Fusion-bonded epoxy-coated rebars

Fusion-bonded epoxy-coated rebars in place for a 6-inch composite structural slab. The completed parking deck will
serve the office building in the background.
Fusion-bonded
epoxy-coated
rebars
Tackling the reinforcing-steel corrosion
problem: prevention versus repair
A
mong the most promising methods of combating
steel rebar corrosion in concrete parking decks
bridge decks and other areas is the use of fusion-bonded epoxy-coated rebars in new construction and in repair. The chief danger to uncoated steel bars in northern and coastal states is from corrosion that occurs after
calcium chloride or sodium chloride seeps into the concrete. The sources of these chlorides are deicers or seawater spray. Many concrete parking ramps and bridge
decks constructed as recently as 5 to 10 years ago are
d e t e ri o rating to the point where major repair or replacement is already necessary. The problem results in
millions of dollars worth of damage each year.
Combating corrosion
The use of a fusion-bonded epoxy coating on rebars
is considered by many engineers to be among the most
effective techniques for combating corrosion though it
has been in use for only a few years. Other approaches— some used in conjunction with epoxy coating—
have met with varying degrees of success. These include
membrane coverings of bridge decks and parking
ramps, latex concrete overlays, corrosion inhibiting admixtures, polymer impregnation, use of galvanized rebars, cathodic protection of rebars, and the Iowa method
of bonding a dense, low-slump concrete to the base. All
these have the purpose of (1) keeping chloride-bearing
water from seeping down through the concrete to the rebars or (2) preventing chloride-bearing water in the concrete from touching the reinforcing bars.
Costs tend to vary widely. Those of such techniques
as polymer impregnation and use of galvanized rebars
fall on the high side. Use of epoxy-coated rebars is usually priced considerably lower.
The rate of deterioration of a concrete deck due to corroding steel increases with time. As the rebars corrode,
the iron oxide which forms causes an expansion in volume of up to 20 times that of the original volume of the
portion of the bar that has corroded. The inevitable result is immense pressure between the bars and the surrounding concrete, which causes the all-too-familiar
Coated rebars are tied with plasticcoated wire to ensure stability
during concrete placement.
The flexibility of the
fusion-bonded epoxy
coating must be sufficient
to prevent cracks and
breaks from occurring in
the coating during
fabrication bending.
cracking and spalling. The resulting disruption of the
surface and the loss of large pieces of concrete, in turn,
mean greater vulnerability to waterborne chlorides,
which leads to more spalling.
Two parking deck projects in the Minneapolis and St.
Paul area—one involving new construction and the other repair—offer a dramatic contrast between the cost of
p re venting rebar corrosion during new construction,
and the cost of repair of an existing structure already
damaged by corrosion.
Fusion-bonded rebars in new construction
A new parking deck constructed at Parkdale Plaza in
St. Louis Park (suburban Minneapolis) consists of a
structural deck and a ground-level slab within an area
that measures approximately 215 by 240 feet. The castin-place upper deck, supported by steel framing, is divided into quarters with good slope for drainage. The
parking structure is designed to accommodate 136 cars
on the upper deck and 140 in the lower section.
A low-slump mix was used with a high cement content
(588 pounds per cubic yard).2 Special care was taken in
selecting the aggregate. The mix contained 6 to 8 percent
air, and a retarder was used to delay set over steel beams
to eliminate minor cracking. The concrete was placed by
pump, enabling the crew on one occasion to install
12,500 square feet in a single day. After curing, a minimum of two coats of sealer was applied.
Central to the design was the use of rebars with a fusion-bonded epoxy coating. The 6-inch-thick composite
deck slab allowed use of 2 inches of concrete cover over
both top and bottom bars, compared with the 3/4 inch
of cover often used on earlier parking decks.
According to the supplier of the coated rebars, the
epoxy coating on projects of this type costs approximately $300 to $350 per ton over the cost of uncoated
steel rebars. Number 4 bars were used in the Pa rk d a l e
Plaza deck. Assuming a rebar weight of approximately
Pumping concrete on the Parkdale
Plaza parking deck.
