AAC blocks are produced through a specific manufacturing process involving key raw materials that are mixed, aerated, and then cured under high pressure and temperature.
The creation of Autoclaved Aerated Concrete (AAC) blocks begins by carefully combining several principal ingredients. AAC blocks are made from a mixture of sand, cement, lime, gypsum, water, and an aerating agent. This precise blend forms the basis of the material's unique properties.
The Mixing and Aeration Process
- Ingredient Combination: The raw materials – sand (often finely ground), cement, lime, gypsum, and water – are accurately measured and mixed into a slurry.
- Aerating Agent Addition: The crucial step for achieving the lightweight, porous structure is the addition of an aerating agent. The aerating agent is typically aluminium powder or paste.
- Gas Production: This agent reacts with the other ingredients, specifically the alkaline components like lime and cement, to release hydrogen gas.
- Expansion and Foaming: This gas expands and forms bubbles within the mixture, resulting in a foam-like substance. This process significantly increases the volume of the mixture and creates millions of tiny air pores throughout.
Setting and Curing
After the mixture has expanded in molds to form 'cakes' of the desired size, it undergoes initial setting. The semi-solid cakes are then cut into block or panel sizes using wires.
The final and critical stage is autoclaving. The cut blocks are placed in an autoclave, a large pressure vessel. Here, they are cured under high-pressure steam and elevated temperatures (typically around 190°C or 375°F and 8-12 bars of pressure) for several hours. This autoclaving process:
- Accelerates the hardening of the material.
- Creates the stable, crystalline structure (primarily calcium silicate hydrates) that gives AAC its strength and durability.
- Ensures dimensional stability.
This combination of specific ingredients, chemical aeration, and high-pressure steam curing is what distinguishes AAC blocks and gives them their characteristic lightness, thermal insulation properties, fire resistance, and strength.
