Saving a piece of history

Challenge

Due to irreversible chloride-induced corrosion, Allt Chonoglais Bridge was unfit to carry future traffic loads. The entire structure had to be replaced with a stronger steel framework.

Solution

The new reinforced structure incorporates stainless steel rebar. Critical sections are reinforced with lean duplex alloys, offering exceptional corrosion-resistance and resulting in a bridge with a durable construction and reduced lifecycle costs.

Delivery

Steel grade: Outokumpu Forta DX 2304
Product form: Rebar

A steady stream of traffic traverses safely across the new 40-meter-long bridge that spans the River Kinglass in north Scotland. Two years earlier, the crumbling bridge was deemed beyond repair. Its structure had suffered from spalling and delamination of the concrete and its flaking exterior exposed severely corroded reinforcement bar inside. Identified as too weak to meet modern traffic needs on the A82 trunk road, the entire bridge needed replacement with a stronger structure.

Instead of extending the bridge’s life through interval construction work, the aim was to find a solution through a life-cycle approach that would extend the bridge’s lifespan with as low maintenance as possible.

 

Resistance to chloride corrosion

“The corrosion of the carbon steel reinforcement was caused by the ingress of chlorides from de-icing salts. Consequently, in more hostile, snow and ice environments, you need a rebar product with greater chloride corrosion resistance,” says Stephen Jones, Rebar Commercial Manager and Head of Long Products Research and Development at Outokumpu.

The project involved the partial demolition of the three-span bridge and its replacement with a composite steel and concrete single-span bridge deck. “The concrete structure incorporates stainless steel rebar in areas exposed to de-icing salts during the winter months. This includes the bridge deck, abutments, wing walls and bearing plinths,” explains Jones.

 

Old made new again

After discussions with Outokumpu, the customer selected Forta DX 2304 rebar due to its competitive cost and exceptional chloride resistance. “This alloy has a chloride threshold level beyond the levels normally expected at typical rebar depths, even in the most severe of chloride environments,” notes Jones.

The new structure meets the needs of modern-day traffic while retaining attractive features of the original bridge, including the locally sourced granite. Behind the traditional aesthetics, the stainless rebar construction will provide a safe and smooth crossing for at least the next 120 years.

Recommended products and insight

Bridges and infrastructure

Bridge projects are in a class of their own – just like Outokumpu stainless steel. Marked by harsh environments, heavy lifetime usage and high aesthetic expectations, bridges demand special considerations upfront if they’re to go the distance.

Structural applications

An inspired choice for load-bearing structures, stainless steel delivers exceptional strength with added benefits – like the corrosion resistance of steel in the Supra range, and light weight of high-strength duplex steel in the Forta range.

Forta

The Forta range contains duplex and other high strength stainless steels that enable thinner structures and weight reduction (measured in Rp0.2 > 400 MPa. PRE 16 to 43).

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