Non-autoclaved aerated concrete: general characteristics, properties and production technology

The adaptable building material known as non-autoclaved aerated concrete (NAAC) is renowned for its special qualities and simplicity of application. Because NAAC doesn’t require high-pressure steam curing like autoclaved aerated concrete does, it’s an affordable option for a variety of construction applications.

This kind of concrete is perfect for energy-efficient buildings because it is lightweight and provides good thermal insulation. In order to create a porous structure, a foaming agent, water, cement, and lime are mixed together during the production process. After that, this mixture is poured into molds and left to cure in the open air.

Because of its fire resistance and acoustic qualities, NAAC is prized for making living areas quieter and safer. Its performance and convenience are further enhanced by its ease of handling and installation, making it a desirable option for the construction industry.

Overview of the main qualities of the material

Based on SNiP, GOST, and product testing results, let’s examine the key characteristics and quality of non-autoclaved aerated concrete blocks. Let’s examine the production technology to determine whether using these products as the primary building material for walls is the right decision.

What is a non-autoclaved aerated concrete block and its scope of application

The same foamed concrete is used to make a non-autoclaved block; however, it is left to harden naturally.

Its range of use is fairly extensive:

• Products are used in low-rise construction for the construction of load-bearing walls and partitions;
• Also used as a filler for a reinforced concrete frame when forming high-rise buildings;
• The use of non-autoclaved aerated concrete is relevant for thermal insulation and reinforcement.

The following elements are indicative of the composition of non-autoclaved aerated concrete:

• Cement;
• Sand;
• Gypsum, ash or chalk;
• Water;
• Aluminum powder as a blowing agent;
• Chemical additives that accelerate the processes of gas formation and hardening.

Depending on density, aerated concrete is separated into:

• Heat-insulating;
• Heat-insulating and structural;
• Structural.

Let’s examine how the block’s primary indicators are impacted by its density.

Table 1 lists the properties of aerated concrete that has not been autoclaved based on density:

Indicator name	Value for non-autoclaved thermal insulation aerated concrete	Value for non-autoclaved structural aerated concrete
Thermal conductivity kcal/m. h. Gy.	0.07-0.16	0.17-0.33
Vapor permeability	—	0.16-0.25
Water absorption	—	8.5-9%
Shrinkage	—	0.033%
Compressive strength kg/cm2	10-29	30-70
Fire resistance
Weight in dry condition kg/m3	350-590	600-1600

Advantages and disadvantages of buildings erected from non-autoclaved aerated concrete

Among the benefits of using non-autoclaved aerated concrete are:

• Low weight of products, combined with a fairly good strength indicator.
• Low thermal conductivity coefficient, can guarantee a high level of temperature preservation in the building.
• Ease of processing, will facilitate the task of erecting walls, and increase the speed of construction. Products are easy to cut with any suitable tool. Almost everyone can build a house made of non-autoclaved aerated concrete.
• The material is environmentally friendly, does not burn and is resistant to biological effects.
• Another advantage is the ability to make a block with your own hands. The production technology is quite simple and does not require the purchase of expensive equipment.
• The vapor permeability and sound insulation values ​​are also at the proper level.
• Frost resistance reaches 50-70 cycles, which is undoubtedly a good result.

Comparatively inexpensive goods. The benefits of products can also be linked to this fact.

Negative aspects are also discussed in great detail; compared to autoclaved aerated concrete, they are significantly more numerous and consist of the following:

• The material is quite fragile and crumbles from mechanical impacts
• The required wall thickness is from 65 cm, which will not allow you to save on construction, but rather the opposite (the blocks will have to be laid in two rows).
• Increased shrinkage level, amounting to from 1 to 2 mm. The consequence can be a violation of not only the external characteristics, but also the operational qualities of the building and the properties of the material.
• The widespread distribution of small-scale handicraft industries should also be attributed to the disadvantages. In this regard, the chances of purchasing low-quality products increase significantly.
• The presence of geometric deviations due to imperfections of equipment and the influence of the human factor during manufacturing.

Kindly take note! The aforementioned fact has the potential to greatly impact both the overall construction speed and the amount of adhesive used when laying blocks.

Products suffer from high moisture absorption because it breaks down their structure and lowers the quality of their properties.

Finishing complexity, mostly as a result of the aforementioned drawback and decreased adhesion of the aerated concrete wall base with finishing materials. Builders consequently have to pay extra for things like reinforcement, specialty costly mixtures, and primer compositions.

Comparison of products with other materials with similar properties

While autoclaved aerated concrete is a unique substance, it shares many characteristics with other wall-building supplies. Let’s use the table to examine this in greater detail.

