Fly ash bricks are manufactured from industrial waste fly ash which is a by-product of coal after it is burnt at thermal power plants, and is usually dumped at the site or ponds, resulting in depletion of top soil, groundwater deterioration and air pollution.
Fly ash bricks are used as building material
Chemical Composition of fly ash
Fly ash consists primarily of oxides of silicon, aluminum iron and calcium. Magnesium, potassium, sodium, titanium, and sulfur are also present to a lesser degree.
Important compositions of fly ash bricks are:
- Fly ash
Comparison of Clay Bricks and Fly Ash Bricks
Advantages of Fly Ash Bricks
The appearance of fly ash bricks is very attractive due to its pleasing color like cement, uniform size, and smooth finish
The compressive strength of fly ash bricks is very high (refer table). Due to high strength no breakages/wastages during transport and handling. The lower thickness of joints and plaster reduces cracking in plaster.
- Thermal Capacity
It absorbs less heat. Hence it keeps your building cooler in summer, hence most suitable for Indian climates.
Fly ash 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
- Sound Insulation:
Construction with fly ash bricks provides decent sound insulation to the building.
- Fire Resistance:
Fly ash bricks are highly fire-resistant.
Fly ash bricks are environmentally friendly as they are made of waste materials that come from combustion of coal in thermal power plants. There is no pollution or environmental damage, considered as a white category product.
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 of fly ash bricks is approximately 30% lower than clay bricks.
Fly ash bricks are lightweight, so it is suitable for multi-storey structures. Less weight means less stress on the building.
Disadvantages of Fly Ash Bricks:
- Not all fly ash is suitable for construction, those are produced in power plants usually compatible with concrete, while others may need beneficiation
- If not made properly, it has no strength and not suitable for construction. Poor quality bricks have negative impact on concrete. It can increase permeability, resulting in damages to the structure.
- Bonding with concrete is lower due to the smooth finish.
- Limitation in size. Only modular size bricks can be produced. The larger size will have more breakages.
- It is only suitable for subtropical areas, or where the climate is warm because fly ash bricks do not absorb heat. But in winter season it is not helpful.
The other issues which impede its full-scale utilization in India:
- Indian fly ash is primarily of the calcareous or class C variety, implying that it possesses not only pozzolanic, but also hydraulic (self-cementing) properties. A fly ash particle binds faster with other fly ash particles to become solid. It is not useful (see 2nd point of disadvantages)
In contrast, European fly ash is of a silicious or class F variety, implying an absence of hydraulic properties.
- The pricing of fly ash is increasingly becoming a contentious issue that is hampering its gainful utilisation.
- Imperfections typical of quasi-markets, such as information asymmetry and high transaction costs, vested interests, technical and technological limitations, and the lack of regulatory oversight and political will, have impeded the flow of fly ash to its most value-adding use.
Other use of fly ash in construction
Researchers at the Indian Institute of Technology (IIT) Hyderabad have developed a cheap waterproofing material by coating fly ash, a waste by-product from coal-based thermal power plants, with stearic acid, which is a surfactant. While fly ash is extremely water-loving (hydrophilic), it turns into a highly water-repelling surface once coated with stearic acid.