UPSC Prelims 2020 Q78: Environment & Ecology – Renewable Energy & Green Technologies

UPSC Prelims 2020, General Studies Paper I · Environment & Ecology

In rural road construction, the use of which of the following is preferred for ensuring environmental sustainability or to reduce carbon footprint? 1. Copper slag 2. Cold mix asphalt technology 3. Geotextiles 4. Hot mix asphalt technology 5. Portland cement Select the correct answer using the code given below:

(a) 1, 2 and 3 only
(b) 2, 3 and 4 only
(c) 4 and 5 only
(d) 1 and 5 only

Answer: (a) 1, 2 and 3 only

Explanation

Rural Road Construction: Environmental Sustainability Materials

Material/Method	Reduces carbon/is eco-friendly?
1. Copper slag	YES - industrial waste reuse
2. Cold mix asphalt	YES - lower heating = less energy
3. Geotextiles	YES - reduces fill requirement
4. Hot mix asphalt	NO - energy-intensive heating
5. Portland cement	NO - high carbon emissions

Environmental rationale:

1. Copper slag: Replaces virgin aggregate (mining reduction)

2. Cold mix: Mixes at ambient temp (vs 160°C for hot mix) -> energy savings ~30%

3. Geotextiles: Stabilize soil without additional material (reduces excavation)

Answer: (a) 1, 2 and 3 only - Copper slag, cold mix, geotextiles are sustainable.

Why each option is right or wrong

(a) CORRECT. Copper slag (1), cold mix asphalt (2), and geotextiles (3) are sustainability-preferred options. Hot mix (4) and Portland cement (5) are carbon-intensive.
(b) Incorrect. Hot mix asphalt (4) is energy-intensive.
(c) Incorrect. Includes Portland cement (5), a high-carbon material.
(d) Incorrect. Includes high-carbon materials.

Key point

Green road tech: Cold mix saves 30% energy vs hot mix. Industrial wastes (slag, ash) reduce virgin aggregate demand. Geotextiles extend pavement life (less frequent rebuilding).

Remember

For environmental sustainability in rural road construction, preferred materials/methods are: (1) Copper slag (industrial waste reuse), (2) Cold mix asphalt technology (lower energy), (3) Geotextiles (reinforcement without extra fill). Hot mix asphalt and Portland cement are carbon-intensive.

Common mistakes

Assuming all asphalt = same carbon footprint. Cold mix is 30%+ less carbon-intensive.
Missing industrial waste reuse benefits - copper slag cuts mining + landfill burden.
Confusing geotextiles (reinforcement) with cement. Geotextiles = natural fibers/polymers, not cement.

Exam tip

Sustainable road construction (India PM-KSY): Focus on cold mix, waste materials (slag, ash), geotextiles. Reduces cost by 10-15% + carbon by ~30%.

Sources

Ministry of Rural Development - Green Road Construction Guidelines
IRC - Rural Road Construction Specifications

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