Steel Slag in Road Construction

In line with Government’s ‘Waste to Wealth’ mission and encouraging environmentally sustainable National Highways construction, a trial use of ‘Steel Slag’ in road construction has been initiated by the National Highways Authority of India (NHAI).

Major Highlights:

  • Earlier, NHAI had announced testing the use of phosphor-gypsum — a by-product of fertilizer production — in road construction on national highways.
  • NHAI has also used fly ash — the fine residue of coal combustion in thermal power plants — for the construction of highways and flyover embankments.
  • NHAI is encouraging the use of waste plastic in road construction. Studies have established that roads built using plastic waste are durable, sustainable and increase the life of bitumen.


  • The initiative will help to address the challenge of shortage of materials used in the development of the National Highways and could replace natural aggregates such as sand, gravel, or crushed stone with the waste material from the steel industry.
  • The use of such materials in road construction shall make construction more economical and will promote the circular economy.

About Steel slag:

  • Steel slag is a solid waste or an unavoidable by-product during the production of steel. It is produced in large quantities (nearly 100-150 kg per tonne of steel) during the separation of the molten steel from impurities in steel-making furnace.


  • Steel slag particles become an integral part of the concrete matrix, acting as a filler and helping to improve the density of the concrete i.e., improve its strength and durability.
  • Steel slag is resistant to weathering and can withstand more load and pressure than traditional aggregates such as gravel and crushed limestone.

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