AAC Blocks: A Cost-effective & Sustainable Alternative to Traditional Clay Bricks

Table of Content:

1. AAC Block
2. AAC Block Bricks: Features
3. AAC Bricks: Arrangement
4. AAC Block Construction: Shape
5. AAC Concrete Block: Advantages
6. AAC Lightweight Block: Disadvantages
7. Installation AAC Block: Finishing
8. Comparison of AAC Blocks: Red Bricks and CLC Blocks

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In modern times, there is a high emphasis on using recyclable or environment-friendly materials. The construction industry is doing its bit by increasing the usage of eco-friendly materials that not only reduce carbon footprint but also save on construction costs. Autoclaved Aerated Concrete (AAC) blocks are superior to conventionally-used pollution-causing materials like burnt clay bricks.

Due to its affordability and sustainability, AAC is widely used in the construction segment in India. In this article, we will go in-depth into AAC blocks and the pros and cons of using them in housing construction.

What are AAC Blocks?

Invented in the 1920s by Swedish inventors Dr. John Axel Eriksson and Prof Henrik Kreuger, AAC blocks are one of the most environment-friendly and lightweight construction materials. They are foam concrete, precast, and sustainable construction material made from calcined gypsum, lime, quartz sand, Portland cement, aluminum powder, and water. Post molding and mixing, the concrete is autoclaved under pressure and heat which provides it with its distinctive properties. Owing to their high strength, thermal insulation, and load-bearing properties, AAC bricks are in high demand. They are used as construction materials for exterior and interior structures. These blocks may be coated with sliding materials (like vinyl siding or veneer brick) or a stucco finish.

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Features of AAC Blocks

1. Lightweight: AAC block weight is 50% lighter than the red clay bricks

2. Fire resistant: Depending on thickness, 2-6 hours

3. Colour: Greyish white

4. Thermal efficiency: Three times greater than red clay bricks

5. Energy efficiency: 25% reduction in air-conditioning costs

6. Water absorption: ~10% of its weight

7. Affordability: Nearly 1/3 the cost of regular bricks

8. Sound insulation: ~42 dB

9. Pricing: Varies based on its manufacturer, size, and strength, ranging from INR 2,000 to INR 3,500 for rectangular AAC blocks of dimensions 60cm X 20cm X 25cm.

Arrangement of AAC Blocks

AAC is available as:

• Blocks: Arranged as stacks manually in a similar manner as in conventional masonry.

• Panels:  Vertically arranged like a thin-layered mortar. AAC panels are placed using cranes due to their large size. For structural purposes, reinforced cells, grouts, and beams are included within the section of the wall

The Shape of AAC Blocks

• Lintel blocks (or U-shaped bond beam): Available in thicknesses of 8, 10, and 12 inches.

• Cored blocks: Used in building vertical reinforced grout cells.

• Tongue-and-groove: AAC blocks or slabs are available in larger sizes. These blocks are linked to adjacent units without the use of mortar at the vertical edges.

Advantages of AAC Blocks

Below are the advantages of using AAC blocks:

• Faster Construction and Better Workability: Being 50% lighter and 10 times larger than traditional bricks, AAC blocks facilitate easier installation by giving desired flexibility that enables making adjustments, shaping, and cutting very easily. As they have consistent dimensions and fewer joints, it enables easy laying and makes the construction process faster. They are also comparatively easier to transport than traditional bricks, thereby helping save on shipping and logistics costs.

• Thermal Insulation and Energy Efficiency: As the materials contain small air pockets, with hydrogen being used to foam the concrete, it leads to excellent heat insulation properties. This allows the temperature to be cooler in summers and warmer in winters, thereby providing ~25% saving on air-conditioning costs. Production of AAC block bricks also involves less energy usage making them energy efficient across their lifecycle. Their excellent heat insulation capacity makes them an excellent choice for interior and exterior construction.

