Fusion-bondedepoxy-coated

rebarsTackling the reinforcing-steel corrosion

problem: prevention versus repair

Among the most promising methods of combatingsteel rebar corrosion in concrete parking decks

bridge decks and other areas is the use of fusion-bond-ed epox y-coated rebars in new construction and in re-p a i r. The chief danger to uncoated steel bars in nort h-e rn and coastal states is from corrosion that occurs aftercalcium chloride or sodium chloride seeps into the con-crete. The sources of these chlorides are deicers or sea-water spra y. Many concrete parking ramps and bri d g edecks constructed as recently as 5 to 10 years ago ared e t e ri o rating to the point where major repair or re-placement is already necessary. The problem results inmillions of dollars worth of damage each year.

Combating corrosion

The use of a fusion-bonded epoxy coating on re b a r sis considered by many engineers to be among the moste f f e c t i ve techniques for combating corrosion though ithas been in use for only a few ye a r s. Other appro a c h-es— some used in conjunction with epoxy coating—h a ve met with va rying degrees of success. These includem e m b rane cove rings of bridge decks and park i n gra m p s, latex concrete ove r l a y s, corrosion inhibiting ad-m i x t u re s, polymer impregnation, use of galva n i zed re-b a r s, cathodic protection of re b a r s, and the Iowa methodof bonding a dense, low-slump concrete to the base. Allthese have the purpose of (1) keeping chlori d e - b e a ri n gwater from seeping down through the concrete to the re-bars or (2) pre venting chlori d e - b e a ring water in the con-c rete from touching the re i n f o rcing bars.

Costs tend to va ry widely. Those of such techniquesas polymer impregnation and use of galva n i zed re b a r sfall on the high side. Use of epox y-coated rebars is usu-ally priced considerably lowe r.

The rate of deteri o ration of a concrete deck due to cor-roding steel increases with time. As the rebars corro d e,the iron oxide which forms causes an expansion in vo l-ume of up to 20 times that of the original volume of thep o rtion of the bar that has corroded. The inevitable re-sult is immense pre s s u re between the bars and the sur-rounding concre t e, which causes the all-too-familiar

Fusion-bonded epoxy-coated rebars in place for a 6-inch composite structural slab. The completed parking deck willserve the office building in the background.

c racking and spalling. The resulting disruption of thes u rface and the loss of large pieces of concre t e, in turn ,mean greater vulnerability to waterborne chlori d e s,which leads to more spalling.

Two parking deck projects in the Minneapolis and St .Paul area—one involving new construction and the oth-er repair—offer a dramatic contrast between the cost ofp re venting rebar corrosion during new constru c t i o n ,and the cost of repair of an existing stru c t u re alre a d ydamaged by corro s i o n .

Fusion-bonded rebars in new construction

A new parking deck constructed at Pa rkdale Plaza inSt. Louis Pa rk (suburban Minneapolis) consists of as t ru c t u ral deck and a gro u n d - l e vel slab within an are athat measures approximately 215 by 240 feet. The cast-in-place upper deck, supported by steel framing, is di-vided into quarters with good slope for dra i n a g e. Thep a rking stru c t u re 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 inselecting the aggre g a t e. The mix contained 6 to 8 perc e n ta i r, and a re t a rder was used to delay set over steel beamsto eliminate minor cracking. The concrete was placed byp u m p, enabling the crew on one occasion to install12,500 square feet in a single day. After curing, a mini-mum of two coats of sealer was applied.

Ce n t ral to the design was the use of rebars with a fu-sion-bonded epoxy coating. The 6-inch-thick compositedeck slab allowed use of 2 inches of concrete cover ove rboth top and bottom bars, compared with the 3/4 inchof cover often used on earlier parking decks.

Ac c o rding to the supplier of the coated re b a r s, thee p oxy coating on projects of this type costs approx i-mately $300 to $350 per ton over the cost of uncoatedsteel re b a r s. Number 4 bars we re used in the Pa rk d a l ePlaza deck. Assuming a rebar weight of approx i m a t e l y

Coated rebars are tied with plastic-coated wire to ensure stability

during concrete placement.

The flexibility of thefusion-bonded epoxy

coating must be sufficientto prevent cracks and

breaks from occurring inthe coating during

fabrication bending.

21⁄2 pounds per square foot and a concrete area of 51,360s q u a re feet, the weight of rebars used in the deck couldbe calculated at a little over 64.2 tonsil For purposes ofthis example, if the cost of coated rebars we re calculatedat $860 per ton, and the cost of uncoated rebars at $540per ton, then the cost differential for the epoxy coatingwould be about 40 cents per square foot or $20,544 forthe entire deck—approximately 3.6 percent of the totalc o s t .

