Dissimilar Metal Contact
Another consideration when
using galvanized reinforcement in concrete
is the possibility of establishing a
bimetallic couple between zinc and bare
steel (i.e., at a break in the zinc coating
or direct contact between galvanized steel
and black steel bars) or other dissimilar
metals. A bimetallic couple of this type in
concrete should not be expected to exhibit
corrosive reactions as long as the two
metals remain passivated. To ensure this is
the case, the concrete depth to the
zinc/steel contact should not be less than
the cover required to protect black steel
alone under the same conditions.
Therefore, when galvanized reinforcement is
used in concrete, it should not be coupled
directly to large areas of black steel reinforcement,
copper, or other dissimilar metal. Bar supports
and accessories should be galvanized. Tie
wire should be annealed wire, 16-gauge or
heavier, preferably galvanized. If desired,
polyethylene and other similar tapes can be
used to provide insulation between dissimilar
metals.