Table 2: Comparing aerated concrete that hasn’t been autoclaved

Name of material	Thermal conductivity	Frost resistance, cycles	Shrinkage	Strength	Water absorption	Wall thickness (minimum)
Non-autoclaved aerated concrete blocks	Up to 0.2	35-75	1-2 mm/m2	25-45	Up to 20%	0.6 meters
Foam concrete	0.14-0.22	From 35	0.4 mm/m2	15-25	10-16%	Minimum – 0.6 m
Brick	0.5	100	6-13%	100-200	12-15 %	Minimum 1.2 m
Polystyrene concrete	0.1-0.2	From 35	0.33 mm/m2	20-30	10-15%	From 0.5 m
Expanded clay concrete	0.4-0.8	From 50	0.3-0.5 mm/m2	25-35	10-15%	From 0.5 m
Wood	0.14	From 30	About 10%	—	20-25%	Minimum – 0.5 m

Distinctive features of non-autoclaved aerated concrete from autoclaved blocks

Let’s now investigate the distinction between autoclaved and non-autoclaved aerated concrete.

The hardening process itself is, of course, one of the primary ones. The fact that these two kinds of blocks are dried in different ways has an impact on the numerical indicator of attributes and qualities.

During the final stage of production, aerated concrete made using the synthetic hardening method is subjected to high temperatures and pressures in an autoclave. Conversely, aerated concrete that has not been autoclaved solidifies naturally.

Several indicators show differences as a result of this variation and certain production nuances, although certain properties remain the same:

• Frost resistance of autoclaved concrete can reach 100, and sometimes 150 cycles, while non-autoclaved concrete cannot boast such a high value – the maximum threshold promised by manufacturers reaches 70 freeze-thaw cycles.
• Aerated concrete of hydration hardening (non-autoclaved) is more susceptible to shrinkage. As a consequence, cracks may appear on the masonry and the surface covered with plaster. This process can be explained by the special treatment of the autoclave, during which it begins to gain strength right at the manufacturing stage.
• In numerical terms, the shrinkage of non-autoclaved aerated concrete is up to 1.5 mm/m2, and autoclaved only 0.3 mm.
• The thermal conductivity coefficient is good for both types. However, the wall thickness with the same indicators of two blocks will be different and differ by about 20-25 cm, not in favor of the non-autoclaved product.
• Soundproofing characteristics are also similar, as is the ability to vapor permeability.
• Both materials can withstand fire and be exposed to the destructive effects of high temperatures for up to 2 hours.
• Also, being environmentally friendly products, they do not cause any harm to the environment.
• It is worth paying attention to the fact that the geometry of the autoclaved block is significantly better. The maximum permissible deviations, in accordance with GOST, should not exceed 3 mm in length, 2 in width and 1 mm in height. For a non-autoclaved block, these indicators reach the following values ​​in numerical terms: 5 mm – in length, 4 mm – in width and 2 – in height.

As a result, both the building process’s speed and the thickness of the masonry layer of mortar or glue will vary.

• The products also have external differences, the main of which is color: the hydration hardening block is gray, and the autoclave is white.
• One of the most important differences is the strength characteristics. With a block density equal to D500, the grade of autoclaved aerated concrete, as required by GOST, must correspond to the indicator 3.5. For a non-autoclave this value barely reaches half.
• Let’s complete the comparison by pointing out the fact of the difference in the main binder component: for non-autoclaved aerated concrete it is always cement, and by autoclaving lime-containing gas silicate blocks are obtained.

Naturally, the latter has less demanding requirements for technical documentation. And this holds true for other attributes as well as strength. Let’s now examine the aforementioned attributes in the form of a table for clarity:

Autoclaved and non-autoclaved aerated concrete are compared in Table 3.

Property name	Value for autoclave	Value for non-autoclave
Frost resistance, cycles	50-100 (sometimes up to 150)	25-75
Thermal conductivity	0.1-0.14	Up to 0.12
Shrinkage	0.3 mm/m2	1-2 mm/ m2
Wall thickness	Minimum 40 cm	Minimum 65 cm
Protective finish	Required	required
Strength grade	1.5-3.5	1-2.5
Cost per m3	More expensive	Cheaper than autoclaved aerated concrete
Choice among leading manufacturers	Quite wide	Not so common, more typical for handicraft and home production
Complexity of production	If there is an automated line or conveyor, there are no difficulties, participation person is minimized	The process takes a lot of time, requires labor costs

After considering the aforementioned, it is likely no longer relevant to ask whether autoclaved or non-autoclaved aerated concrete is preferable.

Analysis of the technological process

Let’s now examine the technology used in the manufacturing of non-autoclaved aerated concrete. What tools and materials are employed in production, and how do proportions of raw materials that are technologically correct impact the quality of the finished product?

