Fly Ash Brick: Advantages, Disadvantages & Comparison

Fly Ash Brick

Fly ash brick, also called fly ash clay brick is made from a combination of fly ash and clay fired at very high temperatures. The mix of fly ash produces brick that has higher levels of calcium oxide. They are less permeable so, they have lower amounts of water penetration, and also they are self-cementing.

They also have higher density, endure freeze-thaw cycles better than clay brick. They have high fire insulation and high strength qualities. The manufacturing method saves energy, reduces mercury pollution in the environment, and mainly costs approximately 20% less than traditional clay brick manufacturing.


Composition of Fly Ash Bricks

Coal dust (ash) has been gotten as waste material from the industry. This ash shifted to the bricks production site where the ash mixed with clay.
Clay is usually implicated during the formation of coal. When coal is burned, the incombustible clay particles are left behind as ash. Currently, pulverised coal technology is preferred because of its better energy efficiency.

A good combination of materials for the manufacturing of fly ash brick is as below,

Fly ash 60%
Sand    30%
Cement  10%

The strength of fly ash brick made with the above combinations is varies from 7.5 MPa to 10 MPa. Fly ash bricks are lightweight and better than clay bricks.
Main components include fly ash, water, cement, and gypsum. Autoclaving raises the solidity of the brick by doing quick curing of the cement. Gypsum acts as a long-term strength gainer. These types of bricks are lighter in weight less than 40% of the weight of standard Bricks while providing similar strengths. The specific gravity remains around 0.6 to 0.65. Using these bricks in construction reduces the dead load.

Fly Ash Bricks Advantages And Disadvantages.


  • They are light in weight.
  • Fly ash bricks are very attractive due to their color, uniform size, and smooth finish.
  • The compressive strength of fly ash brick is very high.
  • Fly ash bricks have high fire insulation.
  • They are less porous and also absorb less water.
  • The required mortar for joints of fly ash bricks is less due to the uniform size.
  • Gypsum plaster can be directly applied to these fly ash bricks.
  • Fly ash bricks are cheaper as compared to clay bricks.
  • These bricks are environmentally friendly.
  • The pozzolanic reaction in between lime or cement and fly ash will significantly generate less heat and thus, prevents thermal cracking.
  • These bricks are highly durable and less permeable.
  • The lower permeability of fly ash mix can efficiently reduce the effects of efflorescence.
  • Due to its lightweight, these bricks are suitable for multi-story buildings.



Depending on the combination of materials mechanical strength can be reduced. This can be partially fixed by including marble powder or mortar between bricks.

  • Large size will have extra breakages.
  • They have high thermal conductivity. More insulation is needed in cold regions.
  • Bonding with concrete is lesser due to the smooth finish.

Comparison of Clay Bricks and Fly Ash Bricks


Fly Ash Bricks         Clay Bricks
These Bricks are made from cement, sand, and fly ash. These bricks are manufactured from Clay Soil.
Fly Ash Bricks has compressive strength of 70 to 100 kg/cm². Clay Brick has compressive strength of 25 to 40 kg/cm².
Fly ash brick has a Cement grey color. Clay brick has mostly red color but can be changed depending on the type of clay used.
Density of fly ash brick is 1700-1850 kg/m3. Density of clay brick is 1600-1750 kg/m3.
Fly ash bricks have water absorption of around 8 to 14 %. Clay bricks have water absorption around 15% to 25 %.
Fly ash brick has a more uniform shape as they are cast in machine mold. Clay bricks do not have a uniform shape as they are hand-molded.