How Steel Slag Roads Are Winning Over Conventional Roads?
Dr. Satish Pandey, Senior Principal Scientist at CSIR-CRRI’s Flexible Pavement Division, leads pioneering research on the utilization of steel slag in road construction. Drawing on extensive laboratory studies and field trials, he shares key challenges and learnings from landmark projects at Hazira, NH-66, and Ziro Valley, where roads built with processed steel slag aggregates continue to deliver exceptional durability, strength, and cost-efficiency, even under heavy traffic and diverse terrains.
What motivated you to explore the use of steel slag in road construction?
The motivation was to address the growing challenge of steel slag disposal. India, as the second largest steel producer in the world, generates nearly 22 million tonnes of steel slag annually as solid waste. Steel slag is slated to increase to 60 million tonnes per annum by the end of 2030 with expected capacity augmentation in different steel plants to achieve 300 million tonnes steel production annually. Hence, it is imperative to find sustainable application of steel slag to facilitate gainful utilization of steel slag.Utilizing steel slag in road construction offers an eco-friendly alternative to landfilling, reduces environmental hazards, conserves natural aggregates, and aligns with India’s waste-to-wealth and circular economy vision.
What research methodology, laboratory techniques, and field performance monitoring tools does CSIR-CRRI use to evaluate the suitability and long-term sustainability of steel slag in road construction?
CSIR-CRRI has developed customized steel slag valorisation technologies to convert different types of steel slag (BOF, EAF and CONARC) into processed steel slag aggregates. The valorization process involves conversion of raw steel slag into stable aggregates through slag pit operation, multi-stage crushing and metallic iron recovery followed by weathering or surface modification to inhibit volumetric expansion.Processed steel slag aggregates are further subjected to detailed physico-chemical characterization coupled with mechanical properties evaluation to assess its suitability as a substitute for good quality natural aggregates in road construction. Field trials are monitored through rutting, roughness, deflection, and skid resistance surveys, supported by core sampling and long-term visual assessment. This integrated approach ensures the suitability and sustainability of slag-based roads.
The Ministry of Steel, MoRTH, and NHAI should utilize CSIR-CRRI’s guidelines to facilitate large-scale utilization of processed steel slag aggregates in road construction.
How does steel slag compare to conventional materials in terms of durability, cost-efficiency, and ease of construction?
Steel slag roads reduce quarrying of natural aggregates, lower carbon emissions, and enable large-scale recycling of industrial waste. Pilot steel slag road projects have shown that the road built using processed steel slag aggregates is 30 to 40% thinner than conventional roads without compromising strength. These roads are also found to be 30 to 40% more economical than conventional roads in 100 to 125 km radial distance around the steel plant. Compared to conventional roads, steel slag pavements are more durable, resistant to weather extremes, and require far less maintenance, resulting in significant cost-efficiency and ease of construction.What measures does CSIR-CRRI take to ensure that roads built with steel slag meet critical performance standards such as rutting resistance and fatigue durability under India’s diverse traffic loads and climatic conditions?
We ensure performance by applying processing protocols, designing roads through calibrated traffic models, and mandating lab evaluations for rutting resistance, fatigue durability, and volumetric stability. Field performance is validated under varied climatic and traffic conditions, ensuring that roads meet critical standards across India’s diverse environments. In situ structural evaluation using heavy weight deflectometer exhibits higher stiffness in pavement layer which place it in a Perpetual Pavement category.
Please share some key challenges and learnings from trail road projects, and what best practices would you recommend for effective implementation and quality control of road projects using steel slag?
The initial challenges included high volumetric expansion, vesicular texture, and porous structure, propensity of high pH and heavy metal leachates, corrosion and carbonation potential.Key learnings from Hazira, NH-66, and Ziro Valley projects show that steel slag roads deliver superior performance and durability, even under heavy traffic and challenging terrains.
Proper preprocessing of slag is essential to control issues like expansion vesicular texture and porous structure, propensity of high pH and heavy metal leachates, corrosion and carbonation potential. Each batch of processed slag should undergo performance-based testing to ensure consistent quality. Training the site teams on handling and laying slag is equally important. Before large-scale use, constructing a pilot stretch helps in verifying field performance.
