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USE OF CORROSION RESISTANT REINFORCING MATERIALS Ray Bottenberg, P.E. Oregon Department of Transportation


Introduction „

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Iron reinforcing bar first used in France in 1850s Steel reinforcing bar first used in England in 1864 First concrete building reinforced with steel in the U.S. was in 1893 in Los Angeles Carbon steel reinforcing bar is uniquely compatible with concrete „ „ „

Steel provides tension load path in concrete Thermal expansion rates are similar High pH in concrete passivates surface of steel


Effect of Salt on Reinforced Concrete

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Salt destroys protective passivated surface on reinforcing bars Salt acts as a catalyst and electrolyte for galvanic corrosion Corrosion products from reinforcing bars expand to 6-11 times the original metal thickness Expansion of corrosion products causes spalling of concrete and loss of protective cover


Sources of Salt Contamination „ „ „

Marine environment Deicing chemicals Some concrete admixtures


Solutions: Epoxy Coated Reinforcing Bar

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Fusion Bonded Epoxy Coating Susceptible to nicks & other mechanical damage Development lengths are longer Severe corrosion at flaws due to small anode effect Prevents future cathodic protection Supported by ODOT Bridge Engineering for applications per BDDM


Solutions: Stainless Steel Reinforcing Bar

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Solid 316L (Austenitic) or 2205 (Duplex) Descaled & pickled to provide ideal passivated surface (high pH not required) Resistant to damage Higher initial cost Currently available with ODOT Special Specification 00530 Supported by ODOT Bridge Engineering for applications per BDDM


Solutions: Hot-Dip Galvanized Reinforcing Bar

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Carbon steel reinforcing bar, hot-dip galvanized Zinc is amphoteric (i.e. susceptible to corrosion in high or low pH) Not currently recommended by ODOT Bridge Engineering


Solutions: “Zbar” „ „ „ „

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Carbon steel reinforcing bar 0.002” thick layer of arc-sprayed zinc Fusion bonded epoxy coating Vendor claims “synergistic” corrosion protection Vendor claimed it can be bent like any other bar Coating failed during bar bending Vendor then claimed that it requires special bending radius and bending temperature Not currently recommended by ODOT Bridge Engineering


Solutions: “NX Clad”

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Carbon steel reinforcing bar 316 stainless steel cladding by powder metal process Cost about 60% of solid 316 reinforcing Clad layer cracked during bending Not currently recommended by ODOT Bridge Engineering


Solutions: FRP Rebar

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Fiber reinforced polymer reinforcing bar Design specifications exist „ ACI 440.1R-03 „ AASHTO LRFD Bridge Design Specifications for GFRP Reinforced Concrete Decks and Deck Systems Not susceptible to salt Can be damaged if moisture penetrates outer layers Bent bars have to be fabricated in factory Appears cost effective on Millport Slough Bridge


Solutions: Economical Stainless Steels

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Enduramet 32 (Nitronic 40) austenitic alloy with manganese, approximately 50% cost of 316 Arminox Alloy 2304 duplex alloy, approximately 60% cost of 316 Similar surface corrosion as 316 Stress corrosion cracking test underway by ODOT Research (bent bars can be susceptible)


Solutions: “MMFX” „ „ „

Proprietary “microalloyed” reinforcing bar Currently not recommended by ODOT Bridge Engineering Potential for test in moderate environment


Summary „

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BDDM provides current guidelines for use of carbon steel, epoxy coated steel, and stainless steel reinforcing bars Two economical stainless steel alloys are being tested, will be added to specs if suitable AASHTO design specifications support FRP reinforcing bars for bridge deck applications


Questions?


Oregon Corrosion Resistant Material Research