels can be leveled with a grater on aerated concrete, but imagine how long it will take.

And now let's think about where the geometry of the blocks will be better, on high-tech factory equipment with autoclaves, or in garage conditions? The answer is obvious!

Most builders believe that the best and most even blocks come from AEROC. The average price per cube of their aerated concrete is 4000 rubles.

Structure homogeneity

Uniformity refers to the number of voids (bubbles) that are distributed in a certain way in aerated concrete, and the more uniform they are, the better. Autoclaved aerated concrete technology guarantees a perfect distribution of voids, due to the fact that bubbles form and immediately harden, and individual blocks are obtained after cutting one large block.

Non-autoclaved aerated concrete is done quite differently. Foam and blowing agents are added to the concrete mix. As a result, bubbles can rise closer to the surface, while heavier elements fall down. As a result, the distribution of bubbles will be uneven.

Now let's think about what it threatens. Firstly, where there are fewer bubbles, there is less strength, and where there are few bubbles, there is a cold bridge through which heat will escape faster. That is, the strength and thermal conductivity of non-autoclaved aerated concrete is very unstable.

Thermal conductivity

Smoothly moving from the topic of structural uniformity to thermal conductivity, let's say that the uneven structure of the bubbles worsens the average thermal conductivity of the block, and it is natural that in autoclaved aerated concrete the uniformity of the bubbles is better and, therefore, the thermal insulation is also better.

Conclusion

Autoclaved and non-autoclaved aerated concrete are very different from each other in a number of parameters, and it can be said with confidence that the autoclaved material is superior to its counterpart in all respects, except for one thing - the price. Yes, non-autoclaved gas blocks cheaper, but if you calculate how many problems arise when laying it, how many additional materials, work and time you have to do, then we advise you to think carefully when making your choice.

It is better to build a house correctly once, from quality material, and be sure that it will stand without problems for many years.

There is currently a growing demand for building blocks made from cellular concrete and you can often hear the question: “what is the difference between autoclaved and non-autoclaved aerated concrete?”. Within the framework of this article, the main differences and indicators of these products will be considered.

Material characteristics

First, we need to clarify the terminology. Cellular concretes are understood to mean all lightweight concretes during the manufacturing process of which cells (pores) are formed in the structure. In turn, it is divided into foam concrete and aerated concrete, depending on the technology for creating pores. The next stage of division occurs depending on the hardening process - autoclave or non-autoclave.

Autoclaving

When steaming the mixture necessary for the production of aerated concrete at a pressure above 12 atmospheric pressure and a temperature above 190 degrees Celsius in devices called autoclaves, a new material is obtained with characteristics that cannot be obtained under normal conditions - this process is called autoclaving. As a result, the structure of concrete changes at the molecular level and a new material with completely unique characteristics is obtained, called tobermorite.

Non-autoclaved concrete is naturally cured or steam-cured concrete, but under normal atmospheric pressure mortar with pores, while autoclaved aerated concrete is an artificially created stone. They are fundamentally different in many respects. They have a different composition and different physical and technical parameters, which are an order of magnitude higher for autoclaved aerated concrete.

Main characteristics of materials:

Quality

The quality of autoclaved aerated concrete is always beyond doubt, since its production is extremely complex and impossible in artisanal conditions. technological process. During production, it is necessary to simultaneously control many processes and parameters, for this modern factories the degree of automation reaches 95 percent and virtually eliminates the possibility of non-compliance with the technology due to human error. Production, as a rule, takes place at large factories and the material is brought to the construction site already in the form of ready-made building blocks. The technology is described in the modern GOST of 2007 and must be confirmed by test reports and product certificates. For the manufacture of foam blocks and aerated concrete, such capacities are not required, and at first glance this seems to be a plus. After all, the product is cheaper. But can you eliminate the risk of low-quality production or even handicraft? When buying autoclaved aerated concrete, this question will not arise, because you can always be 100% sure of its quality.

Uniformity

Non-autoclaved aerated concrete is produced by adding a blowing agent to the concrete mass and mixing it. As a result, there are cases in which the bubbles, having a smaller weight, float up, and the fillers, on the contrary, settle down. As a result, finished products in the form of building blocks are heterogeneous and may even have different parameters. In the case of the production of autoclaved aerated concrete, everything is completely different. The process of gas formation and hardening occurs simultaneously and proceeds evenly throughout the volume of the produced material. As a result, the pores in the finished material are distributed evenly and after the completion of the stage of cutting the finished material into building blocks, they are of perfect quality and uniform structure.

