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Concrete Reinforcement - FRP Rebar

Introduction

Reinforced concrete is a common building material for the construction of facilities and structures.  While concrete has a high compressive strength, it has a very limited tensile strength.  To overcome these tensile limitations, reinforcing bars are used in the tension side of concrete structures.  Steel rebars have been and are an effective and cost-efficient concrete reinforcement, but are susceptible to oxidation when exposed to chlorides.  Examples of such exposure include marine areas, regions where road salts are used for deicing, and locations where salt contaminated aggregates are used in the concrete mixture.

When properly protected from ion attack, steel reinforcement can last for decades without exhibiting any visible signs of deterioration.  However, it is not always possible to provide this kind of corrosion protection.  Insufficient concrete cover, poor design or workmanship, poor concrete mix, and presence of large amounts of aggressive agents all can lead to corrosion of the steel rebar and cracking of the concrete.  

Fiber reinforced polymer (FRP) composite rebar have the potential to address this corrosion deficiency.  FRP rebar can be used as non-prestressed reinforcement in concrete for members subjected to flexure, shear, and compression loadings.  FRP Composite rebar are totally resistant to chloride ion attack, offer a tensile strength of 1½ - 2 times that of steel, weigh only 25% of the weight of equivalent size steel rebar, and are highly effective electromagnetic and thermal insulators.

Features and Benefits

• Non-Corrosive - will not corrode exposed to a wide variety of corrosive elements including chloride ions.

• High Strength-to-Weight Ratio - provides good reinforcement in weight sensitive applications.

• Non-Conductive - provide excellent electrical and thermal insulation.

• Excellent Fatigue Resistance - performs very well in cyclic loading situations.

• Good Impact Resistance - resists sudden and severe point loading.

• Magnetic Transparency - not affected by electromagnetic fields; excellent for use in MRI and other types of electronic testing facilities.

• Lightweight - easily transported in the field without need for expensive heavy lifting equipment.  

Applications

Four general categories of applications where FRP rebars are suitable alternatives to steel, epoxy-coated steel, and stainless steel bars:

Reinforced Concrete Exposed to Deicing Salts

FRP bars can eliminate the corrosion problems and reduce maintenance and repair costs in northern climates where massive quantities of deicing salts are used every year on roads and pavements.  Applications include: parking structures; bridge decks; Jersey barriers, parapets; curbs; retaining walls and foundations; roads and slabs on grade; and many others.

Structures Built in or Close to Seawater

Corrosion of steel reinforcement is a common problem in structures built in or near seawater.  Possible applications are: quays; retaining wall; piers; jetties; caissons; decks; piles; bulkheads; floating structures; canals; roads and buildings; offshore platforms; swimming pools and aquariums; and others.

Applications Subjected to Other Corrosive Agents

Chemical processing industries as well as domestic or industrial wastewaters constitute major sources of corrosion for steel reinforcement.  Typical applications include: wastewater treatment plants; petrochemical plants; pulp and paper mill and liquid gas plants; pipelines and tanks for fossil fuel; cooling towers; chimneys; mining operations of various types, nuclear power plants; and nuclear dump facilities.

Applications Requiring Low Electric Conductivity or Electromagnetic Neutrality

Using steel bars in applications where low electric conductivity or electromagnetic neutrality is needed often result in a complex construction layout, if such use is possible at all. Possible applications are: aluminum and copper smelting plants; manholes for electrical and telephone communication equipment; structures supporting electronic equipment such as transmission towers for telecommunications; airport control towers; magnetic resonance imaging in hospitals; railroad crossing sites, and military structures with requirement for radar invisibility.

Materials and Manufacturing

FRP rebars are primarily manufactured using the pultrusion process.  Surface deformations patterns contribute to the bond to concrete are available as ribbed, sand-coated, and helically wrapped and sand coated.  The most common fiber reinforcements are glass and carbon fibers. Resin systems used to protect the fibers from environmental attack are based on 50 plus years of rigorous corrosion applications.

Codes and Specifications

FRP rebars offer many advantages over other concrete reinforcing products. The properties of the FRP rebars are different from those of steel reinforcement. The design of concrete reinforced with FRP rebars is different in many cases. Design engineers should consider the appropriateness of reinforcing concrete with FRP rebars, keeping in mind the following basic points for design:

• Direct substitution of FRP rebars in concrete members designed with steel bars is not possible in most cases.

• Lower modulus of elasticity and shear strength of FRP rebars will limit the applications to short spans of secondary structural elements.

• Glass FRP rebar is limited to a maximum sustained stress of 20% of the guaranteed design tensile strength.

• Glass FRP rebar applications are limited to the reinforcement of concrete and are not to be used as a pre-stressing or post-tensioning element.

Current publications available for reference:

USA

• ACI 440.1R-01 2001, Guide for the Design and Construction of Concrete Reinforced with FRP Bars, Committee 440, American Concrete Institute, Farmington Hills, MI. (May 2001), www.aci-int.org

• ACI 440R 1996, State-of-the-Art Report on Fiber Reinforced Plastic Reinforcement for Concrete Structures, Committee 440, American Concrete Institute, Farmington Hills, MI. (February 1996), 67 pp.
   

Canada
 

• CAN/CSA-S806-02, Design and Construction of Building Components with Fibre-Reinforced Polymers, Canadian Standards Association, Toronto, Ontario, Canada  (May 2002), 187 pp.

• CAN/CSA-S6-00, Canadian Highway Bridge Design Code, Canadian Standards Association, Toronto, Ontario, Canada (December 2000), 734pp.

• ISIS Canada, Design Manual No. 3, Reinforcing Concrete Structures with Fiber Reinforced Polymers, Canadian Network of Centers of Excellence on Intelligent Sensing for Innovative Structures, ISIS Canada Corporation, Winnipeg, Manitoba, Canada (Spring 2001), 158 pp, www.isiscanada.com

Japan

• Japan Society of Civil Engineers (JSCE), Recommendation for Design and Construction of Concrete Structures Using Continuous Fiber Reinforced Materials, Concrete Engineering Series 23, ed. by A. Machida, Research Committee on Continuous Fiber Reinforcing Materials, Tokyo, Japan, (1997), 325 pp.

Europe

• fib Task Group 9.3, FRP Reinforcement for Concrete Structures, Federation Internationale du Beton, (1999)

• Report # STF 22 A 98741, Eurocrete Modifications to NS3473 When Using FRP Reinforcement, Norway (1998)

Concrete Reinforcement: Rebar Manufacturers

American Composites Manufacturers Association   1010 North Glebe Road, Arlington, VA  22201
P: 703-525-0511  F: 703-525-0743  E: info@acmanet.org
New York Office  600 Mamaroneck Avenue, Suite 429  Harrison, NY  10528 
P: 914-381-3572   F: 914-381-1253