Fly Ash Bricks

Fly Ash Bricks: Benefits, Composition and Manufacturing

Fly Ash Bricks

When we plan to create a new house, many questions and concerns arise. A house is not a temporary building. We want to create a house that will last for an extended period of time. To accomplish this, we select the best methods, materials, and construction techniques. Bricks are one of these materials. In this article, we will discuss the benefits, composition, and manufacturing of Fly Ash Bricks.

What is Fly Ash?

Fly ash is a fine powder which is produced as a byproduct of the combustion of pulverized coal in power plants. Fly ash is a pozzolan, a substance composed of aluminous and siliceous material that, when combined with water, forms cement. When fly ash is combined with lime and water, a compound close to Portland cement is formed. This qualifies fly ash as a primary component of blended cement and bricks, among other construction materials.

Benefits of Fly Ash

In many markets, fly ash is a cost-effective replacement for Portland cement. Fly ash is often considered an environmentally friendly substance since it is a byproduct and has a low embodied energy, which is the amount of energy used in the production and transportation of a building material. By comparison, Portland cement does have a very high embodied energy due to the high temperature needed to manufacture it. Fly ash uses less water than Portland cement and is thus more suitable for use in cold climates. Additional advantages include the following:

  • Produces a variety of setting times
  • Resistant to cold weather
  • Increases in strength depending on application
  • Considered a substance that does not shrink
  • Gives a dense concrete with a smooth finish and fine detail.
  • Produces workable concrete
  • Reduces cracking and permeability
  • Reduces carbon dioxide emissions

Fly ash bricks

Fly ash bricks are high-tech, high-quality bricks that are used to create brick masonry structures. Industrial wastes like fly ash, is used along with cement, and sand/stone dust are used to make fly ash bricks. They are used in place of standard clay bricks and have superior properties. Fly ash bricks are cost competitive with traditional clay bricks and offer many indirect benefits.

Fly Ash Bricks
Fly Ash Bricks (Source)

Fly Ash Bricks Composition

We provide details on the composition of fly ash bricks in this section. Fly ash bricks are primarily manufactured using three distinct mixing ratios. The price of a brick is largely determined by the mix ratio of fly ash bricks used.

First Mix for Fly Ash Bricks

  1. Fly Ash – 56 to 61%
  2. Sand– 21 to 26%
  3. Sludge Lime – 16 to 22%
  4. Gypsum – 4 to 5%

The material used to produce a fly ash brick is determined by the availability of raw materials and the quantity of bricks required. Sludge Lime is recommended because it is less costly than Hydrated Lime. Sludge lime is made from waste material and is less expensive than hydrated lime. Sludge lime is usually damp and lumpy, and is used to manufacture high-quality fly ash bricks.

Second Mix for Fly Ash Bricks

Hydrated lime is used in place of sludge lime in this instance.

  1. Fly Ash – 58 to 66%
  2. Sand– 19 to 28%
  3. Hydrated Lime – 10 to 13%
  4. Gypsum – 4 to 5%

This proportion is commonly used in the manufacture of high-quality fly ash bricks. Due to the ease with which hydrated lime can be obtained, this fly ash brick formulation is used by a large number of fly ash brick manufacturers.

Third Mix for Fly Ash Bricks

  1. Fly Ash 51 – 62%
  2. Sand – 31 to 41%
  3. Cement – 9 to 15%

In this proportion, cement is substituted for gypsum and lime.  Since cement is more expensive than gypsum and lime, this mixture is used only in the absence of gypsum and lime.

Steps to Make of Fly Ash Bricks

1. The Process of Mixing

The raw materials will be first fed into the hopper box, where they are conveyed to the pan through a conveyor belt. The cement and water are combined in the pan for approximately five minutes. In the pan, there is a skipper and roller to effectively combine the raw materials. The mixing method is critical in the production of fly ash bricks.

  1. Squeezing

After mixing, the raw material was conveyed to the hopper via the conveyor belt. The PLC regulates the flow of raw material into the press machine. The raw material is fed into a mold made of high-grade EN31 material and pressed in a machine for producing fly ash bricks. This fly ash brick manufacturing machine is available in both manually and automatically configurations.

3. Cure

Following pressing, the brick is stored in the chamber for 24hrs. Following that, the bricks are stored for 16 to 20 days and are watered twice daily.

The fly ash blocks are now finished.

Fly Ash Bricks
Steps to Make Fly Ash Bricks

Pros of Fly Ash Bricks

1. Physical appearance

Fly ash bricks have an appealing look due to their nice color similar to cement, consistent dimensions, and smooth surface. Due to the standardized size, the amount of mortar required  for plastering is reduced by nearly 40% to 50%. These bricks are free of cracks, wrap deterioration, organic substances, and free lime nodules.

2. Ability to resist stresses

Fly ash bricks have an extremely high compressive strength (10-12 MPa). No fractures during shipping and storage due to the high strength. The thinner joints and plaster minimize the likelihood of plaster cracking. These bricks add no additional load to the structure’s architecture and improve its seismic resistance. It increases the strength of the building with time and provides additional strength to the building.

3. Thermal characteristics

Fly ash bricks have a thermal conductivity of 1.0 – 1.1 W/m2. They conduct heat more efficiently. There is less heat generated by the pozzolanic activity among lime and fly ash. It helps keep your structure cooler in the summer, making it ideal for warm/hot climates.

4. Durable

Fly ash blocks are very durable and impervious to moisture. Reduced permeability effectively mitigates efflorescence’s impact on blocks. These bricks are much less brittle, trap less amount of water, and help to keep walls dry. Additionally, it is very resistant to mild acid and sulfate attack.

5. Insulating Sound

The use of fly ash bricks in the construction of the building offers adequate sound insulation.

6. Resist Fire:

Fly ash bricks are highly resistant to fire.

7. Sustainable

Fly ash bricks are environmentally friendly since they are constructed from waste materials from coal combustion in thermal energy stations. There is also no contamination or environmental hazard associated with this product, which is classified as a white category item.

8. Less time to build

Fly ash bricks are simple to work with and have a low water absorption rate. They do not require a 24-hour submerge in water. A light misting of water prior to use is sufficient. The building method is identical to that of clay bricks and does not require any training for masons.

9. Easy to apply

Due to the lightweight nature of fly ash bricks, they are ideal for multi-story buildings. Reduced weight means reduced stress/strain on the structure. These bricks are suitable for load-bearing exterior walls in low/medium-rise building, non-load-bearing internal walls in low/medium-rise building, and non-load-bearing internally or externally walls in high-rise structures.

Cons of Fly Ash Bricks

  1. Not all fly ash is suitable for construction; some, such as that generated in power stations, is compliant with concrete, whereas others require beneficiation. It is essential to only use fly ash with high quality to avoid damaging the structure.
  2. If not properly constructed, it lacks strength and is unsuitable for building. Bricks of poor quality have a detrimental effect on concrete. It can raise penetrability, leading to structural damage.
  3. Due to the smooth finish, the bond with concrete is reduced.
  4. Size restriction. Only modular-sized bricks are possible. The larger scale would have a greater chance of breaking.
  5. It is only appropriate for subtropical climates or areas with a warm atmosphere, as fly ash blocks do not absorb heat. However, during the winter season, this is ineffective.

Read Also: What is the Best Material for Construction?

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