COMPOSITE MATERIALS

PROJECT

TOMESCU IOANA-CLAUDIA

FILS III AMANAT, GROUP 1

Fiber Reinforced Polymer (FRP) Rebars- V-ROD composite rebars

Reinforced Concrete is a very common building material for the construction of facilities and structures. As complement to concrete's very limited tensile strength, steel rebar has been an effective and cost-efficient reinforcement. However, insufficient concrete cover, poor design or workmanship, and presence of large amounts of aggressive agents including environmental factors all can lead to cracking of the concrete and corrosion of the steel rebar. Steel rebar also conducts electricity and magnetic fields, attributes that are not desirable in many types of medical, nuclear, power generating, and electronic applications. The interest in FRP (Fiber Reinforced Polymer) has arisen recently as prospective substitute for steel. Careful consideration on potential of FRP rebar to fill the cost and performance needs may suggest appropriate solutions.

Recently, composite materials made of fibers embedded in a polymeric resin, also known as fiber-reinforced polymers, have become an alternative to steel reinforcement for concrete structures. Aramid fiber reinforced polymer (AFRP), carbon fiber reinforced polymer (CFRP), and glass fiber reinforced polymer (GFRP) rods are the commercially available products for the construction industry.

They have been proposed for use in lieu of steel reinforcement or steel prestressing tendons in non-prestressed or prestressed concrete structures (ACI 440R 2006). The problems of steel corrosion are avoided with the use of FRPs because FRP materials are nonmetallic and noncorrosive. In addition, FRP materials exhibit several properties including high tensile strength, which make them suitable for the use as structural reinforcement. Furthermore, codes and design guide provisions have been recently prepared for the use of FRP bars in concrete structures for bridges and buildings (ACI 440H 2000; CSA 2000; ISIS-Canada 2000).

The bond characteristics are responsible to transfer the load from concrete to reinforcement and to develop the required stress in the reinforcement for equilibrium, particularly when concrete is cracked. Service limits in FRP reinforced concrete elements such as deflection, crack width and crack spacing are directly influenced by the bond properties of the reinforcement in concrete. Fiber reinforced polymer bars are anisotropic materials. Factors such as type and volume of fiber and resin, fiber orientation and quality control during the manufacturing play a major role in the mechanical characteristics. In the case of Carbon FRP rebar (CFRP Isorod bar from Pultrall, ADS Composites Group), when comparing a steel bar of 11.3 mm diameter with CFRP rebar with similar diameter of about 9.5 mm, the results shows that the tensile stress-strain curves of the CFRP bar are linear up to failure (All FRP bars are linear elastic to failure). The ultimate tensile strength is at least 1500 MPa: 3 times that of steel rebar. The modulus of elasticity of the CFRP bar is 128 GPa, about 65% that of steel. The CFRP bar exhibited almost the same bond strength to concrete as 11.3 mm diameter steel bar. (Benmokrane et al. 2001) As for Glass FRP

bar (ASLAN 100 GFRP bar from Hughes Brothers, Inc.), tensile strength of 9 mm GFRP bar is 760 MPa, and the Modulus of Elasticity is 40.8 GPa, much lower than that of steel.

Fiberglass rebar may be a suitable alternative to steel reinforcing in: Architectural Concrete Concrete exposed to de-icing salts Concrete exposed to marine salts Concrete used near electromagnetic equipment

V-ROD composite rebar is available in both fiberglass and carbon composite material systems. V-ROD fiberglass rebars, with their superior tensile properties, built-in corrosion resistance, and inherent electromagnetic neutrality, offer a unique and economically feasible reinforcing bar for such applications:

CORROSION RESISTANCE - will not rust, and is impervious to the action of salt ions, chemicals, and the alkalinity inherent in concrete.LIGHTWEIGHT - weighs approximately one-quarter the weight of an equivalent size steel bar, offering significant savings in both placement and use.ELECTROMAGNETIC NEUTRALITY - contains no metal, does not conduct magnetic fields, and will not interfere with the operation of sensitive electronic devices such as medical MRI units or electronic testing devices.THERMAL INSULATOR – highly efficient in resisting heat transfer, such as from building exteriors to interiors; will not conduct electricity.

Market Applications 

  Utilizing the above features / benefits, V-ROD has cost effective application as a concrete reinforcing bar in the following markets when analyzed on a life-cycle cost basis:

1. Reinforced Concrete Exposed to Deicing Salts: Parking structures; bridge decks; Jersey barriers; parapets; curbs; retaining walls and foundations; roads and slabs on grade.

2. Structures Built in or Close to Sea Water: Quays; retaining wall; piers; jetties; caissons; decks; piles; bulkheads; floating structures; canals; roads and buildings; offshore platforms; swimming pools and aquariums.

3. Applications Subjected to Other Corrosive Agents: Wastewater treatment plants; petrochemical plants; pulp/paper mills; liquid gas plants; pipelines / tanks for fossil fuel; cooling towers; chimneys; mining operations of various types; nuclear power and dump plants.

4. Applications Requiring Low Electric Conductivity or Electromagnetic Neutrality: Aluminum and copper smelting plants; manholes for electrical and telephone communication equipment; bases for transmission / telecommunication towers; airport control towers; magnetic resonance imaging in hospitals; toll road

sensing arrays and collection booths, railroad crossing sites, and specialized military structures.

5. Tunneling / Boring Applications Requiring Reinforcement of Temporary Concrete Structures: Structures including mining walls; underground rapid transit structures and underground vertical shafts.

6. Weight Sensitive Structures: Concrete construction in areas of poor load bearing soil conditions, remote geographical locations, sensitive environmental areas, or active seismic sites posing special issues that the use of lightweight reinforcement will solve. 

