Explained: Steel Slag — A Game-Changer For Road Construction

India has developed the world's latest Steel Slag Road Technology, which allows for large-scale utilisation of waste slag from steel plants for road construction, according to Jitendra Singh, Union Minister of State (independent charge), Science and Technology.

The technology to use steel slag for road construction was created by the Council of Scientific and Industrial Research (CSIR)-Central Road Research Institute (CRRI), which aims to tackle the issue of slag generated by steel plants.

Border Roads Organisation (BRO) is utilising steel slag, the waste produced during steel production, to construct stronger and more durable roads along the India-China border in Arunachal Pradesh.

Tata Steel provided the steel slag free of cost, which was then transported from Jamshedpur to Arunachal Pradesh by Indian Railways.

V K Saraswat, a member of the Niti Aayog, stated that the CSIR-CRRI steel slag road technology will help the BRO develop long-lasting heavy-duty roads in important border areas.

He underlined the importance of adopting alternative road materials such as processed steel slag aggregates instead of natural aggregates for road development in hilly areas such as Arunachal Pradesh to preserve biodiversity and mountainous terrain.

Union Minister of State for Steel Faggan Singh Kulaste said that the Steel Slag Road technology is playing an important role in realising Prime Minister Narendra Modi’s mission of ‘Waste to Wealth’.

What is Steel Slag Road Technology?

The technology has been developed by the CSRI under a research project in collaboration with the Ministry of Steel, Government of India and four major steel manufacturing companies of the country, viz., ArcelorMittal Nippon Steel, JSW Steel, Tata Steel and Rashtriya Ispat Nigam.

This technology facilitates the large-scale utilisation of waste steel slag in steel plants and has proved very useful in the effective disposal of about 19 million tonnes of steel slag generated in the country.

The advantages of steel slag roads. Not only are they approximately 30 per cent cheaper than conventional paving, but they are also more resilient and resistant to unpredictable weather conditions.

In June of last year, Surat in Gujarat became the first city in India to have a processed steel slag road constructed. This was made possible through a joint-venture project involving the CSIR-CRRI, the Union Ministry of Steel, NITI Aayog, and Arcelor-Mittal Nippon Steel at Hazira.

About one lakh tonne of steel slag aggregate has been used in its construction. No natural ballast of any kind has been used in the construction of this road.

The first road made with steel slag road interpretation technology has become famous for its technological excellence at the national and international levels.

Despite being 30 per cent shallower than roads paved with natural aggregates, the experimental stretch of a six-lane road paved with slag has proven to be highly resistant to weather and heavy truck traffic.

The second steel slag road was constructed at NH-33 Jamshedpur, and the third steel slag road was completed at NH-66 Mumbai to Goa Highway in Maharashtra.

The National Highways Authority of India (NHAI) has also successfully used this technology in road construction on National Highway-66 (Mumbai-Goa) in collaboration with JSW Steel, under the technical guidance of CRRI.

The Process : The slag is a byproduct of a steel furnace, produced when the furnace burns at temperatures of 1,500-1,600 degrees Celsius. It is in the form of molten flux material and is considered an impurity.

To cool the molten material, it is poured into slag pits and undergoes a customised procedure to transform it into stable steel slag aggregates. According to an inventor of steel slag road technology and CRRI principal scientist Satish Pandey, these aggregates possess better material properties compared to the natural aggregates typically used in road construction.

How Steel slag road is different from regular road?

To construct a heavy-traffic road capable of withstanding the load of 1,000 to 1,200 trucks per day, the Indian Road Congress guidelines recommend a road thickness of around 600 to 700 mm on a foundation with eight per cent CBR (California Bearing Ratio).

However, roads made from steel slag can be 30 per cent thinner due to their superior material characteristics. Additionally, the construction costs of these steel slag roads are approximately 30 per cent cheaper. The Hazira road, for example, utilises around one lakh tons of processed steel slag.

