REPLACING THERMAL SPRAYED ZINC ANODES ON CATHODICALLY PROTECTED STEEL REINFORCED CONCRETE BRIDGES Final Report SPR 682 REPLACING THERMAL SPRAYED ZINC ANODES ON CATHODICALLY PROTECTED STEEL REINFORCED CONCRETE BRIDGES Final Report SPR 682 by Xianming Shi, Ph.D., P.E. Jon Doug Cross Levi Ewan Yajun Liu, Ph.D. Keith Fortune for Oregon Department of Transportation Research Section 200 Hawthorne Ave. SE, Suite B-240 Salem OR 97301-5192 and Federal Highway Administration 400 Seventh Street, SW Washington, DC 20590-0003 September 2011 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. FHWA-OR-RD- 12-02 4. Title and Subtitle 5. Report Date Replacing Thermal Sprayed Zinc Anodes On Cathodically Protected Steel Reinforced August 2011 Concrete Bridges 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Xianming Shi, Jon Doug Cross, Yajun Liu, Keith Fortune, Levi Ewan 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Corrosion and Sustainable Infrastructure Lab Western Transportation Institute 11. Contract or Grant No. P. O. Box 174250, Montana State University Bozeman, MT 59717-4250 SPR 682 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Oregon Department of Transportation Final Report Research Section and Federal Highway Administration 200 Hawthorne Ave. SE, Suite B-240 400 Seventh Street, SW Salem, OR 97301-5192 Washington, DC 20590-0003 14. Sponsoring Agency Code 15. Supplementary Notes 16. Abstract This research aimed to address questions underlying the replacement of arc-sprayed zinc anodes on cathodically protected steel reinforced concrete bridges and to develop a protocol to prepare the concrete surface for the new anode, through a combination of literature review, practitioner surveys, laboratory studies, and field investigation (Pier 9 of the Yaquina Bay Bridge, Oregon). Concrete with an equivalent electrochemical age of 5 to 45 years was found to have a reaction layer of ~1 mm. To achieve strong initial bond strength of new zinc to the profiled concrete surface, the current ODOT sandblasting operating configuration (#8 nozzle with high sand volume) is too aggressive and should be changed to #6 nozzle with low sand volume to achieve target RMS macro-roughness of 1.2-2.1 centi-inches and micro- roughness of 3.5-5 μm. It is recommended to adjust the anode removal and surface profiling based on the electrochemical age of the existing concrete. Wherever possible, large aggregates (e.g., diameters ¾ in. and bigger) should be avoided for exposure by surface profiling. For non-electrochemically aged concrete, the surface should be profiled to achieve a RMS macro-roughness of 1.1-1.8 centi-inches and 5-36% exposed aggregates. For existing concrete with relatively high electrochemical age (14 yrs), the surface should be profiled to achieve a RMS macro- roughness of 1.1-1.5 centi-inches and 44-55% exposed aggregates. The following recommendations were made for old anode removal and surface preparation before new anode application: use a reasonably low air pressure and a reasonably hard and dense abrasive material for sandblasting; have a reasonably thin coating per pass during arc-spray operations; and have a slightly thinner overall Zn coating layer (15-17 mils vs. the currently used 17 mils). It is also desirable to have concrete with good surface cohesion strength and a minimum of 150 psi initial bond strength. For existing concrete with an equivalent electrochemical age of more than 8 years, the reaction layer should be completely removed prior to profiling and arc spraying (e.g., 4 mm grinding). 17. Key Words 18. Distribution Statement thermal sprayed zinc, anode replacement, cathodic Copies available from NTIS, and online at protection, reinforced concrete, bridge preservation, surface http://www.oregon.gov/ODOT/TD/TP_RES/ preparation 19. Security Classification (of this report) 20. Security Classification (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 201 Technical Report Form DOT F 1700.7 (8-72) Reproduction of completed page authorized Printed on recycled paper i SI* (MODERN METRIC) CONVERSION FACTORS APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By To Find Symbol LENGTH LENGTH in inches 25.4 millimeters mm mm millimeters 0.039 inches in ft feet 0.305 meters m m meters 3.28 feet ft yd yards 0.914 meters m m meters 1.09 yards yd mi miles 1.61 kilometers km km kilometers 0.621 miles mi AREA AREA in2 square inches 645.2 millimeters squared mm2 mm2 millimeters squared 0.0016 square inches in2 ft2 square feet 0.093 meters squared m2 m2 meters squared 10.764 square feet ft2 yd2 square yards 0.836 meters squared m2 m2 meters squared 1.196 square yards yd2 ac acres 0.405 hectares ha ha