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Publication Number: FHWA-HRT-06-078
Date: June 2006

Job Site Evaluation of Corrosion Resistant Alloys

APPENDIX E FHWA Project Number MT-01-01

TEA-21 INNOVATIVE BRIDGE CONSTRUCTION PROGRAM

Evaluation Report

State: Montana.

State DOT Contact: Mr. Nigel Mends [(406) 444-9221].

NBI Bridge Number: P00001180+0.399-1.

Project Type: Replacement.

Location: Bridge crossing the Middle Fork of the Flathead River on U.S. 2 near Essex, Flathead County, MT.

Innovative Material: Solid Stainless Steel Type [American Iron and Steel Institute] AISI 316LN or 2205 reinforcement and related hardware.

Bridge Description: The new bridge is replacing an older one that is structurally obsolete. It is 190 m long with four spans of lengths 43, 52, 52, and 43 m. The two-lane roadway width is 12 m. Alignment is tangent across the bridge except for the last span which lies on a 5-degree spiral. Four welded plate weathering steel girders, each with a 900x22 mm web and 400 mm wide flange which varies in thickness from 19 mm at midspan to 64 mm over the piers, support the deck. The cast-in-place deck has a constant 2 percent superelevation. The specified deck thickness is 215 mm and the concrete cover over the top reinforcement 60 mm.

Innovation Justification: One end of the bridge terminates on land owned by Glacier National Park and the other on land administered by Flathead National Forest. The Flathead River that the bridge crosses is under jurisdiction of the United States Fish and Wildlife Service. Permitting was complicated because these, as well as the U.S. Army Corps of Engineers and various State agencies, were involved. Consequently, it was reasoned by the Montana Department of Transportation (MDT) that any future repairs, rehabilitations, or replacement would be complex and difficult. The bridge was anticipated to require relatively high maintenance if it were built using conventional reinforcement (ECR) because it is in a heavy snow area that experiences wintertime applications of MgCl2 (liquid form) and numerous freeze-thaw cycles. In addition, because of the rural setting and mountainous surroundings, any bridge closure involves a 480-km (300-mile) detour. For this reason, extra expense that promoted longevity with minimal maintenance was considered justified.

Construction Sequence: The four piers were formed and poured during the second half of 2001, and the deck was placed in June and July 2002. The site was visited on June 24, 2002, at which time approximately two-thirds of the reinforcement had been placed. Figure 35 shows a photograph of the deck at that time.

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Figure 35. View of deck with stainless steel reinforcement placement in progress.

Reinforcement Specification: The reinforcement for both mats was specified as pickled AISI Stainless Steel Type 316LN or 2205 which was to be delivered to the construction site free of any rusting.

Concrete Specification: The concrete was termed, “Special Deck,” with properties as specified in table 10.

Table 10. Concrete mix design.

Cement Content (minimum), kg/m3

390

Water Content (maximum), kg/m3

155

Slump Range, mm

40–80

Air Content, percent

6±1

Maximum Coarse Aggregate, mm

19

Compressive Strength (minimum), MPa

34

Job Contractor:

Frontier West, Inc.

P.O. Box 16295

Missoula, MT 59808

Steel Supplier: Empire Steel. The reinforcing steel was acquired from Spain and shipped to the United States. Cutting and bending, where necessary, were performed in Colorado; and the steel was then shipped to the job site. Guard angles were provided by Watson Bowman Acme Corp. in New York.

Material Cost: The reinforcement cost was estimated as $3.50/kg ($1.60/lb). Five bids were obtained that ranged from $4.10/kg ($1.86/lb) to $5.27/kg ($2.39/lb). The lowest bidder for the overall project was awarded the contract, with the reinforcement cost being $5.20/kg ($2.36/lb). A total of 106.5 tons of reinforcement was required.

Job Site Storage: Two truckloads arrived at the job site on June 13, 2002, and the remaining three truck loads during the week of June 17. These were off-loaded onto wooden 2-ft by 4-ft supports on the ground. Figure 36 shows a photograph of this storage. The storage time was short, as placement commenced shortly after delivery. Packaging and covering are described below. No problems were encountered in connection with delivery and storage.

