Concrete spalling from reinforcement corrosion: the A28 case

On Thursday 29 January 2026, motorists and motorcyclists driving under a viaduct at the Lankhorst interchange (A28/A32, near Meppel) encountered chunks of concrete that had broken off and landed on the road surface. Rijkswaterstaat had to carry out emergency works and temporarily close the road for traffic safety. The cause: corrosion of the steel reinforcement in the concrete. This case exposes a structural problem that goes beyond a single viaduct — and shows why the failure mechanism of traditional reinforcement deserves renewed attention.

What went wrong at the Lankhorst interchange?

The viaduct at the Lankhorst interchange dates from 1976. Investigation after the incident found corrosion of the steel reinforcement in the concrete. In some places, the concrete cover above the reinforcement turned out to be thin, meaning the reinforcement lay close to the surface — and was therefore more vulnerable to the ingress of moisture and de-icing salts that cause corrosion.

This is not an isolated incident. It fits a broader pattern: many Dutch bridges, locks and viaducts date from the 1950s, 60s and 70s and are approaching, or have reached, the end of their technical service life. The Zeeland Bridge, for example, is also undergoing major maintenance in 2026, during which the steel moving sections are being renovated to address cracking and extend the service life by at least 30 years.

Why does reinforcing steel corrode in the first place?

Concrete normally protects the steel reinforcement embedded in it well: the highly alkaline environment of concrete forms a protective layer around the steel that inhibits corrosion. That protective effect disappears as soon as cracks form, or when carbon dioxide and chlorides (for example from de-icing salt) reach the reinforcement through the pores of the concrete. Once started, corrosion spreads: rusting steel expands, which in turn causes further cracking and further damages the concrete layer — a self-reinforcing process that continues to the point where, as at the Lankhorst interchange, chunks of concrete can break loose.

A thinner concrete cover (the layer of concrete above the reinforcement) accelerates this process, because moisture and chlorides have less distance to travel to reach the reinforcement.

The alternative: non-corrosive fibre reinforcement

Synthetic fibres such as aramid and polypropylene have a fundamentally different property than steel: they do not corrode. Where steel inevitably rusts in a damp, chloride-exposed environment, synthetic fibres remain chemically inert. This has two effects relevant to the service life of a structure:

• No corrosion-driven cracking. Because the fibre itself does not rust and therefore does not expand, the self-reinforcing damage process that occurs with steel does not arise.

• Better crack control indirectly also reduces corrosion risk for any remaining steel. In many applications, structural (steel) reinforcement remains necessary for the primary load-bearing capacity of a structure — fibres do not replace this on a one-to-one basis. But because fibres bridge and distribute microcracks in the concrete rather than allowing them to converge into one large crack, moisture and chlorides find it harder to penetrate to any steel present, reducing the risk of corrosion of that steel.

Where is this already applicable today?

It is important to be honest here: for large, primarily loaded structures such as bridges, structural steel reinforcement is generally still required — always seek advice from your structural engineer for this. Fibre reinforcement is not a one-to-one replacement for steel in that kind of application. However, fibre reinforcement is a proven, directly applicable solution for:

• Wearing courses and top layers on bridges and viaducts, where corrosion of thin reinforcement mesh often occurs first.

• Non-primary structural elements: industrial floors, foundations, service areas and linear structures.

• Repair and patch mortars, where a thin, corrosion-prone reinforcement layer is replaced by fibre reinforcement.

• Combination with existing steel reinforcement, where fibres limit cracking around the steel and thereby extend the service life of the whole structure.

What does this mean for managers of ageing infrastructure?

For road authorities dealing with infrastructure from the 1950s, 60s and 70s — which is a significant share of the Dutch network — the incident at the Lankhorst interchange is a warning to look a little further than the visible damage. Where repair work is taking place on a thin, corrosion-prone concrete layer, fibre reinforcement is worth considering as an alternative or supplement to new steel reinforcement — precisely because the risk that leads to this kind of incident (corrosion in a thin concrete cover) simply does not exist with synthetic fibres.

In conclusion

Corrosion of reinforcing steel is one of the main causes of ageing in Dutch concrete structures, and incidents such as the one at the Lankhorst interchange show what can happen once that process is too far advanced. Non-corrosive fibre reinforcement does not solve this specific failure mechanism everywhere — structural steel reinforcement remains necessary in many cases — but for wearing courses, top layers and non-primary elements it offers a direct way to prevent a recurring problem rather than repair it.