Part of Mackenzie King Bridge in 'advanced state of deterioration'

Ottawa's Mackenzie King Bridge is in worse shape than expected, as the city learns that major components of the section over Nicholas Street are in an "advanced state of deterioration."

That's forcing the city to launch another rehabilitation project, over and above ongoing renewal work that has faced repeated delays.

The city is budgeting $5.4 million for the extra work over Nicholas Street, just east of the Rideau Centre, with the project schedule putting the completion date in the summer of 2027.

The existing renewal project covers three sections of the bridge and began in 2022. It includes work on joints, concrete, waterproofing and drainage, as well as narrowing the road to add raised cycle tracks and wider sidewalks.

That work was initially slated to wrap up last year. But the city announced in 2023 that a deteriorated bridge deck and the need for additional concrete repairs would delay completion until the end of this year, a date that was then pushed back to late 2026.

Overpass not included

But that $25-million project did not include the Nicholas Street overpass. Until recently, the city said the overpass was in good condition and did not require structural rehabilitation.

That has proven to be incorrect. Last September, the city retained Parsons and Bridge Check Canada to do a detailed condition assessment on the overpass.

It released the results last week. The assessment found "several components exhibiting significant deterioration requiring rehabilitation in the near future."

Ted Sherwood, an associate professor in structural engineering at Carleton University who specializes in concrete structures, read the Parsons assessment and said the bridge over Nicholas Street seems to be at a tipping point.

"The bridge is not in good condition," he said. "There is a risk of corrosion and continued damage with concrete falling onto pedestrians and traffic below, so I would say now is a good time to do the repairs."

The assessment found cracks on the underside of the bridge deck, as well as the girders and piers that support it. It said the bridge is also suffering from "spalling" and "delamination." Sherwood explained what that means.

"When rebar corrodes inside concrete it expands, and those expansive forces can cause concrete on the surface to fall off and we call those spalls. If it happens over a larger area, we can sometimes call that a delamination," he said. "With the delamination, the rebar can completely separate from the concrete, and that's a very dangerous situation."

Major rehabilitation recommended

Parsons recommended major rehabilitation work on the bridge, and said doing it as part of the existing bridge renewal will reduce both costs and disruption.

Some areas will likely require full removal and replacement, the assessment said. Sherwood called that "a very significant task."

The assessment pegged the cost of the work at more than $3 million. The city's $5.4-million budget includes taxes and a contingency.

The added work is expected to take about seven or eight months. Factoring in design, the city is setting an expected completion date of August 2027. It posted a tender last week seeking a contractor.

Josée Vallée, the city's acting branch manager of municipal design and construction, said that, despite the need for rehabilitation to extend its service life, the bridge remains safe and open to the public.

Sherwood said there is no risk of imminent collapse so long as the bridge is maintained.

The area's city councillor, Stéphanie Plante, called the bridge "crucial for public transportation" and well used by both commuters and residents.

"I'm hoping the fix won't take too long and I am looking forward to getting updates on timelines," she said.