The main differences between autoclaved and non-autoclaved aerated concrete blocks: properties, characteristics, application

It’s important to know the differences between autoclaved and non-autoclaved aerated concrete blocks when selecting building materials. Although these blocks have a similar appearance, they have different qualities and advantages that can affect your construction project.

Autoclaved aerated concrete (AAC) blocks acquire special qualities from a high-pressure steam curing process. Conversely, blocks made of non-autoclaved aerated concrete (NAAC) are cured in a typical atmosphere, giving rise to distinct characteristics.

The main distinctions between these two kinds of aerated concrete blocks will be discussed in this article. Making an informed decision for your construction needs will be aided by your understanding of these distinctions, from their best applications to their properties and characteristics.

Aerated concrete production technology

The technology used to produce autoclaved and non-autoclaved aerated concrete is the same; the only distinctions are in the final stages of material processing and the precision with which the technology is followed. The proportion and type of raw materials used are the same.

Aerated concrete production components include:

• Fine-fraction sand 2-2.5 millimeters
• Portland cement grades M300 and M400
• Lime
• Aluminum powder or paste with an active metal content of 90-95%
• Various additives and modifiers (not necessarily added, needed to improve various performance properties)
• Water

First, prepare a standard cement-sand mortar, transfer it into a mold, and then stir in aluminum powder. Carbon dioxide is produced as a result of the powder and lime reacting, which causes the mass to expand and take the form of a porous structure. In order to speed up the process and ensure that the gas evolution reaction is finished before the cement sets, the form is processed on a vibration platform. But only large factories can benefit from such a procedure.

Foam concrete is a kind of cellular concrete that is made in small workshops. After all, concrete is separated into gas and foam concrete based on the foam formation process. And if gas creates the foam in the first scenario, then chemicals do so in the second.

Special chemical foaming agents are added and whipped to create the cellular structure. The majority of work is done by hand in small, staff-heavy foam concrete production facilities. Although the process of producing aerated concrete is more costly, the finished product has superior qualities and is more stable.

Additionally, there are technological variations between the production of autoclaved and non-autoclaved aerated concrete. When producing autoclaved aerated concrete, the mixture is poured into a mold and the reaction is started. After a set amount of time, the mixture is allowed to partially harden and gain strength, which is necessary to remove the massif from the formwork and cut it into blocks.

To completely remove moisture from the material, the cut blocks are placed in an autoclave and fired at a temperature of +190–200 degrees with a pressure of 8–10 bar. Using an autoclave to process aerated concrete has several benefits, including accelerated hardening, improved strength characteristics, decreased future shrinkage, homogenous structure, and improved block geometry.

Instead of gaining strength in a furnace, non-autoclaved aerated concrete does so naturally, without the help of pressure or temperature to evaporate moisture. Furthermore, forms for casting individual components rather than large forms with additional cutting of aerated concrete blocks are frequently used in the production of this kind of material.

The following regulatory documents are followed in the production of both autoclaved and non-autoclaved aerated concrete: GOST 21520 "Wall blocks made of cellular concrete," GOST 25485 "Cellular concrete," as well as GOST 31360 and GOST 32359.

The primary differences between autoclaved and non-autoclaved aerated concrete blocks are in the methods used during production and the end products. Because autoclaved blocks are cured at high temperatures and pressures, they become denser, stronger, and more uniform—qualities that make them perfect for load-bearing structures. Naturally cured, non-autoclaved blocks are less expensive and lighter; they are appropriate for non-load-bearing walls and insulation. Although both types provide good sound and thermal insulation, their particular uses are limited by the needed structural strength and available funds.

Properties of non-autoclaved and autoclaved aerated concrete

At the output, autoclaved and non-autoclaved aerated concrete are entirely different materials. They differ in both appearance and performance characteristics, so you can tell right away what kind of concrete is in front of you just by looking at it.

External indicators

Solid wood cellular blocks typically conform to the design dimensions more closely. The thickness of the inter-masonry joints is significantly smaller (and that of the cold bridges, correspondingly), they are easier to lay, sealing the seams requires less time, effort, and materials, and finishing the building is simpler.

Aerated concrete that hasn’t been autoclaved is gray, while that has is nearly white. If there are visible inclusions in the structure and the shade is uneven, the material’s quality is probably not very good.

The process of making non-autoclaved aerated concrete is frequently done in an artisanal manner; the material is supplied for construction after the concrete has naturally hardened by simply mixing it and pouring it into formwork. All of this has a detrimental effect on the final material’s quality and key characteristics.

Physical and mechanical properties

Autoclaved aerated concrete demonstrates 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 cannot always withstand can be mounted on walls made of fired blocks.

One of the primary distinctions between the materials is shrinkage; the moisture in unfired aerated concrete leads to the formation of wall cracks. Additionally, density is significant because, as it falls, the shrinkage coefficient rises as residual strength increases. The procedure takes five to ten years. Unfired, autoclaved aerated concrete shrinks by two to three millimeters per millimeter.

