Table of Contents
AAC stands for Autoclaved aerated concrete. It may be defined as a lightweight, precast, foam concrete building material appropriate for making concrete masonry unit-like blocks.
AAC blocks are made of quartz sand, calcined gypsum, lime, cement, water, and aluminum powder. AAC products are cured on heat and pressure in an autoclave.
1. Materials Used
The materials that are used in the preparation of AAC blocks are as follows:
1. Cement
The best cement for the preparation of AAC blocks is OPC grade 53 which sets and hardens and can hook other materials jointly.
2. Fly Ash
Fly ash is a waste industrial product utilized for the deduction of construction costs. The density of fly ash varies from 400-1800 kg/m3. It delivers thermal insulation, fire resistance, and sound absorption.
The type of fly ash utilized in Class C which includes 20% lime (CaO) and loss of ignition not be more than 6%.
3. Limestone
Limestone is obtained either by crushing to fine powder at the AAC factory or by directly purchasing it in powder form from a merchant.
4. Aluminum Powder
Aluminum work as an expansion agent. When the raw material act with aluminum powder, the air bubble is raised due to the reaction between calcium hydroxide, aluminum, and water, and hydrogen gas is discharged.
2. Manufacturing Steps
The manufacturing steps of AAC blocks are as follows:
a. Preparation of raw materials.
b. Mixing Raw Materials
The ratio at which AAC blocks are prepared:
Fly Ash/Sand : Lime : Cement : Gypsum = 69 : 20 : 8 : 3
Aluminum is about 0.08% of total dry materials in the mix and the water ratio is 0.6 – 0.65.
c. Molding, Casting, Rising & Curing
d. Demoulding and Cutting
3. AAC Block Price
Factories of autoclaved aerated concrete prepare blocks varying in various sizes and strengths. So, the price also changes according to manufacturer, size, and strength.
The AAC block price for a rectangular AAC block of size (length X height X weight) of 60 cm x 20 cm x 25 cm can vary between Rs 2,000 and Rs 3,500 per cubic meter in the market.
4. Features of AAC Block
| Colour | Greyish-white |
| Lightweight | 50% lighter than red bricks |
| Fire resistance | Between two and six hours, based on the thickness |
| Energy efficiency | 25% reduction in air-conditioning costs |
| Thermal efficiency | Three times higher than clay bricks |
| Water absorption | About 10% of its weight |
| Sound insulation | 42 dB (approximately) |
| Affordable cost | Nearly one-third of the cost of regular bricks |
5. Uses Of AAC Blocks
The uses of AAC blocks are as follows:
a. Used in construction of apartments, industrial and commercial buildings.
b. Used in the construction of Internal and External walls.
c. Used where construction budget is low.
d. Used in Schools, hotels, and offices due to its excellent heat-insulating properties.
6. Properties Of AAC Blocks & Clay Brick
| 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/mm 2 | 3 – 4.5 (IS 2185 part 3) | 2.5 to 3.5 |
| Normal Dry Density | Kg / m 3 | 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 the block) | – |
7. Difference Between AAC Blocks and Clay Brick
The difference between AAC Blocks and Clay Brick is mentioned below:
| AAC Block | Clay Bricks | |
| Structural Cost | Cheap | Costly |
| Cement Mortar for Plaster & Masonry | Need less due to flat, even surfaces & less number of joints | Requires more due to irregular surface and more number of joints. |
| Breakage | Less than 5% | Average 10 to 12 % |
| Construction speed | Speedy construction due to its big size, lightweight & easy to cut in any size or shape | Comparatively slow |
| Quality | Uniform & Consistent | Normally varies |
| Fitting & Chasing | All kinds of fitting and chasing possible | All kinds of fitting and chasing possible |
| Carpet Area | More due to less thickness of walling material | Comparatively low |
| Availability | Anytime | Shortage in monsoon |
| Energy Saving | Approx. 30% reduction in air-conditioned load | No such saving |
| Chemical Composition | Sand/Flyash used around 60 – 70 % which reacts with Lime & Cement to form AAC | Soil is used which contains many inorganic impurities like sulphates etc. resulting in efflorescence |
8. Advantages of AAC Blocks
The advantages of AAC blocks are as follows:
1. Eco-Friendly and Sustainable
The usage of recycled industrial waste (fly ash), non-toxic ingredients, no emitting gases, and lesser energy consumption results in the ACC Blocks being eco-friendly and sustainable.
2. Lightweight
The bricks are 3 to 4 times heavier than the AAC blocks. The AAC blocks are 30% lighter than that of concrete which assists in decreasing the dead load of the building, thereby authorizing the construction of more elevated buildings.
3. Thermally Insulated & Energy Efficient
Little air voids and the thermal mass of blocks give outstanding thermal insulation, thus decreasing the heating and air conditioning expenses of a building.
4. Fire Resistant
It is non-combustible and can withstand fire up to 1600° C which can resist up to 6 hours of direct exposure.
5. Acoustic Performance
As the AAC block is permeable, the sound absorption quality is outstanding. It delivers sound attenuation of about 42 dB, stopping out all significant sounds and noise which makes it perfect for schools, hospitals, hotels, offices, multi-family housing, and other structures that need acoustic insulation.
6. Easy Workability and Design Flexibility
AAC blocks can be smoothly cut, drilled, nailed, milled, and grooved to suit individual necessities.
7. Seismic Resistant
Lightweight blocks decrease the mass of a design, thus reducing the influence of an earthquake on a building. Non-combustible nature delivers a benefit against fires, which are normally attended by earthquakes.
8. Faster Construction
The preparation of AAC Blocks decreases the construction time by 20%. As various sizes of blocks assist decrease the number of joints in wall masonry. The lighter weight of the blocks drives it easier and faster to move, place and complete the masonry.
9. Disadvantages of AAC Blocks
The disadvantages of AAC Blocks are as follows:
1. Building at the time of the rainy season results in concrete with bubbles that lead to a rupture after building, which can be bypassed by decreasing the strength of the mortar and providing the blocks are dry during and after building.
2. As the AAC Blocks are brittle, they need to be handled more carefully than clay bricks to avoid breakage.
3. The brittle nature of the blocks requires longer, thinner screws when fitting cabinets and wall hangings and wood-suitable drill bits or hammering in.
4. Insulation necessities in more recent building codes of northern European countries would need very thick walls when utilizing AAC independently. Thus multiple builders prefer to utilize traditional building methods establishing an additional layer of insulation around the whole building.
| Read Also: Hollow Blocks |
