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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012

STAINLESS STEEL REBAR FOR LONG SERVICE LIFE

M. J. Correia and M. M. Salta

LNEC, Av. Do Brasil, 101, 1700-066 Lisboa


COMPETITIVE LIFE CYCLE COSTS

CORROSION PREVENTION - STAINLESS STEEL REBAR

for long service life (highly aggressiveconditions) it is generally necessary to provideadditional corrosion preventive measures

STAINLESS STEEL REINFORCING BARS cost effective technical attractive approach

DURABILITY

MAINTENANCE

NEW INSIGHT INTO DESIGN

ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012

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practical evidence of durability is provided by a pier in Progresowhich has been showing a good performance for more than 65years in a subtropical environment without repair and significantroutine maintenance activities

no sign of deterioration, for concrete covers thicker than 20mm, even with chloride contents of up to 1.9% Cl- inconcrete with relatively high porosity [1]

the remaining service life is estimated to be more than 20to 30 year old without significant maintenance

typical applications, which include transport infrastructures,structures in marine environments and rehabilitated historicalstructures are spread all over the world

current experience sustains that it may enable a design life ofmore than 100 years, without significant maintenance

STAINLESS STEEL REBAR – APPLICATIONS

[1] ARMINOX, Pier in Progreso, Mexico:Evaluation of the Stainless SteelReinforcement, March (1999)www.arminox.com


STAINLESS STEEL REBAR - CURRENT SPECIFICATIONS

first standards:

BS 6744:2001 austenitic (1.4301, 1.4436, 1.4429, and 1.4529)

austenitic-ferritic (1.4162, 1.4362, 1.4462 and1.4501)

range sizes from 3 mm to 50 mm

strength levels (200, 500, and 650)

ASTM A955/A955M duplex and austenitic alloys including high

manganese austenitic alloys

strength grades (300, 420, and 520)

European standard (currently in preparation): specifications for performance, mechanical properties

and conditions of testing, as well as guidance on gradeselection

ferritic, austenitic and austenitic-ferritic alloyscorresponding to five grades with yield strengths of450, 500, 550, 600, and 650 Mpa, and an additionalgrade of 200 MPa, especially for plain bars


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STAINLESS STEEL REBAR - DESIGN AND CONSTRUCTION PRACTICES

Guidance on grade selection

environmental aggressivity

corrosion resistance of the alloy

design service life

mechanical and physical requirements

cost aspects

Guidance on the use of stainless steel reinforcement for different service conditions (BS 6744:2001+A2:2009 )



Design durability requirements

concrete cover - 30 mm irrespective of the concrete mix and quality or exposure condition concrete durability and cost

EN 1992-1-1:2004 - minimum cover may be reduced by Δcdur,st, Portuguese Annex adopts a 20 mm value for Δcdur,st - austenitic or duplex

allowable crack width on the concrete surface 0.3-0.4 mm

cracked concrete, with a crackwidth of 0.8 mm at the concretesurface (44 mm cover), underwetting/drying cycles with a 3%NaCl solution

M. J. Correia, M. M. Salta, Stress Corrosion Cracking of Austenitic Stainless Steel Alloys forReinforced Concrete, Advanced Materials Forum III - Mater. Sci. Forum 514-516 (2006)1511-1515.


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Fabrication, transport, storage, andhandling

BS 6744:2001+A2:2009 - bend testedsamples from production batches with nosign of fracture or irregular deformation(specified bend tests).

cut and bend in accordance with BS8666:2005, by the methods commonlyused for carbon steel.

avoid contamination with rust staining fromcarbon steel

Installation, welding, and coupling

stainless steel tying wire and; spacers ofplastic, concrete, or mortar

welding is generally not recommended onsite - reduction in corrosion resistance (millscale and temper colours though beingimproved by pickling or blasting)

reductions in both the critical chloridecontents and the pitting potentials

stainless steel couplers

6 to 10 mm concrete cover – slabs (30x30x10 cm).Periodical exposure to a 3.5 % NaCl solution inalternated dry/immersion cycles


several reviewed field and yard exposure tests of concretespecimens sustain the high corrosion resistance of stainlesssteel rebars comparatively to carbon steel

critical chloride content for rebars embedded in chloridecontaining uncarbonated concrete may be as more than tentimes higher for stainless steel than for carbon steel.

the consequences of galvanic coupling of carbon steel andstainless steel have proven to be negligible in most situationsfound in real structures

useful material for selective application, because it is aless effective cathode than passive carbon steel

STAINLESS STEEL REBAR – CORROSION RESISTANCE

saturated Ca(OH)2 solution with 10 % chloride - Ep > 0.4 VSCE (except for SS3 welded sample, in consequence of itsunavoidable superficial defects)


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new less costly alloys [1]

to minimize the higher cost which is its commonly associated major disadvantage in spite of thebenefits established by a total cost analysis

relations between passive film characteristics and corrosion resistance

critical factors - surface condition, microstructure, chemical composition, and environmentalparameters

STAINLESS STEEL REBAR – LATEST RESEARCH TRENDS

[1] EC-HIPER Project, Increased infrastructure reliability by developing a low cost and high performance stainless steel rebars, GDR1-2000-25601, EC, HIPER Project final report (2005).


Atlantic Area Operational Programme 2007-2013and ERDF are gratefully acknowledged for thefinancial support given to DURATINET project.

THANK YOU

CURRENT RESEARCH FINDINGS AND INCREASING SUCCESSFUL APPLICATIONS ANTICIPATE FURTHER IMPROVEMENTS


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