Fly Ash Bricks: An Eco-Friendly and Durable Building Material

What Is Fly Ash Bricks?

Fly ash bricks are a building component in civil engineering; mostly, they are masonry material. Generally, class C and class F-fly ash, sand/stone dust and water is the ingredient of fly ash bricks.

Fly ash bricks are also termed as ‘self-cementing’ bricks. Fly ash bricks are made of the recycled product, so it’s also an eco-friendly product. Sometimes cement is also added to it as a cementing material. Due to the uniform structure, it.

Advantages & Disadvantages of Fly Ash Bricks

The advantages and disadvantages of fly ash brick are as follows.

Advantages of Fly Ash Bricks

1. Strength of Fly Ash Bricks

As compare to regular fire clay bricks, fly ash bricks have greater compressive strength. The compressive strength of fly ash brick is near about 9-10N/mm2.

The thickness of those bricks are low, so it reduces cracks in plaster. It has a good earthquake resisting property. It increases the strength of the structure.

2. Durability of Fly Ash Bricks

These fly ash bricks are highly durable but less permeable. Due to lower permeability, it reduces the efflorescence effect on brick.

These bricks prevent dampness on the wall because it is less porous, and that’s why it does not absorb more water. It’s highly resistive against acid, water, and sulfate.

3. Appearance of Fly Ash Bricks

The key thing about these fly ash bricks is its appearance. Fly ash bricks are cement-like colour, smooth, even surface, and uniform finish.

Due to the smooth surface, the amount of plaster is reduced to 40% than common plastering. Plaster of Paris or putty can be applied directly on this. Those bricks are free from organic matter, pebbles, etc.

4. Thermal Property of Fly Ash Bricks

Fly ash bricks have an excellent thermal property because of the thermal conductivity of fly ash brick is 0.9-1.05 W/mm², so it absorbs minor heat. For this reason, the building is cool in the summer.

5. Sound Insulation of Fly Ash Bricks

Fly ash bricks have decent sound insulation property than ordinary bricks.

6. Fire Resistance of Fly Ash Bricks

Fly ash bricks are good in fire-resisting than regular fire clay bricks.

7. Sustainability of Fly Ash Bricks

The main ingredient of fly ash bricks is fly ash, and it comes from the thermal power plant. So, it doesn’t damage the environment again; that’s why it’s an environmentally friendly product.

8. Availability of Fly Ash Bricks

Those bricks are generally available near the thermal power station areas, but now days, it’s nearly available in all the places.

Disadvantages of Fly Ash Bricks

There are not so many disadvantages of fly ash bricks, but some are also there. Those are the following-

1. All fly ash bricks are not suitable for construction. It’s necessary to use high-quality fly ash bricks to resist harmful effects.
2. If the fly ash bricks are not appropriately prepared, then it has no strength and not suitable for construction.
3. These bricks are only available in modular size. Larger size bricks are not produced due to cracks.
4. Bonding is less due to a smooth finish; that’s why we need to care about when masonry work is running.
5. In plastering work, plaster doesn’t make a suitable bond with those bricks due to the smooth surface.
6. Fly ash bricks are not suitable in the winter area region.

Fly Ash Bricks Cost

Fly ash brick cost is not higher than ordinary fire clay bricks. The price cost of fly ash bricks are depended upon the following materials-

1. Cost of raw material
2. The proportion of raw material
3. Level of automation
4. Technology adopted
5. Cost of finance
6. Economic of scale

So, above those following points, the cost of fly ash bricks are varying from 8-10 rupees per piece where regular fire clay bricks price is near about 11-12 rupees per piece.

How to Make Fly Ash Bricks

The process of manufacturing fly ash bricks is mainly done by machine. The steps are following-

1. At first, add fly ash at an amount of 57-65%. Fly ash is the fundamental material of this type of bricks.
2. Then river sand or stone dust 18-27%. It acts as a filler material for fly ash bricks.
3. Hydrated lime 9-12%. This is the binding material of fly ash bricks.
4. Gypsum 5%, sometimes cement is also added with this mixture.
5. Then those above products are adequately mixed.
6. After that process, those bricks need compression. So, they are compressed at 28 MPa.
7. Next, it needs a curing process. It cured for 24 hours in a 66°C steam bath.
8. Then, the bricks are toughened with an air entrainment agent and last 100 freeze-thaw cycles.

