Corrosion and Condition Assessment of Galvanized Steel Reinforcement in Concrete Structures

Dr. Jane Jieying Zhang

Critical Concrete InfrastructureOctober 4, 2012

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

Experimental

3

Corrosion Rate vs. Chloride Content

0.001

0.010

0.100

1.000

10.000

100.000

0 4 8 12 16 20 24 28 32 36

Co

rro

sio

n R

ate

(µ

A/c

m2)

Age (month)

0.0% of chlorides

0.5%

1.5%

3.0%

Galvanized Steel

Darwin et al. (2011) Clth (gal) = 1.5 kg/m3

Clth (carbon) = 0.97 kg/m3

Concretes with 1.5% and 3.0% of chlorides

Different Corrosion Stages of Galvanized Steel

6

Yeomans’ Model

7

8

Galvanized Steel and Carbon Steel

0.001

0.010

0.100

1.000

10.000

100.000

0 4 8 12 16 20 24 28 32 36

Co

rro

sio

n R

ate

( µ

A/c

m2)

Age (month)

Carbon Steel

Galvanized steelChloride Concentration = 0.5%

0.001

0.010

0.100

1.000

10.000

100.000

0 4 8 12 16 20 24

Co

rro

sio

n R

ate

( µ

A/c

m2)

Age (month)

Carbon steel

Galvanized steelChloride Concentration = 1.5%

High Chloride Concentration

• Galvanized Steel has clear advantage over carbon steel by its lower corrosion rate

0.001

0.010

0.100

1.000

10.000

100.000

0 4 8 12 16 20 24 28 32 36

Co

rro

sio

n R

ate

( µ

A/c

m2)

Age (month)

Carbon Steel

Galvanized Steel

Chloride Concentration = 3.0%

Monitoring stopped due to delamination of concrete caused by corrosion of carbon steel

Evidences

11

Evidences

12

Evidences

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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

Service life and Condition Assessment

Dam

age

leve

l

Time

Early-age cracking

Rebar corrosion

Internal cracking

Surface cracking

Delaminationor spalling

Service life

Corrosion initiation stage Propagation stage

Cl- Cl-Cl-Cl- Cl-

Early-age cracking Chloride diffusion Rust & stress build-up Concrete damage

Dam

age

leve

l

Time

Early-age cracking

Rebar corrosion

Internal cracking

Surface cracking

Delaminationor spalling

Service life

Corrosion initiation stage Propagation stage

Cl- Cl-Cl-Cl- Cl-

Early-age cracking Chloride diffusion Rust & stress build-up Concrete damage

Condition assessment is the duty of infrastructure owners • Safety• Timely Maintenance•Decision Making

•Repair•Rehabilitation•Removal

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)21

2

)]1([4),,,(

s

th

ccthsi

CC

erfD

ddDCCfT

Zhang, J.Y., Lounis, Z., "Sensitivity analysis of simplified diffusion-based corrosion initiation model of concrete structures exposed to chlorides," Cement and Concrete Research, 36, (7), July, pp. 1312-1323 Zhang, J.Y., Lounis, Z., "Nonlinear relationships between parameters of simplified diffusion–based model for service life design of concrete structures exposed to chlorides," Cement and Concrete Composites, 31, (8), pp. 591-600

Corrosion Initiation Stage

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Galvanized steel provides longer corrosion initiation stage, because Clth(galvanized steel)>Clth (carbon Steel)

Darwin et al. (2011)

The Governing Parameter for Propagation Stage

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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

Half Cell Potential of Carbon Steel

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Half Cell Potential TechniqueThe most widely used corrosion assessment tool

This guideline is for carbon steel only, but not for galvanized steel.

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Condition Assessment Specifications of DOTs

All based on ASTM C 876 or directly use ASTM C 876The 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.

Half Cell Potential of Galvanized Steel

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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

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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. ”

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Zinc used for effective corrosion control of steel reinforcement

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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.

1.The corrosion potential difference (up to 400 mV) of Zinc and Iron is the reason for use of Zinc for protection of steel.

2.Zinc’s lower potential ( beneficial fact) not recognized in the condition assessment guidelines for carbon steel

From Field Inspection

A 2002 Report to ILZRO and AHDGA

• Use condition assessment guideline for black steel (ASTM C-876 )

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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

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

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Laboratory Experimental Study

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Field Experimental Study

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Current Data on carbon steel and galvanized steel

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-800

-600

-400

-200

0

0 50 100 150 200

Co

rro

sio

n P

ote

nti

al (m

V v

s. C

SE)

Age (days)

L2GSa

L3GSa

L4GSa

L5GSa

L6GSa

L6CSaCarbon Steel in Control Mix HPC-6

0.010

0.100

1.000

0 50 100 150 200

Corr

osio

n ra

te (m

A/c

m2 )

Age (days)

L2GSa

L3GSa

L4GSa

L5GSa

L6GSa

According to ASTM guidelines for carbon steel, all galvanized steel bars , measured below -400 mV , are corroding fast.

The actual corrosion condition of galvanized steel: passivation (no corrosion)

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?

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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

Preliminary Data from Electrochemical Cell Study

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Table 1.5 Comparison of corrosion state of carbon steel and galvanized steel

Measured potential Ecorr (mV vs. CSE)

Carbon steel Galvanized steel

Ecorr > 200 Low, 10% risk of corrosion

Passivation

350 < Ecorr < 200 Uncertain -660<Ecorr < 350 High, 90% risk of

corrosion

-860<Ecorr < 660 Uncertain Ecorr < 860 Active corrosion

Measured Corrosion rate Icorr (µm/cm2)

Carbon steel Galvanized steel

1.0 < Icorr High rate Active corrosion 0.5 < Icorr < 1.0 Moderate rate

Passivation

0.1 < Icorr < 0.5 Low rate Icorr < 0.1 Passivation

ASTM C 876-91 ASTM C ######

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

Thank you for your attention