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Fly Ash Bricks - Blessing in Disguise

What Is Fly Ash Brick?

Fly ash bricks are unconventional bricks manufactured from industrial wastes such as fly ash, cement, and sand/stone dust. These types of bricks are nowadays used worldwide with gaining popularity over clay bricks.

Fly Ash Bricks

For construction projects, fly ash bricks are utilized as an alternative to burnt clay bricks. A fly ash brick may withstand more than 100 freeze-thaw cycles if compressed at a pressure of 28 MPa, cured for 24 hours in a steam bath at 66°C, and stiffened with an air-entrainment agent.

These bricks are considered “self-cementing” since class C fly ash contains a significant amount of calcium oxide. Fly ash brick production uses less energy, emits less mercury into the atmosphere, and frequently costs 30% less than traditional clay brick production.

Environmentally friendly hydraulic pressure devices are used to produce fly ash bricks. These bricks have a compressive strength greater than 40 Mpa and are 28% lighter than normal clay bricks.

Composition Of Fly Ash Bricks

The primary materials of fly ash brick are fly ash, stone dust/sand, lime, gypsum, and bonding agent. The mixture is carefully formulated to produce bricks with improved strength, consistency, and homogeneity.

Fly Ash BricksNormal Clay BricksA) Fly ash- 60-65%

Sand/Stone dust- 20-25%

Hydrated lime- 8-12%


B) Fly ash- 50% to 60%

Sand/stone dust – 32%-40%

Cement – 8-10%Silica (sand) – 50% to 60%

Alumina (clay) – 20% to 30%

Lime – 2 to 5%

Iron oxide – ≤ 7%

Magnesia – less than 1%

Fly Ash Brick Manufacturing Process

Advantages Of Fly Ash Bricks

1. Appearance

The appearance of fly ash bricks is very attractive due to their pleasing colors like cement, uniform size, and smooth finish. Due to uniform size, mortar required for walls and plastering reduces almost by 40-50%.

Plaster of Paris (Gypsum plaster), putty can be applied directly without a baking coat of plaster. These bricks are free from cracks, wrap age, organic matter, pebbles, and nodules of free lime.

2. Strength

The compressive strength of fly ash bricks is very high (9-10 N/mm2). Due to high strength, no breakages/wastages during transport and handling. The lower thickness of joints and plaster reduces cracking in plaster.

These bricks do not cause any extra load for the design of structures and provide better earthquake resistance. It improves the strength over time and offers greater strength to the building.

3. Thermal Properties

The thermal conductivity of fly ash bricks is 0.90 – 1.05 W/m2. They absorb less heat. The pozzolanic reaction between fly ash and lime produces less heat. It keeps your building cooler in summer, hence most suitable for Indian climates.

4. Durability

These bricks are highly durable and less permeable. The lower permeability can efficiently reduce the effect of efflorescence on bricks.

These bricks are less porous, absorb less water, and reduce dampness on the walls. It is also highly resistant to attack by mild acid, water, and sulfate.

5. Sound Insulation

Construction with these bricks provides decent sound insulation to the building.

6. Fire Resistance

These bricks are highly fire-resistant compared to normal clay bricks.

7. Sustainability

Fly ash bricks are environmentally friendly as they are made of waste materials that come from the combustion of coal in thermal power plants. There is no pollution or environmental damage, and it is considered a white category product.

8. Buildability

These bricks have easy workability and absorb less water. Unlike clay bricks, they do not require soaking in water for 24 hours. The sprinkling of water before use is sufficient. The construction technique is same as clay brick construction and does not require any extra training for the masons.

9. Availability

These bricks are generally available closer to the thermal power plants. However, finding dealers in all major cities and towns wouldn’t be a problem.

10. Cost

The same number of fly ash bricks will cover more areas than clay bricks. Consumption of mortar is also low. Requires less labour. The cost is approximately 30% lower than clay bricks.

11. Applicability

Due to their lightweight, these bricks are suitable for multi-storey structures. Less weight means less stress on the building.

These bricks can be used in load-bearing external walls in low structures, non-load bearing internal walls in low/mid structures, and non-load bearing internal or external walls in highrise buildings.

Disadvantages Of Fly Ash Bricks

1. Not all fly ash is suitable for construction; those are produced in power plants usually compatible with concrete. It is very important to use only high-quality fly ash to prevent negative effects on the structure.

2. If not made properly, it has no strength and is not suitable for construction. Poor quality bricks have negative impact on concrete. It can increase permeability, resulting in damages to the structure.

3. Bonding with concrete is lower due to the smooth finish.

4. Limitation in size. Only modular size bricks can be produced. The larger size will have more breakages.

5. It is only suitable for subtropical areas or where the climate is warm because these bricks do not absorb heat. But in winter season it is not helpful.

Fly Ash Bricks Uses:

Fly ash bricks are used in

  • Multistorey structures.

  • House construction.

  • Factories.

  • Warehouses.

  • Power plants.

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