Mounts

Since aerated concrete is very durable, it is possible to fix heavy materials and equipment on it. For example, ventilated facades, made not only of light materials, but also heavy porcelain stoneware. In order for the fastening to be reliable, anchor bolts with polyamide expandable elements are used. As a result, when using, for example, a 10x100 anchor, a pull-out load along the axis of up to 700 kg is maintained, which is very close to the values ​​of a solid brick.

Shrinkage

When curing, significant shrinkage of non-autoclaved aerated concrete occurs, as a result of which cracks appear in the finished masonry, plaster falls off, or the finishing layer peels off. All this lasts for 3-5 years until the material reaches its strength. Often, when using such materials, it is impossible to only putty and paint the walls, as a rule, more complex work is required. Inside, you have to finish with plasterboard, and outside, use brick or hinged facades. Such problems do not arise when using autoclaved aerated concrete, since it gains its strength even during the production process. For comparison, the shrinkage rate of autoclaved aerated concrete is 0.5 mm / m, but non-autoclaved from 1 to 3 mm / m.

Production precision

In the production process for non-autoclaved materials, they rely on the indicators of permissible values ​​​​from the old GOST, as a result, finished building blocks have a large difference in geometric characteristics. There are no such problems for autoclaved aerated concrete blocks, since all production is carried out in accordance with modern GOST and the discrepancies in the parameters of the finished product are minimal. Due to the large error in geometric dimensions, a number of problems arise when using non-autoclaved aerated concrete:

• is increasing required amount solution and, as a consequence, the cost of construction.
• Cold bridges form due to thick seams.
• Leveling the surface of the walls becomes a rather laborious process.

thermal insulation

The level of thermal insulation of both materials is very good. But you can consider this issue from the side of efficiency of use different materials and costs to achieve the same effect. The level of thermal insulation, among others, is influenced by such an indicator as the density of the material. The higher the density level, the lower the thermal insulation performance of the building blocks will be. For example, to use the material as a constructive, and even more so for bearing walls, high strength is required. To achieve the desired performance using non-autoclaved aerated concrete, a density of at least 700 kg / m3 is required. This means that for high-quality thermal insulation, the wall thickness should be about 65 cm. Under the same conditions, to achieve the desired level of strength, autoclaved aerated concrete with a density level of 500 kg / m3 can be used and the wall thickness will already be about 40 cm.

Results

At first glance, when building houses, it seems obvious that the price advantage is not in favor of autoclaved aerated concrete. But in the end, taking into account all the shortcomings of non-autoclave materials and the amount needed to eliminate them, this plus comes to naught. Autoclaved aerated concrete is superior to non-autoclaved in almost all respects.

Autoclaved aerated concrete is a type of porous concrete treated in a special way. Manufacturing technology provides such positive traits as lightness, high vapor permeability, dimensional accuracy and excellent thermal insulation. The scope of application is practically not limited by the climatic features of the regions and the size of the structure: it is used both in private construction and in industrial construction. But when choosing, it is important to take into account some requirements for masonry and subsequent finishing, due to fragility and hygroscopicity.

Blocks are made of concrete, filler and water. A mandatory component is a foaming agent - aluminum powder. Reacting with lime, it forms many bubbles distributed throughout the mass. The size of the cavities varies from 1 to 3 mm; they communicate with each other, but are closed. Finished elements - solid cement mixture, consisting of ⅔ of pores. This makes the material very light and significantly reduces raw material costs. Weight depending on density – from 300 to 700 kg/m3.

The composition of autoclaved and non-autoclaved aerated concrete is identical:

• crushed by the wet method quartz sand or washed natural fine fraction - 30-40%;
• Portland cement M400, M500 - from 15 to 50%;
• lime - 12-26%;
• aluminum powder or paste as a blowing agent - 0.1-1%;
• chemical additives that regulate foaming and hardening rate (caustic soda, sodium sulfate, calcium chloride) - 0.05-0.45%;
• water - 45-70% of the total weight of all dry components.

Each manufacturer selects his own recipe and ratio of components, often fillers are replaced with industrial waste and gas-ash concrete.

Production technology

Autoclave blocks are manufactured in accordance with GOST 31360-2007.

