Autoclaved Aerated Concrete blocks also known as AAC blocks have emerged as a revolutionary building material in the construction industry, offering a sustainable and efficient alternative to traditional construction methods. With their lightweight, thermal insulation, and environmental benefits, AAC blocks have gained widespread acceptance across the globe. This article explores the characteristics, manufacturing process, advantages, and applications of AAC blocks, highlighting their significance in modern construction.
What is an Autoclaved Aerated Concrete Block?
Autoclaved Aerated Concrete (AAC) blocks are precast concrete blocks which are light in weight and suitable for concrete masonry units. The block is also lightest among other masonry units such as clay bricks, cement concrete bricks and stones.
AAC Block Size
The nominal dimensions of the block as per IS 2185-3 (1984) shall be as follows:
| Length (mm) | 400, 500 or 600 |
| Width (mm) | 100, 150, 200 or 250 |
| Height (mm) | 200, 250 or 300 |
The maximum tolerance for the block is +/-5mm in length and +/-3mm in width and height.
Materials for AAC Block Production
AAC is created by a unique manufacturing process that involves the use of natural raw materials and aeration. The key components of AAC typically include sand, cement, lime, and aluminium powder. The process involves a chemical reaction that creates hydrogen gas, which, in turn, expands the mixture to form a porous and lightweight structure.
The materials used for producing autoclaved blocks as per IS 2185-3 (1984) are as follows: –
- Cement: – Ordinary Portland cement and Low Heat Portland cement are suitable for AAC block production.
- Fly ash: – The use of fly ash is limited to 20% in cement.
- Lime: – The lime used shall be confined to class C specifications.
- Aggregate: – The fine aggregate shall contain 80 per cent of silica.
- Water: – The water good for consumption shall be used for mixing materials for AAC block production.
- Additive or Admixture: – The additive and admixture use shall be confined to IS 2185-3 (1984).
Also, read: Ordinary Portland Cement: Properties, Composition, Manufacturing And Uses
Classification of AAC Block
The autoclaved cellular concrete blocks shall be classified into two grades as per the compressive strength of the block as suggested by IS2185-1984.
| Density In Oven Dry Condition (kg/m3 ) | Minimum Compressive Strength (N/mm2 ) | Thermal Conductivity In Air Dry Condition (W/m-k) | |
|---|---|---|---|
| Grade-1 | Grade-2 | ||
| 451-550 | 2.00 | 1.5 | 0.21 |
| 551-650 | 4.00 | 3.00 | 0.24 |
| 651-750 | 5.00 | 4.00 | 0.30 |
| 751-850 | 6.00 | 5.00 | 0.37 |
| 851-1000 | 7.00 | 6.00 | 0.42 |
Also, read: Comparison of Brick Masonry and Stone Masonry
Manufacturing Process of AAC blocks
The manufacturing process of AAC blocks typically follows these steps:
- Mixing: Sand, cement, lime, and aluminium powder are mixed together to create a slurry.
- Pouring: The slurry is poured into moulds of various sizes and shapes. This step allows the mixture to take the form of the desired AAC block.
- Rising: Aluminum powder reacts with calcium hydroxide and water to produce hydrogen gas. This gas causes the slurry to rise and expand, creating a porous structure within the material.
- Curing: The formed blocks are then subjected to high-pressure steam curing in autoclaves. This process enhances the physical and chemical properties of the material, contributing to its strength and durability.
Advantages Of AAC
The advantages of using autoclaved cellular concrete blocks are as follows: –
- Light Weight: -These blocks are light in weight due to the aerated air in them. The advantages of being lightweight can contribute to the reduced cost of concrete frame design and the weight of the structure.
- Sound Proof: -It is a very good sound insulation building material. Due to its porous nature, the sound absorption quality is superior to another block and has a sound attenuation of 42 dB. That is why this block is ideal for schools, hospitals, hotels, offices, multi-family housing and other structures which required soundproofing.
- Infill Material: – The block can be used as an infill material for both load-bearing and non-load-bearing structures. For use in partition and panel walls, inner leaf of cavity walls or as backing to a brick masonry wall.
