Corrosion Costs
The
cost of corrosion is a major, and often, unnecessary
burden on society. A recent study commissioned
by the US Federal Highway Administration (
www.corrosioncost.com)
placed the cost at 2.5% of GDP, or close to
$300 billion per year. Highway bridges alone
contributed over $8 billion to the total as
described in an excerpt of the report below.
There are 583,000 bridges in the United States (1998). Of this total, 200,000 bridges are steel, 235,000 are conventional reinforced concrete, 108,000 bridges are constructed using prestressed concrete, and the balance is made using other materials of construction. Approximately 15 percent of the bridges are structurally deficient, primarily due to corrosion of steel and steel reinforcement. The annual direct cost of corrosion for highway bridges is estimated to be $8.3 billion, consisting of $3.8 billion to replace structurally deficient bridges over the next ten years, $2.0 billion for maintenance and cost of capital for concrete bridge decks, $2.0 billion for maintenance and cost of capital for concrete substructures (minus decks), and $0.5 billion for maintenance painting of steel bridges. Life-cycle analysis estimates indirect costs to the user due to traffic delays and lost productivity at more than ten times the direct cost of corrosion maintenance, repair, and rehabilitation.
It is clear that from a Life-cycle perspective
that small increased up front costs to reduce
corrosion an double or triple the life of a
structure are easily justified. Regarding reinforced
concrete structures, increased corrosion protection
comes in many forms, the primary factors being
concrete impermeability and cover over the rebar.
The secondary corrosion barrier is protection
of the bar itself. It is here that galvanizing's
initial cost, field handling characteristics
and overall performance make it an attractive
additional corrosion protection coating for
structures exposed to aggressive chloride rich
environments.
The issue of economics of protecting rebar
is perhaps best summarized in the concluding
remarks form Bob Grimm, a former Materials
Engineer with the New York State Thruway Authority,
in a presentation he gave to the Northeast
States Material Engineers Association on why
the NYSTA changed from epoxy coated rebar to
slightly more expensive galvanized rebar:
"In
summary, as distributors of the public money
we must view full lifetime costs as the major
consideration when selecting systems. If a
less expensive system leaves a shorter life
it’s no bargain. With more movement to 50
to 100 year bridge designs, miniscule cost
differences in bar coatings cannot control
this decision making process."
Reinforcing Steel Cost Comparison
The graph below provides estimated material
costs for various rebar alternatives currently
available as of the end of 2004. While the
absolute numbers are out of date and do not
reflect current steel prices, the differential
costs for various coating alternatives remain
accurate.
| Material |
Cost (US$/lb.) |
| Black |
0.32 |
| Epoxy* |
0.42 |
| Hot-dip Galvanized* |
0.47 |
| Epoxy II* |
0.47 |
| Purple Epoxy* |
0.56 |
| MMFX |
0.58 |
| Stainless Steel Clad* |
1.25 |
| Solid Stainless Steel (316) |
1.61 |
* Includes cost of coating and black steel. Numbers are based off presentations made by FHWA during 2005 to numerous state DOTs.
