Fly ash bricks: composition and mixing ratios

Fly ash bricks are manufactured using various mixing compositions, and the price of the brick depends largely on which ratio is used. The price of a brick is mainly determined by the fly ash bricks mixing ratio chosen, and maintaining quality while optimising cost is essential to business profitability.

Three primary mixing formulations are commonly used.

Mix proportion 1 (most profitable)

• Fly ash: 55 to 60 percent

• Sand or stone dust: 20 to 25 percent

• Sludge lime: 15 to 22 percent

• Gypsum: 5 percent

This composition uses sludge lime, a waste material that costs less than hydrated lime, making it the most economical option.

Mix proportion 2 (widely used)

• Fly ash: 57 to 65 percent

• River sand or stone dust: 18 to 27 percent

• Hydrated lime: 9 to 12 percent

• Gypsum: 5 percent

This ratio uses hydrated lime and is popular because hydrated lime is readily available.

Mix proportion 3 (cement alternative)

• Fly ash: 50 to 60 percent

• River sand or stone dust: 30 to 40 percent

• Cement: 8 to 12 percent

This option replaces gypsum and lime with cement but is rarely used due to higher costs.