DSCN5466 DSCN5467 DSCN5468 DSCN5469 North Approach Spans 596 DSCN5470 DSCN5471 DSCN5472 DSCN5473 North Approach Spans 597 DSCN5474 DSCN5475 DSCN5476 DSCN5477 North Approach Spans 598 DSCN5478 DSCN5479 DSCN5480 DSCN5481 North Approach Spans 599 DSCN5482 DSCN5483 DSCN5484 DSCN5485 North Approach Spans 600 DSCN5486 DSCN5487 DSCN5488 DSCN5489 North Approach Spans 601 DSCN5490 DSCN5491 DSCN5492 DSCN5493 North Approach Spans 602 DSCN5494 DSCN5495 DSCN5496 DSCN5497 North Approach Spans 603 DSCN5498 DSCN5499 DSCN5500 DSCN5501 North Approach Spans 604 DSCN5502 DSCN5503 DSCN5504 DSCN5505 North Approach Spans 605 DSCN5506 DSCN5507 DSCN5508 DSCN5509 North Approach Spans 606 DSCN5510 DSCN5511 DSCN5512 DSCN5513 North Approach Spans 607 DSCN5514 DSCN5515 DSCN5516 DSCN5517 North Approach Spans 608 DSCN5518 DSCN5519 DSCN5520 DSCN5521 North Approach Spans 609 DSCN5522 DSCN5523 DSCN5524 North Approach Spans 610 611 612 613 614 615 616 617 618 619 620 621 622 623 Miscellaneous 624 DSC06671 DSC06672 DSC06673 DSC06674 Waterline and Supports 625 DSC06676 DSC06677 DSC06928 DSCN5609 Waterline and Supports 626 DSCN5755 DSCN5756 Validation Insp 092313 077 Validation Insp 092313 108 Waterline and Supports 627 628 2013 Inspection Update ‐ 10th Avenue Bridge December 16, 2013 Minneapolis, Minnesota Appendix C – Corrosion Mitigation Options 10th Avenue Bridge Rehabilitation Corrosion Mitigation Options 8 November 2013 10th Avenue Bridge Rehabilitation i SRF Consulting Group, Inc. Executive Summary In early October 2013, Vector Corrosion Technologies, Inc. conducted a corrosion investigation of the 10th avenue Bridge substructure to assist SRF provide corrosion mitigation recommendations. Primary testing was conducted on the seven spans and on two bents under expansion joints on the north approach spans. Bridge Description: Originally constructed in 1929, the 10th Avenue Bridge is a seven span, 2,135-foot long, open-spandrel arch bridge across the Mississippi River. The bridge spans a gap between West River Parkway and 2nd Street SE, connecting 10th Avenue SE in the Marcy-Holmes neighborhood of Minneapolis, MN to 19th Avenue South on the West Bank of the University of Minnesota. The bridge is located 300 feet east of Interstate 35W (I-35W), and approximately one-half mile northwest a 55.5-foot roadway and a barrier-protected eight-foot-wide pedestrian facility. This historic arch bridge has a long history of past repairs and it is now time to conduct additional maintenance and rehabilitation repairs. Testing recently conducted on the 10th Ave Bridge indicates that chloride-induced corrosion is one of the primary causes for substructure distress. There are many areas of the structure that are either currently undergoing active corrosion, or are in danger of future corrosion-related damage. Factors informing the selection of a corrosion mitigation system include: • The structure’s age and historical significance • Aesthetics of the structure • Location and extent of chloride contaminated concrete • Required service life of the rehabilitation • Half-cell potential measurements • Initial cost of corrosion mitigation systems • Life-cycle costs for maintenance and replacement of the system • Electrical continuity of embedded steel reinforcement • Extent of concrete damage • Structural deficiencies or concerns Corrosion Mitigation Options Vector Corrosion Technologies, Inc. was tasked to conduct a corrosion investigation of the substructure and to recommend corrosion mitigation options for the various bridge elements and provide the associated costs for each system. The corrosion mitigation options considered fall into four broad categories: 1. Topical treatments 10th Avenue Bridge Rehabilitation ii SRF Consulting Group, Inc. 2. Galvanic protection systems 3. Impressed current systems 4. Electrochemical treatments Topical treatments include the application of barrier coatings, crack sealants, breathable penetrating sealers, and surface applied corrosion inhibitors. Judicial use of topical treatments makes sense when used as part of a proper repair and protection strategy. Galvanic protection options rely on the use of a sacrificial metal producing a small current to counteract the natural electrochemical corrosion process. Galvanic protection involves electrically connecting a sacrificial metal to the reinforcing steel network. This sacrificial metal, predominately zinc, corrodes preferentially to the reinforcing steel and delivers a small electrical current to the reinforcing. This small current forces the cathodic reaction of oxygen reduction to occur on the steel surface. This cathodic reaction increases the local pH on the steel surface, and reduces corrosion activity. Galvanic systems are generally not adjustable after installation and have a