PORTSMOUTH — The Mount Hope Bridge needs $35 million within the next few years for a protective dehumidification system to save its two large supporting cables, or the cost of saving the historic suspension bridge could balloon to $300 million or more.

The Rhode Island Turnpike & Bridge Authority sought a $25 million grant from the federal Department of Transportation’s Rebuilding American Infrastructure with Sustainability and Equity (RAISE) Discretionary Grant program, but was bypassed when the grants were awarded in late November. RITBA planned to match the grant with $10 million of its own capital funding.

“According to a 2016 inspection of the cables at the Mount Hope Bridge, there is significant breakage of the hundreds of wires that make up each of the cables,” RITBA Executive Director Lori Caron Silveira wrote to the Rhode Island House Finance Committee on Dec. 7 first reported by GoLocal Prov.

She is now hoping the state will provide assistance from the $1.1 billion in funding it received from the federal American Rescue Plan.

The suspension bridge, which was built in 1929, has three key components: the two tall towers, the two main cables from which the bridge deck is hung, and the two massive concrete blocks at the Portsmouth and Bristol ends of the bridge that anchor the cables.

The cables are the most vulnerable part because they can corrode in spite of protective coatings. If they deteriorate to the point they have to be supplemented with a parallel cable, it could cost about $300 million, according to Silveira.

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If the original cables have to be replaced, it would cost cost "north of $500 million," she said.

"My engineer always says if you get into that area of replacing the cables altogether, you should also be considering whether that is cost effective, or whether you should be just talking about bridge replacement,," Silveira said. "To replace the bridge would cost $1 billion."

RITBA provided The Daily News with the 27-page RAISE grant application submitted on July 12, a two-page description of the cable repair project, and the letter to the House Finance Committee and its chairman, state Rep. Marvin Abney of Newport.

Silveira also summarized the contents of these documents in a Nov. 16 email to U.S. Sens. Sheldon Whitehouse and Jack Reed and Congressmen David Cicilline and Jim Langevin. She shared that email with The Daily News.  

"It's all about climate change," Silveira said. "We've seen such an increase in the levels of humidity. That is what is accelerating the corrosion process in the wires."

Each main bridge cable is 11 inches in diameter and contains 2,450 individual steel wires bundled in seven strands of 350 parallel wires. A red lead paste is applied over the outer wires of each cable, and then each cable is wrapped in zinc-coated galvanized steel wire. This steel outer coat is then painted.

“Even with these protections, water either typically migrates through compromised areas of the protective barriers, or forms internally by condensation, providing the catalyst for atmospheric corrosion, hydrogen-induced stress-corrosion cracking, and broken wires,” the grant application says.

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"The bridge has been properly maintained. That's why it's 92 years old," Silveira said. "We do tons of maintenance on that bridge and regular inspections. When it was built, today's state-of-the-art technology wasn't available. No one was anticipating that climate change would have the impact it has had." 

“The wire in the cables stretches 2,620 miles and weighs 700 tons,” the Providence Evening Bulletin reported on Oct. 24, 1929, the day the bridge opened.

To prevent further corrosion of the cable, RITBA wants to use a cable dehumidification technology that has been used successfully in other bridges in the U.S., including the twin Chesapeake Bay Bridges; the twin Delaware Memorial Bridges and the South Tenth Street Bridge in Pittsburgh, Pennsylvania. 

With this technology, dried air is injected into a new sleeve around the cable, “where the air is allowed to permeate between the voids of the bridge wires or strands,” according to the project narrative. The length of the cable would be sealed with an elastomeric wrap — keeping the dried-air in and the water out.  

“As the dried-air travels to the exhaust sleeve, it absorbs the water and expels it out of the cable as moisture-laden air,” the project narrative says. “Once the moisture is removed, the dehumidification system maintains the relative humidity within the cable to below 40% and corrosion is considered to cease for all practical purposes.”

A supervisory control and data acquisition system continuously monitors and actively regulates the relative humidity within the cable, 24 hours a day, seven days a week.

If this action is not taken soon, the deterioration of the main cables on the Mount Hope Bridge will continue at an accelerating rate, according to RITBA.

“There is no practical way of replacing the strength lost in a cable due to corrosion,” the project narrative says. “The only proven option available to preserve the remaining strength within the cables is to apply a system of dehumidification.”

The Mount Hope Bridge through the years

“The cables must be put in a dry state by 2028, according to best engineering estimates, in order to preserve sufficient load-carrying capacity in the cables and maintain the bridge with a sufficient factor of safety,” the grant application says.

Based on the experience of other bridge dehumidification projects, it can take anywhere from six months to two years for the humidity in the cables to fall to 40%, depending on the characteristics of the cables, the extent of the oiling, local weather and climate conditions.

“This means that for the dehumidification technology to work, it must be designed, installed, and operating by 2026 in order to provide sufficient time for the humidity in the cables to fall to a level that halts the corrosive process,” the grant application says.

“If funding cannot be secured in time to stabilize the cable deterioration, a full replacement of the cable is required,” the grant application says. “This increases the cost to $250 million to $300 million.”

Approximately 6.9 million vehicles use the bridge annually, according to the state Department of Transportation. Saving the bridge, which is on the National Register of Historic Places, urgently requires help from the federal or state government, according to RITBA.

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As a result of the COVID-19 pandemic leading to lower Pell Bridge toll revenues and decreased gas tax revenues, RITBA expects to collect approximately $20 million less in revenue in fiscal years 2020, 2021, and 2022 than it would have collected based on fiscal year 2019 revenue, according to the project narrative.

“This significant shortfall — which has not been offset by any state or federal support — leaves the agency without the ability to fund this important project without potentially pushing out other capital projects that are included in RITBA’s 10-year capital plan,” the Authority says.