FRP Rebar

The Need
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. For instance, in the USA, almost 40% of bridges are structurally deficient or functionally obsolete, and the percentage is increasing, according to the Federal Highway Administration (Griffiths 2000)
For many years, there have been many studies on this corrosion issue, and 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.

The bond characteristics are responsible to transfer the load from concrete to reinforcement and to develop the required stress in the reinforcement for an 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:

1. Architectural Concrete: cast stone, architectural cladding, balusters, column facades, window lentils, architectural precast elements, hand railing, and statuary and fountains, etc.
2. Concrete exposed to de-icing salts in: bridge decks, railroad grade crossings, median barriers, parking garage elements, and salt storage facilities, etc.
3. Concrete exposed to marine salts in: seawalls, water breaks, buildings & structures near waterfront, aquaculture operations, and floating marine docks, etc.
4. Concrete used near electromagnetic equipment such as: MRI rooms in hospitals, airport radio & compass calibration pads, and concrete near high voltage cables, transformers, substations, etc.

The Benefits

1. Impervious to chloride ion and chemical attack
2. Tensile strength greater than steel
3. 1/4th weight of steel reinforcement
4. Transparent to magnetic fields and radio frequencies
5. Electrically and thermally non-conductive

Based on features above, FRP bars appear to be promising alternative to steel reinforcement in concrete structures such as marine structures, parking structures, bridge decks, highway under extreme environments, and structures highly susceptible to corrosion and magnetic fields.

Status
The earliest commercial uses of FRP composite rebar are approximately twenty-five years old. These original applications were for non-magnetic or radio-frequency transparent reinforcements for magnetic resonance imaging (MRI) medical equipment and specialized defense applications. FRP composite rebars have emerged as the industry standard for this application, eclipsing stainless steel in recent years. As recently as the 1990s, the deteriorating state of the U.S. infrastructure, particularly vehicular highway bridges, caused alternative reinforcements to be considered. Parallel interest in Europe and Japan has helped to make FRP composite rebar an international research topic. According to ACI 440H, the Japanese lead in this field, with more than 100 demonstration projects reported in the literature. One of most important developments is the publication of ACI440.1R-01 Guide for the Design and Construction for Concrete Reinforced with FRP bars. The document is available from ACI and provides the practicing engineering with the necessary information to implement these new FRP bars. In addition, FRP Rebar Manufacturers Council (Chairman: Doug Gremel) was formed by the manufacturers listed on the 'Points of Contact' with the objective of fostering quality assurance and other industry standards amongst manufacturers.

Barriers

1. The cost is $3 to $4/lb (including approx. $1/lb of raw material cost) in case of Glass FRP bar, and Carbon FRP is usually more expensive. (cf. Epoxy coated rebar costs $0.32/lb)
2. Due to the lack of well-established standards, a wide variety of FRP bars is today commercialized, going from the simple smooth bars to bars treated to improve bond characteristics. Therefore, a better understanding of mechanical properties and bond behavior is needed for a rational approach to the design of FRP reinforced structures.
3. Field bends are not allowed, and not-weldable, so consideration on differences in construction operations of regular steel rebar should be applied from the design phase.
4. Lack of familiarity by practicing engineers can cause lower productivity than prospected.

Points of Contact

1. Gremel, Doug. Director, Non-Metallic Reinforcing,
   Hughes Brothers, Inc. 210 N. 13th Street, Seward, NE 68464
   Phone: (402) 646-6211
   Fax: (402) 643-2149
   Email: doug@hughesbros.com
   Website: http://www.hughesbros.com
2. Dow Chemical - Fulcrum Company. Building 3 #4,
   312 Washington Street, Wellesley Hills, MA 02481
   Phone: (781) 431-6439
   Fax: (800) 409-4144
   Email: drvanderpool@dow.com
   Website: http://www.dow.com
3. Pultrall, ADS Composites Group. 1191, Rue Huppe, Thetford Mines, Quebec G6G 7Y6, Canada
   Phone: (418) 335-3202
   Fax: (418) 335-5117
   Email: eric.martin@adsinc.ca
   Website: http://www.pultrall.adsinc.ca
4. Marshall Industries Composites,
   Inc. 2250 Central Point Parkway, Lima, OH 45804
   Phone: (419) 221-1444
   Fax: (419) 222-5442
   Email: info@c-bar.com
   Website: http://www.c-bar.com
5. FRP Rebar Manufacturers Council.
   600 Mamaroneck Ave. 4th Floor,
   Harrison, NY 10528-1632
   Phone: (914) 381-3572
   Fax: (914) 381-1253

References

1. Marshall Industries Composites, Inc. Website: http://www.c-bar.com
2. Hughes Brothers, Inc. Website: http://www.hughesbros.com
3. Putrall, ADS Compsites Group Website: http://www.pultrall.adsinc.ca
4. Griffiths, J. R. "Plastic Highway Bridges", Cambridge Scientific Abstracts, 2000
5. Benmokrane et al. "Mechanical and Bond Properties of New Generation of ISOROD CFRP Reinforcing Bars for Concrete Structures", technical progress report, 2001, ISIS Canada
6. Market Development Alliance of the FRP Composite Industry (MDA) Website: http://www.MDAcomposites.org
7. Gremel, D. "FRP Rebar - A State of the Industry Report Manufacturing, Construction, Economics and Marketing", Proceedings of the Workshop Comsposites in Construction: A Reality, 20-21 Jul., 2001, Anacapri, Italy.