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Q26 (IAS/2020) Environment & Ecology › Pollution & Conservation › Waste management practices Official Key

Steel slag can be the material for which of the following ? 1. Construction of base road 2. Improvement of agricultural soil 3. Production of cement Select the correct answer using the code given below :

Result
Your answer: —  ·  Correct: D
Explanation

The correct answer is Option 4 (1, 2 and 3) because steel slag, a byproduct of steelmaking, possesses physical and chemical properties that make it highly versatile for industrial and agricultural applications.

  • Construction of base road: Steel slag is characterized by high bulk density, durability, and excellent abrasion resistance, making it an ideal aggregate for road base, sub-base layers, and asphalt mixtures.
  • Improvement of agricultural soil: It is rich in calcium, magnesium, and silicon. It acts as a soil conditioner to neutralize acidity (similar to lime) and provides essential micronutrients, enhancing soil productivity.
  • Production of cement: Due to its high lime content, ground granulated steel slag is used as a raw material in cement kilns or as a mineral admixture in blended cement, reducing carbon footprints and energy consumption.

Since all three applications are scientifically validated and widely practiced, 1, 2, and 3 are correct.

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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. Steel slag can be the material for which of the following ? 1. Construction of base road 2. Improvement of agricultural soil 3. Productio…
At a glance
Origin: Mostly Current Affairs Fairness: Low / Borderline fairness Books / CA: 0/10 · 10/10
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This is a classic 'Waste-to-Wealth' question. UPSC moved from its favorite topic 'Fly Ash' to 'Steel Slag'. While standard books define slag as a waste product, the application part comes from the 'Circular Economy' theme in current affairs (e.g., Surat's steel slag road). If a non-toxic bulk industrial waste exists, the government likely has a policy to put it into roads or cement.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Is steel slag suitable for use as base material in road construction (construction of base road)?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"In 1992, steelmaking slag was also des-ignated for use as road base course material."
Why this source?
  • Explicitly states that steelmaking slag was designated for use as road base course material.
  • Notes the material properties (hardness, wear resistance) that make it suitable for aggregate and base use.
Web source
Presence: 5/5
"Experience in the United States, Belgium, Japan, The Netherlands, and Germany has shown that steel slag, properly selected, processed, aged, and tested, can be used as granular base for roads in above-grade applications."
Why this source?
  • Reports international experience showing steel slag can be used as granular base for roads when properly processed and aged.
  • Highlights favorable mechanical properties (high stability, good soundness) for use in granular base.
Web source
Presence: 5/5
"It is generally used as an aggregate in road construction as base/sub -base, in asphalt mixtures and in waterway construction."
Why this source?
  • Identifies basic oxygen furnace slag as generally used as an aggregate in road construction specifically as base/sub-base.
  • Places steel slags in common practice for base/sub-base and asphalt mixtures, supporting suitability for base roads.

Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 28: Manufacturing Industry and The Iron and Steel Industry > The making of different types of iron and steel > p. 285
Strength: 5/5
“1, 650°C (3, 000°F). The oxygen in the ore and the carbon in the coke combine to form a gas (oxide of carbon) while the impurities in the ore combine with the limestone to form slag. The molten iron is then drawn off from the furnace base and led into moulds to solidify as pig iron which has a carbon content of 34%. 2. From the pig iron the following iron products are obtained as a result of further processing. (a) Cast iron is made by reheating the pig iron with steel scrap and then pouring the heated material into sand or metal moulds.”
Why relevant

Explains that impurities combine with limestone to form slag during iron/steel making, identifying slag as a common by‑product of steel production.

How to extend

A student could infer slag is widely available near steel plants and then check local maps or industry locations to judge availability and logistics for using it in road bases.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > Advantages: > p. 67
Strength: 4/5
“• Cement can be replaced by fly ash upto 35%, thus reducing the cost of construction, making roads, etc, • Fly ash bricks are light in weight and offer high strength and durability, • Fly ash is a better fill material for road embankments and in concrete roads. • Fly ash can be used in reclamation of wastelands. • Abandoned mines can be filled up with fly ash. • Fly ash can increase the crop yield and it also enhances water holding capacity of the land.”
Why relevant

Shows that industrial by‑products (fly ash) are already accepted as fill/base materials in road construction, giving a precedent for using other industrial wastes like slag.

How to extend

One could extend this analogy by comparing known properties and standards for fly ash base use to published tests for steel slag (e.g., compaction, drainage, durability) to assess suitability.

FUNDAMENTALS OF HUMAN GEOGRAPHY, CLASS XII (NCERT 2025 ed.) > Chapter 5: Secondary Activities > Access to Raw Material > p. 38
Strength: 4/5
“Raw material used by industries should be cheap and easy to transport. Industries based on cheap, bulky and weight-losing material (ores) are located close to the sources of raw material such as steel, sugar, and cement industries. Perishability is a vital factor for the industry to be located closer to the source of the raw material. Agro-processing and dairy products are processed close to the sources of farm produce or milk supply respectively.”
Why relevant

Notes industries based on bulky raw materials locate close to sources to minimise transport costs, implying heavy by‑products (slag) would be economical to use near steel plants.

How to extend

A student could use maps of steel plants and road projects to evaluate whether proximity makes slag a cost‑effective base material option.

Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 28: Manufacturing Industry and The Iron and Steel Industry > The properties of lron and Steel > p. 284
Strength: 3/5
“Iron and steel, which form the basis of ferrous metallurgical industries, are of the greatest importance in modern industry because they are capable of very extensive application. Their important properties are summarized below: l. Great strength and toughness. Iron and steel being so strong and tough are indispensable in modern constructional and mechanical engineering industries. 2. Great elasticity. Steel can withstand great stress and strain without appreciable distortion and is excellent for making machines and transporting vehicles. 3. High ductility. Steel can be drawn into bars, tubes, wires or plates without snapping. It is thus very useful for making machine parts and tools.”
Why relevant

Summarizes iron and steel properties (strength, toughness, elasticity), suggesting materials associated with steel production may yield mechanically robust aggregates.

How to extend

One could reason that if slag inherits mechanical robustness, lab tests for load‑bearing, abrasion and toughness would help confirm its fitness as a base material.

Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 28: Manufacturing Industry and The Iron and Steel Industry > NATURE, PROPERTIES AND USES > p. 283
Strength: 3/5
“Iron is the commonest, cheapest, and most versatile of all metals. It is, in fact, the base of the modern industrial complex. About 90 per cent of the world's iron ore is used in the making of steel. A host of secondary industries are based on iron and steel, including mechanical, constructional and electrical engineering, shipbuilding, the making of rails, automobiles, aircraft, bridges, machines and other equipment”
Why relevant

States steel is central to construction and many secondary industries, implying large volumes of steel production (and hence slag) exist that might be repurposed for construction uses.

How to extend

A student could combine this with production statistics (outside these snippets) to estimate potential slag supply for road base applications in a region.

Statement analysis

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Statement analysis

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