AAC Blocks manufacturing process

AAC Blocks manufacturing process follows Mixing, dosing, Casting, Rising, pre-curing, Demolding, cutting, steam Curing, and transporting.

In this way blocks are prepared and transported.

Introduction

Autoclave Aerated Concrete (AAC)

It is a form of cellular concrete and low-density cementitious product of calcium silicate hydrates in which the low density is obtained by the formation of microscopic air bubbles, mainly due to chemical reaction formed inside the liquid mass.

The air bubbles are uniformly distributed and are retained in the matrix on the setting, hardening, and subsequent curing with high-pressure steam in an autoclave to produce a homogeneous structure of macroscopic voids or cells.

Key points:

• AAC was first commercially produced in the year 1923
• It was introduced by a Swedish scientist.
• IS codebook for AAC: IS 2185-3 (1984)

AAC Blocks manufacturing process

Flow chart for Autoclaved Aerated Concrete production, i.e AAC blocks manufacturing process:

Step-1: Preparation of raw materials

Raw materials or Ingredients for AAC blocks manufacturing process are cement, sand, lime, fly ash, Gypsum, and Aluminum.

Raw material preparation is an important part of any manufacturing process.

Cement-53-grade Ordinary Portland Cement (OPC) from
the manufacturer is required for manufacturing AAC Blocks.

Fly ash or sand: Fly ash is mixed with water to form fly ash
slurry. The slurry thus formed is mixed with other ingredients
like lime powder, cement, gypsum, and Aluminum powder
in proportionate quality to form blocks.

Limestone powder: Lime powder required for AAC
production is acquired by crushing limestone to fine
powder at AAC factory or purchasing it directly from other companies.

Gypsum: Gypsum is readily available in the market.

Step-2: Mixing and dosing

Some Limitations are:

• FLY ASH OR SAND : LIME:CEMENT: GYPSUM = 69:20:8:3,
• Aluminum is mixed about 0.08% of total dry materials in the mix,
• water ratio = 0.60 – 0.6

The cycle of mixing and pouring is 5.5 minutes and first all the
ingredients are poured into different containers according to mix
proportions.

Then control system pours into a mixing drum and once the mixture
is ready to set then using the dosing unit, concrete is poured into
molds.

For AAC blocks manufacturing process, entire dosing and mixing operation
is completely automated and requires minimum human
intervention.

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Step-3: Casting, Rising, Pre-curing, demolding, and cutting

Based on installation capacity molds size is fixed and generally it will be 4.2m x 1.2m x 0.65m in size

While slurry is mixed and poured into greased molds, Aluminum
reacts with Calcium Hydroxide and water and releases hydrogen gas.

chemical reaction ( 2Al + 3Ca(OH)2 + 6H2O → 3CaO.Al2O3.6H2O + 3 H2 )

This leads to the formation of tiny cells causing the slurry mix to expand and it takes about 1-2hrs. This is known as the pre-curing process. Such expansion may be thrice its original volume.

After rising and getting enough strength to withstand its own weight then Demolding and cutting is done with required dimensions

Step-4: Curing and transporting

Using Autoclave AAC is cured–a large pressure vessel An autoclave is normally a steel tube of 3m diameter and 45 meters long.

Steam is fed into the autoclaved at high pressure, typically reaching a pressure of 800kPa to 1200 KPa and a temperature of 180°C for at least 5hrs.

Properties of blocks mainly depend on steam curing and raw material proportions.

When the blocks attain required properties are stored in
an area and transported.

Dimensions and Applications of the block

Based on thickness different sizes are available in the market;

• 4 Inch
• 6 Inch
• 8 Inch
• 9 Inch

Applications: These blocks are used in residential and commercial buildings also institutional. A special application of AAC such as firewalls and soundproof walls

Advantages