Corrosion and Condition Assessment of
Galvanized Steel Reinforcement in Concrete Structures
Dr. Jane Jieying Zhang
Critical Concrete Infrastructure
October 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
100.000
0.0% of chlorides
Galvanized Steel
0.5%
1.5%
Corrosion Rate (µA/cm2)
10.000
3.0%
1.000
0.100
0.010
0.001
0
4
8
12
16
20
24
28
32
36
Age (month)
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
Yeomans’ Model
6
7
8
Galvanized Steel and
Carbon Steel
100.000
Carbon Steel
Chloride Concentration = 0.5%
Galvanized steel
1.000
0.100
100.000
Carbon steel
Chloride Concentration = 1.5%
Galvanized steel
0.010
10.000
0.001
0
4
8
12
16
20
Age (month)
Corrosion Rate ( µA/cm2)
Corrosion Rate ( µA/cm2)
10.000
241.000 28
32
36
0.100
0.010
0.001
0
4
8
12
Age (month)
16
20
24
High Chloride
Concentration
• Galvanized Steel has clear advantage over carbon steel
by its lower corrosion rate
100.000
Monitoring stopped due to delamination of
concrete caused by corrosion of carbon steel
Corrosion Rate ( µA/cm2)
10.000
1.000
0.100
Carbon Steel
Chloride Concentration = 3.0%
Galvanized Steel
0.010
0.001
0
4
8
12
16
20
Age (month)
24
28
32
36
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
Service life
Corrosion initiation stage
Propagation stage
Damage level
Delamination
or spalling
Surface
cracking
Internal
Rebar cracking
corrosion
Early-age
cracking
Time
Cl- Cl-
Early-age cracking
Cl- Cl- Cl-
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
2
Parameter)
d
Ti  f (Cs , Cth , D, d c ) 
c
4 D[erf 1 (1 
Cth 2
)]
Cs
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
Galvanized steel provides longer corrosion initiation stage,
because Clth(galvanized steel)>Clth (carbon Steel)
Darwin et al. (2011)
17
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
18
Half Cell Potential of
Carbon Steel
19
Half Cell Potential
Technique
The most widely used corrosion assessment tool
This guideline is for carbon steel only,
but not for galvanized steel.
20
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.
21
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
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
25
From Field Inspection
A 2002 Report to ILZRO and AHDGA
• Use condition assessment guideline for black steel (ASTM C-876 )
26
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
27
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
0
1.000
L2GSa
L2GSa
L4GSa
-200
L5GSa
Corrosion rate (mA/cm2)
Corrosion Potential (mV vs. CSE)
L3GSa
L6GSa
Carbon Steel in Control Mix HPC-6
L6CSa
-400
L3GSa
0.100
L4GSa
L5GSa
-600
L6GSa
0.010
-800
0
50
100
150
Age (days)
According to ASTM
guidelines for carbon steel, all
galvanized steel bars ,
measured below -400 mV , are
corroding fast.
200
0
50
100
150
200
Age (days)
The actual corrosion condition
of galvanized steel: passivation
(no corrosion)
31
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
Table 1.5 Comparison of corrosion state of carbon steel and galvanized steel
Measured potential
Ecorr (mV vs. CSE)
Ecorr > 200
350 < Ecorr < 200
-660<Ecorr <350
-860<Ecorr <660
Ecorr <860
Measured Corrosion rate
Icorr (µm/cm2)
1.0 < Icorr
0.5 < Icorr < 1.0
0.1 < Icorr < 0.5
Icorr < 0.1
Carbon steel
ASTM C 876-91
Low, 10% risk of
corrosion
Uncertain
High, 90% risk of
corrosion
Carbon steel
High rate
Moderate rate
Low rate
Passivation
Galvanized steel
ASTM C ######
Passivation
Uncertain
Active corrosion
Galvanized steel
Active corrosion
Passivation
34
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