Corrosion and Condition Assessment of Galvanized Steel Reinforcement in Concrete Structures

1. Corrosion and Condition Assessment of Galvanized Steel Reinforcement in Concrete Structures Dr. Jane Jieying Zhang Critical Concrete Infrastructure October 4, 2012

2. Introduction and Outlines • Corrosion of Galvanized Steel in Concrete • Projects • Corrosion performance in chloride laden environments • Comparison with carbon steel • In HPC and OPC • Corrosion measurement techniques • Half-cell potential techniques, Linear Polarization Resistance, AC impedance • Autopsy of concrete • Condition Assessment of Galvanized Steel in Concrete • A newly-started consortium project • Partners: MTQ, Corbec, Daam Galvanizing, Red River Galvanizing Inc, Galvcast MFG.Inc, Manitoba Infrastructure and Transportation (Manitoba DOT),South Atlantic LLC, New Jersey Galvanizing

3. Experimental

4. Corrosion Rate vs. Chloride Content Darwin et al. (2011) Clth (gal) = 1.5 kg/m3 Clth (carbon) = 0.97 kg/m3

5. Concretes with 1.5% and 3.0% of chlorides

6. Different Corrosion Stages of Galvanized Steel Yeomans’ Model

9. Galvanized Steel and Carbon Steel

10. High Chloride Concentration • Galvanized Steel has clear advantage over carbon steel by its lower corrosion rate

11. Evidences

12. Evidences

13. Evidences

14. Condition Assessment • Considerations of asset owners • Need a steel that is more corrosion resistant than carbon steel • Knowledge has been established over years, especially corrosion initiation stage • Corrosion rate of galvanized steel • In protection stage • In propagation stage. • Validation of corrosion mechanisms. • How to manage/maintain their asset afterwards • Condition Assessment

15. Service life and Condition Assessment • Condition assessment is the duty of infrastructure owners • Safety • Timely Maintenance • Decision Making • Repair • Rehabilitation • Removal

16. Four Governing Parameters for Initiation Stage Ti time to onset of corrosion Cs surface chloride concentration (Environmental Exposure) Clth chloride threshold value (Material Property, Steel) D  chloride diffusion coefficient (Material Property, Concrete) dcdepth of concrete cover over the reinforcing steel (Design Parameter)

17. Corrosion Initiation Stage Galvanized steel provides longer corrosion initiation stage, because Clth(galvanized steel)>Clth (carbon Steel) Darwin et al. (2011)

18. The Governing Parameter for Propagation Stage Ti–c  time from onset of corrosion to surface crack Icorr corrosion rate (steel + concrete + environment) Ti–c  accelerated corrosion environment in this study << in field condition Ti–c Comparative study with carbon steel

19. Half Cell Potential of Carbon Steel

20. Half Cell Potential Technique The most widely used corrosion assessment tool This guideline is for carbon steel only, but not for galvanized steel.

21. Condition Assessment Specifications of DOTs All based on ASTM C 876 or directly use ASTM C 876 The technique was pioneered by Stratfull and co-workers at the Caltrans, and now used worldwide. MTO “ 928.07.03.03 Concrete Removal Survey a) Visual and Delamination Survey - A visual and delamination survey shall be carried out for all concrete removals. b) Corrosion Potential Survey (Half-Cell) - When specified in the Contract Documents a corrosion potential survey will be carried out on all surfaces where concrete is to be removed based on corrosion potential criteria. Alberta Infrastructure uses -0.300 V as the potential, which indicates corrosion, is occurring.

22. Half Cell Potential of Galvanized Steel

23. Using ASTM C 876 for Galvanized Steel • Corrosion potentials of galvanized steel are different from those of carbon steel • Half-cell potentials mean different corrosion risks for galvanized steel • No guidelines for galvanized steel

24. From infrastructure owners MTO 2005 report “ The Long Term Performance of Three Ontario Bridges Constructed with Galvanized Reinforcement , ”By F. Pianca and H. Schell “According to ASTM C-876 if the steel reinforcement is passive the potential measured is small (0 to-200 mv) against a copper/copper sulphate cell. If the passive layer is failing and increasing amounts of steel are dissolving the potential moves towards –350mv. At more negative than -350mv the steel is usually corroding actively. The interpretation of the active/passive steel reinforcement in concrete is based on empirical observation of the probability of corrosion in structures containing black steel. However a means of interpreting half-cell data is not currently available in the literature for galvanized reinforcement in concrete. ”

25. Zinc used for effective corrosion control of steel reinforcement The lower the electrode potential, the higher the tendency for the metal to corrode Zinc, for example, has a tendency to corrode when connected to steel. The corrosion potential difference (up to 400 mV) of Zinc and Iron is the reason for use of Zinc for protection of steel. Zinc’s lower potential ( beneficial fact) not recognized in the condition assessment guidelines for carbon steel

26. From Field Inspection A 2002 Report to ILZRO and AHDGA • Use condition assessment guideline for black steel (ASTM C-876 )

27. NRC’s Corrosion Assessment Techniques for Concrete • Half-Cell Potential Method • tendency and probability • Linear Polarization Resistance Method • Rp • AC Impedance Method Electrochemical Impedance Spectrum • Re, Cd, Rp

28. NRC Research Expertise in Corrosion • Corrosion of Reinforcing Steel in Concrete • Corrosion Mechanisms • Performance of Carbon Steel and Corrosion Resistant Steels • Galvanic Coupling Corrosion • Corrosion in Concrete Patch Repair • Service Life Prediction and Performance-based Durability Design • Condition Assessment of Corrosion • Condition Assessment of Galvanized Steel in Concrete Structures

29. Laboratory Experimental Study

30. Field Experimental Study

31. Current Data on carbon steel and galvanized steel The actual corrosion condition of galvanized steel: passivation (no corrosion) According to ASTM guidelines for carbon steel, all galvanized steel bars , measured below -400 mV , are corroding fast.

32. Challenges for Galvanized Steel from using Carbon Steel Guidelines • For a surveyed potential falling between -350 mV to about -550 mV vs. CSE, a typical range indicating that carbon steel has started to corrode fast, does it mean that • zinc coating is passivated (not corroding)? OR • substrate carbon steel has started to corrode fast?

33. Research Project Condition assessment and corrosion mitigation of galvanized steel in concrete bridge decks, for • Better service life prediction • Timely maintenance strategy • Extension of service life • Experimental Investigation • Characterize corrosion of galvanized steel • Identification of Key parameters: chloride concentrations, concrete mix design, and environmental exposures • Modeling and Develop guidelines for interpretation of corrosion measurement • Field Validation

34. Preliminary Data from Electrochemical Cell Study ASTM C 876-91 ASTM C ######

35. Partners of the newly started consortium project • MTQ (Quebec DOT) • Corbec • Daam Galvanizing • Red River Galvanizing Inc. • Galvcast MFG.Inc • Manitoba Infrastructure and Transportation (Manitoba DOT) • South Atlantic LLC • New Jersey Galvanizing Need more support of the consortium in order to conduct field studies for validation Contact : Jieying.Zhang@nrc.ca or Our business manager Enzo.Gardin@nrc.ca

36. Thank you for your attention