february 2010 vol. 32 no. 2

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February 2010 Vol. 32 No. 2

26 b idg Fo mwo k in b ckp ck

37 a Fitting M mo i l

fo J m s e. ro ts, Pe

41 Viscosit —It’s Onl P tof th eq tion

Bridges &

Highways

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february 2010 Vol. 32 No. 2

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BRIDGES & HIGHWAYS

26 Bridge Formwork in a Backpack Innov tiv composit t chnolog s d to const ct ch s

30 Bridge Beam Series Introduced

31 Excellence in Concrete Pavementsam ic n Conc t P v m nt associ tion ann l aw ds

37 A Fitting Memorial for James E. Roberts, PEa idg hono ing li d vot d to p lic s vicby Craig Copelan and Alfred R. Mangus

41 Viscosity—It’s Only Part of the EquationInt ctions with solid s c c itic lby James Warner

ALSO FEATURING

45 Green Concrete Goes for the Gold at 2010 Winter Olympicsfl sh s h lps ch s st in ilit go lsby R. Doug Hooton and Anne Weir

49 Plastic Shrinkage Cracking in Internally Cured MixturesP w tt d lightw ight gg g t c n d c c ckingby Ryan Henkensiefken, Peter Briatka, Dale P. Bentz, Tommy Nantung,and Jason Weiss

55 ASCC Position Statement #31acc pt l us o C lci m Chlo id in Conc t

56 International Partnersa po t om rILeM—Th Int n tion l union o L o to i s ndexp ts in Const ction M t i ls, S st ms, nd St ct s

74 Concrete Q&A How Low Is Too Low o 7-D C lind b k?

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B i F w i B c c

Innov tiv composit t chnolog s d to const ct ch s

I n late 2008, the Maine Department of Transportation(DOT) built a buried arch bridge constructed with

composite materials to replace a 70-year-old deterioratedstructure. What makes the Neal Bridge in Pittsfield, ME,unique is that it’s the first of its type to use rigidifiedinflatable composite arches produced at the Universityof Maine (U-Maine).

Researchers at the university’s AEWC AdvancedStructures & Composites Center have developed theBridge-in-a-Backpack™, a lightweight, corrosion-resistant

system for short- to medium-span bridge construction

using fiber-reinforced polymer (FRP) composite archtubes that act as reinforcement and formwork for cast-in-place concrete. Bridge-in-a-Backpack arches are light-weight, easily transportable, rapidly deployable, and donot require the heavy equipment or large crews neededto handle traditional construction materials.

BaCkgroundU-Maine’s AEWC Center team, led by Director Habib

Dagher, Professor of civil/structural engineering, conceivedthe bridge design as a novel use of composite materialsto simplify construction and reduce the maintenanceand life-cycle costs associated with buried structures.The lightweight carbon fiber composite arches aremanufactured by inflating a bladder within a tubular(braided) carbon textile, bending the unit to the properbridge vertical profile, and then infusing the textile with athermosetting resin. The composite arches provide threesimultaneous functions for the concrete: they serve asstay-in-place forms, external reinforcement, and protectiveshells against freezing-and-thawing damage.

The system capitalizes on the inherent property of anarch to transform vertical loads to internal axial forces,the superiority of concrete in sustaining compressiveloads, and the versatility and strength of composite

materials. During accelerated fatigue testing, concrete-filled arches were subjected to the equivalent of 50 yearsof truck traffic over an interstate bridge. Results showedthat the concrete arches retained their full capacity afterfatigue testing had been completed.

Specimens were subjected to static testing to failureand their load deflection response and ultimate strengthswere studied. Excellent correlation was seen betweenexperimental and predicted results, providing a highlevel of confidence in the modeling technique. The archstructure forms three plastic hinges and maintains peakloading during strength testing. Further tests have

demonstrated that the arches are extremely ductile

After a braided fiber sleeve is placed over the air bladder, thebladder is inflated and the assembly is placed on a form of thedesired geometry. Forming and infusion can be performed in ashop or in the field ( Photo courtesy of AEWC Center )

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when compared with conventionalreinforced concrete.

InstallatIonWhile the Neal Bridge arches

were manufactured at the AEWCComposites lab at U-Maine, it ispossible that arches used on futureprojects will be constructed at thejob site. Arches would arrive rolled up(sized to fit in a duffle bag, inspiringthe name “Bridge-in-a-Backpack”).Once unrolled, the braided fibersleeve would be placed over an airbladder, and the bladder would beinflated. The assembly would thenbe placed on an arch form, and thesleeve would be infused with resin.A composite arch would be readyfor installation after the resincured overnight.

Each Neal Bridge arch has a12 in. (305 mm) diameter and spans35 ft (11 m). Twenty-three arches,spaced at approximately 2 ft (0.6 m)on center, were built for use in the44 ft (13.5 m) wide bridge. After thearches were trucked to the site,they were lowered into place witha truck-mounted boom crane andmanually set. All 23 arches wereplaced in a single day. Once in place,the arch bases were encased in ashallow concrete footing.

A 4 in. (102 mm) deep corrugatedFRP decking was installed over thearches with self-tapping screws thatbecame concrete anchors once thearches were filled with concrete. Thearch tubes were filled with a self-con-solidating, expansive cement concrete

mixture pumped into the archesthrough fill pipes preinstalled in thetop of each arch. About 1 hour wasneeded to fill the arches with a totalof 26 yd 3 (20 m 3 ) of concrete.

Concrete was also placed over thecorrugated decking. Once hardened,the concrete deck and the anchorspreviously screwed through thecomposite tubes formed a lateralforce-resisting diaphragm. Twenty-fourhours after the concrete was placed,

composite spandrel walls were erected.

Arches cure on the form ( Photo courtesy of AEWC Center )

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Head walls were constructed with an FRP sheetpile system and the wing walls were constructed froma prefabricated concrete T-wall retaining wall system.Paving was placed on about 4 ft (1.2 m) of a granular sandbackfill that was compacted over the arch structure.

Construction of the superstructure was completed in 2 weeks,

including installation of sensors to be used by U-Maineresearchers to monitor the bridge’s performance.

Future developmentBecause the new system has standard details at

the foundation, head walls, wing walls, and backfill,

Arches for the Neal Bridge being placed in position ( Photocourtesy of AEWC Center )

Installation of the composite decking ( Photo courtesy of AEWC Center )

Completed superstructure for the Neal Bridge ( Photo courtesy of AEWC Center )

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construction costs are competitivewith standard construction. Thesejoint-free, steel-free structures are,however, expected to provide100-plus years of service, with verylittle maintenance.

Since the Neal Bridge wasconstructed, the McGee Bridge inAnson, ME, was built using the newtechnology. Lessons learned fromthe Neal Bridge project were applied,resulting in thinner arch walls,increased arch spacing, a lighterweight headwall, and improvedheadwall details. Superstructureconstruction was reduced to 1 weekon the second bridge, which wascompleted in September 2009.

Advanced InfrastructureTechnologies, LLC—a private companycommercializing the Bridge-in-a-Backpack—has plans to build fivebridges with spans from 24 to 60 ft(7 to 18 m) in the next 2 years aspart of the Governor’s CompositesInitiative in the state of Maine.

For more information, visitwww.aewc.umaine.edu andwww.aitbridges.com .

Note: Portions reprinted with permission of

Maine DOT.

Neal Bridge in service, Pittsfield, ME ( Photo courtesy of AEWC Center )

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