Adopting CSIR CRRI’s guideline for processing of steel slag, enforcing strict quality control at steel plants, and conducting trial sections are best practices for implementation. Performance testing for durability and moisture resistance, along with independent third-party checks during construction, ensures consistent results in such road projects.
How is CSIR-CRRI addressing concerns related to leachate or potential toxicity associated with the use of steel slag in road construction?
Conversion of steel slag from amorphous to crystalline phase minimizes the potential of heavy leaching from the slag. Probability of environmental contamination via leachate and toxicity can be assessed through TCLP test using ICPMS technique as US EPA protocol 311. Steel slag aggregates developed through a customized steel slag valorisation process were found to be safe on various environmental safety standards for road application.What long-term monitoring and performance evaluation systems has CSIR-CRRI implemented to validate the structural integrity, durability, and environmental safety of roads built with steel slag?
For steel slag roads, CRRI follows a structured long-term performance monitoring system that includes regular checks like rut depth and roughness surveys, deflection testing, and core sampling. A comprehensive environmental assessment has ruled out any potential risks through pH and TCLP tests, confirming safety under real-world applications. A long-term framework includes monitoring rutting, roughness, cracks, and deflection over years, supported by core analysis and periodic surveys.Steel slag road sections, that is, six lane roads built at Hazira, Surat, NH-66 Mumbai–Goa Highway, Ziro Valley Arunachal Pradesh, NH-33, Jharkhand, and Adani Hazira Port continue to show high durability and minimal distress, validating the long-term safety and structural integrity of steel slag roads.
From a researcher's perspective, what policy or regulatory changes do you believe would accelerate the adoption of steel slag in both highway and rural road construction?
CSIR-CRRI has developed a comprehensive “Guidelines for Processing and Utilization of Steel Slag as Processed Steel Slag Aggregates in Road Construction”. These guidelines are the outcome of five long years of comprehensive research sponsored by the Ministry of Steel. MoRTH and NHAI should utilize these guidelines at the earliest to facilitate large-scale utilization of processed steel slag aggregates in road construction.The Ministry of Steel, in conjunction with the Indian Railways, have found the mechanism to extend subsidy on transportation of steel slag aggregates. Placing steel slag in the fly ash tariff class rendered the processed steel slag aggregates cheaper when at a far distance from the steel plant. This approach will particularly benefit regions where good-quality natural aggregates are scarce, enhancing pavement life and ensuring cost-effective and sustainable construction.
Pilot steel slag road projects have shown that such roads, in comparison with conventional roads, are 30–40% thinner without compromising strength and 30–40% more economical as they require far less maintenance.
What is your long-term vision for sustainable and circular road construction using steel slag and other industrial by-products?
My vision is to integrate road construction into the broader circular economy framework, where processed steel slag aggregates become mainstream construction inputs. This transformation will reduce reliance on virgin aggregates, cut greenhouse gas emissions, and help India to achieve its sustainable development goals. CRRI’s role will be to keep advancing research, codifying guidelines, and training engineers to make circular road construction a nationwide reality.Dr. Satish Pandey is a Senior Principal Scientist and Head of the Flexible Pavement Division at CSIR-CRRI, New Delhi, and a Professor at the Academy of Scientific and Industrial Research. With 19 years of experience in Transportation and Highway Engineering, he specializes in pavement analysis and design, development of cost-effective construction materials and technologies, rehabilitation and maintenance of pavements, and utilization of waste and marginal materials in road construction.
He is the inventor of multiple innovative technologies transforming road construction and maintenance:
- Steel Slag Road Technology – India’s first steel slag road at Hazira, Gujarat
- REJUAPVE Technology – Asphalt pavement recycling
- TERASURFACING Technology – Industrial waste-based preventive maintenance
- MACROSURFACING Technology – Rehabilitation of distressed concrete pavements
- Modified Mix Seal Surfacing (MSS+)
- Cold Mix Technology
Published on:
13 November 2025
Published in: NBM&CW NOVEMBER 2025
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