School of Civil and Environmental Engineering Durability of Precast Prestressed Concrete Piles in Marine Environment: Reinforcement Corrosion and Mitigation – Part 1 Final Report Prepared for Office of Materials and Research Georgia Department of Transportation GDOT Research Project No. 07-30 Task Order No. 02-55 by Robert Moser, Brett Holland, Lawrence Kahn, Preet Singh, and Kimberly Kurtis June 2011 Contract Research GDOT Research Project No. 07-30 Task Order No. 02-55 Durability of Precast Prestressed Concrete Piles in Marine Environment: Reinforcement Corrosion and Mitigation Part 1 Final Report Prepared for Office of Materials and Research Georgia Department of Transportation By Robert Moser, Brett Holland, Lawrence Kahn, Preet Singh, and Kimberly Kurtis, June 2011 The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Georgia Department of Transportation. This report does not constitute a standard, specification or regulation. i Executive Summary Research conducted in Part 1 has verified that precast prestressed concrete piles in Georgia’s marine environment are deteriorating. The concrete is subjected to sulfate and biological attack and the prestressed and nonprestressed reinforcement is corroding. Concrete is reported as “soft” in many bridges; and exterior cracking indicates reinforcement corrosion. Researchers reviewed concrete durability and reinforcement corrosion research and experiences. These reviews gave the necessary background to evaluate the condition of Georgia’s prestressed concrete piles and to establish future tests for strand corrosion and for concrete mix design experiments. Based on discussions with the Bridge Maintenance Engineer, four 40-ft lengths of piles were removed from the Turtle River Bridge and transported to Georgia Institute of Technology. The forensic examination of the piles indicated that after 32 years in service, the concrete within the water had suffered from biological attack by sponges which consumed the limestone aggregate, and the cement had deteriorated due to sulfate attack. Prestressing strands and tie reinforcement had severely corroded in spash zones due to high levels of chloride. Concrete above water was in good condition. Experiments on the corrosion resistance of typical A416 prestressing strand wire and on 7-wire prestressing strands were conducted. Solutions represented various chloride conditions; concentrations varied from none to twice that of seawater. Georgia marsh conditions have an average chloride content about one-half that of open seawater. For wire in good quality, non- carbonated concrete, corrosion is very limited. In carbonated concrete, corrosion starts quickly at low chloride concentrations. The experiments further showed that prestressing strands exhibit a 60-70% reduction in corrosion resistance when compared with wires and reinforcing bars because of crevices created in the stranded geometry. Future experiments must consider such crevice corrosion. Most of the past corrosion research did not consider this effect of crevice corrosion due to stranding. Six alloys of stainless steel were considered for potential use as prestressing wire and strand. Most stainless steels are not capable of developing the high strength needed for prestressing applications. Change in structure of the steel due to cold drawing has the potential for making the steel very susceptible to corrosion. Further, stainless steels such as the nitronic 33 used in older Navy piles have high stress relaxation. While all six will be investigated in Part 2, the most promising alloys are 2205 and 2304. Such stainless steel prestressing strands seem to be the best solution for providing durable piles in the marine environment. Based on the research conducted in Part 1, research in Part 2 will concentrate on (1) concrete mixes which have improved sulfate resistance, resist biological attack and have the ability to self-heal cracks caused by pile driving, and (2) determination of stainless steel ii properties including corrosion resistance, stress relaxation, yield strength, ultimate strength and ductility. The result of the research will be recommendations for high-performance concrete for marine piles and for corrosion-resistant high-strength stainless steel prestressing reinforcement. iii Acknowledgements The research reported herein was sponsored by the Georgia Department of Transportation through Research Project Number 07-30, Task Order Number 02-55. Mr. Paul Liles, Assistant State Preconstruction Engineer, Mr. Myron Banks, Concrete Engineer, Mr. Mike Clements, Bridge Maintenance Engineer, Ms. Supriya Kamatkar, Research Engineer, Mr. Kevin Schwartz, Bridge Inspection Engineer, Mrs. Lisa