Cathodic Protection of Concrete Bridges: a Manual of Practice
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SHRP-S-372 Cathodic Protection of Concrete Bridges: A Manual of Practice J. E. Bennett John J. Bartholomew ELTECH Research Corporation Fairport Harbor, Ohio James B. Bushman Bushman & Associates Medina, Ohio Kenneth C. Clear K. C. Clear, Inc. Boston, Virginia Robert N. Kamp Consulting Engineer Albany, New York Wayne J. Swiat Corrpro Companies, Inc. Medina, Ohio Strategic Highway Research Program National Research Council Washington, DC 1993 SHRP-S-372 ISBN 0-309-05750-7 Contract C-102D Product No. 2034 Program Manager: Don M. Harriott Project Manager: It. Martin (Marty) Laylor Consultant: John P. Broomfield Production Editor: Cara J. Tate Program Area Secretary: Carina S. Hreib December 1993 key words: bridges bridge maintenance bridge rehabilitation cathodic protection chlorides corrosion corrosion prevention corrosion rate CP electrochemical methods reinforced concrete Strategic Highway Research Program National Academy of Sciences 2101 Constitution Avenue N.W. Washington, DC 20418 (202) 334-3774 The publication of this report does not necessarily indicate approval or endorsement of the findings, opinions, conclusions, or recommendations either inferred or specifically expressed herein by the National Academy of Sciences, the United States Government, or the American Association of State Highway and Transportation Officials or its member states. © 1993 National A_zademy of Sciences I.SM/NAP/1293 Acknowledgments The research described herein was supported by the Strategic Highway Research Program (SHRP). SHRP is a unit of the National Research Council that was authorized by section 128 of the Surface Transportation and Uniform Relocation Assistance Act of 1987. This report is a compilation of work by ELTECH Research Corporation, Corrpro Companies, Inc., and Kenneth C. Clear, Inc. Each of these organizations is acknowledged for their effort in writing this report. to, 111 Contents List of Figures ....................................... ix List of Tables ....................................... xiii Abstiact . ......... .... • • • • .. .. • .... ....... .1 Executive Summary ..................................... 3 1. Introduction ....................................... 5 2. Corrosion and Cathodic Frotection Fundamentals ................ 11 Corrosion of Metals ................................ 11 Corrosion of Steel in Concrete ......................... 15 Cathodic Prctection Fundamentals ....................... 18 3. Design .......................................... 25 Types of Cathodic Protection Systems ..................... 26 Anode Systems for Deck Surfaces ...................... 29 Anode Systems for Substructures ...................... 44 Selection of Anode Systems ........................... 51 Cathodic Protection Systems for Deck Surfaces .............. 54 Ancde Systems for Substructures ...................... 56 Selection of Other Elements ........................... 57 Establishing Cathodic Protection Zones ................... 57 Determining Design Current Requirements ................ 57 Power Supply and Electrical Components ................. 59 Reference Cells and Monitors ........................ 64 Remote Monitoring Units ........................... 68 V Estimating the Cost of Cathodic Protection .................. 70 Orde:r-of-Magnitude Estimate ......................... 70 System Estimate ................................. 72 Cathodic Protection Monitoring and Maintenance Costs ......... 80 Patching Costs .................................. 80 4. Construction ...................................... 85 Contractor Submissions .............................. 85 Materials and Equipment ........................... 86 Detai.led Design ................................. 86 Activation Report ................................ 86 Operation and Maintenance Manuals .................... 87 Anode System Installation ............................ 87 Anode Systems for Bridge Decks ...................... 87 Substructure Systems ............................. 106 Installation of Components ........................... 110 Discontinuous Reinforcing Steel ...................... 111 Wire Connections to Reinforcing Steel .................. 112 Installing Rebar Probes and Reference Cells ............... 115 Installing the Rectifier Controller ..................... 116 Making Final DC Wire Connections ................... 116 Setting the System for Operation ....................... 118 Polarization Decay Testing ......................... 119 E l_x_gI Testing ................................ 120 Criteria Discussion .............................. 122 Additional Testing Devices ......................... 124 Project Documentation ............................ 