The Advantages, Manufacturing, and Technical Specifications of AAC Blocks


Autoclaved Aerated Concrete (AAC) is a certified green building material known for its eco-friendliness and exceptional properties. Developed in 1924 by a Swedish architect, AAC offers numerous advantages over traditional construction materials like clay bricks. In this blog post, we’ll examine the manufacturing process, technical specifications, and a detailed comparison between AAC blocks and clay bricks. Let’s explore why AAC blocks have gained popularity in the construction industry.

Manufacturing Process of AAC Blocks

Materials Used

  1. Cement The suitable cement for AAC block manufacture is OPC grade 53, which sets and hardens effectively, binding other materials together.
  2. Fly Ash Fly ash, an industrial waste product, is utilized to reduce construction costs. It provides thermal insulation, fire resistance, and sound absorption. Class C fly ash with 20% lime content is preferred.
  3. Limestone Limestone is either crushed to a fine powder at the AAC factory or purchased in powdered form.
  4. Aluminum Powder Aluminum serves as an expansion agent, creating air bubbles during the reaction between calcium hydroxide, aluminum, and water, resulting in hydrogen gas release.

The Manufacturing Process

Step 1: Raw Material Preparation

Raw material preparation involves mixing fly ash with water to create a slurry, which is then mixed with cement, gypsum, and aluminum powder in the right proportions.

Step 2: Dosing and Mixing

Precise dosing and mixing are crucial for product quality. The ratio for AAC block manufacture is Fly Ash/Sand:Lime:Cement:Gypsum = 69:20:8:3, with a small percentage of aluminum and specific water ratios.

Step 3: Casting, Rising, and Curing

  • Molds of various sizes are used.
  • A thin layer of oil is applied to molds to prevent sticking.
  • Aluminum reacts, causing expansion and the formation of tiny cells, ensuring lightweight and insulating properties.
  • The curing process involves autoclaving in a high-pressure vessel.

Step 4: Demoulding and Cutting

Once the blocks reach cutting strength, they are demolded and cut according to requirements. Common AAC block sizes are 600 x 200 x 100, 600 x 200 x 150, and 600 x 200 x 200.

Technical Specification of AAC Blocks and Clay Bricks

Property Comparison

PropertyUnitsAAC BlockClay Brick
Sizemm600 x 200 x (75 to 300)230 x 75 x 115
Size Tolerancemm± 1.5± 05 to 15
Compressive StrengthN/mm²3 – 4.5 (IS 2185 part 3)2.5 to 3.5
Normal Dry DensityKg/m³550 – 6501800
Sound Reduction IndexDb45 for 200 mm Thick Wall50 for 230 mm Thick Wall
Fire ResistanceHrs.2 to 6 (Depending on Thickness)2
Thermal Conductivity “K”W/m-K0.16 – 0.180.81
Drying Shrinkage%0.04% (Size of block)

Comparison between AAC Blocks and Clay Brick

Parameter Comparison

ParameterAAC BlockClay Bricks
Structural CostSteel Saving Upto 15%No Saving
Cement MortarRequires less due to flat surfaces & fewer jointsRequires more due to irregular surfaces & more joints
BreakageLess than 5%Average 10 to 12%
Construction SpeedSpeedy construction due to size & weightComparatively slower
QualityUniform & ConsistentVaries
Fitting & ChasingAll kinds of fitting and chasing possibleAll kinds of fitting and chasing possible
Carpet AreaMore due to less wall thicknessComparatively lower
AvailabilityAnytimeShortage in monsoon
Energy SavingApprox. 30% reduction in air-conditioned loadNo such saving
Chemical CompositionUses sand/fly ash with lime & cementSoil used with inorganic impurities

Advantages of AAC Blocks

  1. Eco-Friendly and Sustainable AAC blocks use recycled industrial waste, non-toxic ingredients, emit no harmful gases, and consume less energy, making them eco-friendly and sustainable.
  2. Lightweight Being 3 to 4 times lighter than bricks, AAC blocks reduce the dead load of buildings, allowing for taller constructions.
  3. Thermally Insulated & Energy Efficient Tiny air pores and thermal mass provide excellent insulation, reducing heating and cooling costs.
  4. Fire Resistant AAC blocks are non-combustible and can withstand high temperatures, making them fire-resistant.
  5. Acoustic Performance Their porous nature offers superior sound absorption, making AAC ideal for sound-sensitive environments.
  6. Easy Workability and Design Flexibility AAC blocks are easy to cut, drill, and shape, providing design flexibility.
  7. Seismic Resistant The lightweight nature of AAC reduces the impact of earthquakes, enhancing structural safety.
  8. Faster Construction AAC blocks reduce construction time by 20% due to their size and ease of handling.

Disadvantages of AAC Blocks

  1. Installation in Rainy Weather AAC blocks can crack during installation in rainy weather, but this can be mitigated with appropriate mortar and block drying.
  2. Brittle Nature They are more brittle than clay bricks, requiring careful handling to prevent breakage.
  3. Special Fasteners Longer, thinner screws and wood-compatible drill bits are needed for fittings due to AAC’s brittle nature.
  4. Insulation Requirements In some regions, additional insulation may be required to meet newer building code standards, increasing construction costs.

In conclusion, AAC blocks offer a compelling alternative to traditional construction materials, with their eco-friendliness, superior properties, and numerous advantages making them a popular choice in the construction industry. Despite some disadvantages, their positive attributes make them a worthy consideration for sustainable and efficient building projects.

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