• In a ball mill, sand is mixed with water and ground to a sand slurry.
• Sand with all other components is placed in a sealed container.
• A homogeneous mixture with the introduced blowing agent is poured into large molds up to half the volume.
• After foaming is completed, it is sent for preliminary hardening.
• Solid large blocks are cut into standard elements, a comb and a groove are formed.
• Placed in a special installation - an autoclave. In it, they are treated with hot steam and high pressure.

It is the production process of autoclaved aerated concrete that differs from non-autoclaved aerated concrete. The latter is immediately poured into molds of the required size and dries naturally, therefore it has large discrepancies from the standard dimensions, less clear angles and is inferior in strength. Its manufacture does not require the purchase of an expensive autoclave; therefore, such a product is less expensive.

Autoclaving removes the remaining moisture and changes the characteristics of the material particles. They are converted into an artificial mineral - tobermorite. Products obtained in this way are much stronger, withstand more freezing cycles and have an extended service life. The block is in the autoclave chamber for at least 10 hours.

Advantages and disadvantages of aerated concrete

Autoclave elements have improved performance, but the whole group is united by a large number of advantages over other types of products for the construction of walls, ceilings and partitions:

1. The dimensions are standardized, the maximum deviation of the geometry does not exceed 2-3 mm - this allows you to make a thin seam, devoid of cold bridges.
2. Aerated concrete is easily processed, cut and drilled.
3. Not included harmful substances. The aluminum content is minimal, moreover, it is in a bound state, so the material is recognized as environmentally friendly. Even exposure to open flame does not lead to the release of toxic fumes.
4. Complete fire safety. The blocks not only do not burn, but are also able to withstand prolonged exposure to high temperatures without destruction.
5. The breathable structure creates a favorable microclimate in the room with optimal humidity.
6. It is not subject to any biological influence and rotting.

Aerated concrete structure can have thin walls and still be warmer than a standard brickwork. This reduces heating costs by 25-30%. Soundproofing properties are several times better in comparison with concrete, wood and bricks.

The light weight of the blocks provides savings on the arrangement of the foundation. It also allows you to make elements of large size, while lifting for one person. Construction is much faster and without the use of special equipment.

The main drawback is hygroscopicity, but it is easy to eliminate: it is enough to cover the walls under the finish immediately after completion of work. Care must be taken, as the products are fragile and can break on impact. There are strict restrictions on the number of storeys for elements of different densities and requirements for strengthening window and doorways. Autoclaved aerated concrete has a high cost compared to non-autoclaved.

Scope of application

By changing the number and size of pores (density) and the ratio of the main components, manufacturers receive blocks of different properties:

1. Heat-insulating with a density up to 400 kg/m3. It is worth buying for the construction of small buildings or wall insulation from other materials.
2. Structural and heat-insulating - 500 kg / m3. They can be bought for a private or low-rise building.
3. Structural, the most dense - 700 kg / m3. Suitable for load-bearing walls, but with a load limit. The structure must be no higher than 3 floors.

Autoclaved aerated concrete is used mainly in private construction for the construction of cottages, country houses, garages, outbuildings. But it is also suitable for load-bearing walls of low-rise buildings, as well as for masonry in frame structures without a limit on the number of storeys. Successfully used to create insulated attics.

Autoclaved aerated concrete is an artificial material that has proven itself in the construction of industrial and residential buildings. It is a type of cellular concrete. Since the material is becoming more and more popular in the construction of private buildings, you should know what its characteristics are, what autoclaving is, the differences between autoclaved concrete and non-autoclaved concrete, their pros and cons.

Figure 1. Autoclaved aerated concrete

Autoclaving provides accelerated hardening of concrete. The difference between building materials and analogues is higher strength.

Autoclaving is a process of steaming under conditions high temperature environment and high pressure. It flows in special metal capsules. When the finished blocks are loaded into the autoclave, the pressure is 0.8-1.3 MPa, and the temperature rises to 175 0 -191 0 C. Approximately 12 hours pass until complete hardening.

Autoclaved aerated concrete undergoes changes at the molecular level. As a result of processing, the formation of a new mineral tobermorite occurs. It has unique properties. The main feature that distinguishes autoclaved concrete from non-autoclaved one is that the first is an artificially obtained stone, and the second is a hardened sand-cement mortar.

Autoclaved aerated concrete blocks have special characteristics: composition, operational features, physical and technical parameters. According to most indicators, autoclaved and non-autoclaved concrete are different.