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Figure 36. Photograph of bundled/wrapped bars at the job site.

Presence of Carbon Steel: Shear studs on the top girder flanges are carbon steel. Figure 37 shows how these penetrate the bottom mat of stainless steel. The specification requires that there be no contact between the studs and reinforcement. This was accomplished using plastic caps over the studs. These had not been placed at the time on this site visit, and so they do not appear in figure 37. Stainless steel in the structure backwalls is tied to black bar.

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Figure 37. View showing carbon steel shear studs protruding through bottom mat of stainless steel reinforcement.

Problems: The following difficulties were encountered when incorporating stainless steel into this project.

  1. MDT personnel indicated that industry was very encouraging with regard to using stainless steel reinforcement but was less than enthusiastic when specialized treatment and handling became involved. As one example, the supplier’s pickling bath was 10 m long; and they would not invest in lengthening this to accommodate longer bars. Consequently, longer bars had to be cut for pickling and unnecessarily spliced when placed. This increased cost because of the additional material required for the lap splices.

  2. The bars were processed and packaged in Spain using Teflon-coated stainless steel bands and a water-repellant, heavy paper-like wrapping. This wrapping can be seen in figure 36. When these bundles were opened at the job site, the reinforcement was clean and bright, and no rust spots were evident. However, bundles that were opened in Colorado for cutting and bending exhibited rust spots. Figure 38 shows examples of these. Such corrosion apparently resulted because carbon steel (nonstainless) handling and bending equipment was used in conjunction with the cutting and bending operations. This is in spite of a preconstruction meeting with the supplier, at which time the need for special handling was discussed and agreed to. The bent bar details were repackaged in cardboard boxes only, as shown in figure 39. MDT is requiring that rusted bars be retreated in place according to ASTM Specification A380-94a.

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(a)

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(b)

Figure 38. Examples of rust spots on reinforcement: (a) bundled bent bars in opened cardboard container and (b) straight reinforcement in place.

  1. Procurement of the expansion joint guard angles was expensive because, first, the manufacturer treated this as a special order and, second, they were not used to fabricating stainless steel. The guard angles arrived at the site packaged with carbon steel bands. Figure 40 is a view of a guard angle in place.

  2. Placement of the stainless steel rebar was estimated to have taken 1.5–2 times longer than for conventional steel. This resulted because stainless steel chairs were not available as epoxy-coated ones are for ECR, and reinforcement had to be tied with wire individually to each plastic chair. Figure 41 shows an array of chairs on the deck in preparation for placement of the top mat (see figure 35 also), and figure 42 shows a closeup view of a completed placement area where both the top and bottom bars are tied with wire to a chair. This difficulty should be overcome as stainless steel reinforcement use becomes more common, at which time stainless steel or plastic chairs should be available.

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Figure 39. View showing cardboard packaged bent reinforcement details.

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Figure 40. View of a guard angle adjacent to an expansion joint.

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Figure 41. Array of plastic chairs to which bars from both mats are tied.

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Figure 42. Closeup view of a plastic chair to which bars are tied.

  1. MDT personnel assumed that the reinforcement would be AISI 316LN rather than 2205, which was also allowed, because the former is less expensive. Compositional analyses subsequent to placement revealed, however, that the reinforcement was 2205. While this, in and of itself, was not a problem, it does point out a need for identity confirmation of as-received stainless steel reinforcement.

  2. Mass of the #22 (metric designation) stainless steel bars averaged 2.80 kg/m3, whereas the specification requires 2.85 kg/m3. Consequently, the bar mass was 98 percent of what was required. The reduced mass was subtracted from payment to the contractor based on the bid price per kg.

  3. The specification deformation height for the #13 (metric designation) bars was 0.51 mm, whereas the actual height was approximately 0.33 mm (65 percent of what was required). A percentage reduction of payment to the contractor, based upon the bid price, resulted.

Material Acquisition: Four bent bar details were made available from the job site for testing by FAU and FDOT. Figure 43 shows examples of these.

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Figure 43. Examples of stainless steel reinforcement details acquired from the job site

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