21⁄2 pounds per square foot and a concrete area of 51,360
square feet, the weight of rebars used in the deck could
be calculated at a little over 64.2 tonsil For purposes of
this example, if the cost of coated rebars were calculated
at $860 per ton, and the cost of uncoated rebars at $540
per ton, then the cost differential for the epoxy coating
would be about 40 cents per square foot or $20,544 for
the entire deck—approximately 3.6 percent of the total
cost.
By contrast, Conservative estimates of replacement
Costs range from $13 to $15 per square foot, which is
many times the estimated cost of using the coated re-
Fusion-Bonded rebars: Update
Fusion-bonded epoxy coatings for rebars are not
applied on the job. Instead, the bars are coated in a
strictly controlled factory process where epoxy powders are fusion-bonded to the steel surface after the
steel has been shotblasted. The National Bureau of
Standards found that such coatings should be about
0.005 to 0.009 inch thick for adequate protection
against chloride attack and adequate flexibility during bending. The coated bars are bundled together
with nylon rope to minimize damage from rough
handling during shipping and storage.
There is a trade association of 20 companies that
manufacture epoxy powders or fabricate coated rebars and supply them throughout the United States
and Canada:
Fusion Bonded Coaters Association
25 Glen Head Road
Glen Head, New York 11545
Phone: 516- 676-7811
The association presents a technical seminar on
the first day of each semiannual meeting. These
bars initially. Various studies, moreover, have shown that
use of the epoxy coating can greatly increase the effective lifespan of such structures.
Fusion-bonded rebars for repair
A project undertaken by a St. Paul retail outlet involves
the ramps of two side-by-side parking structures which
have suffered extensive spalling and other deterioration.
The structures—one of approximately 10,000 square
feet and the other approximately 7000 square feet—
were constructed with uncoated rebars. Subsequently
both were subjected to calcium chloride attack from auseminars are open to contractors, engineers, designers and others in the industry without charge, providing they preregister.
The association is preparing standard specifications that should be available soon. The American
Society for Testing and Materials is also pre p a ri n g
standard specifications. The Ohio Department of
Transportation has published proposed specifications for epoxy coated rebars that include such items
as coating materials, surface preparation, thicknesses, curing, fabrication provisions, handling requirements, placement, field-coating touchup, measurement and basis of payment. Copies of the Ohio
document, “Epoxy Coated Reinforcing Steel, Proposal Note Number 112, December 4, 1978,” are available from
Concrete Reinforcing Steel Institute
180 North LaSalle Street, Room 2110
Chicago, Illinois 60601
Phone: 312-372-5059
The Kentucky Highway department now requires
all new bridge decks to be built with epoxy-coated
rebars.
Major spalling on the bottom of a ramp in a St. Paul parking
facility that was later repaired.
Epoxy-coated rebars in place on rebuilt ramp.
Entire floors were removed and replaced
with fusion-bonded epoxy-coated rebars
and new concrete.
placement remains effective long into the future and
that spatting does not again become a problem, the architect/engineer specified epoxy-coated rebars and extreme care was taken in the project to ensure that all
standards pertaining to the concrete construction—the
mix, the aggregates, air entrainment and other factors—
were strictly adhered to.
tomobile-borne deicing salts and the ramps required periodic maintenance and repair during their first 16 years
of life. Finally, a repair project that may well cost in excess of $100,000 was undertaken on the 7000-squarefoot structure. In all probability, similar work will have to
be done on the larger structure.
In this most recent repair-replacement project, half of
the 7000-square-foot ramp was replaced, while the other half was repaired with an overlay, since it was originally constructed over the store and could not be removed without serious disruption of business.
A major dilemma facing the owners of the parking facility involved repair versus replacement. Both prospects
represented a major expense. To ensure that concrete re-
Credits:
Owner of Parkdale Plaza: MEPC Properties Inc., St. Louis
Park, Minnesota
Architects: Baker Associates Inc., Minneapolis
Engineers: Clark Engineering, Minneapolis
Contractors: Acton Construction Company, Hugo, Minnesota
Coated rebar supplier: Simcote Inc., Newport, Minnesota
Powdered epoxy supplier: 3M, St. Paul, Minnesota
PUBLICATION #C800587
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