Composition of aerated concrete and the technology of its production in industrial and domestic conditions

Autoclaved aerated concrete (AAC), another name for aerated concrete, is a widely used building material that is highly regarded for its exceptional thermal insulation qualities and low weight. It is a flexible option for a range of construction projects due to its distinctive composition and manufacturing method. You can better appreciate the advantages and uses of aerated concrete if you know how it’s made and what ingredients it contains.

Cement, lime, sand, water, and a trace amount of aluminum powder are the primary components of aerated concrete. Tiny air bubbles are created throughout the mixture as a result of a chemical reaction that happens when these materials are combined. This produces a lightweight, porous material that is excellent for insulation and is simple to work with.

It is possible to produce aerated concrete both domestically and industrially. The mixture is put into sizable molds in an industrial setting and autoclaved—a high-pressure steam curing process—followed. The strength and stability of aerated concrete are derived from this process. It can also be produced on a smaller scale with less complicated equipment, making it available for do-it-yourself projects or smaller projects.

Knowing the ingredients and manufacturing process of aerated concrete can help you better understand its benefits and future applications, whether you’re building a new house, adding an addition, or you’re just looking for creative building materials. Let’s examine in more detail what makes this material unique and how it can be produced in both large-scale and smaller-scale environments.

Composition of Aerated Concrete	Production Technology
Cement	Mix cement, lime, and water to create a slurry.
Lime	Add aluminum powder to the slurry for gas formation.
Water	Pour the mixture into molds for shaping.
Sand	Allow the mixture to rise and set for initial hardening.
Aluminum Powder	Remove the formed blocks from the molds.
Gypsum	Cure the blocks in an autoclave for final hardening.

Why aerated concrete

Against the backdrop of natural stone and brick, the following is a brief summary of its benefits:

• Excellent thermal insulation qualities. Thermal conductivity of aerated concrete blocks is three times lower than that of brickwork;
• Vapor and air permeability. This means that a house made of aerated concrete will never be stuffy or damp;
• Easy processing. In particular, you can cut a block with a density of up to D600 using a regular garden saw;

• Large block size, which greatly speeds up the construction process;
• Ideal geometry (in the case of autoclaved aerated concrete) and precisely maintained block dimensions. These features make it possible to reduce the thickness of masonry joints to a minimum, and, therefore, get rid of cold bridges – areas of masonry with high thermal conductivity;

Note that aerated concrete is applied to cement glue with a minimum filler fraction size rather than a cement-sand mortar. With the glue, you can get the seam down to 2-3 mm in thickness.

• Competitive price (from 3,000 rubles per cubic meter), approximately corresponding to the cost of aerated concrete’s main competitor – hollow ceramic bricks.

A warning: the bending strength of aerated concrete blocks is low. This is why the foundation must be extremely rigid because any bending will cause the walls to fissure. Additionally, armored water is supplied to one-story aerated concrete buildings, and arm cards are provided to houses with two or more floors.

Components and Requirements

Thus, the components and composition of aerated concrete.

Water

Quantity: 250–300 liters for every cubic meter of completed product.

GOST 23732-79, which controls water quality for the preparation of concrete and cement mortars, must be followed. GOST R 51232-98 states that drinking water (or, to put it another way, water from any building’s cold water supply system) can also be used for mixing.

If the water source is a well or wells, it is best to draw from surface aquifers; low to medium hardness and low salinity are needed to prepare aerated concrete.

A crucial point to remember is that the mixing water needs to be heated to between 40 and 60°C. Its heating will cause the cement to hydrate more quickly, hastening the ripening of the blocks and increasing their ultimate strength. The line’s increased productivity will more than offset the cost of heating.

Cement

Every builder is familiar with Portland cement, which is used as a binder in non-autoclaved aerated concrete blocks:

• Quantity: from 260 to 320 kg per cubic meter of finished product, depending on the grade of Portland cement and the requirements for the final strength of the blocks.
• Quality: Portland cement must meet the requirements of GOST 10178-85. Grades of cement suitable for the manufacture of naturally hardened aerated concrete blocks are M 400 D 20 and M 500 D 20.

Important: there needs to be an adequate amount of soluble alkalis in cement. By adding lime binder (slaked lime) or caustic soda (caustic soda NaOH), their deficiency is made up for. The distinct white or light gray color of the blocks is a result of both gas formation and lime addition.

Filler

250 to 350 kg per cubic meter is the quantity. The precise mass of the filler is determined by the final density and strength requirements of the aerated concrete; the block can withstand a higher compression load when its density is higher.

Type: Dolomite flour, ground limestone, boiler room and CHP ash, river, sea, or career sand, and other mineral fillers can all be found in an aerated concrete unit.

• The minimum fraction size. The smaller the filler, the less pores will be and the more smooth the surface of the block will become;

• Lack of foreign inclusions (branches, stones, organic garbage);
• Minimum silt and clay impurities.

Modifiers

The concrete additives’ ability to ripen more quickly serves this function.

The maximum quantity per cubic meter is 3 kg.

