which is a government specification.”
The three-coat system used on the
on-ramp and other sections of the
bridge consists of Series 90-97
Tneme-Zinc, a zinc-rich urethane
primer, followed by an intermediate
coat of Series 27 F.C. Typoxy, a
polyamide epoxy. The finish coat,
Series 73 Endura-Shield, an aliphatic
acrylic polyurethane, provided pro-
tection from exterior weathering,
abrasion and corrosive fumes.
Overall, nearly 16,000 gallons of coat-
ings have been used, representing
15% of the entire bridge. “The coating
system provides the sacrificial corro-
sion performance of the zinc primer,
the barrier protection of the epoxy
intermediate coat and the UV resist-
ance of the Series 73,” Mitkus said.
“We have done a number of overpass-
es and bridge structures over the past
20 years that use a very similar coat-
ing system, including work for the
Massachusetts Turnpike Authority.”
Each coating project was complicat-
ed by the need for full containment to
prevent abrasives and paint from
damaging automotive and truck traf-
fic. “This is a major artery from the
north coming into Boston, so there’s
no way to shut down the bridge for
recoating,” Mitkus noted. “In addition
to protecting traffic, there’s the lead
issue. A dense urban population is in
proximity to the bridge, so there can-
not be any abrasives or dust contain-
ing lead paint drifting onto surround-
ing properties. That was a major con-
cern for Massport.”
Mitkus expects an increase in
major bridge maintenance and repair
projects during the next five to 10
years. “You’re going to see a definite
increase in bridge coating because of
the growing need,” he predicted.
“There are bridges all over the coun-
try that are in disrepair, so we’re see-
ing more federal stimulus funding
being allocated toward fixing the
infrastructure.” (Source: Tnemec)
The Tobin Bridge Project
The Maurice J. Tobin Memorial Bridge connecting the
Charlestown section of Boston with Chelsea uses a
high-tech structural monitoring system for real-time
information about stresses and loads, plus a high-per-
formance coating system from Tnemec for corrosion
protection. “The bridge opened for traffic in 1950, so
it’s an older structure,” Tnemec coating consultant
Larry Mitkus acknowledged. “The bridge is 2 1/4-
miles long, so coating projects are broken into sepa-
rate contracts. Tnemec coating systems have been
used for the last three contracts on the bridge, includ-
ing the ramp leading up to the seven-lane toll plaza
on the southbound deck.”
With more than 80,000 motorists using the Tobin
Bridge daily, all recoating work is conducted under full
containment. “In addition to protecting the traffic
from the coatings, these are lead abatement projects,
so you can’t allow any abrasives containing lead dust
to drift onto surrounding properties,” Mitkus
explained. “This is a major artery from the north com-
ing south into Boston, so there’s no way to shut down
the bridge during maintenance.”
For each project, the structural steel was prepared
in accordance with SSPC-SP10/NACE No. 2 Near-
White Metal Blast Cleaning and primed with Series
90-97 Tneme-Zinc, a moisture-cured, zinc-rich ure-
thane primer that was spray-applied. An intermediate
coat of Series 27 F.C. Typoxy, a versatile polyamide
epoxy, was spray-applied, followed by a finish coat of
Series 73 Endura-Shield, an aliphatic acrylic
polyurethane that is highly resistant to abrasion,
ultraviolet (UV) light, and exterior weathering. “We
worked closely with the engineers in designing the
coating system, which ended up being used as the
standard for quality,” Mitkus noted.
Because of its rapid curing characteristics, Series 90-97
Tneme-Zinc was used as the primer on the Tobin Bridge in
Chelsea, MA, allowing the intermediate coat to be applied
the same-day.
