This article explains everything related to fly ash bricks.
Table of Contents
What Are Fly Ash Bricks?
Fly Ash Bricks are manufactured from industrial wastes like fly ash, cement, sand/stone dust. Fly ash bricks are nowadays utilized worldwide with gaining popularity over clay bricks. In this article, different advantages and disadvantages of fly ash bricks are discussed.
Brief History
Household and industrial activities traditionally considered coal dust as a byproduct and collected it as waste. “Scavengers” used to gather coal ash during the 19th century and transport it to local brick works, where they would mix it with clay. The revenue generated from selling the ash would typically cover the costs of waste collection.
Clay particles are commonly trapped during the coal formation process. When coal burns, the non-combustible clay particles remain behind as ash, which forms cinders through prolonged residence time in grate boilers.
Nowadays, pulverized coal technology is preferred for its enhanced energy efficiency. In this case, the pulverized clay particles escape along with flue gases and settle as ash in bag filters or electrostatic precipitators (ESPs), resulting in the term fly ash.
Composition
Fly ash bricks are mainly made of fly ash, a byproduct of coal combustion in thermal power plants. Manufacturers typically mix fly ash with sand or stone dust, hydrated lime, and gypsum to create the bricks.
Fly ash: Power plants generate fly ash as a fine powder from coal combustion. Manufacturers use it as the primary material for fly ash bricks due to its pozzolanic properties. Fly ash reacts with lime to form a cement-like substance, which hardens the bricks.
Sand or stone dust: Manufacturers add sand or stone dust to the mixture to increase the strength and durability of the bricks. It also helps in reducing the cost of production.
Hydrated lime: Manufacturers add hydrated lime to act as a binding agent. It reacts with fly ash and sand to form a strong bond and increases the strength of the bricks.
Gypsum: Gypsum is added as a filler material to the mixture. It also helps in controlling the setting time of the mixture.
Some manufacturers may also add cement, water, and chemical additives to improve the properties of the bricks. The proportions of each material may vary depending on the desired properties of the bricks and the manufacturing process.
Manufacturing Of Fly Ash Bricks
Fly ash bricks are made by mixing hydrated lime powder, gypsum, and burnt clay particles (oxides of clay) obtained from burning coal, which contains clay from the mines. This mixture is then ground to form a slow-setting pozzolana cement, using the same process as cement factories where clay and limestone are burnt with coal and gypsum.
To form the fly ash bricks, the mixture is pressed at low pressure and low moisture content in a hydraulic machine. This machine is specially designed to give a high-pressure load at a slow rate of around 350kg/square inch. The pressure is held for a desired time to ensure that the bricks reach their ultimate strength.
Advantages Of Fly Ash Bricks:
1. Appearance:
The appearance of fly ash bricks is very fascinating due to their pleasing color like cement, uniform size, and smooth finish. Due to uniform size, mortar needed for walls and plastering cut down almost by 40-50%. Plaster of Paris (Gypsum plaster), putty can be applied directly without a baking coat of plaster. Fly ash brick is free from cracks, wrap age, organic matter, pebbles, and nodules of free lime.
2. Strength:
The compressive strength of fly ash bricks is very higher (9-10 N/mm2). Because of higher strength no breakages/wastages during transport and handling. The lower thickness of joints and plaster decrease cracking in plaster. These bricks do not cause any additional load for the design of structures and provide better earthquake resistance. It improves the strength over time and offers greater strength to the structure.
3. Thermal Properties:
The thermal conductivity of fly ash bricks is 0.90 – 1.05 W/m2. They acquire less heat. The pozzolanic reaction between fly ash and lime generates less heat. It keeps your building cooler in summer, thus most suitable for hot climates.
4. Durability:
Fly ash bricks are extremely durable and less permeable. The lower permeability can efficiently decrease the effect of efflorescence on bricks. These bricks are less porous, absorb less water, and decrease dampness on the walls. It is also highly resistant to attack by moderate acid, water, and sulfate.
5. Sound Insulation:
Construction with fly ash bricks gives decent sound insulation to the building.
6. Fire Resistance:
Fly ash bricks are extremely fire-resistant.
7. Sustainability:
Fly ash bricks are eco-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, considered as a white class product.
8. Buildability:
Fly ash bricks have easy workability and sorb less water. They do not need to soak in water for 24 hours. The sprinkling of water before use is adequate. The construction method is the same as clay brick construction and does not need any additional training for the masons.
9. Availability:
These bricks are normally available closer to the thermal power plants. Even so, 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 compared to clay bricks. Consumption of mortar is also inferior. Need less labor. The cost of fly ash bricks is approx 30% lower compared to clay bricks.
11. Applicability:
Fly ash bricks are lightweight, so it is appropriate for multi-story structures. Less weight means less stress on the building. These bricks can be utilized in load-bearing external walls in low/mid structures, non-load bearing internal walls in low/mid structures, and non-load bearing internal or external walls in high rise buildings.
Disadvantages Of Fly Ash Bricks:
- Not all fly ash is appropriate for construction, those are produced in power plants usually compatible with concrete, while others may need beneficiation. It is very crucial to use only high-quality fly ash to prevent negative effects on the structure.
- If not made properly, it has no strength and not desirable for construction. Poor quality bricks have a negative impact on concrete. It can enhance permeability, resulting in damages to the structure.
- Bonding with concrete is low due to the smooth finish.
- Limitation in size. Solitary modular size bricks can be produced. The larger size will have more breakages.
Applications And Uses
- Construction of walls and partitions in residential and commercial buildings.
- Paving outdoor pathways and walkways.
- Construction of boundary walls and fences.
- Construction of retaining walls and dams.
- Making arches and lintels in buildings.
- Building pillars and columns for support.
- Making window sills and frames.
- Construction of garden walls and planters.
- Making fireplaces and chimneys.
- Building outdoor barbeque and grilling areas.
- Making swimming pool decks and walls.
- Construction of water tanks and reservoirs.
- Building garages and sheds.
- Making boundary markers and signposts.
- Building public toilets and washrooms.
- Making boundary walls for sports fields and stadiums.
- Construction of industrial buildings and warehouses.
- Making storage rooms and sheds.
- Building schools and community centers.
- Construction of hospitals and healthcare facilities.
Faqs
Yes, they are often more cost-effective than traditional clay bricks because they require less energy to produce, have a longer lifespan, and require less maintenance.
Yes, they have a higher compressive strength than traditional clay bricks and are less susceptible to damage from weather and moisture.
Fly ash bricks utilize a waste material, require less energy to produce, have better thermal insulation properties, and reduce energy consumption in buildings, contributing to a greener environment.