Laboratory and Field Evaluations of
Corrosion Resistance Reinforcement
Virginia Concrete Conference
Bridge Breakout Session
March 4, 2011
9:00—9:30 a.m.
Presented By: Stephen R. Sharp, Ph.D., P.E.
Overview
• Information from several research projects
– Corrosion Resistant Reinforcing Steel Testing
• VCTIR
– Stephen R. Sharp
• VDOT – Materials Division
– Larry J. Lundy , Harikrishnan Nair
• Virginia Polytechnic Institute and State University
– Cris D. Moen, Josiah Johnson, Brian Sarver
– Route 123 Bridge over Occoquan River
– Accelerated Test Method for CRR
March 4, 2011
2
Overview continued
• VDOT Bridge-deck reinforcing steel type is
changing
Coated
Alloyed
• Higher performance concrete needs higher
performance steel rebar
• Methodology for
accepting CRR is
important
– testing for alloying
– mechanical properties
– corrosion resistance
March 4, 2011
3
Why is it Important to Understand these
Different Alloys?
• Old Specification
– One Rebar Grade – ASTM A615 Grade 60
– Differentiated by color
• Black
• Grey (galvanized)
• Green/yellow/purple/etc. (epoxy-coated)
• New Specification
– Multiple alloy grades
• ASTM A955 – multiple grades of stainless steel bar
• ASTM A1035 – MMFX, etc.
• AASHTO MP13 – Multiple grades of stainless steel
clad bar
March 4, 2011
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Lessons Learned: Many Varieties
Cost of Bars Range from $0.33 up to $3.50 / lb.
March 4, 2011
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Lessons Learned: Stainless Steel Cost
• Alloyed steels are sensitive to alloy costs
and some are more sensitive than others.
• Steels with lower nickel and molybdenum
provide greater price stability
March 4, 2011
6
Publications on Corrosion Resistance
• FHWA, VCTIR &
others have
sponsored a
number of studies
• Different bars
exhibit different
levels of corrosion
resistance
March 4, 2011
Improved
Moderate
High
Corrosion
Corrosion
Corrosion
Resistance Resistance Resistance
MMFX2,
2101LDX
(unpickled),
2201
Clad Bar,
2304
316LN,
304,
2205
7
Lessons Learned: Visual Assessment of
Different Bars
Carbon steel
MMFX2 Duracor
• Different Types of Bars Can Look
Similar
March 4, 2011
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Lessons Learned: Visual Assessment
of A Single Bar Type
The Same Type of Steel Can Look Very Different
March 4, 2011
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Lessons Learned: Manufacturers Markings
N 32
2205
Same bar markings, yet different alloys
March 4, 2011
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Lessons Learned: Magnetic Response
Bar
MMFX2 Black 2101 2304 2205
Steel
Mart./
Aus.
Res†
0.16
Fer./ Dup. Dup.
Pear.
0.85
0.91
1.3
N32
304
316
Dup.
Aus.
Aus. Aus.
2.7
>25
>25
>25
†Response
measured using
coating thickness gage
2205
316
March 4, 2011
11
Lessons Learned: X-Ray Fluorescence
• Provides a means of quickly identifying
the composition of rebar in the lab or field
• Performed following Manufacturers
Guidelines
– Turn on x-ray fluorescence analyzer
– Allow to warm up for 5 minutes
– Perform Checks
• If XRF checks, proceed with
analysis
• if not, calibrate instrument and
recheck
• Alloy Identification Within Seconds
– longer analysis time for greater accuracy
• Total test time (warm-up + calibration)
– less than 10 minutes
• Provides alloy type,% confidence of alloy
ID, list % elements detected, and
confidence limit per element detected
March 4, 2011
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Lessons Learned: Visual Bar Assessment
Care must be taken when accepting bars at the
jobsite based on visual assessment and markings.
– A magnet can be used as a rough sorting method
to differentiate between magnetic and nonmagnetic alloys.
– Handheld XRF devices can be useful in
determining alloy composition.
– Industry should push ASTM to revise the
standards that govern the bar markings and
include a requirement that markings be added
that indicate the type of steel.
