How is STEEL SLAG helping INDIA'S ROADS?

- Vedant Goel

Managing Director, Neo Mega Steel LLP

The next time you pick up a fork and spoon to polish off a treat, know for a fact that a part of the steel that makes the spoon-fork called slag, a by-product, goes into the making of various products, including roads, glass, ceramics and cement. In fact, with each passing day, the uses of steel slag could match those of the final steel itself.

Ore that we see being excavated from the earth and dumped on trucks is subject to processing in a range of furnaces in the presence of various other chemicals (including lime and coking coal) to remove the presence of different elements, be it metal-based or otherwise. Prominent 'impurities' include copper, lead, nickel and silica in various forms and densities. When subjected to high temperatures and various flux chemicals, these 'impurities' rise to a different level and are removed from the furnace by various means. These so-called 'impurities' is slag. Its characteristics include:

• Stable at temperatures close to 1,000^oC: A property most looked forward to in construction and road-making for various reasons, it starts with being made part of asphalt (tar) or cement. Neither asphalt at its hottest state nor heated lime that forms the majority of cement roads can materially change the slag's composition or physical characteristics. A dense matter, water does not affect slag in any material way. These properties help slag maintain the form and shape of the road.
• When subjected to temperatures beyond 1,200^oC in the blast/arc furnace, limestone and silica that constitute slag fuse to form something that's as hard as ceramic and just as wear-resistant - quite unlike naturally occurring stone which forms the aggregate that goes into the making of most roads.
• The presence of fused and heated silica makes pieces of slag extremely rough on the outer surface, a property which aids in adequate adhesion.
• The fused mix of calcium and silica makes slag extremely dense with very low permeability, which does not let water or any other element pass through.
• Slag is also heavy for its volume, making it ideal when restricting movement in any direction.

Roads, a necessity anywhere in the world, ought to have specific characteristics, including: cost-effectiveness, durable and long-lasting, weather and wear resistance, easily available, and environmentally sound. Slag as aggregate in road-making matches all these points in every count!

Cost-effectiveness

You can't make steel without bringing about slag. It's like trying to burn diesel without raising smoke! Anywhere in the world, when iron ore is fed into the furnace, there are two clear lines of output: steel (in basic or advanced form) and slag (again in basic or advanced form). The more steel produced, the more slag. While steel has its marked uses, what does one do with its lumpy, stone-like by-product besides dumping it in landfills? Among others, it can just as easily be repurposed to form all forms of aggregates, from large lumps to almost sand-like particles with the very basic of machinery like crushers and sieves, otherwise used in crushing naturally occurring rocks and stones.

Durable and long-lasting

Subject to incredible heat that almost turns it into a liquid, slag with its mix of sedimentation and chemicals including calcium and silica cool to forms a substance which is said to rival ceramic in density. With technology now available to break it into sizes as required, it can turn any road, be it of asphalt or concrete, into a timeless classic with just the right amount of longevity while carrying tonnes of movement.

Weather and wear resistance

Steel slag has high abrasion resistance, soundness characteristics, bearing strength and durability. Coupled with its immense bulk density, strength, abrasion resistance and rough texture, it is best for making wear and wear-resistant roads in the most economical way, given that such a road would outlast its usage by large margins.

Easily availability

India's per capita consumption of 75 kg of steel is way, way below the world's average of 233 kg (and certainly below China's +500 kg) though the country is gearing up to be producing 300 MMTs of steel by 2030, making it one of the largest producers of steel. The scope for the production of steel is thus immense and inevitable. After going through its share of being part of landfill material and other myriad uses, it will be seen seriously in creating infrastructure given its volumes. That said, given that it can very easily be converted into forms that find easy application in road construction - compared with the blasting, transport, crushing and grading of natural stone, India would most naturally turn to steel slag for its roads.

Environmentally sound

There was a time in India when moving mountains made sense to make way for roads. It would clear and hurdle, and the aggregate thus produced found its way into making the road bed. With most mountains disappearing to make way for roads and other forms of construction, and rocks therein going into related or unrelated creations, India, in parts, suddenly finds that there aren't enough mountains to move! That said, you can't endlessly move natural structures to facilitate roads and other forms of construction or use the former as aggregates in the latter. Sooner or later, India would be at a crossroads where it would have to choose between saving the environment or going ahead with a very destructive form of construction. Into this conundrum comes a saviour. Steel slag! It not only aids in making roads but every other creation where tough, wear-resistant aggregates are a dire necessity. The added advantage of slag is that (given its composition) it isn't affected by weather, unlike natural stones and is perfect for roads on coasts or places where aggregates get exposed to the elements, including moisture and salts.

Like always, it's a necessity that's behind every invention. When rocks disappear with overuse, science and observation bring the perfect substitute: Slag!

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