New York State Thruway Authority
The New York State Thruway Authority
(NYSTA) has recently begun to specify hot-dip
galvanized rebar for all of its current and
future bridge decks. The thruway consists
of over 600 miles of toll roads comprising
major sections of Interstates 87, 84, and
90, with sections connecting to other interstate
highways and toll roads to four neighboring
states and Canada. Most of the NYSTA’s 810
bridges are installed in fresh water environments,
with the exception of a few that are close
to the Atlantic Ocean and qualify as located
in a marine environment. In addition to the
close proximity to water, the bridges undergo
freeze-thaw cycles, and have heavy exposure
to deicing salts and industrial pollution,
all adding up to a highly-aggressive corrosive
environment. The need to protect these bridges
from corrosion became a major concern to the
thruway authority during the early 1960’s,
when maintenance and inspection revealed extensive
corrosion to previously installed bridge decks
that incorporated bare steel reinforcement
in the concrete.
Based on an FWHA endorsement
and research conducted by numerous states,
the New York Bridge Authority had seemingly
solved its corrosion problem by implementing
the use of epoxycoated rebar in bridge decks
during the early 1980s. In as little as ten
years, doubts began to rise regarding the
protection provided by these epoxy-coated
systems. Within another four years, cracks
began to appear in these bridge decks, at
which time the thruway authority decided to
utilize hot-dip galvanized rebar as its corrosion
protection method of choice.
Another concern regarding the
performance of epoxy-coated reinforcing steel
arose during the NYSTA’s pursuit to find an
alternative corrosion protection system. Epoxy
coatings were exhibiting inferior bonding
to the concrete. When removing sections of
concrete from epoxy-coated rebar during a
repair of an improperly designed pier, the
concrete was easily broken away from the epoxy-coated
rebar. By specifying hot-dip galvanized rebar,
this problem was eliminated due to the superior
bond developed between the galvanized rebar
and concrete.
The cathodic and barrier protection provided
by hot-dip galvanized rebar has reduced repair
costs incurred in handling the rebar in the
field. Epoxy-coated rebar was getting damaged
in the field due to rough handling at some
of the New York bridge installations during
the 1980s. Epoxy coatings only supply barrier
protection for the underlying steel. If epoxy
coatings become damaged during handling or
installation, the barrier becomes broken and
the corrosion protection for the rebar has
been compromised. The superior bond strength
and hardness properties of hot-dip galvanized
coatings make it tough to damage under any
material handling conditions, and if damaged
does occur, the exposed bare steel will be
protected by the sacrificial cathodic action
of the surrounding zinc.
Life cycle cost analysis was performed by
the NYSTA to compare the costs of galvanized
and other competing coating systems. Initially,
the cost of hot-dip galvanized rebar was slightly
greater than epoxy coatings and bare steel
on a per pound basis. However, the amount
of rebar required for an epoxy-coated rebar
installation is far greater than for black
or galvanized rebar. Lap splices are significantly
increased when specifying epoxy coated rebar.
This fact alone brings the initial cost of
specifying hot-dip galvanized rebar to an
extremely competitive position. On a life
cycle cost analysis, the maintenance-free
hot-dip galvanized rebar is unmatched.
