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Quantifying the Duration of the Corrosion Propagation Stage in Stainless Steel Reinforcement

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Quantifying the Duration of the Corrosion Propagation Stage in Stainless Steel Reinforcement Report prepared by: Julio Saire Yañez Nelly S. Orozco Martínez Gray Mullins Christopher L. Alexander FINAL REPORT (Project BDV25-977-56) QUANTIFYING THE DURATION OF THE CORROSION PROPAGATION STAGE IN STAINLESS STEEL REINFORCEMENT Final Report to Florida Department of Transportation Christopher L. Alexander (PI) Gray Mullins (Co – PI) Ronald Simmons (FDOT Project Manager) Tampa, FL 33620 December 2020 1 Disclaimer page The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the Florida Department of Transportation. 2 Universal conversion table 3 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle 5. Report Date Quantifying the Duration of the Corrosion Propagation Stage in November 25, 2020 Stainless Steel Reinforcement 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. N. S. Orozco, Julio Saire Yañez, C. L. Alexander, G. Mullins 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Department of Civil and Environmental Engineering University of South Florida (USF) 11. Contract or Grant No. Tampa, FL 33620 BDV25-977-56 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Final Report 2/5/18 – 12/30/20 14. Sponsoring Agency Code 15. Supplementary Notes 16. Abstract Present durability projections for concrete reinforced with stainless steel (SS) are limited in that, while accounting for a substantial increase in the corrosion initiation stage (CIS) duration, credit tends not to be given for any added corrosion propagation stage (CPS) duration over that of carbon steel (CS). The objectives of this work were to: (1) develop a rational quantitative estimate of the duration of the corrosion propagation stage of concrete reinforced with SS in current and anticipated FDOT practice, establishing alternative corrosion monitoring methods if needed; (2) apply the findings as inputs to damage function models to determine how any resulting added durability credit can be used to optimize materials and design options. Experiments were performed to obtain estimates of corrosion rates, corrosion morphology, and the critical corrosion penetration. The results were then used to suggest a service limit state that accounted for the mechanical properties of the steel. The results were incorporated into durability projections to provide recommendations of concrete cover to be used based on service conditions. 17. Key Words: Durability, Corrosion rate, corrosion 18. Distribution Statement morphology, critical corrosion penetration, limit state 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 163 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 4 Acknowledgements The assistance of Professor Francisco Presuel from Florida Atlantic University in providing a legacy specimen for autopsy is gratefully acknowledged. The assistance of student participants in the University of South Florida, College of Engineering Research Experience for Undergraduates (Maria Cardoso, Justin Silnutzer, and Sachintha Wickramaarachchi) is also acknowledged. Thanks is given to Professor Emeritus Alberto Sagüés for critical review of the document. 5 Executive summary Durability of Florida Department of Transportation (FDOT) reinforced concrete structures is greatly limited by corrosion of the steel reinforcement. This issue becomes even more critical in structures exposed to aggressive environments such as marine structures. The FDOT has instituted corrosion prevention strategies such as increased concrete cover thickness, higher concrete quality, and corrosion- resistant alloys such as stainless steel (SS) for some applications. Over the past couple of decades, SS reinforcement has garnered attention due to its increased durability. Several investigations have found that the cumulative cost of structures reinforced with SS may be considerably lower than that of plain carbon steel (CS). The service life of steel reinforcement is typically divided into two stages: the corrosion initiation stage (CIS) and corrosion propagation stage (CPS). The durability of SS reinforcement has been commonly approached using the model proposed by Tuutti1 where the service life of a structure, which is the time required for corrosion loss in the steel to reach a serviceability limit state, is determined by the added duration of the CIS and the CPS . The increased durability of SS reinforcement has been mostly attributed to a greater corrosion initiation threshold (CT) which could be up to one order of magnitude greater when compared to that of CS. Nevertheless, no significant benefit has been associated to extents attributed to the subsequent CPS. Hence, existing durability projections of concrete reinforced with SS are limited by the scarce information available regarding the CPS yielding to highly conservative approaches based on investigations performed on concrete reinforced with CS. This investigation compiles relevant information from literature focusing on the few cases where SS reinforcement had reached, and preferably finalized, the corrosion propagation stage. The information garnered was compared to laboratory experimental results obtained at the Infrastructural Corrosion Laboratory of the University of South Florida. The reliability of the most commonly used corrosion detection and monitoring methods were examined in SS reinforcement and alternatives were stablished if necessary. In addition, different failure mechanisms were examined as a first approach to determine the expected limit state of SS reinforced concrete considering aspects such as corrosion morphology, corrosion products, and corrosion rates. In addition, the effect of the concrete condition was also taken into consideration to predict potential limit states for SS reinforced concrete. Results from this and previous investigations were used to update existing durability estimates of the duration of the corrosion propagation stage of concrete reinforced with SS in current FDOT practices. These updated estimates were in the form of cumulative quantitative damage functions that could be translated into future cost estimates that could be used to avoid over-specification for certain alloys of SS reinforcement. Any propagation stage added credit identified by this research – as well as any limitations that were uncovered – can then be used for rational decisions on rational design and material selection decisions. Up to now, it has not been possible to implement such decisions because the information was lacking. 6 Table of contents Disclaimer page ............................................................................................................................................. 2 Universal conversion table ............................................................................................................................ 3 Technical Report Documentation Page ........................................................................................................ 4 Acknowledgements ....................................................................................................................................... 5 Executive summary ....................................................................................................................................... 6 List of figures ............................................................................................................................................... 10 List of tables ................................................................................................................................................ 15 1 Introduction ........................................................................................................................................ 17 1.1 Background statement ................................................................................................................ 17 1.2 Project objectives ........................................................................................................................ 19 2 Literature review ................................................................................................................................. 20 2.1 Review of propagation stage literature for actual structural service ......................................... 20 2.1.1 SS performance in structures in service .............................................................................. 20 2.1.2 Summary of findings on SLS mode and duration of the propagation stage ....................... 22 2.1.3 Summary of findings on methods of detection and measurement of corrosion of SS reinforcement ..................................................................................................................................... 24 3 Experimental methods ........................................................................................................................ 25 3.1 Reinforced concrete beams with chloride-contaminated section ............................................. 25 3.1.1 Materials ............................................................................................................................. 25 3.1.2 Specimen preparation ......................................................................................................... 27 3.1.3 Data acquisition .................................................................................................................
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