Sikes, Bridge Liasson, Mr. Michael Garner, Bridge Liasson, Mr. Andy Doyle, State Bridge Inspection Engineer, Mr. Jeff Carroll, Materials and Research Branch, Mr. Brian Scarbrough, Area Engineer, and Mr. Slade Cole, Assistant Area Engineer of GDOT provided many valuable suggestions throughout the study. The opinions and conclusions expressed herein are those of the authors and do not represent the opinions, conclusions, policies, standards or specifications of the Georgia Department of Transportation or of other cooperating organizations. Mr. Daniel Schuetz assisted with the production of the corrosion test specimens, and Mr. Jamshad Mahmood helped with the corrosion experimental setups and potentiostats. Messrs. Fred Aguayo, Robert Heusel, and Armin Vosough assisted with the forensic investigation of piling from the Turtle River Bridge. Mr. Jeremy Mitchell provided help and expertise with equipment and research tasks at the Georgia Tech Structures Laboratory. Messrs. Richard Potts and Alan Pritchard of Standard Concrete Products provided expertise and valuable suggestions throughout the study. Mr. Bill McClenathan, Brian Burr, Jon Cornelius, and colleagues from Sumiden Wire Products Corporation provided valuable insights into the production of materials for stainless steel prestressing wire and strand; their assistance and expertise are gratefully acknowledged. iv Table of Contents Executive Summary ii Acknowledgments iii Table of Contents iv Chapter 1. Introduction 1-1 2. Background – Corrosion Mechanisms in Reinforced and Prestressed Concrete 2-1 Structures 3. Background – Concrete for Marine Piles 3-1 4. Background – Interviews 4-1 5. Georgia Coastal Bridge Inspections 5-1 6. Forensic Investigation of Turtle River Bridge Piles 6-1 7. Preliminary Corrosion Studies on Carbon Steel A416 Prestressing Strand 7-1 8. Preliminary Corrosion Studies on Stainless Steel Prestressing Strand 8-1 9. Future Studies Planned for Part 2 9-1 10. Conclusions 10-1 Appendix A: Inspection Reports A-1 Combined References R-1 v 1. Introduction 1.1 Purpose and Objectives The purpose of the overall research project is to determine methods which may be applied economically to mitigate corrosion of reinforcement in precast prestressed concrete piles in Georgia’s marine environments. The overall goal is to improve the durability of bridge piles so that a design life of 100 years may be achieved. The research has four specific objectives. The first objective is to determine the extent of corrosion damage in Georgia’s structural concrete bridge piling and the success of methods used to improve the durability of bridge piles in Georgia. The second objective is to fully document past research and investigations on the durability of structural concrete in the marine environment with particular emphasis on the corrosion of reinforcement and its mitigation. The latter includes learning from state departments of transportations: finding from their experiences with corrosion mitigation including the effect of concrete quality and cover and with regard to types of reinforcement, their metallurgy and coatings. The third objective is to perform a preliminary experimental investigation on the corrosion of reinforcement in concrete piles in Georgia by measuring corrosion potential and by characterization of concrete, steel, and reinforced concrete, including samples obtained from the field. The durability of these field and laboratory samples will be compared to the findings from the literature study to see how Georgia’s marine environment and construction matches that found from the other states. The fourth objective is to identify what, if any, further research needs to be undertaken to determine improved methods to increase the durability of piles in Georgia’s marine environment. 1.2 Need for Research The maintenance costs for Georgia bridges are growing. There is a need to reduce maintenance costs. Further, the Federal Highway Administration has mandated that the design life of new bridges be between 75 and 100 years; the Georgia State Bridge Engineer has suggested that the design life be 100 years. Some prestressed concrete piles in the coastal region of Georgia have been shown to have severe corrosion damage in the splash zone after less than 25 years of service. Therefore, the current design standards for assuring durability of new structures are not sufficient if the 100- year design life is to be achieved. New standards must be developed and implemented; but what those standards are is unknown. One suggestion is to require that concrete for precast prestressed piles be High-Performance Concrete (HPC) with a rapid chloride ion permeability of less than 2000 coulombs.