hectares 2.47 acres ac 2 2 2 2 ii mi square miles 2.59 kilometers squared km km kilometers squared 0.386 square miles mi VOLUME VOLUME fl oz fluid ounces 29.57 milliliters ml ml milliliters 0.034 fluid ounces fl oz gal gallons 3.785 liters L L liters 0.264 gallons gal ft3 cubic feet 0.028 meters cubed m3 m3 meters cubed 35.315 cubic feet ft3 yd3 cubic yards 0.765 meters cubed m3 m3 meters cubed 1.308 cubic yards yd3 NOTE: Volumes greater than 1000 L shall be shown in m3. MASS MASS oz ounces 28.35 grams g g grams 0.035 ounces oz lb pounds 0.454 kilograms kg kg kilograms 2.205 pounds lb T short tons (2000 lb) 0.907 megagrams Mg Mg megagrams 1.102 short tons (2000 lb) T TEMPERATURE (exact) TEMPERATURE (exact) °F Fahrenheit (F-32)/1.8 Celsius °C °C Celsius 1.8C+32 Fahrenheit °F *SI is the symbol for the International System of Measurement ACKNOWLEDGEMENTS The authors acknowledge the financial support provided by the Oregon Department of Transportation (ODOT) as well as the Research & Innovative Technology Administration (RITA) at the U.S. Department of Transportation for this project. The authors are indebted to the ODOT Research Coordinator Steven Soltesz and other members of the Technical Advisory Committee (James Garrard and Ray Bottenberg of ODOT, Tim Rogers of FHWA, and Bernie Covino of NETL), for their continued support throughout this project. We owe our thanks to the National Energy Technology Laboratory (NETL) for providing the electrochemically aged concrete slabs from previous laboratory studies. We appreciate the following professionals who provided assistance to this research: Rich Wanke and his staff at Great Western Corporation for conducting all the arc spray of zinc on concrete surfaces for this work and for conducting the surface preparation of various laboratory and field concrete samples (including those on the Yaquina Bay Bridge). We appreciate the editorial service provided by our colleague Andrew Scott at WTI. Finally, we owe our thanks to all the professionals who provided input to our surveys related to cathodic protection and thermal sprayed zinc technologies. DISCLAIMER This document is disseminated under the sponsorship of the Oregon Department of Transportation and the United States Department of Transportation in the interest of information exchange. The State of Oregon and the United States Government assume no liability of its contents or use thereof. The contents of this report reflect the view of the authors who are solely responsible for the facts and accuracy of the material presented. The contents do not necessarily reflect the official views of the Oregon Department of Transportation or the United States Department of Transportation. The State of Oregon and the United States Government do not endorse products of manufacturers. Trademarks or manufacturers’ names appear herein only because they are considered essential to the object of this document. This report does not constitute a standard, specification, or regulation. iii iv REPLACING THERMAL SPRAYED ZINC ANODES ON CATHODICALLY PROTECTED STEEL REINFORCED CONCRETE BRIDGES TABLE OF CONTENTS 1.0 INTRODUCTION 1 1.1 PROBLEM STATEMENT 1 1.2 OBJECTIVES OF THE STUDY 1 1.3 THERMAL SPRAYED ZINC AND ODOT EXPERIENCE 1 1.4 SCOPE OF WORK AND REPORT ORGANIZATION 4 2.0 CP TECHNOLOGIES FOR REINFORCED CONCRETE: INTRODUCTION AND RECENT DEVELOPMENTS 5 2.1 INTRODUCTION 5 2.2 ANODE MATERIALS 8 2.2.1 Impressed Current Cathodic Protection Systems 9 2.2.2 Sacrificial Anode Cathodic Protection Systems 12 2.3 CP PERFORMANCE CRITERIA AND MONITORING TECHNIQUES 14 2.3.1 CP Performance Criteria 14 2.3.2 Monitoring of CP Performance 19 2.4 ANODE SERVICE LIFE PREDICTION 20 2.5 THERMALLY SPRAYED ZINC ANODE INSTALLATION AND REPLACEMENT 22 2.5.1 Concrete Surface Preparation 22 2.5.2 Anode Installation and Replacement 24 2.6 CATHODIC PROTECTION MODELING 25 2.6.1 The Concrete Domain 25 2.6.2 The Rebar Domain 27 2.6.3 Boundary Conditions 27 2.7 RECENT DEVELOPMENTS IN CP TECHNOLOGIES 31 2.7.1 Solar Power 31 2.7.2 Galvanic Batteries 32 2.7.3 New Galvanic Anodes 32 2.8 CONCLUSION 33 3.0 SURVEY OF THE CURRENT PRACTICE 35 3.1 SURVEY OF CP TECHNOLOGIES 35 3.2 ADVANCED SURVEY OF THERMAL-SPRAYED ANODE CP TECHNOLOGY 42 3.3 KEY FINDINGS FROM THE SURVEYS 53 3.3.1 Anodes to protect bridge substructures in coastal environments 53 3.3.2 Key factors affecting anode-concrete bonding 54 3.3.3 How to best ensure the quality of prepared concrete surface 54 3.3.4 Quality of anode coating application 55 3.3.5 Removal of old anode coating 55 4.0 INVESTIGATING METHODS OF ZINC ANODE REMOVAL AND CONCRETE SURFACE PREPARATION 57 4.1 INTRODUCTION 57 v 4.2 A PRELIMINARY INVESTIGATION