With reference to ‘fly ash’ produced by the power plants using the coal as fuel, which of the following statements is/are correct?

1. Fly ash can be used in the production of bricks for building construction
2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete
3. 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

The correct answer is 1 and 2 only.

Explanation:
Fly ash is a fine powder that is a byproduct of burning pulverized coal in electric generation power plants. Let us analyze each of the given statements to understand why statements 1 and 2 are correct, while statement 3 is incorrect:

1. Fly ash can be used in the production of bricks for building construction:
This statement is correct. Fly ash is widely used in the manufacturing of fly ash clay bricks or fly ash-lime-gypsum bricks. These bricks are lightweight, stronger, and more durable compared to conventional clay bricks, and using fly ash helps recycle an industrial waste product.

2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete:
This statement is correct. Fly ash possess pozzolanic properties, meaning it reacts with calcium hydroxide (liberated during cement hydration) to form compounds with cementitious properties. Replacing a portion of Portland cement (typically 15% to 30%) with fly ash improves the workability, strength, and chemical resistance of concrete while reducing the carbon footprint of cement production.

3. Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements:
This statement is incorrect. While fly ash contains substantial amounts of silicon dioxide (SiO₂), calcium oxide (CaO), aluminum oxide (Al₂O₃), and iron oxide (Fe₂O₃), it is not composed of silicon dioxide and calcium oxide "only". Furthermore, fly ash contains trace amounts of various toxic heavy metals and elements such as arsenic, lead, mercury, cadmium, and cobalt, which can pose environmental and health hazards if not managed properly.

Therefore, statements 1 and 2 are correct, making "1 and 2 only" the correct option.