Features of masonry autoclaved aerated concrete

When erecting buildings from material produced using an aerated concrete autoclave, you need to know a few general rules masonry and have an idea about the features of working with aerated concrete blocks:

• To begin with, tubs always choose the most protruding corner. This will be the place with the minimum layer thickness.
• Laying the first row is carried out using a cement-sand mortar.
• Then aerated concrete blocks distributed to other corners. When laying, they act as landmarks. A cord is stretched between them.
• In cases where the length of the wall exceeds 10 meters, several additional ones are installed between the corner landmark blocks.
• The initial row is laid out completely. If gaps occur during operation, the blocks are cut to the required size with an electric saw or a hacksaw.

• After a short break (2-3 hours), the first row is reinforced.
• When laying the remaining rows, glue is mainly used. It is applied with a trowel and leveled with a comb. The seams are displaced by 20%.
• Since the adhesive sets quickly, it is recommended to level the aerated concrete blocks as quickly as possible. It is almost impossible to correct the defects.

Pros and cons of materials

Autoclaved blocks have a number of advantages over non-autoclaved concrete:

• Strength. On walls made of autoclaved aerated concrete, it is allowed to mount shelves, cabinets, as well as objects that have a large mass. For example, air conditioners. Aerated concrete that has not been autoclaved cannot withstand such loads.
• High quality. Since it is possible to produce autoclaved aerated concrete only in industrial environment, in terms of quality, it compares favorably with non-autoclaved counterparts, which are often produced by artisanal methods.
• Less shrinkage during operation. The amount of shrinkage directly depends on the strength of the building material. The average value for autoclaved aerated concrete is 0.5 mm / m, for non-autoclaved - up to 3 mm / m.

The pros and cons of autoclaved aerated concrete are presented in the table:

Advantages	Flaws
Strength.	Absorption of moisture, which at low temperatures destroys the structure of autoclaved aerated concrete.
Environmental friendliness, safety for the environment.	Problems with fixing fasteners, the need to use specialized products for aerated concrete.
Fire resistance.	Fragility, which is often detected already at the stage of transportation.
Ease of cutting and grinding.
Vapor permeability, providing a comfortable microclimate.
Thermal conductivity, which ensures the preservation of heat in buildings.
Frost resistance, allowing to withstand up to 150 cycles of freezing and thawing.
Resistant to mold and rot.

Overview of the main qualities of the material

Figure 2. Autoclaved aerated concrete

Taking into account the advantages and disadvantages of autoclaved aerated concrete blocks, the main properties can be distinguished:

• Strength. Autoclaved aerated concrete has the following characteristics: density up to 800 kg / m 3, compressive strength class B2.5-B3.5.
• Stability of quality, which is regulated by GOST, adopted in 2007. Products manufactured at industrial enterprises are accompanied by quality certificates.
• Homogeneity of the material. Its difference lies in the fact that in the course of production, the processes of gas formation and hardening occur simultaneously in the entire volume of raw materials. Ready-made aerated concrete blocks have pores of the same size, they do not have air pockets.
• Eco-friendly, breathable. In buildings made of autoclaved aerated concrete blocks, a microclimate is maintained, similar to the climate of a wooden frame. In the production, mineral raw materials are used that are resistant to mold, fungus, and decay.
• Shrinkage. Aerated concrete blocks are not subject to shrinkage deformations, as they gain sufficient strength during production and processing in an autoclave.
• The accuracy of geometric dimensions. This indicator is determined by GOST. Deviations should not exceed 2 mm in width, 3 mm in length and 1 mm in thickness. In the production of aerated concrete building materials, they resort to cutting large arrays. This allows you to maintain the required block sizes with high accuracy, which ultimately improves the quality of the masonry.

Aerated concrete production technology

The technological process includes the following steps:

• Combination of water and sand with particle size reduction.
• The introduction of lime, cement and table salt. Mixing of raw materials.
• Pouring the resulting solution into the formwork.
• Hydrogen reaction with the release of gas, which creates a porous structure.
• Hardening of the mass within 2-3 hours.
• Block cutting with industrial strings.
• Autoclaving of aerated concrete.

Areas of use

The scope of autoclaved aerated concrete is not limited to the construction of industrial buildings. The material is used for the construction of residential buildings.

The blocks are suitable for laying single-layer or double-layer exterior walls. Partitions of fire-prevention rooms are made of them.

Other areas of use:

• construction of floor slabs in buildings;
• production of wall panels for industrial and residential buildings.

