Introduction
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
- Cement The suitable cement for AAC block manufacture is OPC grade 53, which sets and hardens effectively, binding other materials together.
- 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.
- Limestone Limestone is either crushed to a fine powder at the AAC factory or purchased in powdered form.
- 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
| Property | Units | AAC Block | Clay Brick |
|---|---|---|---|
| Size | mm | 600 x 200 x (75 to 300) | 230 x 75 x 115 |
| Size Tolerance | mm | ± 1.5 | ± 05 to 15 |
| Compressive Strength | N/mm² | 3 – 4.5 (IS 2185 part 3) | 2.5 to 3.5 |
| Normal Dry Density | Kg/m³ | 550 – 650 | 1800 |
| Sound Reduction Index | Db | 45 for 200 mm Thick Wall | 50 for 230 mm Thick Wall |
| Fire Resistance | Hrs. | 2 to 6 (Depending on Thickness) | 2 |
| Thermal Conductivity “K” | W/m-K | 0.16 – 0.18 | 0.81 |
| Drying Shrinkage | % | 0.04% (Size of block) | – |
Comparison between AAC Blocks and Clay Brick
Parameter Comparison
| Parameter | AAC Block | Clay Bricks |
|---|---|---|
| Structural Cost | Steel Saving Upto 15% | No Saving |
| Cement Mortar | Requires less due to flat surfaces & fewer joints | Requires more due to irregular surfaces & more joints |
| Breakage | Less than 5% | Average 10 to 12% |
| Construction Speed | Speedy construction due to size & weight | Comparatively slower |
| Quality | Uniform & Consistent | Varies |
| Fitting & Chasing | All kinds of fitting and chasing possible | All kinds of fitting and chasing possible |
| Carpet Area | More due to less wall thickness | Comparatively lower |
| Availability | Anytime | Shortage in monsoon |
| Energy Saving | Approx. 30% reduction in air-conditioned load | No such saving |
| Chemical Composition | Uses sand/fly ash with lime & cement | Soil used with inorganic impurities |
Advantages of AAC Blocks
- 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.
- Lightweight Being 3 to 4 times lighter than bricks, AAC blocks reduce the dead load of buildings, allowing for taller constructions.
- Thermally Insulated & Energy Efficient Tiny air pores and thermal mass provide excellent insulation, reducing heating and cooling costs.
- Fire Resistant AAC blocks are non-combustible and can withstand high temperatures, making them fire-resistant.
- Acoustic Performance Their porous nature offers superior sound absorption, making AAC ideal for sound-sensitive environments.
- Easy Workability and Design Flexibility AAC blocks are easy to cut, drill, and shape, providing design flexibility.
- Seismic Resistant The lightweight nature of AAC reduces the impact of earthquakes, enhancing structural safety.
- Faster Construction AAC blocks reduce construction time by 20% due to their size and ease of handling.
Disadvantages of AAC Blocks
- Installation in Rainy Weather AAC blocks can crack during installation in rainy weather, but this can be mitigated with appropriate mortar and block drying.
- Brittle Nature They are more brittle than clay bricks, requiring careful handling to prevent breakage.
- Special Fasteners Longer, thinner screws and wood-compatible drill bits are needed for fittings due to AAC’s brittle nature.
- 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.