Bridges on track to open soon

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Construction of the two new $20.1m Waitaki Bridges, the first state highway bridges in the South Island constructed using weathering steel, is progressing well with the opening of the first of the two planned for February next year.

New Zealand Transport Agency Waitaki Bridges Project manager Steve Proud said all of the concrete work to the second bridge was complete and steel structural beams were starting to be erected.

When the steel beam work is completed, expected to be around the end of November, the pre-cast concrete deck will start being put in place.

“We’re hoping, at this point in time, to open the first bridge [on the Kurow side] in January/February next year,” he said.

The second bridge is also cracking on, and is expected to open, weather dependent, in about July next year.

When construction of the girders for the decks of the new bridges begins this month, motorists could be forgiven for thinking the bridges are being built from recycled “rusty” steel, Mr Proud said.

The two new bridges will be the first state highway bridges in the South Island to be constructed using weathering steel, a high-strength, low-alloy steel that develops a weathered, rusty, look.

The weather-resistant steel was chosen as an environmentally-friendly option, which would also have economic and health and safety benefits in the long term.

“The bridges will not need to be painted at the time of construction and there is no associated ongoing painting maintenance cost,” he said.

The rusting process is started in the same way as conventional steel, but the specific alloying elements in weathering steel produce a stable rust layer that adheres to the base metal. Over time – two to five years – the orange-brown appearance changes to a characteristic dark-brown.

“This rust patina develops under alternating conditions of applying water and drying the steel to produce a protective barrier that prevents further oxygen or moisture reacting with the steel,” he said.

Mr Proud said, while not suitable for all locations, the Waitaki Bridges were in the ideal environment for this form of construction.

“The choice of weathering steel also reflects the heritage of the existing bridges and harmonises with the environment,” he said.

The Transport Agency’s first bridge to be built from weathering steel was on the State Highway 1 Mercer to Longswamp off-ramp. The bridge was built in 2006 and the protective layer has been slowly forming, the uncoated steel changing from rusty red-brown to dark brown.

The two new two-lane bridges being built on State Highway 82, between Kurow and Hakataramea, replace two ageing single-lane wooden bridges over the Waitaki River and are part of the Transport Agency’s $1 billion programme of investment in Canterbury’s transport network from 2012 to 2015.

About 25 people, of the site team, have been stationed in Kurow, from out of town, since construction started. Mr Proud said hoteliers, motels and rental property owners had all benefited by the construction.

By Rebecca Ryan