Disadvantages Autoclaved Aerated Concrete (AAC) Blocks

Civil Engicon Team
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Update: May 29, 2024

What is Full Form of AAC Block?

Full form of AAC block is "Autoclave Aerated Concrete Block", it is lightweight, precast, eco-friendly, cellular concrete building material made with fine aggregates, cement, and an expansion agent that causes the fresh mixture to rise like yeast in bread dough. It contains closed air pockets inside that makes it three times lighter than traditional red bricks. Also, it is known for load-bearing capabilities, high insulation properties, and durability.

Disadvantages of AAC (Autoclaved Aerated Concrete) Blocks

Autoclaved Aerated Concrete (AAC) is a lightweight, precast building material which is also known as foam concrete. It is made from natural raw materials including sand (or fly ash), lime, cement, water, and a small amount of aluminum powder. These materials are mixed to form a slurry, which is then poured into molds. The aluminum powder reacts with the lime and cement, causing the mixture to expand and form gas bubbles, creating a highly porous structure.

Autoclaved Aerated Concrete (AAC) Blocks: Disadvantages

How AAC Concrete (AAC) Blocks are Made?

Raw materials including sand (or fly ash), lime, cement, water, and a small amount of aluminum powder are mixed together to form a slurry. Then, the slurry is poured into large molds. The aluminum powder reacts with the lime and cement, releasing hydrogen gas and causing the slurry to expand and form millions of tiny air bubbles. 
The mixture is allowed to set and partially harden in the molds, forming a "green cake." The green cake is removed from the molds and cut into blocks or panels of the desired size using steel wires or a cutting machine. The cut blocks are placed in an autoclave- it is a large, pressurized steam chamber. Here, they are subjected to high temperatures (around 180-200°C) and pressure (approximately 12 bar) for several hours. This process gives AAC its final strength and dimensional stability. After autoclaving, the blocks are cooled, inspected for quality, and then packaged for shipment.
The result is a strong, durable, and thermally efficient building material that is also fire-resistant and soundproof. AAC blocks and panels are commonly used in construction for walls, floors, and roofs. Its lightweight nature reduces the structural load on buildings, and its insulating properties can lead to energy savings in heating and cooling.

Types of Autoclaved Aerated Concrete (AAC) Blocks

Autoclaved Aerated Concrete (AAC) blocks come in various types, each designed for specific construction needs. Here are the main types:

Standard Blocks:
Description: Typically rectangular and used for general construction purposes.
Sizes: Common sizes include 600x200x100 mm, 600x200x150 mm, etc.
Uses: Suitable for load-bearing and non-load-bearing walls in residential and commercial buildings.

Reinforced Blocks:
Description: Contain steel reinforcements for added strength.
Sizes: Larger and heavier than standard blocks.
Uses: Ideal for applications requiring additional structural support, such as beams, lintels, and other load-bearing elements.

High-Strength Blocks:
Description: Higher density and compressive strength compared to standard blocks.
Sizes: Various sizes similar to standard blocks but with enhanced properties.
Uses: Suitable for high-load applications, including multi-story buildings and industrial structures.

Cladding Panels:
Description: Larger, thinner panels designed for exterior cladding.
Sizes: Can vary significantly, often custom-sized to fit specific projects.
Uses: Used for exterior wall cladding, providing insulation and a decorative finish.

Partition Blocks:
Description: Thinner than standard blocks, designed for internal partitions.
Sizes: Typically around 600x200x75 mm or similar.
Uses: Ideal for non-load-bearing interior partition walls.

Floor and Roof Panels:
Description: Reinforced panels designed to bear loads as floors and roofs.
Sizes: Larger sizes tailored to span significant distances.
Uses: Used in constructing floors and roofs, offering both structural support and insulation.

U-Blocks (also known as Lintel Blocks):
Description: U-shaped blocks used to form lintels and beams.
Sizes: Sized to fit standard wall dimensions.
Uses: Provide structural support over openings such as doors and windows.

Eco-Friendly Blocks:
Description: Manufactured with sustainable materials and processes.
Sizes: Similar to standard blocks but with a focus on environmental impact.
Uses: Preferred in green building projects for their reduced environmental footprint.

Each type of AAC block offers unique benefits, making them versatile for various construction applications while maintaining the lightweight, insulating, and fire-resistant properties characteristic of AAC materials.

Disadvantages of Autoclaved Aerated Concrete (AAC) Blocks

Autoclaved Aerated Concrete (AAC) blocks have many advantages, they also have some disadvantages given below-

AAC blocks can be more brittle than traditional concrete, making them susceptible to cracking and damage if not handled properly.

Limited Load-Bearing Capacity: 
While AAC blocks are strong, they may not be suitable for very high load-bearing applications compared to traditional concrete or bricks.

Water Absorption:
AAC blocks can absorb moisture, which can lead to issues such as reduced strength and thermal insulation properties if not properly sealed or coated.

Higher Initial Cost:
The initial cost of AAC blocks can be higher than that of traditional concrete blocks or bricks, although this may be offset by savings in energy and labor costs over time.

Specialized Labor Required:
Working with AAC blocks may require specialized skills and knowledge, which can limit their use in areas where such expertise is not readily available.

Limited Availability:
In some regions, AAC blocks may not be as widely available as traditional building materials, leading to potential supply issues.

Anchoring and Fixing:
Special considerations are needed for anchoring and fixing items to AAC walls due to their porous nature, which might require specific types of fasteners or adhesives.

Thermal Movement:
AAC blocks can exhibit thermal movement, necessitating proper control joints and considerations in design to accommodate expansion and contraction.

Advantages of Autoclaved Aerated Concrete (AAC) Blocks

Autoclaved Aerated Concrete (AAC) blocks offer several advantages given below. These advantages make AAC blocks a popular choice in modern construction for both residential and commercial buildings.

AAC blocks are about three times lighter than traditional red bricks, reducing the structural load on buildings and making them easier to handle and transport.

High Insulation:
Excellent thermal insulation properties help maintain consistent indoor temperatures, leading to energy savings in heating and cooling.

Fire Resistance:
AAC blocks are highly fire-resistant, providing enhanced safety and protection in case of a fire.

Sound Insulation:
The porous structure of AAC blocks offers good sound insulation, reducing noise transmission between rooms and from external sources.

Made from natural, non-toxic materials and producing less waste during manufacturing, AAC blocks are considered a green building material.

AAC blocks are resistant to pests, mold, and mildew, and they do not rot, ensuring long-lasting performance.
Precision and Uniformity:
Manufactured to precise dimensions, AAC blocks ensure consistent quality and minimal need for on-site adjustments, leading to faster construction times.

Ease of Installation:
The lightweight nature and larger size of AAC blocks compared to traditional bricks allow for quicker and easier installation, reducing labor costs and construction time.

AAC blocks can be easily cut, drilled, and shaped with standard tools, allowing for flexible and creative design options.

Energy Efficiency:
The combination of thermal insulation and reduced thermal bridging contributes to lower energy consumption for heating and cooling, enhancing overall building efficiency.


What is AAC Block?

AAC is a certified green building material known for its lightweight, load-bearing capabilities, high insulation properties, and durability. It is also three times lighter than traditional red bricks, making it an excellent choice for environmentally friendly construction.

What is Size of AAC Block?

Size of AAC block is 600 mm x 200 mm x (75 to 300) mm with ±1.5 mm tolerance, its normal density is 550 – 650 kg per meter cube. 

One AAC Block Equal to How Many Bricks?

By volume, one AAC block is equal to approx 7 clay bricks.

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