Page 247 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

CORROSION CONTROL OF BRIDGES 225

rebar decks as evaluated by transportation agencies was good. The epoxy-coated rebar
did not perform as well in cracked concrete as it did in uncracked concrete. Corro-
sion was observed on epoxy-coated rebars extracted from locations having heavy
cracking, shallow concrete cover, high concrete permeability and high chloride con-
centrations. Reduced adhesion and softening of coating occurs because of prolonged
exposure to a moist environment. The number of defects in the epoxy coating had
a strong influence on the adhesion and performance of epoxy-coated bar. There was
no significant premature concrete deterioration that can be attributed to corrosion of
the epoxy-coated rebar. Thus use of good-quality concrete cover, adequate inspec-
tion finishing and curing of concrete and the use of epoxy-coated rebar resulted in
effective corrosion for bridge decks since 1975.
At present, epoxy-coated rebar is the most common corrosion protection sys-
tem and is used in 48 states. At present, there are nearly 20,000 bridge decks using
fusion-bonded epoxy-coated rebar as the preferred protection system. This amounts
to nearly 95% of new deck construction since the early 1980s.
The data from the Concrete Reinforcing Steel Institute (CRSI) shows that more
2
than 3.6 billion kg (4 million tons) of epoxy-coated rebar (150 million m reinforced
concrete) were used as of 1998. A significant amount of the epoxy-coated rebar
was used in bridge decks. Over time, the formulation of epoxy has been modified
to achieve better performance of the epoxy coating.

4.9.1.2 Metal-Coated/Clad Rebars and Solid Corrosion-Resistant Alloy Rebars
The most promising corrosion-resistant rebars are galvanized (zinc-coated) rebars,
stainless steel-clad rebars, and solid stainless steel rebars. Titanium has also
been considered as a rebar metal, but its cost is prohibitive although it is highly
corrosion-resistant.

4.9.1.2.1 Galvanized Rebars Hot-dipped galvanized coatings for reinforcing steel
in concrete have been used since the 1940s. ASTM A767 “Standard Specification
for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement” specifies the
3
requirements for the galvanized coating. Class I coating has 1070 g of zinc per m , and
3
class II has 610 g/m . The effectiveness of galvanized rebars in extending the life of
reinforced concrete structures is questionable. In other applications, galvanized steel
has been useful in extending the life of structures exposed to atmospheric conditions
and low-chloride underground environments though not high-chloride environments.
Although galvanized rebar may prove to be beneficial in certain chloride media it
may not withstand the degree of corrosivity of deicing salts.

4.9.1.2.2 Stainless Steel Rebars Research in stainless steel rebars consists of clad
stainless steel over a carbon steel substrate and solid stainless steel rebar. The primary
concerns of cladding when stainless steel alloy is chosen are the following:

1. Adherence to rebar substrate.
2. Defects formed after bending.
3. Uniform cladding thickness (typical value is 0.5 mm)