Route 66 Bridge
Deck, Pennsylvania, USA - 30 Years and Counting
Athens Bridge,
Pennsylvania, USA
Route 66 Bridge Deck, Pennsylvania, USA -
30 Years and Counting
The
recent refurbishment of a Route 66 bridge
deck south of Kittanning, PA, provided a unique
opportunity to assess the performance of galvanized
rebar after more than 30 years of service.
The bridge was built in 1973 using galvanized
rebar in the deck. The bridge deck remains
in excellent condition but the Pennsylvania
DOT wanted to replace the post and beam medial
barrier with a more secure concrete Jersey
barrier. This required removing the entire
middle section of the deck and exposing the
galvanized rebar for inspection. Test found
the chloride content in the concrete surrounding
the rebar to be 5 lbs/yd 3, far exceeding
the chloride threshold for corrosion of black
rebar.
Inspection
of the rebar showed that coating was in excellent
condition with coating thicknesses still exceeding
ASTM A767 specification for new galvanized
rebar. Also noted during concrete removal
was the tenacious bond of the galvanized rear
to the surrounding concrete, thereby confirming
the excellent bond strength obtained from
galvanized coatings. No refurbishment of the
concrete deck was required; the original rebar
remained in place when the Jersey barrier
was poured. Complete test results are available
in attachment.
Athens
Bridge, Pennsylvania
The
Pennsylvania DOT has specified galvanized
reinforcement for decades. One such bridge,
the Athens Bridge, was built in 1973 and is
an eleven-span, four-lane, divided bridge
that uses only hot-dip galvanized reinforcing
bars. The Athens bridge deck was inspected
eight years after installation to ensure that
hot-dip galvanizing was protecting the bridge
from corrosion. Concrete cores were drilled
and an analysis of chloride contamination
and coating thickness was conducted. The chloride
levels found in the cores exhibited concentrations
between 1.8 to 7.9 lbs/yd3 of concrete, where
the high end of these concentrations is well
above the threshold for active corrosion to
occur on bare steel. Despite these extremely
corrosive conditions, the coating thickness
measurements indicated galvanized coatings
in excess of 15 mils (approximately three
times the coating thickness required on newly-galvanized
rebar according to ASTM A 767). In all instances,
the galvanized rebar showed no signs of corrosion.
The Athens Bridge was later inspected in
1991 and 2001, and the analysis generated
similar results. No sign of active corrosion
on the galvanized reinforcement was found
and coating thickness measurements reported
were in excess of ten mils. These current
coating thicknesses indicate an estimated
40-plus years of
additional maintenance-free corrosion protection.
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