Prelims 2020

Q. 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
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
Correct Answer : a) 1, 2 and 3 only

Question from UPSC Prelims 2020 GS Paper


Copper Slag

Copper slag is a by-product of copper extraction. Its use in road construction can be considered environmentally friendly because it recycles a waste product that would otherwise require disposal, potentially in landfills. It can be used as a replacement for sand in concrete mixtures or as a sub-base material in road construction. This contributes to sustainability by reducing the demand for virgin materials.

Cold Mix Asphalt Technology

Cold mix asphalt technology allows for the production and placement of asphalt at lower temperatures compared to traditional hot mix asphalt. The lower temperatures mean that less energy is required for heating, leading to a reduction in carbon emissions. Additionally, cold mix asphalt can often be produced using more recycled materials than hot mix asphalt, further enhancing its environmental benefits.


Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. They are often made from synthetic polymers (such as polypropylene, polyester, and polyethylene) or natural fibers, and their use in road construction can improve soil stabilization and drainage, reducing the need for natural aggregate materials and promoting longer road life. This can lead to less frequent road repairs and maintenance, indirectly contributing to sustainability.

Hot Mix Asphalt Technology

Hot mix asphalt technology is a traditional method of producing asphalt that involves heating the asphalt binder to decrease its viscosity and mixing it with heated aggregate materials. While effective for creating durable road surfaces, the process is energy-intensive and produces significant carbon emissions. Therefore, it is less preferred from an environmental sustainability perspective compared to cold mix asphalt technology.

Portland Cement

Portland cement is a key ingredient in concrete and is widely used in road construction. However, the production of Portland cement is energy-intensive and generates a significant amount of CO2 emissions. While concrete roads are durable, the environmental impact of cement production makes this option less desirable for reducing carbon footprint.

Given the analysis above, the options that are preferred for ensuring environmental sustainability or to reduce carbon footprint in rural road construction are:

  • Copper slag (1), due to its recycling of waste materials.
  • Cold mix asphalt technology (2), because of its lower energy requirements and potential for using recycled materials.
  • Geotextiles (3), as they can improve road durability and reduce the need for virgin materials.

Therefore, the correct answer is: a) 1, 2, and 3 only

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