FLY ASH BRICKS

Fly ash brick (FAB) is a building material, specifically masonry units, containing class C or class F 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

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.

1) Loss on Ignition (LOI); fly ash loses weight when it burns at about 1000 °C due to presence of carbon and water. The weight loss happens due to carbon combustion and moisture evaporation is called "Loss on Ignition(LOI)". This is expressed as percentage. The lower the loss of Ignition, the better will be fly ash. As per BIS it should not be more than 5%.

2) Fineness; the fine fly ash has more surface area available to react with lime, thus more will be the pozzolanic activity of fly ash. The greater pozzolanic activity contributes to the strength of fly ash brick. As per BIS it should not be more than 320 m2/kg.

3) Calcium (CaO) content; the pozzolanic reactivity of fly ash is more in high calcium fly ash. The greater the pozzolanic activity leads to higher the strength of fly ash brick. As per ASTM C618 fly ash is classified into two; Class C contains more than 10% lime and Class F fly ash contains less than 10% lime.

Advantages

It reduces dead load on structures due to light weight (2.6 kg, dimension: 230 mm X 110 mm X 70 mm).
Same number of bricks will cover more area than clay bricks
High fire Insulation
Due to high strength, practically no breakage during transport and use.
Due to uniform size of bricks mortar required for joints and plaster reduces almost by 50%.
Due to lower water penetration seepage of water through bricks is considerably reduced.
Gypsum plaster can be directly applied on these bricks without a backing coat of lime plaster.
These bricks do not require soaking in water for 24 hours. Sprinkling of water before use is enough.

Disadvantages

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. 3. It is only good for the places like subtropical area or area where climate is warm because it doesn't absorbs heat. But during cold it is not helpful.