AAC Blocks- an alternative Sustainable Material to Red Clay Bricks.

AAC Blocks Introduction:     AAC Blocks also known as autoclaved cellular concrete ( ACC ) or autoclaved lightweight concrete ( ALC ), was invented in the mid-1920s by the Swedish architect and inventor Johan Axel Eriksson. His purpose for designing AAC was to reduce consumption of timber and provide a cheaper and sustainable building solution. Thanks to his efforts, we have with us a product that offers great opportunities to construction industry across the globe.


source: google.co.in

The nomenclature might vary depending on geography. Some of the commonly used names for Autoclaved Aerated Concrete are Siporex, Ytong, Hebel, Thermostone, Planstone, Precast Aerated Concrete (PAC), etc.

AAC Block is a lightweight, precast building material that simultaneously provides structure, insulation and fire and mold resistance. AAC products include AAC blocks, AAC U-Blocks, AAC wall panels, AAC floor and roof panels, and AAC lintels .

(AAC  Blocks are the unique and excellent type of building materials due to its super-heat, fire and sound resistance. AAC blocks are lightweight and offer ultimate workability, flexibility and durability.)

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Aerated Concrete Blocks – AAC is produced from the common materials lime, sand, cement and water, and a small amount of rising agent. After mixing and molding, it is then autoclaved under heat and pressure to create its unique properties. AAC has excellent thermal insulation and acoustic absorption properties. AAC is fire and pest resistant and is economically and environmentally superior to the more traditional structural building materials such as concrete, wood, bricks, and stone.

AAC is manufactured by a process that involves slurry preparation, foaming/rising, cutting and steam curing (aka autoclaving). Although Autoclaved Aerated Concrete sounds very sci-fi, raw materials used in a manufacturing process are very common and easily available across the globe. It is made a mixture of sand or fly ash (or pond ash), lime, cement, gypsum, an aeration agent (usually Aluminium paste or powder) and water. Fly ash or pond ash is an industrial waste generated by thermal power plants. Aeration process releases Hydrogen (H2) creating tiny cells inside a green cake. The chemical reaction due to the aluminum paste provides AAC its distinct porous cellular structure.This cellular structure imparts lightness, and thermal insulation properties and acoustic insulation to AAC products, completely different compared to other lightweight concrete materials. aac-blocks gif 1    

source: aeratedconcreteblock.com

AAC Blocks and AAC Panels

AAC products are available in various shapes and sizes. Most commonly used forms are AAC blocks, reinforced and non-reinforced panels, slabs (tongue & groove) etc. to cater to varying requirements of construction industry.

AAC blocks and other products offer superior performance and reduced project cost due to bigger size and light-weight. Bigger size leads to faster layings at sites. Reduced weight translates to reduced dead-weight on structures. In addition to this, AAC blocks offer higher thermal insulation compared to clay bricks. This reduces investment as there is no need to install additional insulation products. Better insulation leads to reductions in energy cost for heating/cooling purpose. Walls built using AAC blocks or panels can withstand fire for a long period of times compared to other conventional walling material.

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Usage of AAC products not only leads to a constructive use of polluting industrial waste like fly ash or pond ash but also reduces usage of non-renewable resources like topsoil. AAC industry also reduces pollution as it does not rely on open kilns used for baking clay bricks. Especially in countries like India, Autoclaved Aerated Concrete products offer a sustainable and eco-friendly construction product with reduced project cost. Increased usage of AAC products will offer faster and cost-efficient construction, reduction in pollution and reduced usage of topsoil.

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Building constructed using Autoclaved Aerated Concrete (AAC) blocks

Along with a brief overview of AAC blocks, here is a list of common sizes of AAC blocks for quick reference:

Sr. No. Length (mm) Height (mm) Breadth (mm)
1 600 200 75
2 600 200 100
3 600 200 150
4 600 200 200
5 600 200 225
6 625 240 75
7 625 240 100
8 625 240 150
9 625 240 200
10 625 240 225

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Multi-storied building using AAC blocks vs clay bricks



Pile of Autoclaved Aerated Concrete (AAC) blocks at a construction site

Advantages of AAC blocks

Advantages of AAC blocks are varied and many depending upon local conditions. Some of those advantages from India’s point of view are mentioned below:




80% of the volume of an AAC block is air and are about 50% lighter than clay bricks or concrete blocks (CMU) of equivalent size. This translates into a less dead weight of a building and allows entire structure to be lighter, therefore reducing the amount of steel and concrete used in structural components like beams, columns and roof/floor slabs.