By contrast, Co n s e rva t i ve estimates of re p l a c e m e n tCosts range from $13 to $15 per square foot, which ismany times the estimated cost of using the coated re-

bars initially. Va rious studies, more ove r, have shown thatuse of the epoxy coating can greatly increase the effec-t i ve lifespan of such stru c t u re s.

Fusion-bonded rebars for repair

A project undertaken by a St. Paul retail outlet invo l ve sthe ramps of two side-by-side parking stru c t u res whichh a ve suffered extensive spalling and other deteri o ra t i o n .The stru c t u res—one of approximately 10,000 squarefeet and the other approximately 7000 square feet—we re constructed with uncoated re b a r s. Su b s e q u e n t l yboth we re subjected to calcium chloride attack from au-

Pumping concrete on the ParkdalePlaza parking deck.

Fusion-Bonded rebars: Update

Fusion-bonded epoxy coatings for rebars are notapplied on the job. Instead, the bars are coated in as t rictly controlled factory process where epoxy pow-ders are fusion-bonded to the steel surface after thesteel has been shotblasted. The National Bu reau ofSt a n d a rds found that such coatings should be about0.005 to 0.009 inch thick for adequate pro t e c t i o nagainst chloride attack and adequate flexibility dur-ing bending. The coated bars are bundled togetherwith nylon rope to minimize damage from ro u g hhandling during shipping and stora g e.

T h e re is a trade association of 20 companies thatm a n u f a c t u re epoxy powders or fabricate coated re-bars and supply them throughout the United St a t e sand Ca n a d a :

Fusion Bonded Coaters Association 25 Glen Head Ro a dGlen Head, New Yo rk 11545Phone: 516- 676-7811

The association presents a technical seminar onthe first day of each semiannual meeting. These

seminars are open to contra c t o r s, engineers, design-ers and others in the industry without charg e, pro-viding they pre re g i s t e r.

The association is pre p a ring standard specifica-tions that should be available soon. The Ameri c a nSociety for Testing and Ma t e rials is also pre p a ri n gs t a n d a rd specifications. The Ohio De p a rtment ofTra n s p o rtation has published proposed specifica-tions for epoxy coated rebars that include such itemsas coating materi a l s, surface pre p a ration, thickness-e s, curing, fabrication prov i s i o n s, handling re q u i re-m e n t s, placement, field-coating touchup, measure-ment and basis of payment. Copies of the Oh i odocument, “Ep oxy Coated Re i n f o rcing Steel, Pro p o s-al Note Number 112, December 4, 1978,” are ava i l-able fro m

Co n c rete Re i n f o rcing Steel In s t i t u t e180 No rth LaSalle St reet, Room 2110C h i c a g o, Illinois 60601Phone: 312-372-5059

The Kentucky Highway department now re q u i re sall new bridge decks to be built with epox y- c o a t e dre b a r s.

t o m o b i l e - b o rne deicing salts and the ramps re q u i red pe-riodic maintenance and repair during their first 16 ye a r sof life. Fi n a l l y, a repair project that may well cost in ex-cess of $100,000 was undertaken on the 7000-square -foot stru c t u re. In all pro b a b i l i t y, similar work will have tobe done on the larger stru c t u re.

In this most recent re p a i r- replacement project, half ofthe 7000-square-foot ramp was replaced, while the oth-er half was re p a i red with an ove r l a y, since it was ori g i-nally constructed over the store and could not be re-m oved without serious disruption of business.

A major dilemma facing the owners of the parking fa-cility invo l ved repair versus replacement. Both pro s p e c t sre p resented a major expense. To ensure that concrete re-

placement remains effective long into the future andthat spatting does not again become a problem, the ar-chitect/engineer specified epox y-coated rebars and ex-t reme care was taken in the project to ensure that alls t a n d a rds pertaining to the concrete constru c t i o n — t h emix, the aggre g a t e s, air entrainment and other factors—we re strictly adhered to.

Credits:Owner of Parkdale Plaza: MEPC Properties Inc., St. LouisPark, MinnesotaArchitects: Baker Associates Inc., MinneapolisEngineers: Clark Engineering, MinneapolisContractors: Acton Construction Company, Hugo, Minneso-taCoated rebar supplier: Simcote Inc., Newport, MinnesotaPowdered epoxy supplier: 3M, St. Paul, Minnesota

Major spalling on the bottom of a ramp in a St. Paul parkingfacility that was later repaired.

Epoxy-coated rebars in place on rebuilt ramp.

Entire floors were removed and replacedwith fusion-bonded epoxy-coated rebarsand new concrete.

PUBLICATION #C800587Co py right © 1980, The Ab e rdeen Gro u p

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