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 4

Lessons Learned: Many Varieties

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

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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 Improved Corrosion Resistance Moderate Corrosion Resistance High Corrosion Resistance MMFX2, 2101LDX (unpickled), 2201 Clad Bar, 2304 316LN, 304, 2205 March 4, 2011 7

Lessons Learned: Visual Assessment of Different Bars

Carbon steel MMFX2 Duracor

• Different Types of Bars Can Look Similar March 4, 2011 8

Lessons Learned: Visual Assessment of A Single Bar Type

The Same Type of Steel Can Look Very Different

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Lessons Learned: Manufacturers Markings

2205 N 32 Same bar markings, yet different alloys

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Lessons Learned: Magnetic Response Bar Steel MMFX2 Black 2101 2304 2205 Mart./ Aus.

Fer./ Pear.

Dup. Dup.

Dup.

Res

†

0.16

0.85

0.91

1.3

2.7

† Response measured using coating thickness gage

N32 Aus.

304 316 Aus. Aus.

>25 >25 >25 316 11 2205 March 4, 2011

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 12

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 March 4, 2011 14

Lessons Learned: Elongation Bar Elong (%) MMFX 2 8 Dura Corr 10 Black Steel 12 SS Clad 19 2304 2205 N32 20 28 39 March 4, 2011 15

Lessons Learned: Percent Reduction in Cross-Section Bar Red.(%) Black Steel 7.5

SS Clad 21.5

N32 35.8

MMFX 2 38.5

316 LN 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

March 4, 2011

Bar diameter measurement

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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

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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 19

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% March 4, 2011 21

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 22

Lessons Learned: Route 123 Bridge Deck 1.75”-2.25” Ave.

Total Chloride, lb/yd 3 • Uncracked ▪ 0.380

• Cracked ▪ 2.404

Resistivity, K Ω cm • No. of Points ▪ 38 • Median ▪ 57 • Mean ▪ 55 • Standard Deviation ▪ 16 Half-Cell, mV vs CSE • No. of Points ▪ 1149 • Median ▪ -92 • Mean ▪ -101 • Standard Deviation ▪ 51 March 4, 2011 23

Lessons Learned: Route 123 Bridge Deck continued March 4, 2011 24

Lessons Learned: Route 123 Bridge Deck continued March 4, 2011 25

Lessons Learned: Route 123 Bridge Deck continued March 4, 2011 26

Lessons Learned: Route 360 Over Banister River, Halifax County • Void between clad layer and black steel core March 4, 2011 27

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 28

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 March 4, 2011

(From VTRC 04-R5)

• End protection evaluation?

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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. March 4, 2011 32

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 33

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