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AAC products have a cellular structure created during the manufacturing process. Millions of tiny air cells impart AAC products a very light weight structure. The density of these light-weight AAC blocks usually ranges between 400 – 800 kg/m3. Yes, AAC blocks are lighter than water and literally float on water.

Easy Workability



AAC blocks are very easy to work with. The blocks are easy to install, nail, drill and cut for pipes and conduits. It can be cut accurately reducing the amount of waste generated.It can be cut or drilled using normal tools used with wood. Since AAC is cured using steam, it is ready to be used as soon as it comes out of an autoclave.


AAC products can be used to make any design, be it carving or irregular shapes. Moreover, it can be manufactured in various shapes and sizes to suit intended purpose.

Single Product Solution

Buildings constructed with AAC blocks do not require separate insulation products reducing construction cost, energy footprint and environmental impact of buildings.

Environmental Impact

AAC manufacturing process requires less energy, has very low emission and does not generate any waste products. Moreover, since AAC  blocks are light weight, it saves energy required for transportation and leads to reduced CO2 emissions by transport vehicles. Since AAC blocks are made from fly ash or pond ash– an industrial waste product – generated by thermal power plants, it offers a low cost and sustainable solution for today and tomorrow by using these waste materials to constructive use for ACC manufacturing. 


Buildings constructed using AAC products have lower ’embodied energy’.AAC blocks are certified Green Building Material and a requisite for green buildings. Using AAC blocks and panels is highly recommended for any ‘Green Building’ project.

Easy Transportation

It is easy to transport AAC blocks as it does not suffer from high transit breakage usually associated with clay bricks.


AAC blocks do not lose strength or deteriorate over time. Buildings constructed with AAC blocks do not require routine repairs that are required for buildings using clay bricks.Structures built with AAC products have a long life and retain good finish even after decades. Although an actual life of AAC products depends on various factors, as per various standards institutes, the lifespan of AAC may go up to 100 years or more.


Aerated concrete blocks have been tested in colder climates and have proved to have a high resistance to frost. They have also proved to have great durability in other climates as well.

Seismic Resistant



AAC products do not decay, rust, deteriorate or burn. Building constructed using AAC products have a better chance of surviving earthquakes due to reduced weight of an entire building. As it is noncombustible in nature, it becomes highly recommended for areas with high seismic activity.

Weather Resistant

AAC structures are known to maintain structural integrity in heavy rains, extremely low temperature and salty air.

Pest Resistant

The primary raw material used to manufacture AAC blocks and panels is fly ash. Fly ash (or pond ash) is an inert material and does not allow termites or other pests to survive.

Thermal Insulation

Due to cellular structure, AAC products offer excellent thermal insulation. Usage of AAC products leads to energy savings for HVAC (Heating Ventilation And Cooling) needs. Use of AAC products offer walling, insulation and fire protection solution eliminating need for different materials for different needs.

Shorter Project Duration

Buildings can be built with AAC blocks 50% faster compared to clay bricks. This translates to lower project completion times benefiting project developers.

Fire Resistance


source: google.co.in

AAC products offer amazing fire resistance. 8” wall made from AAC blocks can resist fire for up to five hours.

Due to high fire resistance offered by AAC blocks, structures made from AAC blocks have a high rate of survivability in case of fire.

Sound Insulation

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Tiny air pockets created during AAC manufacturing process stop sound from propagating from one end of the wall to another. Sound insulation of a wall built using AAC is much higher than a wall of similar thickness built using other materials. Some AAC companies even offer special AAC products produced specifically for sound insulation.