Gas-forming additive

Concrete foaming is caused by aluminum powder. When alkali is present, the reaction between aluminum and water takes the following form: 2AL + 6 H2O = 2AL(OH)3 + 3H2. The process of adding hydroxyl groups to aluminum atoms releases free hydrogen, which is what forms closed pores in the mass of concrete.

500–700 grams per cubic meter is the quantity. Requirements: PAP-1 or PAP-2 aluminum powder is utilized.

Fascinatingly, when combined, fine powder dusts, so an aqueous suspension is frequently used in its place.

Mold lubricant

Lubricant makes the mold perfectly clean after removing the block from it without altering its geometry. Quantity: up to 0.5 kg per completed cubic meter.

Note: Spent oil from diesel cards cannot be used to lubricate forms. The high soot content in them is the reason for the instruction.

Technology

Industrial conditions

Under conditions of large-scale production, aerated concrete is made as follows:

1. The components (Portland cement, sand or other filler, lime, modifiers and blowing agents) are loaded into separate bins;
2. The coarse filler is ground into mineral flour;
3. The components are dosed depending on the requirements for the density of the finished blocks and mixed with water in a concrete mixer;
4. The mixture is poured into a large-volume mold, where gas formation gives it a porous structure. The mold is placed on a vibration table. Vibration helps to achieve uniform, void-free filling;
5. In the pre-ripening chamber (the so-called hot tunnel), in 3-4 hours at a temperature of about 40°C, the mixture gains strength sufficient for stripping (removal from the mold);

1. On the cutting line, the array is transformed into separate blocks. High-strength metal strings are used for cutting. Since cutting is performed in three planes, the array is turned during the cutting process;

Note: At this point, blocks can have tongue-and-groove locks formed on them to improve masonry adhesion both within and between rows, as well as hand grips to make block transportation easier.

1. Formed, but not yet strengthened, blocks enter the autoclave. Their maturation takes place under excess pressure (about 12 kgf/cm2), high humidity and temperature (+180°C). Autoclaving ensures complete absence of shrinkage and cracks;

1. The blocks, which have passed quality control and are packed in polyethylene, are loaded onto pallets and sent to the finished product warehouse.

Handicraft production

The components’ approximate composition and proportions will be as follows if you are making aerated concrete blocks by hand:

• Sand — 180 kg;
• Cement — 100 kg;
• Water — 60 liters;
• Caustic soda — 600 g;
• Aluminum powder — 230 g;

Beneficial: Adding 1.5 kg of sodium sulfate—a potent laxative, incidentally—to the mixture is a good idea. It will expedite the aerated concrete’s maturation significantly.

And this is a detailed explanation of the technology used in the manufacture of handmade blocks:

1. Pour water heated to 60 degrees into a concrete mixer (from a hot water supply or, which is much better, from a boiler);
2. Pour in 2/3 of the total amount of sand and half of the cement;
3. Stir for 10 minutes;
4. Add the rest of the sand and cement while continuously stirring;
5. Pour in caustic soda, sodium sulfate (optional) and aluminum powder diluted with water;

Note: Paraffin is applied to PAP powder particles to ensure safe storage. Dilute the powder with warm water and add regular washing powder to wash it off. Three to five percent of the total amount of powder is added. More will result in less gas formation.

1. Stir for another minute, then pour the mixture into pre-greased molds and cover them with plastic wrap for 10 minutes;

1. After the mixture rises to the maximum and settles, cut off everything that protrudes beyond the mold;
2. After 24 hours, unload the set blocks from the molds, store them and wait for them to gain full strength within 2-4 weeks.

Aerated concrete takes a month to reach its full strength at room temperature and without the use of maturation-accelerating additives.

Having a temperature between +5 and +25 degrees Celsius and no drafts in the room where the blocks are formed and dried is a useful requirement.

Because of its insulating qualities and lightweight nature, aerated concrete is a highly adaptable and effective building material. Because of the ingredients in it—lime, cement, sand, water, and an aerating agent—tiny air bubbles can form throughout the material, giving it strength and insulation.

Aerated concrete production on an industrial scale requires exacting procedures for mixing, dosing, and curing. It is a dependable option for major construction projects because of these measures that guarantee consistent quality and performance. The material’s qualities are further improved by the use of molds and autoclaves, which guarantee consistency and longevity.

Aerated concrete production in a home environment necessitates close attention to the ratios of mixture and curing conditions. Even though it might not achieve the same consistency as aerated concrete made in an industrial setting, it’s still a workable solution for smaller projects or do-it-yourselfers who want to take advantage of its special qualities.

All things considered, aerated concrete, whether made at home or in a factory, provides a practical and sustainable answer for contemporary building requirements. Because of its composition and manufacturing process, it can be used for a variety of purposes, such as thermal insulation and walls and partitions.

The main components of aerated concrete, such as cement, lime, sand, and aluminum powder, will be examined in the article "Composition of Aerated Concrete and the Technology of Its Production in Industrial and Domestic Conditions," which will also detail the meticulous procedures required to make it in both large-scale factories and homes. We’ll explain how these components work together to produce a building material that is both lightweight and adaptable and is renowned for having good insulating qualities. We’ll also point out how the production processes vary and are similar depending on the size of the operation.

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Production of aerated concrete blocks. Scheme.

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