Page 248 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

226 CORROSION CONTROL AND PREVENTION

4. Metallurgical changes because of the cladding process that may affect the cor-
rosion resistance.

It must be noted that the chloride threshold for pitting in a nonhomogenous envi-
ronment such as concrete can be significantly less than the value in the same aqueous
environment. Thus, it is necessary that any work must involve a realistic concrete
environment. For example, the use of stainless steel piping in underground pipelines
has been discontinued because of pitting and subsequent perforation of the pipe in
nonhomogenous unsaturated soil environments with relatively low chloride contents.
Pitting in reinforced concrete bridge components is not as significant as decreasing
average corrosion rate (overall metal loss).
McDonald et al. studied the performance of solid stainless steel rebars (types 304
and 316) and found that they performed well while ferritic stainless steels (types 405
and 430) developed pitting (15). Studies by McDonald et al. reported investigations
on a 10-year exposure of 304 stainless steel in Michigan and Type 304 stainless steel
clad rebar in a bridge deck in New Jersey and found no corrosion (15). In a study by
Virmani and Clemena, the type 316 stainless steel-clad rebar extended the estimated
time to the cracking of the concrete beyond 50 years, but not as much as solid types
304 and 316 stainless steels (100 years) (16).
In addition, McDonald et al. (15) reported on two highway structures constructed
with stainless steel rebar. No corrosion was observed for solid 304 stainless steel
rebar in a bridge deck in Michigan as well as in New Jersey. The chloride levels
in both bridge decks were below or at the threshold level for corrosion initiation in
black steel rebars. It is estimated that the use of solid stainless steel rebar provides an
expected life of 75–100 years (15, 16). McDonald et al. estimated the costs, at three
installations, of the use of solid stainless steel and found the overall cost to be 6–16%
higher than black steel (17).
Stainless steel rebars have been reported to be used in several projects in the United
States, including Michigan and Oregon (17). The expected life of structures using
stainless steel rebars was stated to be 120 years.
Fluctuation in the cost of raw materials used in the production of stainless steel
impacts on the economic viability of the use of stainless steel rebars in concrete decks.
The rebar cost also depends on the grade of stainless steel used.
From the point of view of cost, it is preferable to use stainless steel-clad rebar
instead of stainless steel rebar. It is estimated that the use of stainless steel-clad rebar
provides an expected life of 50 years. The cost of stainless steel cladding can vary
depending on the raw material market prices just like solid stainless steel, but also
depends on the cladding manufacturer, cladding thickness, and the chosen grade of
stainless steel. With proper quality control, stainless steel-clad rebar promises to be an
effective means of control for bridge deterioration because of corrosion of reinforcing
steel.

4.9.1.3 Alternative Means of Protection In addition to the use of coated or alloy
rebar, other means to mitigate corrosion of reinforcing steel in bridge structures
consist of use of high-performance concrete, corrosion-inhibiting admixtures, or a