The historic Longfellow Bridge over the Charles River between Cambridge and Boston, Massachusetts opened in August 1906. It brings ~28,000 motor vehicles and ~90,000 train transit users to and from the city each day, so there is never a convenient time for maintenance on the 1,767-foot (538.6 m) long bridge — known by its iconic “salt and pepper” towers. But over a century of operation took a cumulative toll on the original steel substrate. The only minor rehabilitation took place in 1959, with a few lesser emergency repairs in 2002.
Earlier this decade, the Massachusetts Department of Transportation (MassDOT) realized a major revamp couldn’t be deferred any longer. Many floor beams, stringers, and connecting rods suffered from major steel section loss, and the famed arches and bearings needed repair. Specifiers for the multi-million-dollar project said 70 percent of the riveted box beam structural steel should be removed and replaced with shop-fabricated galvanized box beams and metalized steel, while the remaining 30 percent of steel, existing arches, cross bracing, and handrails of historic value needed refurbishment.
As part of that process, both new beams and existing renovations required extra coating protection from corrosive marine and traffic elements.
“With the amount of weight, trains, traffic, and pedestrians, it was left a little too long,” Paul Blake, project manager with Tri-State Painting, LLC (TSI), said of the bridge’s condition. “It was in pretty bad shape.”
Bridging the Gap
With the immense size and complexity, this wasn’t a job for any coatings applicator. Special requirements included scheduling around other trades, meeting strict Boston Historical Society criteria, working alongside government representatives, and keeping at least one lane open for vehicles, bicycles, and pedestrians. Even a navigable waterway underneath had to remain clear for duck boats and pleasure craft!
Fortunately for the J.F. White-Skanska-Consigli J.V. general contractor and MassDOT, TSI embraced the challenge and had ample pedigree. “It was a very unique project,” said Blake, whose company celebrates its 40th anniversary this year. “There were so many trades, and they had to keep trains moving and have it open to commuters as well as pedestrians and boats going underneath the bridge. The phasing was unbelievable in that they had to move trains onto the roads and then move them back.”
The rehabilitation project, which began in 2014 and concludes this year, required constant communication with site officials regarding other trades. This included electricians, demolition crews, granite cleaners, divers to fix piers under water, plumbers, and soil experts.
“Normally, we’re the last guys in,” Blake said. “But here, you had dozens of other trades all trying to work in a small window. We had to work around everyone else’s schedule and not overlap. That made it challenging. Phasing and not being linear was very important.”
Blake said daily morning briefings and toolbox talks were essential to keeping crew members aware of everything going on at the site.
The project’s scope posed unique physical challenges. To start with, Safway’s QuikDeck scaffolding system enabled TSI’s crew of 35 to 40 to access all sides of the elevated structure. For sloped areas, temporary steps were installed and rig cables utilized. “It was a good, solid platform, as opposed to something that bounces around,” Blake said. “But as the spans get bigger, the slope can be aggressive, so we put steps across.”
Barges were parked underneath the bridge to ensure all jobsite equipment and accessories were always close by, and Indian Valley tarps and blankets were used in a robust containment system for each phased section to protect vehicles and pedestrians.
Safety considerations were paramount to crew members themselves, too. Standard personal protective equipment (PPE) included safety glasses, hard hats, work boots, and gloves, while MSA Safety provided double retractable lanyards for fall protection. Nova 2000 hoods were used during blasting, while 3M’s full- and half-face respirators were used when sanding or spraying. Safety patrol boats were stationed nearby each day.
The bridge’s daily importance justified an expedited schedule, which meant working winter months in New England’s cold climate. To get around this and make sure materials did not freeze, the TSI crew stored coatings at the company’s home base in New Hampshire and then brought down only what they would need for each day in heated trucks. The general contractor used water bubblers around barges and indirect fired heaters in material containment areas.
“We’d pretty much run heaters 24 hours a day through the winter,” Blake recalled.
New Winter Coat
With new batches of material arriving daily, crew members worked deliberately in small sections over four years to coat both the original steel and newly fabricated beams. The multi-layer coating system with a polysiloxane topcoat, approved by government officials, was manufactured by AkzoNobel’s International brand.
“When we initially saw the system, it seemed shop-favorable because some of the potlifes are very short, as opposed to being more user-friendly,” Blake said. “But the DOT picked polysiloxane because it retains such a high gloss. It’s a historic bridge with new components. Some of the polyurethanes get dull earlier on.”
The original steel substrates were blasted utilizing a 65,000-cfm (1,840.6 m³/min.) Advanced Recycling Systems trailer-mounted blast machine. The machine included two 1,600-cfm (45.3 m³/min.) Ingersoll Rand compressors, with a Chesapeake blend as recyclable media and Bellemare 30/60 MaxiBlast (iron silicate) as disposable media. All blasting was done behind tarps and to the NACE No. 2/Society for Protective Coatings (SSPC) Surface Preparation (SP) 10 standard for a near-white commercial blast cleaning. Blasting activities utilized Class 1A containment with dust collection to maintain negative air pressure and curb any incidental releases. Air monitoring was performed and hazardous waste collected with a high-efficiency particulate air (HEPA) vacuum recycling unit to prevent any contaminants from falling into the Charles River or affecting other trades.
“When blasting, you have to clean it up before the shift ends,” Blake said. “It cures out overnight. You stripe for a day, and the next day you spray.”
Workers used Graco King 56:1 airless spray units to apply the Interzinc 22HS silicate at approximately 3 mils (76.2 microns) dry film thickness (DFT) as a primer; the Intergard 475 HS epoxy at approximately 6 mils (152.4 microns) DFT as the intermediate coat; and the Interfine 979 polysiloxane at approximately 5 mils (127.0 microns) DFT as the topcoat. When spraying, crew members regularly had their blood monitored to test for any excessive exposure.
Meanwhile, for new steel components — fabricated by Boston’s Duncan Galvanizing — crew members used the Graco units to spray the Intergard 345 epoxy at approximately 5 mils (127.0 microns) DFT and then the Interfine 979 topcoat at approximately 5 mils (127.0 microns).
“A big issue we had early on was overspray on the new steel, so we had a lot of protection wrapping with tarps and blankets,” Blake explained. “We learned after one span that the more time you take to protect from overspray, the better the [painting] outcome. We didn’t want to load up the new concrete. We wanted nice, crisp lines where the steel met the concrete. Boats will look up, so we had a conscious effort to work on aesthetics. It would definitely stand out.”
With most painting now complete, their work is doing just that.
“The products were great,” Blake said. “We thought we’d have a little more trouble, but we haven’t. The finish has been amazing, and the gloss hasn’t changed at all.”
All Longfellow Bridge work is expected to wrap up by the end of 2018, and thanks in large part to TSI’s crew, Boston locals and tourists can now appreciate a revitalized landmark.
“The DOT has had at least three or four guys on the bridge at all times, and they love it,” Blake said. “We’ve had two years in a row with 96 percent or better positive feedback. Some of the stuff upstream, we finished at least three years ago, and it looks like we just finished painting it.”