What is AAC Blocks?

What is AAC Block?

Autoclaved aerated concrete (AAC), also known as autoclaved  cellular concrete (ACC), autoclaved lightweight concrete (ALC), autoclaved concrete, porous concrete, Ytong, Hebel Block, Aircrete, thermalite.

When AAC was first developed?

AAC was developed in 1924 by a Swedish architect who was looking for alternative building material with wood-like properties good thermal insulation, solid structure and easy to work with but without the inconvenience of combustibility, decay and termites. It has been refined into a highly thermally insulating concrete material for indoor and outdoor construction. AAC products contain blocks, wall panels, floor and ceiling panels and lintels.


Advantages of AAC Blocks

AAC block offers several significant advantages over other cement construction materials, one of the most important being its lower environmental impact.

  1. Improved thermal efficiency reduces the heating and cooling load in buildings.
  2. The Workability allows accurate cutting, which minimizes the generation of solid waste during use.
  3. It has a lower environmental impact in all phases of its life cycle, from the processing of raw materials to the disposal of waste.
  4. It’s Lightweight saves cost and energy in transportation.                                     
  5. Its Lightweight saves labour expenses.                                                                        
  6. Lightweight increases chances of survival during seismic activity.
  7. Larger size leads to faster masonry work.
  8. Termite/Pest Resistant, Cost-Effective, Precision,
  9. Earthquake Resistant.
  10. Easy Workability and Design Flexibility.
  11. Thermally Insulated & Energy Efficient, Fire Resistant, Eco-friendly.

ACC Blocks size  

S.No.Particulars     Size (L x B x H) in mm
1Size 1         600×200×200
2Size 2         600×200150
3Size 3         600×200×100
4Size 4         600×300×200
5Size 5         600×300×100
6Size 6         600×400×250

Applications of AAC Blocks

  1. Hotels, Motels & Restaurants
  2. Industrial & Cold Storages 
  3. Hospitals & Medical Clinics 
  4. Retail & Warehouses 
  5. Office & Religious Buildings 
  6. Power Plant & Fire Walls
  7. Public Facilities
  8.  Single & Multi-Family Homes 
  9.  Shaft walls     
  10.  Education Institutes Construction     
  11.  Auditorium & Theaters 
  12.   Multi-storey Buildings 

Technical Comparison of Blocks

ParameterAAC BlockConcrete BlockBrick
Size(600x200x100-300) mm(400x200x100-200) mm(230x115x75) mm
Compressive Strength30 – 50/Kg/3Cm240 – 50/Kg/Cm225 – 30/Kg/Cm2

Dry Density


1800 Kg/Cum

1950 Kg/Cum

Fire Resistance
4-6/Hour Depending On Thickness

Sound Reduction Index(DB)60 For 200 mm thick wall_40 For 230 mm Thick Wall
Thermal Conductivity w/(Km)0.25


Physical Properties of Autoclaved Cellular Concrete Blocks Clauses (4.1,8.3,8.4,8.5,11.2,11.3 and 11.4) IS :2185(Part-3) 1984

S.No.Density in oven-dry conditionCompressive strength min grade 1 N/mm2Compressive strength min grade 2 N/mm2Thermal conductivity in air-dry condition w/MK
1451 to 55021.50.21
2551 to 650430.24
3651 to 750540.30
4751 to 850650.37
5851 to 1000760.42

ACC Block Plant

1Material hopper10Cutting machine
2Slurry making tank11Tilting crane
3Slurry making pit tank12Windless machine
4Silo13Steam trolley car
5Pouring section platform14Autoclave
6Pouring mixer15Ferry car outlet
7Ferry cart16Side plate return roller system
8Mould box17Finish block dispatch point
9Ground crane

Raw Material Required

Fly Ash /65-70%

Fly-ash material is freely available in Thermal power plant. A lot has been said about this raw material in Different forums & Environmentalists. There are no taxes levied on this item.

 Lime / 8-12%

Different qualities of lime are available and depending on the raw materials. The mix design can be chosen to get the optimal quality of production. Quick lime is a requirement for giving the real aeration to the product.

OPC Cement / 10-15%

The project aims to utilize OPC cement as the main binder material. it will give faster strength to the blocks besides giving improved consistent quality. it also ensures better cost-effectiveness for the same. Using OPC cement will be a standardized practice.

Gypsum / 4.5-5%

This too is an industrial waste. This is available as an industrial by-product of Fertilizer plant.gypsum is responsible to give long term strength to block.

Aluminum Powder / 0.5%

Finely ground aluminium powder is used in very limited quantity (less than 0.5%) so that it reacts with active lime, and silica in base material to make the aeration, and swell the product, making it very light in weight. The density of the product reduces to 600-650 kg/cum.

Procedure OF Production

1.  Firstly, batch the measured raw material.

2.  Feed raw material into pouring mixer for slurry making.

3.  pour the mixer slurry into the mould.

4.  After pre-curing under a certain temperature and time, the block would reach certain hardness &

5.  Tilting crane separate the already- formed material from the mould and transfer it with side plate to the cutting cart.

6.  Cutting machine horizontally & vertically cut the foamed material.

7.  Group of steam Trolley with cake move into Autoclaves.

8.  In Autoclaves sustained pressure & temperature is maintained for curing cake.

9.   crane transfer the finished product to the dispatch point.

10. Move the finished blocks out of Autoclaves.

11. Packed for loading.

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