124 5. Operation and Maintenance ............................ 127 Performing Monthly Monitoring of the System ............... 128 Monthly Detailed On-Site Monitoring .................... 128 Section One -- General Information .................... 130 Section Two -- Operational Data ...................... 135 Section Three -- Embedded Instrumentation ............... 136 Remote Monitoring ............................... 137 vi Conducting Annual Inspections ........................ 139 Review of Monthly Monitoring Data ................... 140 Detailed Visual Inspection .......................... 140 Polarized and Instant-Off Measurements ................. 141 Electrical Resistance Measurements .................... 142 Performance Adjustment Testing ...................... 142 Adjust System as Required ......................... 143 Prepare Annual Inspection Report ..................... 143 Remedial Measures ............................... 144 Basic Troubleshooting ............................ 144 References ........................................ 148 Appendix A: Tentative Guide Specification for Cathodic Protection of Concrete Bridge Decks 650 Bridge Deck Cathodic Protection ....................... 1 651 Coke Asphalt Cathodic Protection System ................ 34 652 Non-Overlay Slotted Cathodic Protection System ............ 43 653 Distributed Anode CP System with Cement Overlay .......... 50 650A Bridge Deck Cathodic Protection Tentative Specification Annex . 64 Appendix B: Tentative Guide Specification for Cathodic Protection of Concrete Bridge Substructures 655 Bridge Substructure Cathodic Protection .................. 1 655A Bridge Substructure Cathodic Protection Specification Annex .... 28 656 Conductive Coating Anode Cathodic Protection System ........ 29 657 Thermally Sprayed Zinc Anode Cathodic Protection System ..... 34 658 Mesh Anode CP System with Shotcrete Overlay ............ 38 Appendix ..................................... 60 vii List of Figures Chapter 2 Figure 1. Iron ore naturally reverts to iron oxide ................. 11 Figure 2. The basic elements of all corrosion cells ................ 12 Figure 3. A battery is a corrosion cell ........................ 13 Figure 4. Single metal corrosion cell ........................ 14 Figure 5. Differences in chloride ion concentration establish differences in the electrical potential that forms the active-passive steel ...................................... 16 Figure 6. The potential difference causes corrosion reactions to occur at the rebar in the chloride-contaminated concrete ............ 16 Figure 7. Corrosion-induced cracking of concrete ................. 17 Figure 8. Schematic of cathodic protection system components ......... 18 Figure 9. An AC adapter for a calculator is a simple type of AC/DC rectifier .................................... 19 Figure 10. Cathodic protection rectifier ........................ 19 Figure 11. Placing conductive coke asphalt over pancake anodes ........ 21 Figure 12. Hand placing FHWA conductive polymer into anode slots covering platinum wires and carbon strands .................... 21 Figure 13. Mixed-metal oxide ribbons installed in anode slot ........... 21 Figure 14. Mixed-metal oxide mesh installed on a bridge deck prior to concrete overlay .............................. 22 Figure 15. Installation of conductive polymer mounds over carbon strands ..................................... 22 Figure 16. Application of conductive paint on a bridge substructure .................................. 22 Figure 17. Arc-sprayed zinc anode installation on a bridge substructure .................................. 23 Figure 18. A silver-silver chloride reference cell installed in a bridge deck. (Note that no reinforced steel is exposed.) .......... 23 Figure 19. Macrocell corrosion probe placed in concrete. (Note that steel is exposed.) ................................. 24 ix Chapter 3 Figure 20. Conductive polymer slotted system ................... 35 Figure 21. Conductive polymer mounded system .................. 37 Figure 22. Titanium mesh anode system ...................... 43 Figure 23. Conductive coating system ......................... 47 Figure 24. Area for steel density calculation ..................... 61 Figure 25. Wire sizing .................................. 65 Chapter 4 Figure 26. Conductive coke-asphalt overlay system ................ 88 Figure 27. Placing conductive coke asphalt over pancake anodes ........ 89 Figure 28. Slotted anode system ............................ 89 Figure 29. Prior to placement of any anode system, the deck should be checked for thin cover areas ....................... 90 Figure 30. The concrete cover meter is used to check areas of suspected thin cover more precisely ......................... 91 Figure 31. Diagram of complete slotted anode system ............... 92 Figure