Necessary equipment and materials

It is immediately worth paying attention to the fact that the production of non-autoclaved aerated concrete, despite the great popularity of autoclaved aerated concrete, is still carried out at some enterprises. Accordingly, the set of equipment for home use and for factory use will differ.

The following equipment will be necessary for full-scale production:

• Aerated concrete mixer;
• Block mold;
• Block cutting machine;
• Manual dispenser;
• Measured capacity;
• Block pallets.

It might also be necessary to use transportation means for volumetric production. The list of ingredients for non-autoclaved aerated concrete is part of the recipe.

Step-by-step description of the work flow during production

The following steps are part of the traditional process for making non-autoclaved aerated concrete:

• First, the forms are prepared: they are lubricated with a specialized emulsion to facilitate the removal of products. The solution is mixed in accordance with all the requirements for proportions.
• The finished mixture is poured into the forms and left to stand.
• Next, excess is removed and the block massif is cut.
• The blocks are kept until a condition suitable for stripping, after which the products are moved to wooden pallets.

Now, let’s use the table to examine each step in more detail.

Table 4: Detailed manufacturing instructions for non-autoclaved aerated concrete production.

Cement supply	Is carried out manually into the dosing hopper. The cement dose is controlled using sensors. Upon reaching the required quantity, the bunker is overturned and the cement gets into the skip hoist, or rather into its can.
Sand supply	It is done in the same way as cement
Water supply	The liquid is heated to 40 degrees and sent to the intermediate dispenser. It has a fairly wide neck, which allows water to quickly pour into the main mixer for mixing with the remaining components.
Adding a foaming agent	Aluminum powder is most often used. Dosing is done using a measuring vessel.
Mixing of components	Water is the first to enter the mixer. It is first turned on to form a funnel. Next, bulk ingredients are sent there, and chemical additives are the last.

Kindly take note! The tasks in home production are completed in the same order. The solution is poured into molds of a specific size, which are then removed to yield a finished block, after the components are manually weighed using scales. That is, a cutting machine is not used in an effort to save money.

You can learn more about the production process in-depth from the video included in this article.

Characteristic	Description
Definition	Non-autoclaved aerated concrete (NAAC) is a lightweight building material made from a mix of cement, lime, sand, water, and an aerating agent. Unlike autoclaved aerated concrete, NAAC is cured without high pressure.
Density	NAAC typically has a lower density compared to regular concrete, making it lighter and easier to handle. Its density usually ranges from 400 to 1,200 kg/m³.
Thermal Insulation	Due to its cellular structure, NAAC provides excellent thermal insulation, helping to keep buildings warm in winter and cool in summer.
Sound Insulation	NAAC also offers good sound insulation properties, reducing noise transmission between rooms and from outside.
Fire Resistance	NAAC is fire-resistant and can withstand high temperatures, making it a safe choice for fire protection in building construction.
Production Process	The production of NAAC involves mixing the ingredients, pouring the mixture into molds, and allowing it to cure at room temperature. The process is simpler and less energy-intensive than autoclaved methods.
Applications	NAAC is commonly used for walls, partitions, and insulation panels in both residential and commercial buildings due to its lightweight and insulating properties.
Advantages	Its main advantages include low weight, good thermal and sound insulation, fire resistance, and ease of handling and installation.
Disadvantages	NAAC can have lower compressive strength compared to other concrete types and may be more susceptible to moisture damage if not properly sealed.

Because it is lightweight and insulating, non-autoclaved aerated concrete, or NAAC, provides a flexible and effective option for construction. Because NAAC does not go through steam curing like autoclaved varieties do, its production process is less energy-intensive and more flexible to meet different building needs.

The superior thermal insulation of NAAC is one of its main advantages. Because of this, it’s a fantastic option for energy-efficient buildings, lowering the cost of heating and cooling. Furthermore, its light weight makes handling and construction faster, which can save project costs overall.

Despite its many benefits, NAAC is not without its drawbacks. For example, its compressive strength is not as high as that of autoclaved aerated concrete. This implies that it might not be appropriate for all kinds of structures, especially those that have to support a large amount of weight.

In conclusion, the practical advantages of non-autoclaved aerated concrete in terms of thermal insulation and user-friendliness make it stand out. Determining whether a material is appropriate for a given construction project requires knowledge of its properties and manufacturing process.

A popular building material, non-autoclaved aerated concrete (NAAC) is lightweight, highly insulating, and simple to work with. Because NAAC is not produced using high-pressure steam curing as its autoclaved counterpart is, its production process is simpler and uses less energy. This kind of concrete is a popular option for a variety of construction applications because it combines the advantages of low density and high thermal insulation with ease of shaping and installation. Making educated decisions about incorporating NAAC into projects is made easier for builders and architects when they are aware of its general features, properties, and production technology.

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