Pack Rust Identification and Mitigation Strategies for Steel Bridges Mark Bowman P.E. Ph.D. Chintan Patel Professor of Civil Engineering Graduate Research Assistant School of Civil Engineering Purdue University SPR 4121 1 Study Advisory Committee •Timothy Wells (PA) •Stephanie J. Wagner (BO) •Christopher Wheeler •Jose Ortiz •Michael Black •Nathaniel Pfeiffer 2 3 Major Tasks •Literature review. •Reviewing existing mitigation strategies and repair procedures for selected DOTs. •Pack rust in Indiana Bridges. 3 Task 1 Literature Review 4 Pack Rust or Crevice corrosion •Localized attack on metal surface. •Crevice formed between two joining surfaces. • Metal – Metal • Metal – Non-metal 5 Initiation Process • Crevice corrosion initiation process • Differential oxygen concentration needed • Aqueous solution(water), pathway for ions to flow • Process accelerated • [Cl¯] present • pH acidic present 6 Mechanism • Formation of differential oxygen concentration cell. Steel Specimen 7 Mechanism 8 • Inhibitors like chromium decreases the corrosion rate. • Severe corrosion takes place near the mouth of the crevice. Crevice pH < 7 Bulk pH > 7 H+ Steel Specimen 9 Attributes of crevice corrosion •Crevice height •Ranging from 0.1 mm to 3 mm. •Large enough to allow entry of electrolyte (water) •small enough to not allow electrolyte to flow out. • Rust build-up eventually seals the crevice and the corrosion process stops. (U.R.Evans, researcher in corrosion science) On contrary • Sealing the crevice without neutralizing the active corrosion product can cause accelerated corrosion.(Roads and Bridges, Sept,2003) 11 Task 2 Mitigation strategies and repair procedures of selected DOTs 12 Mitigation and repair strategies •Stripe coat •Caulking •Penetrating sealer •Backer rod 13 Stripe coat 14 Caulking 15 Penetrating sealer • Has viscosity to penetrate into the crevice. • Ability to neutralize the corrosive environment inside the crevice. 16 Backer rod and sealant Sealant Backer Rod 17 State Dept. of Transportation Stripe coat (21 states) Caulking (10 states) Penetrating sealers Backer rod (5 states) (2 states) Alabama, California, California, Delaware, Washington, Oregon, Delaware, Florida, Florida, Iowa, Missouri, Iowa, Washington Georgia, Illinois, Indiana, Maryland, Missouri, Illinois, Delaware Iowa, Maryland, Ohio, Oregon, Massachusetts, Washington, West Minnesota, New Jersey, Virginia New York, North Carolina, North Dakota, Ohio, Oregon, South Dakota, Virginia, West Virginia, Wisconsin 18 Repair Procedure Oregon • Remove pack rust by mechanical cleaning, and heating water-saturated pack rust to a minimum of 250 °F and a maximum of 400 °F, or • Using 35,000 psi ultra-high pressure water jet. 19 Missouri • Calcium sulfonate rust penetrating sealer • Suitable for any steel structure that has developed pack rusting in overlapping steel plates, joints or at bolted areas. • Applied in accordance with SSPC-PA1. 20 Missouri Continued. • Can be applied to • bearings, • overlapping steel plates, • pin connections, • pin and hanger connections and • locations where • rust bleeding, • pack rust, • layered rust occurs. 21 Washington Pack rust of 1/16 inch or greater. • Clean to a depth of ½ of the gap width, maximum of ¼ inch. • Cleaned gap treated with rust penetrating sealer. • Apply Caulk to form watertight seal. If gap greater than ¼ inch • Gap should be filled with foam backer rod material. • Apply sealant over the backer rod. 22 Task 3 Pack Rust in Indiana Bridges 23 Pack Rust in Indiana Bridges •Gathered relevant pack rust information from Bridge inspection reports. 