defined service life based on the quantity of sacrificial metal provided. Impressed current cathodic protection works on the same principle as galvanic protection, except the power is delivered to the structure from an external source. Impressed current systems use an inert anode system, typically mixed metal oxide coated titanium or ceramic, to distribute the current to the concrete. In this system electrical connections are made to the reinforcing and the anode system, and DC current is supplied through a rectifier. Impressed current systems have the advantage of being adjustable and can have an extended service if regularly maintained. Electrochemical treatments are essentially temporary impressed current systems using an external anode system. These treatments supply a current to the system that is at least an order of magnitude larger than an impressed current system. The primary benefits of these treatments are 1) it removes the source of the problem; and 2) there is no additional maintenance requirement once complete. The primary electrochemical treatments in use today are chloride extraction and realkalization. Both systems require a continuous reinforcing steel network. Specific corrosion mitigation options considered for the 10th Avenue Bridge are described in the following sections and the body of the report. Each system provides a level of corrosion protection; however some may be better suited for this structure than others based on the final budgetary, service life, and other requirements. Please see summary table in Appendix B for estimated costs and considerations related to this project. Investigation Findings The corrosion investigation findings indicate the predominant areas of substructure distress include: 1. Deck beams, piers, and spandrel columns exposed to chloride contamination from leaking expansion joints; 10th Avenue Bridge Rehabilitation iii SRF Consulting Group, Inc. 2. Delamination of the arch concrete due to corrosion of the structural steel angle truss and reinforcement embedded within the arches; 3. Spandrel columns are cracked adjacent to the arch connections. This allows chloride laden runoff direct access to the reinforcing steel and can cause severe localized corrosion. Other key findings indicate that: 1. The reinforcing steel network is mostly discontinuous. This means that the individual reinforcing members are not in contact with each other, or that a layer of rust has developed between contact points. This finding means that reestablishing electrical continuity is a prerequisite to employing global galvanic, impressed current and electrochemical treatment options. Targeted and distributed galvanic solutions can be employed by reestablishing electrical continuity locally. The costs associated with re-establishing electrical continuity within each element are included in the cost matrix. 2. The reinforcement layers were reversed for the spandrel columns investigated. This means that vertical bars are on the exterior layer and are not confined by hoops or ties. This structural deficiency may require enlarging or adding reinforcement to the piers and spandrel columns requiring rehabilitation. Bridge Deck One of the key areas of concern is preventing further chloride penetration from the bridge deck. Leaking expansion joints are the predominant source of deicing salt contamination to the substructure below and expansion joint distress is evident. It is recommended that: 1. Expansion joint replacement should include a continuous line of Galvanode DAS 0.25 lb/LF anodes along the construction joint on either side of the joint. 2. Deck cracks should be sealed with low viscosity epoxy or methyl methacrylate resin. 3. Sealing the deck with a breathable silane or siloxane to reduce the rate of chloride buildup in the concrete. Spandrel Columns and Cap Beams under Expansion Joints Large areas of delaminated concrete were noted on the beams under expansion joints. Two options were considered for corrosion mitigation of these beams. 1. Total replacement with a barrier coating 2. Partial depth repairs with distributed galvanic anodes and a barrier coating These two options are essentially equivalent with respect to service life. If the level of reinforcing damage is relatively small, the recommended option should be based on bid pricing. If the level of reinforcing damage is significant, replacement is more appropriate. It is recommended that both scenarios be included in the bid package as alternates. The barrier coating should be a low viscosity penetrating epoxy primer with a pigmented aliphatic urethane top coat for UV resistance. 10th Avenue Bridge Rehabilitation iv SRF Consulting Group, Inc. Galvanode DAS 0.25 lb/LF distributed galvanic anodes are recommendations for 1. Cap beam top