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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
13
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
17
Galvanized steel provides longer corrosion initiation stage, because Clth(galvanized steel)>Clth (carbon Steel)
Darwin et al. (2011)
The Governing Parameter for Propagation Stage
18
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
19
20
Half Cell Potential TechniqueThe 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 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
22
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
23
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. ”
24
Zinc used for effective corrosion control of steel reinforcement
25
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 )
26
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
28
Laboratory Experimental Study
29
Field Experimental Study
30
Current Data on carbon steel and galvanized steel
31
-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?
32
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
34
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 : [email protected] or
Our business manager [email protected]
Thank you for your attention