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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

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presented by stephen r sharp ph d p e

Laboratory and Field Evaluations of Corrosion Resistance ReinforcementVirginia Concrete ConferenceBridge Breakout SessionMarch 4, 20119:00—9:30 a.m.

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

overview
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
overview continued

Coated

Alloyed

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
why is it important to understand these different alloys
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
lessons learned many varieties
Lessons Learned: Many Varieties

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

lessons learned stainless steel cost
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
publications on corrosion resistance
Publications on Corrosion Resistance
  • FHWA, VCTIR & others have sponsored a number of studies
  • Different bars exhibit different levels of corrosion resistance
lessons learned visual assessment of different bars
Lessons Learned: Visual Assessment of Different Bars

Carbon steel

MMFX2

Duracor

  • Different Types of Bars Can Look Similar
lessons learned visual assessment of a single bar type
Lessons Learned: Visual Assessment of A Single Bar Type

The Same Type of Steel Can Look Very Different

lessons learned manufacturers markings

2205

N 32

Lessons Learned: Manufacturers Markings

Same bar markings, yet different alloys

lessons learned magnetic response
Lessons Learned: Magnetic Response

†Response measured using

coating thickness gage

2205

316

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

Lessons Learned: X-Ray Fluorescence
lessons learned visual bar assessment
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.
relative rib area measurements
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

lessons learned example of influence of relative rib area
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)

lessons learned material properties
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
lessons learned costs
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.
lessons learned astm a1035
Lessons Learned: ASTM A1035
  • ASTM A1035-09

The chromium content range listed eliminates all

candidate materials with a content greater than 10.9%

lessons learned astm a955
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%

lessons learned route 123 bridge deck
Half-Cell,

mV vs CSE

No. of Points

1149

Median

-92

Mean

-101

Standard Deviation

51

Lessons Learned: Route 123 Bridge Deck

1.75”-2.25” Ave.

Total Chloride, lb/yd3

  • Uncracked
    • 0.380
  • Cracked
    • 2.404

Resistivity,

KΩ cm

  • No. of Points
    • 38
  • Median
    • 57
  • Mean
    • 55
  • Standard Deviation
    • 16
lessons learned route 360 over banister river halifax county
Lessons Learned: Route 360 Over Banister River, Halifax County
  • Void between clad layer and black steel core
lessons learned route 360 over banister river halifax county continued
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
lessons learned route 360 over banister river halifax county continued29
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
summary
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.
summary continued
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.
summary continued33
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

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