7. Thermally Sensitive Applications: Apartment patio decks; thermally insulated concrete housing and basements including ICF construction; thermally heated floors and conditioning rooms.

DESIGNING WITH COMPOSITE REBAR

The mechanical properties of FRP reinforcing bars differ from those of conventional steel rebar in a number of areas.  As a result, several issues arise in the development of a design methodology for concrete structures reinforced with such bars. The general design recommendations for flexural concrete elements reinforced with FRP reinforcing bars are presented in ACI 440.1R-06 (2006), Guide for the Design and Construction of Structural Concrete Reinforced with FRP Bars, as reported by the American Concrete Institute (ACI) committee 440.

The design philosophy adopted for FRP bars allows consideration to be given to either FRP rupture or concrete crushing as the mechanism that controls failure.  It is based on limit states design principles.  An FRP reinforced concrete member is designed based on its required strength, and then checked for fatigue endurance, creep rupture endurance, and serviceability criteria. In most cases, serviceability criteria or fatigue and creep rupture endurance limits will control the design.

Design engineers should consider the appropriateness of reinforcing concrete with FRP bars, keeping in mind the following basic points in their designs:

Direct substitution of FRP bars in a concrete member designed with steel bars is not possible in most cases.

Lower modulus of elasticity and shear strength of composite rebar may limit the applications where FRP bar can be utilized.

Glass FRP bar is limited to a maximum sustained stress of 25% of the guaranteed design tensile strength.

Glass FRP bar applications are limited to the reinforcement of concrete and should not be used as a prestressing or post-tensioning element.

APPLICATION GUIDELINES

The following general requirements and recommendations are provided for using V-ROD fiberglass rebars in the construction of reinforced concrete structures.

HANDLING AND STORAGE

V-rod reinforcing bars, while being very durable, are made with a matrix of synthetic resin rendering them liable to surface damage if abused. Deep scoring with sharp objects will reduce their durability and performance capacity. Therefore, care is advised in the handling of these materials during storage and placement. If conditions on the job site permit, then bars should be delivered to a storage area. FRP bars are more tolerant of handling, storage and placement variations than epoxy-coated bars, but need to be more carefully handled than uncoated steel reinforcing bars.

The following specific storage and handling guidelines will minimize any damage to the bars or the bar handlers:

Bars should be handled with heavy duty working gloves to avoid hand cuts and injuries from sharp edges.

When storing bars outdoors, placing them directly on the ground should be avoided. Timber pallets should be placed under the bars to keep the bars free from mud and to provide easy access.

V-ROD is highly corrosion resistant, but ultraviolet rays and chemical substances can induce undesirable surface blemishes if stored in such conditions for extended periods of time. If stored outdoors, the bars should be covered with opaque plastic or other types of cover to protect the bars from the external environment. Protection from moisture exposure is not needed.

Dirt, oil or grease that is present on the bars in significant quantities should be removed before placing concrete by using high-pressure water or wiping or spraying the bars with suitable solvents.

V-ROD reinforcing bars are light and flexible in comparison to steel rebar. Hoisting bundles of bars should be done carefully until all involved personnel are familiar with the way the bar reacts to handling. It is desirable to use a spreader bar to facilitate handling and prevent excessive bending.

V-ROD bars can be quickly and easily cut with a high speed grinding cutter, diamond-bladed chop saw or a hacksaw. Bars should never be sheared.

PLACEMENT AND ASSEMBLY

Placing of V-ROD reinforcing bars is done in a similar fashion to steel bars. Unless otherwise specified in project specifications, the bars should be placed within the tolerances specified in ACI 117 (“Standard Tolerances for Concrete Construction and Materials”). Common placing practices should apply with the following exceptions:

Because it is lightweight, fiberglass reinforcement should be adequately secured in the forms to prevent displacement by concrete placement or workers. Plastic non-corrosive chairs can be used to elevate the rebar on spacing determined by the bar diameter.

Plastic or nylon ties, and plastic snap ties can be used in tying the bars in applications where corrosion resistance or total absence of metals is paramount. Standard metal tie wire, coated tie wire, and stainless steel tie wire can also be used. Fiberglass rebar can also be lap spliced to metal rebar. Mechanical fastening devices should not be used.

Whenever continuity is required in the reinforcement, lapped splices should be used. Mechanically connected or welded splices are not possible with the composite reinforcing bars. The length of lap splices varies with concrete strength, type of concrete, rebar grade, size, spacing and cover. In the absence of other specifications, an overlap of forty (40) bar diameters should be utilized.

BENDS

V-ROD is a thermoset composite, and cannot be bent after it has been polymerized (cured). Since it is shipped in a fully cured form, it cannot be bent on job site. Bends can be produced during the manufacturing process in most shapes that can be obtained with steel rebar, although typically a little more generous bend diameter will be required. As a general guideline, multiplying the bar diameter (in inches) by a factor of 4 will give you an approximate minimum bend radius for a 90-degree bend. Similarly, multiplying the bar diameter by a factor of 8 will give you the minimum bend diameter for a 180-degree bend. In any job where bending dimensions are critical, bending capability should be verified prior to placing an order. Based on testing, approximately 50% of the guaranteed design strength of a straight bar remains after making a bend.

QUALITY CONTROL

V-ROD meets ISO 9001:2000 standards. Through routine sampling and inspection, quality control tests are carried out during production to ensure that products meet all specifications and are within exact dimensional tolerances. Certification to these results is available by prior request. Test reports are also available from third-party independent

testing agencies and universities regarding specific product performance in the following areas:

Mechanical properties, including tensile strength, tensile modulus of elasticity, fatigue strength and ultimate strain.

Bond strength Durability in alkaline environments.

REFERENCES:

http://rebar.ecn.purdue.edu

http://www.fiberglassrebar.com/