Transforming By-products into Opportunity

POSCO, one of the world’s leading steel producers, is demonstrating a novel approach to sustainability by repurposing its steel by-products. Among these, steel slag stands out, accounting for over 75% of the total waste generated during the production of molten metal. This leftover material, once considered industrial refuse, is now being seen as a vital resource in the construction of long-lasting roads.

What is Steel Slag?

Steel slag is a residue left after extracting iron from iron ore during the steelmaking process. It appears in solid, rocky form, and has typically been discarded or only minimally repurposed. However, studies and engineering trials have found that steel slag possesses higher strength and angularity than traditional natural aggregates such as gravel or sand. These characteristics make it an ideal candidate for heavy-duty infrastructure applications, especially asphalt road pavement.

Growing Demand for Durable Road Infrastructure

According to the Korea Expressway Corporation, the demand for highway asphalt pavement is steadily increasing, especially with the rise in large vehicle traffic and unpredictable climate conditions. At the same time, the supply of first-class natural aggregates required for constructing durable roads is shrinking. This scarcity has prompted researchers and infrastructure companies to look for sustainable alternatives, and steel slag has emerged as a frontrunner.

Superior Performance Under Stress

POSCO’s research has revealed that asphalt roads constructed with steel slag have up to 2.2 times greater durability than those built with conventional materials. This extended road life, reaching up to 64 months, results from the angular nature and consistent shape of the slag, which allows for tighter interlocking, like well-fitted puzzle pieces. This ‘engagement effect’ enhances both structural stability and overall strength of the road surface, reducing the likelihood of cracks and potholes.

A Joint Venture for Smarter Roads

In response to these findings, POSCO has partnered with domestic asphalt concrete (ascon) manufacturers to develop new asphalt mixtures using steel slag as aggregate. In 2024, the team successfully applied the mixture to five sections of National Route 3, marking a major step in the practical rollout of this innovation. These road sections are now serving as pilot areas to monitor real-world performance and validate lab results.

Circular Economy in Motion

This initiative aligns with POSCO’s larger vision of contributing to a circular economy and eco-conscious society. By recycling what was once industrial waste, the company not only reduces the burden on landfills but also conserves natural resources that would otherwise be extracted for road construction. It is a prime example of industrial symbiosis, where the waste of one process becomes the raw material for another.

Economic & Environmental Advantages

Steel slag offers dual benefits: it reduces material costs and lowers environmental impact. The cost of processing and transporting steel slag is relatively low compared to quarrying natural aggregates. Moreover, using recycled materials cuts down emissions associated with aggregate mining and hauling. The net result is a greener, more cost-efficient model for infrastructure development.

Looking Ahead

Given the successful early results, POSCO plans to expand its use of steel slag in public infrastructure projects across South Korea. With more roads being built or repaired each year, the demand for high-strength, sustainable materials will only grow. If this trend continues, steel slag may soon become a mainstream component in global road construction.

Key Takeaways

• POSCO is using steel slag, 75% of its steelmaking by-products, as a strong and eco-friendly material for asphalt road construction.

• Roads paved with steel slag show up to 2.2 times higher durability and last up to 64 months longer than those built with natural aggregates.

• POSCO collaborated with ascon manufacturers and applied the slag-based asphalt on five sections of National Route 3 in 2024.