The demand for autoclaved aerated concrete is so high that the producers of this material have united in a national association, which is designed to discuss the prospects for the development of the industry and develop new requirements for quality and innovative approaches to the organization of production.

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Aerated concrete is classified as cellular concrete and is a uniformly closed air pores, equally distributed throughout the material. Aerated concrete blocks are an ecological and high quality product. They are available in precise sizes and have the correct shape, are easy to work with and are ideal for finishing.

Aerated concrete is distinguished by the type of binder composition and the type of hardening. The product being processed high pressure and temperature in a specialized oven - an autoclave, has a name - autoclaved aerated concrete. It has many positive characteristics, and the use of this material improves the quality of construction, and, importantly, significantly reduces the cost of building a structure.

Such cellular concrete is made from crushed quartz sand, gypsum, cement, lime (quicklime), andrigide and water. At the exit, autoclaved aerated concrete is obtained by 2/3 filled with air pores. Proportions of aerated concrete mortar for an autoclave oven according to the standard:

• cement - 20%;
• quartz sand - 60%;
• quicklime - maximum 20%;
• aluminum residues - no more than 1%.

Manufacturing process of autoclaved aerated concrete

It is made using the following technology:

• Sand and water are combined and ground into sand slurry.
• The resulting mass is poured into a mold for a chemical reaction between an alkali solution and highly dispersed aluminum. This process promotes hydrogen formation to form bubbles.
• Hydrogen bubbles foam the solution and create a porosity structure. It is at this stage that the concrete is distributed into molds and left to ripen and harden for 2-3 hours.
• The hardened material is cut with industrial strings into blocks of a given size.
• The blanks are sent to the final stage - for steaming in an autoclave, where the blocks are processed in temperature regime 180-200 degrees under pressure for 12 hours. An autoclave is a sealed chamber where a product is processed that requires heating under a pressure greater than atmospheric pressure.

Autoclaving removes excess moisture from the product, completing the curing process, after which the cellular concrete acquires its final properties.

Advantages of Porous Autoclaved Concrete

The uniqueness of this material lies in:

• low thermal conductivity;
• increased fire resistance, it is able to hold fire for up to 7 hours or more;
• breathability due to increased breathability;
• mechanical strength;
• lightness due to low density;
• immunity to attack by pests;
• resistance to decay and moisture;
• ensuring the right microclimate in any season.

Gas blocks are able to keep burning up to 7 hours or more

The fact that autoclaved aerated concrete blocks combine the main qualities of wood and brick makes it a unique product. And if we take into account the high frost resistance of the material (it can withstand up to hundreds of frosts and thaws), it becomes clear that this construction material can be applied, regardless of the regional climate, without exception.

It is also worth noting the flexible indicators of such a block. Its flexibility allows you to create structures of various shapes, embodying various architectural ideas.

The scope of application for the autoclave block is very wide: construction of cottages, low-rise buildings and skyscrapers, industrial and commercial construction, reconstruction work, construction of foundations. Autoclaved aerated concrete does not require a large set of tools to work. Quite enough:

• notched trowel (for working with mortar);
• coarse-toothed hacksaw (for cutting non-standard);
• coarse sandpaper (for leveling);
• rubberized mallet (for laying blocks);
• containers for the solution (any convenient one, you can also use a bucket).

Features of autoclaved aerated concrete

Porous concrete is special for its low weight. Thanks to this, production allows the production of larger sizes, namely: length - 62.5 cm, height - 20 (up to 25) cm, width - 10 (up to 40) cm. Cellular concrete is a very light material. Its lightness and increased size make the construction of it easier and speed up the process several times. It facilitates installation so much that not only a specialist, but also an ordinary consumer is able to cope with it.

The advantage of gas blocks is perfectly even corners and plane

Virtually all batches in the production of such products provide the same unit size. The maximum error is from 1.5 to 3 mm for any direction. Such forms overestimate the angular and rib norms for the release. It turns out the clarity of geometric proportions due to the autoclave furnace. It is in it that the surfaces acquire smoothness, and the corners - clarity.

For laying concrete bricks, it is recommended to use an adhesive mortar. Such a layer will not only be a more economical option, but will also ensure the solidity of the building. This means that it will preserve and increase its thermal insulation performance. If you choose a solution, add some glue to it, and also ensure that the mixture is more soft. This will help to avoid "cold bridges" on the seam.