Fly ash brick

Fly ash brick (FAB) is a building material, specifically masonry units, containing class C fly ash and water. Compressed at 28 MPa (272 atm) and cured for 24 hours in a 66 °C steam bath, then toughened with an air entrainment agent, the bricks last for more than 100 freeze-thaw cycles. Owing to the high concentration of calcium oxide in class C fly ash, the brick is described as "self-cementing". The manufacturing method saves energy, reduces mercury pollution, and costs 20% less than traditional clay brick manufacturing.

The raw materials

Funton Creek. Presumably this was a navigable channel in the days when the brick works was serviced by barges bringing fly-ash from London and returning with loads of bricks.

The raw materials for fly ash Acc Blocks are:

Material	Mass
Fly ash	45%
Sand/stone dust	40%
Lime sludge	10%
Gypsum	5%
Total formula of material	100%

Fly ash bricks are lighter than clay bricks.

Main ingredients include fly ash, water, quicklime or lime sludge, cement, aluminum powder and gypsum. The block hardness is being achieved by cement strength, and instant curing mechanism by autoclaving. Gypsum acts as a long term strength gainer. The chemical reaction due to the aluminum paste provides AAC its distinct porous structure, lightness, and insulation properties, completely different compared to other lightweight concrete materials. The finished product is a lighter Block - less than 40% the weight of conventional Bricks, while providing the similar strengths. The specific gravity stays around 0.6 to 0.65. This is one single most USP of the AAC blocks, because by using these blocks in structural buildings, the builder saves around 30 to 35 % of structural steel, and concrete, as these blocks reduce the dead load on the building significantly

Advantages

1. Same number of bricks will cover more area than clay bricks
2. High Fire Insulation
3. Due to high strength, practically no breakage during transport and use.
4. Due to uniform size of bricks mortar required for joints and plaster reduces almost by 50%.
5. Due to lower water penetration seepage of water through bricks is considerably reduced.
6. Gypsum plaster can be directly applied on these bricks without a backing coat of lime plaster.
7. These bricks do not require soaking in water for 24 hours. Sprinkling of water before use is enough.

Disadvantages

1. Mechanical strength is low. But this can be rectified by adding marble waste, or Mortar between blocks.
2. Limitation of size. Only modular size can be produced. Large size will have more breakages.

References

• Standards of Brick Development Association
• Complete information of Flyash Bricks