Prelims 2015 · archive
EasyWith 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.
Answer & explanation
Answer: (a) 1 and 2
Fly ash is a useful building material. It goes into bricks and partly replaces Portland cement in concrete, so statements 1 and 2 are correct. Statement 3 is wrong for two reasons: fly ash also contains alumina and iron oxide, and it carries trace toxic metals such as arsenic, lead and cadmium.
- ✓ 1. India's Fly Ash notification (1999) mandates the use of fly ash in manufacturing ash-based products such as cement, concrete blocks and bricks. Fly ash bricks are a standard building material.
- ✓ 2. Fly ash is a pozzolan, so it can be used as a partial substitute for Portland cement in concrete.
- ✗ 3. Silica, alumina and iron oxide are the main constituents of fly ash, and lime (CaO) is present in some fly ashes, so it is not made of SiO2 and CaO only. It also carries trace elements such as arsenic, cadmium, lead, mercury and selenium, so it is not free of toxic elements.
Remember · Fly ash is used in bricks, cement and concrete, but it is not inert. It contains silica, alumina, iron oxide, lime and toxic trace metals such as arsenic, lead and mercury.
Sources
- MoEF&CC – Guidelines for disposal/utilisation of Fly Ash (Office Memorandum) ↗ “The Fly Ash notification (1999) mandates the use of fly ash for the purpose of manufacturing ash-based products such as cement, concrete blocks, bricks, panels or any other material”
- US EPA – Coal Combustion Residual Beneficial Use Evaluation: Fly Ash Concrete and FGD Gypsum Wallboard ↗ “Fly ash may be used as a partial substitute for the portland cement in concrete because it is a pozzolan … These include aluminum, antimony, arsenic, barium, beryllium, boron, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, molybdenum, nickel, selenium, silver, strontium, thallium, uranium, vanadium, and zinc.”
Question: UPSC Civil Services (Preliminary) 2015, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·