Laboratory and Field Evaluations of Corrosion Resistance Reinforcement

Virginia Concrete ConferenceBridge Breakout Session

March 4, 20119:00—9:30 a.m.

Presented By: Stephen R. Sharp, Ph.D., P.E.

March 4, 2011 2

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 3

Overview continued

• VDOT Bridge-deck reinforcing steel type is changing

• Higher performance concrete needs higher performance steel rebar

• Methodology for accepting CRR is important– testing for alloying – mechanical properties– corrosion resistance

Coated Alloyed

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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

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Cost of Bars Range from $0.33 up to $3.50 / lb.

Lessons Learned: Many Varieties

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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

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Publications on Corrosion Resistance

• FHWA, VCTIR & others have sponsored a number of studies

• Different bars exhibit different levels of corrosion resistance

Improved

Corrosion

Resistance

Moderate Corrosion

Resistance

High Corrosion Resistance

MMFX2, 2101LDX

(unpickled),

2201

Clad Bar,

2304

316LN,

304,

2205

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Carbon steel MMFX2 Duracor

Lessons Learned: Visual Assessment of Different Bars

• Different Types of Bars Can Look Similar

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Lessons Learned: Visual Assessment of A Single Bar Type

The Same Type of Steel Can Look Very Different

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N 322205

Same bar markings, yet different alloys

Lessons Learned: Manufacturers Markings

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Lessons Learned: Magnetic Response

Bar MMFX2 Black 2101 2304 2205 N32 304 316

Steel Mart./ Aus.

Fer./ Pear.

Dup. Dup. Dup. Aus. Aus. Aus.

Res† 0.16 0.85 0.91 1.3 2.7 >25 >25 >25

†Response measured using

coating thickness gage

3162205

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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

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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 non-magnetic 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.

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Lessons Learned: Uniaxial Tensile Test

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Lessons Learned: Elongation

Bar MMFX2

DuraCorr

Black Steel

SS Clad

2304 2205 N32

Elong (%)

8 10 12 19 20 28 39

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Lessons Learned: Percent Reduction in Cross-Section

Bar Black Steel

SS Clad

N32 MMFX2

316 LN

DuraCorr

Red.(%) 7.5 21.5 35.8 38.5 48.5 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

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Lessons Learned: Example of Influence of Relative Rib Area

Black:

Rr = 0.80,

NX (clad):

Rr= 0.53

• Relative Rib Area Makes A Difference

(From VTRC 04-R5)

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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

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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.

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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%

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Lessons Learned: ASTM A955

• ASTM A955-06a

• A955-09b & A955-10

Loss of ASTM A276 decreased the number of UNSdesignated stainless steel products by nearly 93%

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Lessons Learned: Route 123 Bridge Deck

Half-Cell, mV vs CSE• No. of Points

▪ 1149• Median

▪ -92• Mean

▪ -101• Standard

Deviation▪ 51

Resistivity, KΩ cm

• No. of Points▪ 38

• Median▪ 57

• Mean▪ 55

• Standard Deviation▪ 16

1.75”-2.25” Ave.Total Chloride,

lb/yd3

• Uncracked▪ 0.380

• Cracked ▪ 2.404

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Lessons Learned: Route 123 Bridge Deck continued

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Lessons Learned: Route 123 Bridge Deck continued

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Lessons Learned: Route 123 Bridge Deck continued

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Lessons Learned: Route 360 Over Banister River, Halifax County

• Void between clad layer and black steel core

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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

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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

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Future Evaluation: Route 460 Over Route 29 Bypass, Campbell County

• Placed Late 2001/Early 2002

• End protection evaluation?

(From VTRC 04-R5)

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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.

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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 stress-strain behavior, elongation and reduction in cross-section upon fracture can significantly vary for different CRR alloys.

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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

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