With reference to 'fly ash' produced by the power plants using 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.
- (a) 1 and 2 ✓ UPSC's answer
- (b) 2 only
- (c) 1 and 3
- (d) 3 only
Why the answer is (a)
• Fly ash, the fine residue from burning pulverised coal, is used to make bricks (fly-ash bricks are mandated near thermal plants) (statement 1) and as a pozzolanic replacement for 15–35% of Portland cement in concrete (Portland Pozzolana Cement) (statement 2).
• Statement 3 is wrong: besides silica and calcium oxide, fly ash contains alumina, iron oxide and toxic trace elements such as arsenic, mercury, lead and cadmium.
• India generates over 200 million tonnes a year, with utilisation now above 80%.
• Hence 1 and 2, option (a).
Why the other options are wrong
- (b) 2 only
- Statement 1 on bricks is also correct.
- (c) 1 and 3
- Statement 3 is wrong: fly ash contains toxic elements.
- (d) 3 only
- Statement 3 is wrong.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2015, held on 23 August 2015. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.