Korea's Steelmakers, Expressway Operator and Asphalt Producers Sign MOU to Put Steel Slag in Highway Pavements

The deal at a glance

Three organisations signed a memorandum of understanding on 11 August 2026 to promote the use of steel slag as aggregate in "eco-friendly" asphalt pavement:

• Korea Iron & Steel Association (KOSA) — the industry body representing Korean steelmakers, which supplies the slag.
• Korea Expressway Corporation (KEC / 한국도로공사) — the state-owned operator and maintainer of the national expressway network, which owns the pavement specifications and the maintenance pipeline.
• Korea Ascon Industry Cooperative Federation (한국아스콘공업협동조합연합회) — the federation of domestic asphalt-mix (ascon) producers, which operates the mixing plants that would actually consume the slag.

In other words, the MOU ties together the three links of a supply chain — by-product producer, specification/site owner, and material processor — which is exactly the combination that previous, more fragmented attempts to commercialise slag aggregate in Korea lacked.

What is known: the MOU exists, it was announced by KOSA on 11 August 2026, and its stated purpose is introduction (도입) of steel-slag asphalt on an unspecified scale.

What is not yet known: the tonnages, the specific expressway sections, the timeline, any price or offtake commitments, and whether the relevant Korean standards — the ascon cooperative's group standard (단체표준) for asphalt mixtures and KEC's own construction specifications — have been amended to accept slag aggregate. Until those change, an MOU cannot by itself move material.

Why steel slag is a harder sell than it looks

Steel slag is not a niche by-product in Korea; it is a bulk one. Korean integrated mills generate several million tonnes a year of converter (steelmaking) and blast-furnace slag combined, and the industry has spent more than two decades trying to move it up the value chain rather than into low-grade fill and reclamation.

The technical problem is that not all slag is interchangeable:

The free-lime problem is the crux. Converter slag that has not been properly aged or stabilised can swell after it is laid, cracking or heaving the pavement above it. That is why slag has historically gone into unbound layers — roadbase and embankment — where some movement can be tolerated, rather than into bound layers such as asphalt wearing courses, where a millimetre of expansion becomes a maintenance claim.

The Korean term 제강슬래그 specifically denotes steelmaking (converter/electric furnace) slag, not the easier-to-place blast-furnace material. The MOU's framing around steel slag rather than slag generally is therefore a meaningful signal: it targets the harder fraction.

What makes asphalt a plausible destination

Asphalt is attractive because:

1. It is a large, recurring consumer. Expressway maintenance and rehabilitation consume aggregate continuously, in a predictable annual rhythm.
2. Slag has genuinely good engineering properties for it. Steel slag is hard, angular and rough-textured, which tends to improve aggregate interlock and skid resistance — a real safety argument on high-speed expressways, and a reason the material is accepted in asphalt in Japan, Germany and parts of the US.
3. It displaces imports and quarried stone. Korea is aggregate-poor in the metropolitan regions where slag is generated, so slag aggregate shortens haul distances and reduces quarry pressure — the core of the "eco-friendly" (친환경) claim.
4. It offers slag a higher-value outlet. Diverting tonnage from roadbase and land reclamation into asphalt improves the by-product economics for the mills.

The three-party structure is the interesting part

Most slag-recycling announcements in Korea have been bilateral — a mill and a research institute, or a mill and a construction company. Those tend to produce demonstration stretches and papers rather than routine commercial use.

This MOU is different because it brings in the two gatekeepers whose approval is effectively mandatory for scale-up:

• KEC writes the specification. If KEC's expressway construction and maintenance specifications do not permit slag aggregate in a given asphalt layer, no contractor will buy it, regardless of price. KEC also controls the maintenance schedule, i.e. the demand signal.
• The ascon federation controls the plants. Asphalt is a hot, short-lived product: it must be mixed close to where it is laid and paved within hours. Even a fully approved material will not be used unless the roughly 500-plus domestic batch plants are willing to hold slag in their stockpiles, adjust their mix designs and take on the quality-control burden.

Getting both gatekeepers to sign the same document is a shortcut through the standardisation process — or at least an attempt at one.

The standard-setting bottleneck

The unresolved question is the status of the ascon cooperative's group standard (단체표준) for asphalt mixtures. Korean public procurement typically references either KS standards or recognised group standards; if the group standard still excludes or tightly caps slag aggregate, the MOU's objectives cannot be delivered through ordinary tender documents. The same applies to KEC's internal specification revisions, which take time and require test-track evidence.

A reasonable expectation, based on how similar materials have been introduced in Korea, is a phased path: demonstration sections, performance monitoring over at least one or two freeze–thaw and summer-heat cycles, then specification revision, then volume. That would put meaningful commercial consumption well beyond 2026 even in a best case.

Steel-industry implications

For Korean steelmakers the deal matters less for the revenue — slag aggregate sells for a fraction of steel's per-tonne value — than for three other reasons:

1. By-product cost avoidance. Slag that cannot be sold must be stockpiled, processed or landfilled, all of which carry cost and regulatory exposure. Every tonne placed in a highway pavement is a tonne that does not need a disposal route.

2. Resource-circulation credentials. Korean mills face increasing pressure — from regulators, customers and export-market carbon rules — to demonstrate circular-economy performance. A government-owned expressway network accepting steel slag is a highly legible credential, and one that travels well in ESG reporting and in the sustainability documentation that accompanies steel exports to the EU and elsewhere.

3. Capacity headroom. As mills modernise and, in some cases, expand, slag generation is not shrinking. Securing a durable, specification-backed outlet in a bound layer is worth more strategically than a one-off sale.

Notably, steel itself is barely involved: no new steel grade or product is implied here. The steel industry's role is as a materials supplier, and the article's value to steel professionals lies mainly in the by-product and ESG dimensions rather than in demand for finished steel.

What to watch

• Specification documents. The single most informative development would be a revision to KEC's construction specification and/or the ascon federation's group standard naming steel slag aggregate, with a permitted replacement ratio.
• A demonstration section. Look for a named expressway route and an announced test stretch with instrumentation (expansion, stiffness, skid resistance).
• Tonnage figures. Any published target — even a pilot-scale one — converts the MOU from intent into a plan.
• Mix-design guidance. Pre-treatment requirements (aging, steam treatment, or blending to control free CaO) will determine whether plants can realistically adopt the material without new equipment.
• Procurement language. The clearest sign of real adoption is slag aggregate appearing as an approved material in an actual tender or maintenance contract, not in a press release.

Assessment

The MOU is best read as a procedural milestone rather than a commercial one. It is meaningful because it enrols the two organisations that have historically blocked scale adoption — the specification owner and the mixing industry — rather than because it commits tonnage.

Two things determine whether it succeeds. Technically, whether pre-treated converter slag can meet the volumetric-stability requirements that expressway pavements demand. Institutionally, whether the standard-setting process moves fast enough to keep the three parties aligned before the next round of maintenance planning cycles.

Given the lack of published tonnage, schedule, sites or specification changes, the honest reading is that steel slag in Korean expressway asphalt remains a demonstration-stage proposition as of the announcement. Readers should treat the 11 August 2026 MOU as the starting gun for a standards and pilot-testing process, not as evidence that the material is already being laid at scale.