UPSC Prelims 2015 Q18: Environment & Ecology – Pollution & Waste Management
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.
- (a) 1 and 2
- (b) 2 only
- (c) 1 and 3
- (d) 3 only
Answer: (a) 1 and 2
Explanation
Fly ash from coal-based power plants
Fly ash is the fine powder left when coal is burnt.
| Statement | Verdict | Fact |
|---|---|---|
| 1. Fly ash can be used in the production of bricks for building construction | Correct | Fly ash bricks are light and strong |
| 2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete | Correct | Used in Portland Pozzolana Cement |
| 3. Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements | Incorrect | It also has aluminium and iron oxides and toxic heavy metals such as arsenic, lead and mercury |
Other uses of fly ash:
| Use | Detail |
|---|---|
| Roads and embankments | Fill material |
| Mines | Filling of abandoned mines |
| Agriculture | Soil conditioner, in limited doses |
Rules require power plants to reach 100 percent utilisation of fly ash.
Answer: (a) 1 and 2.
Why each option is right or wrong
- (a) CORRECT. Fly ash is used in bricks and as a part-replacement for Portland cement.
- (b) Incorrect. Statement 1 is also true: fly ash goes into bricks.
- (c) Incorrect. Statement 3 is false; fly ash does contain toxic elements.
- (d) Incorrect. Statement 3 is false because of the words 'only' and 'does not contain any'.
Key point
Fly ash: coal residue with oxides of silicon, aluminium, iron, calcium and toxic heavy metals; used in bricks, cement, roads and mine filling.
Remember
Fly ash: useful in bricks and cement, but toxic.
Common mistakes
- Accepting 'only' and 'does not contain any' in statement 3.
- Thinking fly ash is pure waste with no use.
- Confusing fly ash (rises with flue gas) with bottom ash.
Exam tip
Two absolutes in one statement ('only', 'not any') make it false.
Sources
- Ministry of Environment, Forest and Climate Change — Fly Ash Utilisation Notification
- Central Electricity Authority — Report on Fly Ash Generation and Utilisation