Steel slag, a by-product of steel making, is produced during the separation of the molten steel from impurities in steelmaking furnaces. This process generates slag as a molten liquid melt and is a complex solution of silicates and oxides that solidifies upon cooling. Significant quantities of steel slag are generated every day from steel industries. Therefore, slags can become one of the promising materials in various applications such as in the transportation industry, construction, cement production, waste water and water treatment. With proper processing, steel slag can be re-used in road construction as an aggregate material.
Under the Honorable Prime Minister’s initiative of conversion of Waste to Wealth, the technology for modification of steel slag for use as aggregate for bituminous construction work has been developed by Central Road Research Institute-Council of Scientific and Industrial Research (CRRI-CSIR). Border Roads Organisation took the initiative for its trial/validation on Joram Koloriang Road stretch in Yazali district, Arunachal Pradesh, in different terrains and climatic conditions in collaboration with CRRI, New Delhi.
A team of BRO Officials and CRRI Scientists planned the logistics arrangements to make the trial successful in a time-bound manner while ensuring all the quality aspects.
All the logistics aspects such as collection of steel slag of various sizes in requisite quantity, shipment from source to nearest rail head to the trial site, further shipment to the site by road, processing of slag with hydrophobic chemicals considering the high rainfall area, preparation of Job Mix Formula and other activities needed for execution were identified to streamline the conduct of the trials. Selection of trial site was done carefully to incorporate challenging conditions to ensure its validation in all types of terrain and climatic conditions.
Steel slag in its natural form is unsuitable for use as aggregate due to its intrinsic high porosity and ferrous impurities. After proper treatment of the slag, it is crushed to produce aggregates of required sizes.
The steel slag aggregate used in this trial was generated at Tata Steel Plant, Jamshedpur, Jharkhand, and was transported from Jamshedpur to Arunachal Pradesh by Indian Railways - free of cost. A total of 21 wagons carrying 900 MT steel slag material were dispatched from Jamshedpur railway station, Jharkhand, to Harmuti railway station in Arunachal Pradesh, on 02 November 2022. This was flagged off virtually by Dr Jitendra Singh, Union Minister of Science & Technology. The rakes arrived at Harmuti on 06 November 2022 and were further transported to the trial site.
Execution of Task
The mixing was done at a 20-30 TPH plant located approximately 15 km away from the road stretch where the trial was conducted. Shipment time of a vehicle load from plant to site was approximately 40 minutes which is relevant with respect to heat retention property of steel slag aggregates. The mix temperature at plant was kept between 150-155ºC. The laying temperature was between 140-110ºC. Laying was done in accordance with conventional method of resurfacing. Considerable heat retention was seen in the mix which may be attributed to excessive heat retention of the steel aggregates. Excessive lateral and longitudinal movements were observed during compaction. However, density was seen to be achieved in fewer number of rollers passes. This may be the result of better compaction due to good mechanical interlocking of the steel aggregates because of their cubical shape and higher percentage of fractured faces.
Comparison of Properties
The properties of the bituminous mix taken at Hot Mix Plant of the resurfacing work using steel slag and the adjacent stretch of resurfacing work using stone aggregates were compared. The comparison is given in table 1.
|Properties||Bituminous Concrete with Stone Aggregates||Bituminous Concrete with Steel Slag Aggregates|
|Marshal Stability Value, KN||10||19|
|Flow Value, mm||3.50||2.50|
|Bulk Density, gm/cc||2.30||2.56|
After construction of the road, a cost benefit analysis was carried out to ascertain the advantages accrued out of this methodology. The cost benefit analysis of steel slag aggregates in comparison to stone aggregates is given in table 2.
|Item||Bituminous Concrete with Stone Aggregates||Bituminous Concrete with Steel Slag Aggregates|
|(a)||Cost of work (Lakhs)||71 .74||81.68|
|(b)||Expected Life (years)||5||8 (Estimated)|
|(c)||Cost of road Maintenance over 15 Years period (Lakhs)||215.20||163.36|
In addition to cost saving, there is a positive environmental impact of the use of steel slag. Slag is an industrial waste generated during the steel making process. Electric Arc Furnace Slag (EAFS) and Ladle Furnace Slag (LFS) are both produced at different stages of the steel making process. As part of this research, extensive engineering and environmental tests have been undertaken by researchers on steel slag aggregates to evaluate their potential impact on environment and it has been found that both EAFS and LFS pose no environmental risks for use as aggregates in roadwork applications.
By using steel slag aggregates in road construction, this waste material is given a new purpose and is kept out of landfills, reducing waste along with reduction in the use of stone quarries, especially in environmentally fragile hilly regions of the country, thereby having a positive impact on the environment.
Apart from being environmentally friendly, roads constructed using steel slag aggregate will be more durable. This will lead to reduction in their maintenance cost which will be economically beneficial in the long run. The engineering properties of LFS aggregates with their satisfactory geotechnical and environmental results, particularly high CBR values, indicates that the material is ideal for use as a construction material in roads for wearing courses, bases, subbases, and engineering fills.
EAFS, with its comparatively lower CBR value, has been found to be only suitable for use as a construction material for subbases and engineering fills. The usage of steel slag aggregates in roads would bring about a practical end-of-life alternative for their sustainable reuse and possibly divert large amount of these waste materials from landfills.
This initiative of converting Waste to Wealth by using a waste product and gainfully utilizing it for making environment friendly and durable roads even in high rainfall areas has been lauded by the Hon’ble Prime Minister of India.