The property of thermal conductivity indicators varies as well; the lower the density, the more heat-intensive the material. The best option for lowering wall thermal conductivity is to use aerated concrete that has a lower density and high strength indicators.

Differences: pros and cons of materials

Concrete blocks that have been autoclaved and aerated exhibit notable differences from unfired material in a number of areas. Blocks are used for a variety of tasks depending on their properties, which are important for different kinds of construction. You must first review all the specifications, benefits, and drawbacks of any material before utilizing it for your work.

Strength

Natural hardening gas concrete is not as durable, especially when it is brand-new. Setting strength takes a lot of time. However, the aerated concrete autoclave helps the strength to pass through more quickly (accelerates hundreds of times); as a result, the strength of autoclaved concrete is 1.5–2 times that of unfired concrete after steam processing at a high temperature.

Thus, autoclave brands D500 and D600, for instance, show strength at B2.0-in3.5; a non-circulated brand of a similar kind will, at most, give class B2.

Block geometry

The uniformity of the blocks and their adherence to these specifications are crucial during the building process. No matter what kind of building is being constructed—a residential home, a garage, or a bathhouse—the more meticulously the blocks are made, the higher the masonry quality. After all, if something goes wrong, the thermal insulation qualities are diminished, cold bridges are formed, and the level difference is leveled with mortar or glue.

Shrinkage during the process is adversely affected by thick seams, and cracks may develop. This can be prevented by using a standard hand saw to remove the level difference on aerated concrete using a float. However, in this instance, the labor and time costs are just too high. Building a structure out of smooth autoclaved aerated concrete right away is far simpler and less expensive.

Homogeneity of the structure

The quantity of bubbles in the material and how evenly they are distributed define the homogeneity of the structure. The better the material, the more homogeneous it is; this improves quality. Because autoclaved aerated concrete blocks are made quickly, harden right away, and are then divided into individual blocks, they have a more uniform structure.

The production process for non-autoclaved aerated concrete is different; foam and blowing agents may not be distributed evenly, causing heavy components to fall and bubbles to frequently float upward. This has detrimental effects on construction: cold bridges form in areas where there are few bubbles, and strength declines in areas where there is a significant bubble accumulation. Features are erratic.

Possibility of fastening

Aerated concrete that has been autoclaved is a sturdy substance that can support the attachment of heavy appliances and components. Facades composed of heavy porcelain stoneware or even lightweight expanded clay can be fastened. Thus, a pull-out load of roughly 700 kg can be easily supported by a 10×100 anchor. In other words, you can secure air conditioners, boilers, cabinets, shelves, and fasteners without worrying that they will fall along with a portion of the wall.

Aerated concrete that hasn’t been autoclaved is far less resilient; in certain cases, you can even manually drive screws or nails into it. Lightweight objects are secured with a costly two-component chemical anchor instead of mechanical fasteners.

Shrinkage during drying

Selecting autoclaved blocks for masonry should result in less shrinkage over time. Concrete has already strengthened during firing and has a maximum shrinkage rate of 0.5 mm/m, whereas non-autoclaved aerated concrete has a significantly higher shrinkage rate of approximately 5 mm/m.

Severe shrinkage of non-autoclaved aerated concrete buildings can lead to a variety of problems, including peeling plaster, masonry cracking, and the appearance of cracks. Up until the concrete reaches its peak strength, all of this can go on for a few years.

Environmental friendliness

The building can breathe, autoclaved aerated concrete promotes the best possible microclimate, and it is completely safe for the environment. Since aerated concrete is made of mineral raw materials, it is resistant to mold, moisture, and rotting.

The use of chemical additives to form foam in the production of non-autoclaved aerated concrete already lowers the operational safety of the product. Chemicals are frequently added to the block using fiber that has been impregnated with unique thiocyanates, chlorides, and acids. This is even riskier because these compounds have the potential to leak out and gradually build up in the home’s air.

The primary distinctions between autoclaved and non-autoclaved aerated concrete blocks can have a significant impact on the materials you select for building projects. Blocks of autoclaved aerated concrete (AAC) have superior strength, homogeneity, and insulating qualities because they are cured in a high-pressure steam chamber. Because of this, AAC blocks are perfect for both structural and non-structural uses, particularly in areas where strong thermal performance is required.

As opposed to AAC, non-autoclaved aerated concrete (NAAC) blocks are cured under standard atmospheric conditions, which may result in quality variances and decreased overall performance. However, NAAC blocks are typically easier to produce and more cost-effective, which makes them appropriate for smaller projects or scenarios where money is a major concern.

There are certain advantages and possible disadvantages to both varieties of aerated concrete blocks. Your decision should be based on the particular requirements of your project, taking into account things like your budget, the structural specifications, and the insulation requirements. Knowing these distinctions will help you make a decision that will improve the longevity and effectiveness of your construction project.

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