- Fast Construction: – Due to the large size and true to its dimension and shape, the construction work is rapid. Therefore, more walls are laid per man-hour compared to other wall construction.
- Cost Saving: – There are cost savings by using such blocks in multiple ways. One of the cost savings can be seen through its larger size advantage. Due to the large size, a lesser number of blocks fill the wall and mortar joints are reduced. This reduces the cost of labour, mortar and the number of blocks itself.
- Attractive Appearance: -Because of its appealing appearance which can blend perfectly with any materials used for the construction of buildings.
Also, read: What are Refractory Bricks? | Fire Brick | Firebrick
Disadvantages of AAC Block
- Brittle nature: – As this block is brittle in nature, care should be considered during handling, transporting and laying. Due to its brittle nature, hammering and nailing to such a block wall is not advisable. For fixing cabinets and another wall hanger it requires longer, thinner screws which imply to hanger cost.
- Installation of AAC block during rainy weather is known to crack after installation.
Comparison between AAC Blocks and Clay Brick
| Parameter | AAC Block | Clay/Red Brick Bricks |
|---|---|---|
| Speedy construction due to its big size, light weight & ease of cutting in any size or shape | Cost savings for steel up to 15% | No Saving |
| Breakage | Less than 5% | Average 10 to 12 % |
| Construction speed | Speedy construction due to its big size, light weight & ease to cut in any size or shape | Comparatively slow |
| Size (LXBXH) | 600cmX20cmX10-30cm | 19cmX9cmx9cm(Standard size) 20cmX10cmX10cm(Nominal size) |
| Compressive Strength | 35-40kN/m2 | 25-30kN/m2 |
| Mortar consumption in cum of 1:6 | 0.5bag if cement | 1.35bag of cement |
| Finishing adaptation | All kinds of finishing can be adopted | Same as the AAC block |
| Fire Resistance | 2-6 hours depending on the thickness | 2hours |
Also, read: Comparison Between AAC and Fly Ash Blocks: 10 Points of Comparison
FAQs
Q: What are AAC blocks?
A: AAC blocks, or Autoclaved Aerated Concrete blocks, are lightweight, precast building blocks made of cement, lime, sand, gypsum, and aluminium powder. They are produced in different sizes and densities and have a cellular structure with millions of tiny air pockets, which gives them excellent thermal insulation properties.
Q: What are the binding materials for AAC blocks?
A: Binding materials used for AAC blocks are traditional cement mortar and AAC adhesive only. However, cement mortar for the AAC block should be used as a thin layer. It is advisable to use pre-mix AAC adhesive to lay AAC blocks due to cost efficiency and high adhesive strength.
Q: What is the curing period of AAC blocks?
AAC blocks and their adhesive do not need curing. All you get is time for carrying out other work. It achieves its strength immediately after it is set and no curing is needed. It takes 3-4 hours for the adhesive or mortar to set after laying.
High-pressure steam curing is done on AAC blocks in the factory.
Q: What is the alternative to AAC blocks?
There are many alternatives to AAC blocks if necessary or required at the site. However, the advantages of AAC blocks will overcome the need for alternative or substitute AAC blocks. ACC block has very good sound and fire resistance properties. Light in weight and larger in size which reduces the construction period in general. Effective in laying and providing good workability.
Nevertheless, Fly Ash bricks, CLC bricks, and Hollow bricks can be used as alternatives to AAC blocks.
Q: How are AAC blocks made?
A: AAC blocks are made through a process called autoclaving, which involves mixing the raw materials and pouring them into moulds. The mixture is then allowed to cure and harden before being cut into blocks of the desired size. The blocks are then placed in an autoclave, where they are subjected to high pressure and temperature, which causes the aluminium powder to react and release gas, creating the cellular structure of the blocks.
Q: What sizes and shapes do AAC blocks come in?
A: AAC blocks come in a variety of sizes and shapes to meet different construction needs. Standard sizes include 600mm x 200mm x 100mm, 600mm x 200mm x 150mm, and 600mm x 200mm x 200mm. Custom sizes can also be made. The blocks can be cut into different shapes and angles to fit specific building designs.
