Corrosion Control Study
Studies have indicated the most important factor leading to excessive corrosion is the runoff of water contaminated with deicing salts through leaking deck seals, expansion dams or open joints. To minimize this problem the following should be considered.

Eliminate joints whenever possible. Jointless bridges up to 400' in length have been used successfully. Such designs incorporate integral abutments with piling flexible enough to accommodate girder translations. Bridges up to 1600' in length, with joints only at the abutments, have likewise performed successfully. The combination of Weathering Steel and jointless or minimum joint decks offers owners structures of long-term durability and low-maintenance cost.

Use troughs beneath open finger-type joints as part of a system to discharge runoff away from the superstructure elements.

Seal all other joints. Neoprene compression seals are commonly used in this application. However, experience indicates many of these do leak over time due to traffic and bridge movements.

Recognize the potential for leakage through sealed joints and overflow from blocked troughs. Provide a second line of defense by coating the girders beneath deck joints. Typical distances for this partial painting are l-1-1/2 times the girder depth on either side of the joint.

Control roadway drainage. Minimize scuppers in order to maximize flow through them and prevent blockage. Divert approach roadway drainage away from the bridge structure. Provide adequate drainage beneath overpass structures to prevent bonding and continual traffic spray from below.

Another factor important to the successful performance of Weathering Steel structures is the elimination of any details that prevent normal wet-dry cycles. The retention of water, dirt and other debris must be avoided. All details should be designed to take advantage of natural drainage. Tubular and box sections should either by sealed or adequately vented to allow air circulation to prevent condensation and to allow drainage.

Weathering Steel, like most steel compositions, releases dissolved iron when water washes or drains over exposed surfaces. The precipitation of the dissolved iron can cause staining on adjacent surfaces, particularly when the steel is subjected to frequent rainfall during the early months of exposure. If these surfaces are light in color and/or porous in nature, this staining may be objectionable. Although this staining potential usually decreases as the steel weathers and the tight protective oxide is formed, it may be present for several years or an indefinite period, depending on variable environmental factors.

The best way to minimize staining is to incorporate permanent design details that will divert runoff water away from adjacent vulnerable materials. In bridge construction, the most severe staining condition occur prior to the placement of the deck. Designers have used a number of details, and in some cases various combinations, to cope with the staining condition. Temporary polyethylene coverings, gutter and downspout systems, adequate overhangs, drip plates, special flashing, and similar provisions will usually do the job.

Another method to reduce stain penetration is to apply liquid silicon or other type sealers to porous masonry. Some surface discoloration still may occur, but, in some applications, may not be objectionable. Also, it has been claimed that these "stained" sealed coatings will fade and weather-off with time. If this protective measures does not prove adequate, staining can be removed by using proprietary chemical stain removers or, if necessary and applicable, sandblast cleaning. Caution should be exercised in using stain removers; manufacturer's recommendations should be obtained and followed.

The following is a summary of methods designers have used to minimize staining:

Drip Pans In several installations, pans made from steel or fiberglass have been placed under the bearings and cantilevered out from the pier. These pans direct the rust-laden water away from the piers to a location which will not cause major staining. Where the piers are very high, however this system may permit the wind to blow rust-laden water back to the pier surface.

	Sloping Abutments, Pier Details and Drains Various combinations of sloping and concave surfaces used on abutments and piers in conjunction with drains provide an economical method of minimizing staining. The rust-laden runoff water is directed to areas which are not readily visible. Drains then collect this water and carry it away.

	Drip Plates A small plate attached to the bottom flange of a girder can divert water off the structure before it runs onto another bridge component.

Polyethylene Covering One method to minimize staining prior to deck placement is to cover the pier caps with a polyethylene sheet until the bridge deck has been poured. Be sure to provide an effective wrapping which will not be easily damaged by wind gusts and construction operations. Once the deck is to place and a system installed to carry away the rust-laden water, the plastic sheets can be removed. In several instances, this technique has been used successfully in combination with pier coatings.

	Preformed Elastomeric Compression Joints Preformed elastomeric compression joints, when installed and functioning properly, provide a thorough seal against deck surface water. These joints help prevent water from draining through and staining the substructure surfaces.

Pier Coatings
To reduce penetration by rust stain, liquid silicon sealers or other formulations can be applied to porous materials such as brick, stone, and concrete. Designers using this method of protection must understand that the pier in some cases will be discolored by the treatment. Although the coating reduces penetration of the stain, some surface discoloration may be noticeable because of oxide deposits. Coatings may break down and disappear with time, thus allowing the piers to develop a natural color.

Cleanup
Staining is not a new problem nor is it unique to Weathering Steel. It is a characteristic of all structural materials. If all preventive measures fail, the stained areas can still be cleaned either by sand-blasting or by using one of several proprietary chemical stain removers.

Summary
Staining is most severe when Weathering Steel is subjected to prolonged rainfall during early months of exposure. That is when protection against staining is most important. Nightly condensation is the best aging agent available and does not usually result in significant staining.

Inspection and Maintenance
Effective inspection and maintenance programs are essential to the successful performance of all structures, not just those built with Weathering Steel. Particular attention should be given to those drainage systems on and beneath the structure and its approaches. Troughs must be kept open and sealed joints resealed. Debris and salt deposits should be periodically flushed from the structure itself, particularly beneath joints and around the bearings. Vegetation should be cleared from pier and abutment areas to enhance air circulation and the subsequent weathering of the steel.

Fatigue
The issue of fatigue life of uncoated Weathering Steel has been addressed by the AASHTO Subcommittee on Bridges and Structures. The Subcommittee concluded that Weathering Steel can be considered the equivalent of painted steels in evaluating fatigue life for all AASHTO stress categories except Category A. The allowable stress ranges for Weathering Steel Category A details are noted separately by AASHTO in the current specification. Category A is essentially the base metal in either a rolled section or a plate. This is the area of the highest allowable ranges and typically does not control the design of a member.

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