Previous Year Question
With reference to ‘fly ash’ produced by the power plants using coal as fuel, which of the following statements is/are correct?
Fly ash can be used in the production of bricks for building construction.
Fly ash can be used as a replacement for some of the Portland cement contents of concrete.
Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements.
Select the correct answer using the code given below:
1 and 2
2 only
1 and 3
3 only
Correct Answer: A
Detailed Solution
Fly ash is a fine particulate residue produced by burning pulverised coal in thermal power plants.
It rises with combustion gases and is generally collected using equipment such as electrostatic precipitators.
Fly ash can be used in the construction of cement, concrete, bricks, blocks, roads and embankments.
In the manufacture of fly-ash bricks, it is mixed with binding materials such as lime, gypsum or cement.
This can reduce the consumption of natural soil and the need to dispose of fly ash.
Therefore, Statement 1 is correct.
The reactive silica and alumina present in fly ash provide it with pozzolanic properties.
It can react with calcium hydroxide to form additional cementitious compounds.
Therefore, fly ash can be used as a replacement for a part of Portland cement in concrete.
Its use can improve the long-term strength and durability of concrete and reduce the requirement for cement clinker.
Therefore, Statement 2 is correct.
Fly ash is not composed only of silicon dioxide and calcium oxide.
It may also contain other mineral components, including aluminium oxide, iron oxide and magnesium oxide.
Depending on the source of coal, toxic trace elements such as arsenic, lead, mercury, chromium and selenium may also be present in it.
Therefore, Statement 3 is incorrect and the correct answer is 1 and 2.