AAC blocks specifications – (Autoclaved aerated concrete), Composition

In this article you will get introduction, composition, manufacturing and AAC blocks specifications. The specifications of AAC blocks contains General Size,Thickness Minimum, Compressive Strength, Minimum Dry density, Thermal Resistance, Allowable Shear Stress, Sound Absorption, Fire Resistance, Thermal Conductivity, Drying Shrinkage etc.

Let us start from the introduction of AAC blocks.

What is AAC blocks?

AAC blocks specifications - (Autoclaved aerated concrete), Composition
AAC blocks
  • AAC block is a special type of concrete block made up of fine aggregates, Portland cement, water, and another expansion agent (Aluminum powder).
  • AAC block was developed in 1924 by a Swedish architect. AAC block is alternate materials for building materials that have similar properties as wood. As we know, wood has good thermal insulation, solid structure, and easy to work, combustible, decay, and termite damage. But AAC blocks minimize the disadvantage of using timber as a construction material. The combustible, decay, and termite damage can be totally removed using this block.
  • The AAC products not only include AAC block, but they also include wall panels, floor and roof panels, lintels, etc.

Uses of AAC Block

  • Used in commercial, industrial and residential applications
  • AAC is well suited for high-rise buildings and those with high-temperature variations,
  • Suitable for use in areas with extreme temperatures.
  • It reduces the weight of the superstructure, so used in light construction.

AAC blocks specifications

AAC blocks specifications - (Autoclaved aerated concrete), Composition
AAC Block Specifications
Properties of AAC BlockSpecifications
General Size625 mm * 240 mm * (75-300) mm
Minimum Compressive Strength3 to 4.5 N/mm2 (IS 2185)
Minimum Dry density450 to 650 Kg/m3
Thermal Resistance0.8-1.25 per inch of thickness
Allowable Shear Stress8-22 psi
Sound AbsorptionUp to 42 De
Fire Resistance4* Hours
Thermal Conductivity0.16 to 0.18 W/Mk
Drying Shrinkage0.04% of the size of AAC block
AAC Block Specifications


1. Fly-ash – 59%

2. Cement (usually OPC grade 53) -33%

3. Lime – 8%

4. Aluminum powder – 0.07%

Manufacturing Process of AAC Block

  • First a fall, autoclaved aerated concrete is produced by mixing silica or sand or fly ash with cement, lime, water, and expansion agents such as aluminum powder.
  • After mixing, this concrete is poured into the mould of standard size.

(For structurally reinforced AAC product, steel rebar or mesh is also placed in mould.)

  • When we mix the aluminum powder with silica or other material containing silica, there is the formation of hydrogen gas. As a result, the concrete gets expand five times its original volume. Such a process is called aeration. So it is renamed as aerated.
  • Then, the hydrogen gas escape by leaving voids in between concrete, and this mould is removed and cut into small pieces (Waste during cut can be recycled).
  • Then, pass these pieces into the autoclave. The temperature of autoclave has reached about 190° Celsius and pressure about 8 bars to 12 bars.
  • Under such steam and pressure, sand reacts with calcium hydroxide to form calcium silicate hydrate, which gives high strength to the AAC block.
  • Then, curing is done and removed AAC block is ready for use in the construction site.

Advantage of AAC Block

  • Due to lightweight, it
    • Save cost and energy in transportation
    • Save labor expenses
    • Increase the chance of survival during seismic activity
  • Lower Environmental Impact (Use of fly ash)
  • Improve thermal efficiency reduces the heating and cooling load in the building.
  • Increases workability, allows accurate cutting,
  • The generated solid waste can be reused.
  • Termite resistant (does not affected by termite like in timber)
  • Cost-effective
  • Earthquake resistant and design flexibility
  • Thermally insulated and Energy efficient
  • Fire-resistant and ecofriendly
  • The size of the AAC block is generally large which leads to faster masonry work.
  • Reduces a dead load of building on the foundation.

Disadvantage of AAC Block

  • Higher initial cost
  • Scarcity of manufacturing plants
  • Brittle nature, so handled and transported carefully.
  • Installation during rainy season leads to crack after installation.
  • For the partition wall, the thickness of the AAC block will be more. So, clay brick is preferred.

How to calculate a number of AAC blocks and the quantity of mortar in a wall?

I hope this article on “AAC blocks specifications” remains helpful for you.

Happy Learning – Civil Concept

Contributed By,

Civil Engineer – Sumit Paudel

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"Structural Engineer" with over 5 years of experience in estimation, structural design, and surveying. I am passionate about using my skills to create safe and sustainable structures. I am also a keen writer, and I enjoy sharing my knowledge and experiences with others.

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