Fly ash bricks are lightweight bricks that are prepared using fly ash, water and aggregates like sand, gypsum, lime, and stone dust. These are greyish and have a uniform shape as they are cast in the machine mould. Due to this uniform size, the mortar required for walls reduces by 40-50%. It can save plastering work up to 15%. Fly ash bricks are lightweight and are used in multi-storey buildings, factories, warehouses, power plants and high-rise buildings.   

Fly ash bricks are of two types, namely

1. Normal fly ash is made of cement, water, fly ash and stone dust.
2. Fly ash lime gypsum (FLAG) bricks are made up of cement, water, fly ash, stone dust, limestone and gypsum.

Mixing ratio

• The percentage of fly ash in the normal ratio is 55-60%, sand is 20-25%, sludge lime is 15-20% and gypsum is 5%.
• The ratio in the profitable ratio is 60-65% for fly ash, 18-27% for sand, 8-12% for sludge lime and remains the same at 5% for gypsum.

Advantages of fly ash bricks

• It reduces the dead load of the building due to its lightweight.
• It is eco-friendly and causes low pollution.
• These offer high fire and thermal insulation.
• These are strong and durable, thus there is no breakage during transportation.
• It has high strength ranging from 7.5-10 MPa.
• A single fly ash brick can replace multiple normal bricks by reducing the amount of mortar and joints.

Disadvantages of fly ash bricks

• These don’t absorb heat and thus are not effective in colder climates.
• These have less mechanical strength, which can be improved by applying mortar between the bricks.
• These can be only produced in modular size. Increasing the size can amplify their chances of breaking down.
• In the case of masonry work, only concealed wiring is possible.

Red Bricks

Standard bricks or red bricks are probably one of the oldest bricks produced. These are produced by mixing water, clay, sand, lime and other aggregates. These are hand-made and don’t have a uniform shape. These are red to brown, depending upon the clay and the duration of baking. These are heavier and require more mortar.

Advantages of red bricks

• Red bricks are easier to prepare as their raw materials are easily available.
• These are easily reusable and recyclable.
• They are fire-resistant, soundproof and provide thermal insulation.
• These have a compressive strength of 3-3.5 MPa.
• These can be used in load-bearing structures.

Disadvantages of red bricks<

• These are highly time-consuming.
• These are tougher to clean.
• Red bricks are not resistant to shocks and cannot be used in high seismic zones.
• They have low tensile strength and can also cause fluorescence when not exposed to air.

Differences between fly ash bricks and red bricks

These were the advantages, disadvantages and differences between the fly ash bricks and red bricks. Historically speaking, red bricks have been more popular and widely used. But with developments and changing customer needs, fly ash bricks have started replacing them due to their advanced features. Hopefully, this article was helpful to you.

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