Over the past 60 years, Halifax Harbour Bridges (HHB) has experimented with a number of paints and coatings to protect its two suspension bridges.
Painting such large pieces of infrastructure by hand using seasonal workers is a daunting task…and as the bridges age, an expensive one. In the HHB 10-year capital and maintenance plan deemed “necessary and appropriate by the Nova Scotia Utility and Review Board in October 2021, more than $75 million has been earmarked for paint and steel work.
Early bridge painting efforts involved three coats of a lead -based oil alkyd mixture, but with the development of new options – and an increasing awareness of environmental and health concerns –coating systems that are safer for workers and better for the bridges have been adopted.
But for all of the care painters have taken, recent coating failures, rust issues and steel section losses clearly indicate the existing coating system is no longer effective.
“You can’t just put layers upon layers of paint for 50 years and expect the kind of protection we need to guarantee the integrity of the bridge,” says Ahsan Chowdhury, HHB’s Chief Bridge Engineer.
Future painting efforts will requires the removal of the existing coatings system to bare steel, the identification and repair of required steel work, and then using industry best practices, implementation of a new corrosion protection system.
The coating work will require full containment, special access, environmental control, abrasive blasting, and the application of a three-coat system. The project must be conducted safely, with little or not impact on the environment, and minimal disruption to the neighbours.
The next phase of work – the main towers and truss spans- will be detailed in a $30 million tender to be issued in early 2023, but associated tenders for the decking system, steel piers and approach spans are expected to total an estimated $75 million.
We are looking for the most cost-effective way to protect the bridges and minimize future maintenance for the next 25 years,” says Chowdhury.