So, this is the whole process of manufacturing fly ash bricks. It does not require great manpower; that’s why the cost of this product is low. The proportion of those materials are also correctly maintained because of the whole process is done by machine.

Compressive Strength of Fly Ash Bricks

1. As compared with normal fire clay bricks, fly ash bricks have more compressive strength.
2. When the fly ash bricks are constructed, then it got extreme pressure (near about 28 MPa).
3. Where the ordinary fire clay bricks have a compressive strength of 3.5 N/mm², the compressive strength of fly ash bricks is 10-12 N/mm².

Fly Ash Brick Size

1. Fly ash bricks are produced in various sizes, but usually, the available size in the marketplace is 230mm x 110mm x 70mm.
2. The weight of that particular size of brick is 6 kg. So, it reduces the dead load of the structure due to its lightweight.
3. Due to this type of compact uniform size and high compressive strength, there is no breakage in the transportation system.

Fly Ash Block Size

1. Fly ash block is the bigger version of fly ash brick. The same material produces it, and the same process is applied for preparing it.
2. The size of fly ash brick is 24in x 8in x 4in
3. These blocks are mainly used in the partition wall and the sidewall.
4. The cost of fly ash block is approximately 50 rupees per piece in India (but it varies in a different place)

So, we see that the fly ash brick is economical, and it’s decent to use for residential purposes as well as commercial purposes.

FAQs on Fly Ash Bricks

What are fly ash bricks?

Fly ash bricks are masonry materials made from fly ash, sand/stone dust, and water, sometimes with the addition of cement. They are known for being an eco-friendly product due to their use of recycled materials from thermal power plants.

What are the main ingredients of fly ash bricks?

The main ingredients are class C or class F fly ash, sand or stone dust, water, hydrated lime, and sometimes gypsum or cement.

What are the advantages of fly ash bricks?

1. Strength: Higher compressive strength (9-10 N/mm²) compared to regular fire clay bricks.
2. Durability: Highly durable with low permeability, reducing efflorescence and dampness.
3. Appearance: Uniform, smooth finish with reduced plastering needs.
4. Thermal Properties: Excellent thermal conductivity, keeping buildings cooler in summer.
5. Sound Insulation: Better sound insulation than ordinary bricks.
6. Fire Resistance: Superior fire resistance compared to fire clay bricks.
7. Sustainability: Environmentally friendly due to the use of recycled fly ash.
8. Availability: Widely available, especially near thermal power stations.

What are the disadvantages of fly ash bricks?

1. Not all fly ash bricks are suitable for construction; quality must be ensured.
2. Improperly prepared bricks lack strength.
3. Limited to modular sizes; larger sizes are prone to cracking.
4. Smooth finish may reduce bonding strength in masonry work.
5. Plaster may not bond well due to the smooth surface.
6. Not suitable for use in extremely cold regions.

How much do fly ash bricks cost?

The cost varies depending on factors such as raw material costs, production methods, and location. Generally, they cost between 8-10 rupees per piece, which is lower than the 11-12 rupees per piece for regular fire clay bricks.

How are fly ash bricks manufactured?

The manufacturing process involves:

1. Mixing fly ash (57-65%), sand/stone dust (18-27%), hydrated lime (9-12%), and gypsum (5%) or cement.
2. Compressing the mixture at 28 MPa.
3. Curing the bricks in a 66°C steam bath for 24 hours.
4. Toughening with an air entrainment agent and undergoing freeze-thaw cycles.

What is the compressive strength of fly ash bricks?

Fly ash bricks have a compressive strength of 10-12 N/mm², significantly higher than the 3.5 N/mm² of ordinary fire clay bricks.

What are the standard sizes of fly ash bricks and blocks?

1. Fly Ash Bricks: Typically 230mm x 110mm x 70mm, weighing around 6 kg.
2. Fly Ash Blocks: Larger size, usually 24in x 8in x 4in, used for partition and sidewalls.

What are fly ash bricks primarily used for?

They are used in various construction applications, including residential and commercial buildings, due to their strength, durability, and cost-effectiveness.