According to B R Bhatt, Engineer at SMC's Road Development Department, "the approximate construction cost per square metre of a processed steel slag road is Rs 1,150 as opposed to Rs 1,300 for a bitumen road and Rs 2,700 for a cement or concrete road.

Because of its inherent high strength and stiffness, steel slag bituminous surfacing will provide a more lasting heavy load road surface in the face of harsh weather conditions in hilly regions.

Surface temperature of the road during peak summer time was found limited to 1 to 2 celsius higher than conventional bituminous road built with natural aggregates, according to Pandey. Thermocouples are embedded in the road to measure temperature.

However, because natural materials are extracted and treated, such roads have a far reduced carbon footprint. Furthermore, after mining and crushing, the material must be transported from one location to another. There is no blasting, drilling, or crushing in steel slag roads because the material is waste from the steel industry that is treated and changed to the form of aggregate material needed in the building.

The use of waste steel slag in road construction reduces pollution caused by nearby waste dumps. Steel waste particles also enter the air and soak into the ground, reaching the subsurface water table.

How will steel slag roads affect vehicles?

When it comes to the effects of such roads on vehicles, experts say the effect on tyres will be insignificant. Steel slag melts at temperatures above 1000 degrees Celsius, while peak summer temperatures in India do not exceed 45 degrees Celsius. Furthermore, the upper layer is composed of bitumen layers.

Is steel slag road Eco-friendly?

According to Surat Municipal Corporation (SMC) Road Development department authorities, using processed steel slag in road construction allows for the sustainable use of waste and minimises reliance on perishable natural aggregates.

This process is also expected to reduce GHG emissions and the carbon footprint of road construction activity, and it is consistent with India's commitment to UN Sustainable Development Goal No. 9 of building resilient infrastructure through inclusive and sustainable industrialisation and green technologies.

This new technological approach also addresses the issue of environmental degradation caused by waste steel slag and unsustainable natural aggregate mining and quarrying.

Steel slag roads have been shown to last ten years as opposed to three to four years for bitumen roads, significantly lowering maintenance expenses.

Scope for India

The abundance of steel slag generated as a byproduct of India's steel industry presents a significant scope for the country.

Being recognised as the world's second-largest steel producer, India currently produces around 19 million tons of steel slag annually, and this is expected to increase to 60 million tons by 2030. With approximately 200 kg of slag generated for every tonne of steel production, finding efficient disposal methods for steel slag is crucial to mitigate environmental challenges.

One of the major issues is the accumulation of large heaps of steel slag around steel plants, causing water, air, and land pollution.

To address this problem, the Steel Ministry is collaborating with the Ministry of Science and Technology and the Ministry of Road Transport and Highways to explore the potential of steel slag road technology across the country.

By utilising steel slag in road construction, India can turn this waste into a valuable resource and address both environmental and infrastructural concerns. Steel slag road technology has shown promise as a cost-effective and durable alternative to traditional materials like bituminous concrete, making it an attractive option for building resilient roads.

The scope for India lies in actively promoting the use of steel slag in various applications, particularly in road construction, which not only helps manage the waste but also contributes to greener and cleaner infrastructure development.

Way Forward

Under Prime Minister Narendra Modi's leadership, India's National Highways network has witnessed remarkable growth, with the addition of approximately 50,000 km of new highways in the last nine years.

The construction speed has more than doubled during this period, reaching an impressive rate of 29 km per day, up from 12 km per day in 2014.

Furthermore, India currently boasts the world's second largest National Highways network, spanning 1.45 lakh km, behind only the United States.

As India continues to invest in expanding its National Highways network, incorporating steel slag road technology can play a vital role in enhancing the sustainability and efficiency of road construction practices.

By establishing a connection with the market and actively promoting the usage of steel slag, the industry can effectively contribute to the growth and maintenance of the highway network.

Such efforts will undoubtedly pave the way for a more robust and modern transportation infrastructure in the country.