March 4, 2011
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Lessons Learned: Uniaxial Tensile Test
March 4, 2011
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Lessons Learned: Elongation
Bar
MMFX Dura Black SS 2304 2205 N32
2
Corr Steel Clad
Elong
8
10
12
19
20
28
39
(%)
March 4, 2011
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Lessons Learned: Percent Reduction in
Cross-Section
Bar
Black SS
Steel Clad
Red.(%) 7.5
21.5
March 4, 2011
N32
35.8
MMFX 316
2
LN
38.5 48.5
Dura
Corr
52.6
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Relative Rib Area Measurements
• ASTM A615
• Takes into account both the rib height and spacing
Cord width measurement
Rib spacing measurement
Rib height measurement
Bar diameter measurement
March 4, 2011
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Lessons Learned: Example of Influence
of Relative Rib Area
• Relative Rib Area
Makes A Difference
(From VTRC 04-R5)
Black:
Rr = 0.80,
NX (clad):
Rr= 0.53
March 4, 2011
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Lessons Learned: Material Properties
• Lesson Learned → Knowledge of the material
properties and how each bar will interact with
the concrete is important.
– Alloying changes not only the corrosion
resistance, but other material properties as
well.
– With several companies producing different
types of bars, features vary and can result in
different responses when loaded to failure
• Differences in relative rib area
• Debonding of clad from steel
March 4, 2011
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Lessons Learned: Costs
• The initial cost of CRR is a function of the
reinforcement specified and ranges from
about the same as ECR to 3 times more.
• The additional initial cost of solid stainless
CRR is typically less than 5 percent of the
total project cost.
• The cost of one deck overlay far exceeds
the extra cost of solid stainless
reinforcement.
March 4, 2011
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Lessons Learned: ASTM A1035
• ASTM A1035-09
The chromium content range listed eliminates all
candidate materials with a content greater than 10.9%
March 4, 2011
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Lessons Learned: ASTM A955
• ASTM A955-06a
• A955-09b & A955-10
Loss of ASTM A276 decreased the number of UNS
designated stainless steel products by nearly 93%
March 4, 2011
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Lessons Learned: Route 123 Bridge
Deck
1.75”-2.25” Ave.
Total Chloride,
lb/yd3
• Uncracked
▪ 0.380
• Cracked
▪ 2.404
March 4, 2011
Resistivity,
KΩ cm
Half-Cell,
mV vs CSE
• No. of Points
▪ 38
• Median
▪ 57
• Mean
▪ 55
• Standard
Deviation
▪ 16
• No. of Points
▪ 1149
• Median
▪ -92
• Mean
▪ -101
• Standard
Deviation
▪ 51
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Lessons Learned: Route 123 Bridge
Deck continued
March 4, 2011
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Lessons Learned: Route 123 Bridge
Deck continued
March 4, 2011
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Lessons Learned: Route 123 Bridge
Deck continued
March 4, 2011
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Lessons Learned: Route 360 Over
Banister River, Halifax County
• Void between clad layer and black steel
core
March 4, 2011
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Lessons Learned: Route 360 Over
Banister River, Halifax County continued
• Rust does not penetrate through the stainless cladding
• Deep groove is present along the rolling direction,
reducing clad thickness
March 4, 2011
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Lessons Learned: Route 360 Over
Banister River, Halifax County continued
• Average Clad Thickness 0.7-mm
• Thinnest Value: 0.215-mm
• Thickest Value (excluding stainless bulb area):1.351-mm
March 4, 2011
29
Future Evaluation: Route 460 Over
Route 29 Bypass, Campbell County
• Placed Late
2001/Early 2002
• End protection
evaluation?
(From VTRC 04-R5)
March 4, 2011
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Summary
• VDOT is implementing CRR
• Visual assessment can not be relied on to
determine bar type
• Steel fabricator markings cannot be relied on
to identify the type of steel.
• Magnetic sorting provides a quick and easy
method for differentiating between magnetic
and nonmagnetic alloys.
March 4, 2011
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Summary continued
• X-ray fluorescence provides a practical, and
much needed, method for positively
identifying bars.
• Relative rib area should be monitored as it
varies from producer to producer.
• Uniaxial tensile tests provide the stressstrain behavior, elongation and reduction in
cross-section upon fracture can significantly
vary for different CRR alloys.
March 4, 2011
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Summary continued
• Corrosion and mechanical testing of CRR is
necessary to identify the most cost effective
bars with acceptable properties.
• Simple quality control measures need to be
established to ensure VDOT receives the
corrosion protection it needs
• VDOT should evaluate using VTM for their
acceptance criteria while pursuing a single
CRR test method via AASHTO
March 4, 2011
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Thank You – Questions?
Acknowledgements: Federal Highway Administration,
VDOT Materials Division, VDOT Structure and Bridge
Division, University of Virginia, Virginia Center for
Transportation Innovation and Research, and Virginia
Polytechnic Institute and State University