• Earthquake Resistant: AAC block construction gains a higher level of strength during its manufacturing process. This provides durability to the finished structure, making them capable of handling higher seismic loads than conventional bricks during earthquakes.

• Fire Resistant: Since AAC concrete block material is non-combustible with fire resistance of up to 6 hours (depending on thickness of block) and temperature resistance of 1,200 degrees Celsius, they are a better material for fire safety than conventional building materials.

• High Compressive Strength: of AAC block of 3 to 5 N/mm², making it stronger and better than conventional bricks of same density.

• Affordable and Sustainable: AAC block bricks are made from natural, non-toxic and biodegradable raw materials, with minimal wastage from their production process. Furthermore, some of the waste and offcuts generated can be used in aggregates or recycled. They are stable and durable, preventing mold or rot. AAC lightweight blocks are also economical as they are energy-efficient, and easy to install with minimal labour costs.

• Soundproof and Moisture-Proof: The porous and lightweight structure of AAC blocks enables high sound reduction, making them widely used in the construction of hospitals, hotels, schools, offices, studios etc. The macro-pores inside AAC blocks ensure low absorption of water, providing better moisture protection.

• Pest Resistant: Since AAC blocks are prepared from inorganic materials which helps in protecting these structures from pests like rodents, termites etc

Disadvantages of AAC Blocks

• Costing: While AAC are beneficial in terms of cost, durability and eco-friendliness, they are largely used in large scale high rise commercial, residential and infrastructure projects. However, when it comes to small-scale building projects, red bricks are still widely used. For small load-bearing structures, AAC is expensive as buying a small number of AAC blocks for these structures can be a lot costlier.

• Cracks in Wall: Precaution needs to be taken to eliminate drying shrinkage and stress concentration cracks.

• Installing During Rains: As AAC blocks can crack after installation in moist weather, care needs to be taken by reducing strength of the mortar and ensuring the blocks are dry during and post installation.

• Drilling vs Nailing: To fix furniture on AAC blocks, one needs to use a drill bit instead of nails.

• Brittle Nature: AAC needs to be handled more delicately than clay bricks to avoid breakage. They require longer, thinner screws when fitting cabinets, wall hangings, and wood-suitable drill bits. 

• Insulation Requirements: Newer building codes in some regions require very thick walls when clay bricks are used. Hence, many builders continue using traditional building materials and install an additional layer of insulation around the entire building.

Installation and Finishing of AAC Blocks

The process of Installing AAC blocks is similar to that of conventional concrete masonry. AAC panels are placed using cranes. Based on the finishing, the panels are either directly adhered (such as in masonry veneers) or attached mechanically to AAC’s surface. 

In terms of finishing, AAC blocks are available in stucco type finishes. The polymer-modified plaster provides sealing against the entry of water; however, it allows moisture vapo for breathability. Directly applied veneers are lightweight and can be built as cavity walls. Conventional siding materials are generally mechanically connected to the wall’s face. Furring strips must be used in cases where back ventilation of the siding material is required.

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Comparison of AAC Blocks Against Red Bricks and CLC Blocks

AAC vs Red Bricks: AAC blocks are 80% lighter, more environment- friendly and cheaper than conventional red clay bricks. AAC involves less usage of steel and cement, thereby reducing the cost. It also allows for better durability and improved thermal and sound insulation than red bricks.

AAC vs CLC Blocks: Cellular Lightweight Concrete (CLC) blocks are produced from CLC or foam concrete. They are made by combining cement and fly ash slurry with preformed foam. While CLC blocks are cheaper than AAC blocks, they have lesser compressive strength compared to AAC.

Conclusion

AAC is an innovative building material with unique properties that make it a better alternative to using traditional clay bricks and this is why its popularity is steadily growing in many Asian countries including India. Though the usage of AAC blocks in India is still in its nascent stages, it is one of the fastest growing building material segments, due to its increased demand for high rise commercial spaces and housing units in the country.