24 Typical Members Affected by Pack Rust •Bearings(Rocker, some cases Elastomeric) •Splice connections •Hinge-pin connection •Gusset plate and other connections •Beam cover plates •End diaphragms 25 Bearings 26 Pack Rust 27 Pack Rust 28 Pack Rust 29 30 Pack Rust 31 Splice plates Pack rust 32 Pack rust 33 Hinge-pin connection Pack Rust 34 Pack rust 35 Gusset plates, battens and angles 36 37 38 39 Cover plates 40 41 Diaphragms 42 Cross bracings connections Pack Crossrust bracing fallen down 43 Statistical Analysis on Data Collected • Total state owned steel bridges in 4 districts inspected – 1235 • No. of bridges with some form of pack rust – 422 44 Percentage of Bridges with Pack Rust 60 56 % 50 43 % 40 31 % 30 Percentage 22 % 20 10 0 Fort Wayne Crawfordsville Greenfield Seymour 45 PERCENTAGE OF BRIDGES WITH PACK RUST BASED ON FEATURE INTERSECTED Water Body Road RR Abandoned RR 75 69 61 60 63 54 48 43 39 37 33 35 26 26 28 20 FORT WAYNE CRAWFORDSVILLE GREENFIELD SEYMOUR BERCENTAGE OF BRIDGES WITH PACK RUST OF BRIDGES WITH PACK BERCENTAGE DISTRICTS 46 MEMBER WISE COUNT Fort Wayne Crawfordsville Greenfield Seymour 94 60 50 46 42 34 36 28 NUMBER NUMBER OF BRIDGES 14 10 12 10 12 7 5 7 4 6 4 7 0 0 0 2 0 2 0 1 47 COMPARISON OF PERCENTAGE OCCURRENCE OF PACK RUST Fort Wayne Crawfordsville Greenfield Seymour 45 29 21 19 18 17 12 8 PERCENTAGE OF OCCURRENCE PERCENTAGE SPLICE BEARING 48 District wise Salt usage (lane-miles) salt (tons) (tons/lane-miles) Fort Wayne 4,652 47000 Annual10.1 Winter Maintenance Report FY 2013 by Phil Ivy Crawfordsville 4,699 44000 9.4 Greenfield 4,500 60000 13.3 Seymour 4,693 41500 8.8 49 Splice plate pack rust in detail 50 Severity rating for pack rust in splices Rating 1 Severe PR - > ¾ inch bowing of splices or bolt failure 51 Rating 2 Moderate to severe PR - ¼ to ¾ inch bowing of the splice plates Rating 3 Moderate PR – Visible bowing of the splice plates < ¼ inch of PR 52 Rating 4 Minor to moderate PR - Visible corrosion @ middle of splice Connection. Rating 5 Minor PR - Rust bleeding @ middle of splice Connection. 53 YEARS AFTER PAINTING VS. PACK RUST SEVERITY IN SPLICES (4DISTRICTS) 45 40 35 32 30 25 20 15 12 10 Number of years after painting after Number of years 5 0 0 1 2 3 4 5 6 Pack Rust Severity 54 AGE AFTER BUILT VS. PACK RUST SEVERITY IN SPLICES (4DISTRICTS) 90 80 70 56 60 50 45 40 30 20 Avg. age at pack rust detection pack rust at age Avg. 10 0 0 1 2 3 4 5 6 Pack rust severity 55 PERCENTAGE OF BRIDGES FORT WAYNE 21 PERCENTAGE OF BRIDGES WITH PACK 16 INTERSECTED DISTRICT BREAKUP 11 RUST IN SPLICES OVER FEATURE 0 CRAWFORDSVILLE 17 Water 15 6 Roads 0 RR Abandoned RR GREENFIELD 12 6 5 25 13 SEYMORE 7 7 14 56 PERCENTAGE OF BRIDGES WITH PACK RUST IN SPLICES OVER FEATURE INTERSECTED 15 10 9 7 PERCENTAGE OF BRIDGES PERCENTAGE WATER ROADS RR ABANDONED RR FEATURE INTERSECTED 57 Trends for Cover Plates Cover plate condition vs age after painting 30 25 21 20 15 9.9 10 5 2.5 Age ofpack rust after painting after ofpack rust Age 0 minor moderate severe Condition 58 Conclusions • Pack rust frequently occurs in Indiana bridges • Most common locations • Bearings(top and bottom) • Splice plates (joints) • Hinge-pin connections • Gusset plates • Lower chords of truss • No correlation between pack rust occurrence and salt usage. 59 Conclusions • Common mitigation and repair methods • Stripe coat • Caulking • Penetrating sealer (Promising mitigation and repair method) 60 Future Tasks • Investigate remaining 2 districts of Indiana. • Investigate strength degradation due to pack rust. • Review repair strategies for Indiana. Questions ? 62.