Sound absorption properties of AAC makes it an ideal material for reducing ambient noise. AAC blocks are well-suited for establishments like hospitals and offices situated in noisy areas.

High Survivability

Millions of air pockets in AAC blocks cushion structure from major force and prevents progressive collapse of a building. AAC structures are known to maintain structural integrity despite of seismic activity (earthquakes), heavy rains, extremely low temperature and salty air.

Disadvantages of AAC Blocks:

They are also some disadvantages and limitations of AAC block use, which are discussed below.

Energy and Pollutants

Aerated concrete blocks are made of inorganic materials, but they do not release negative wastes or pollute the environment. However, the process of autoclaving the concrete requires a lot of energy, which gives it an environmental disadvantage.


Aerated concrete blocks are mostly beneficial in climates that have big temperature fluctuations over the course of a 24-hour period. This is particularly for sunnier climates that yield a long period of hot days and cold nights. This is because of the high thermal mass that these blocks provide. The walls made from these blocks react similar to a sponge during the hot sunny hours and then releases the heat later when the temperature gets colder.

Insulation Performance

Aerated concrete blocks have an excellent insulation performance of up to ten times higher than that of ordinary cement blocks. This is great. However, when compared to conventional block concrete and porous concrete, they are not as high in performance as materials such as insulated concrete forms or structural insulated panels.


Aerated concrete blocks have open cells that are easily damaged when exposed to the environment. This damage can be a result of debris or water. Professionals recommend using a high permeable exterior finish for the exterior, and a low vapor one for interior finishes.

AAC blocks vs clay bricks:

AAC blocks are a relatively new phenomenon in Indian construction industry. Although first AAC blocks plant in India was set up in early 1970s by Siporex at Pune, it is only recently that manufacturing and usage of AAC blocks have reached sizeable number. In spite of drastic growth in manufacturing of AAC products, the fact is that market share of AAC products is very small compared to red clay bricks. There are various reasons for this.We have provided a comparison between AAC blocks vs clay bricks and we let you be the judge for selecting the best product to suit your needs.

Serial Parameter AAC Blocks Clay Bricks
1 Soil Consumption Zero soil consumption. Primary raw material for AAC blocks is fly ash. This fly ash is industrial waste generated by coal-based thermal power plants. One sq ft of carpet area with clay brick walling will consume 25.5 kg of top soil.
2 Fuel Consumption One sq ft of carpet area with AAC blocks will consume 1 kg of coal. One sq ft of carpet area with clay bricks will consume 8 kg of coal.
3 CO2 Emission One sq ft of carpet area will emit 2.2 kg of CO2. One sq ft of carpet area will emit 17.6 kg of CO2.
4 Labour Organized sector with proper HR practices. Unorganized sector with rampant use of child labour.
5 Production Facility State-of-the-art factory facility. Unhealthy working conditions due to toxic gases.
6 Tax Contribution Contributes to government taxes in a form of Central Excise, VAT and Octroi. Does not contribute to a government exchequer.
7 Size 600 / 625 mm x 200 / 240 mm x 100-300 mm 225 mm x 100 mm x 65 mm
8 Variation in Size 1.5 mm (+/-) 5 mm (+/-)
9 Compressive Strength 3-4 N/m2 2.5-3 N/m2
10 Dry Density 550-700 kg/m3 1800 kg/ m3
11 Fire Resistance (8″ wall) Up to 7 hours. Around 2 hours
12 Cost Benefit Reduction in dead-weight leading to savings in steel and concrete. None
13 Energy Saving Approximately 30% for heating and cooling. None

AAC blocks are ideal for all kind of structures such as schools, hospitals, hotels, offices, independent housing, apartments etc.The advantages of a use of AAC block in a construction sector are much more as compared to its disadvantages and also a better alternative to Red Clay Bricks.

AAC factories create many jobs, directly and indirectly creating a social impact. Along with it, they pay Excise Duty and VAT contributing to a national economy.




Overview of Autoclaved Aerated Concrete (AAC) Products



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