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Carbon
Fiber Reinforced Polymer (CFRP) Laminates for Structural Strengthening
The Need
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Strengthening measures are required in
structures when they are required to accommodate increased loads. Also, when there are
changes in the use of structures, individual supports and walls may need to be removed.
This leads to a redistribution of forces and the need for local reinforcement. In
addition, structural strengthening may become necessary owing to wear and deterioration
arising from normal usage or environmental factors. Concrete structures need to be strengthened for any of the following
reasons:
- Load increases due to higher live loads,
increased wheel loads, installations of heavy machinery, or vibrations.
- Damage to structural parts due to aging of
construction materials or fire damage, corrosion of the steel reinforcement, and/or impact
of vehicles.
- Improvements in suitability for use due to
limitation of deflections, reduction of stress in steel reinforcement and/or reduction of
crack widths.
- Modification of structural system due to the
elimination of walls/columns and/or openings cut through slabs.
- Errors in planning or construction due to
insufficient design dimensions and/or insufficient reinforcing steel.
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The Technology
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The pultruded CFRP laminate reinforcing
consists of bonding the CFRP strip with the concrete structure using a high-strength epoxy
resin as the adhesive. The CFRP strips are manufactured using a pultrusion process. The
pultrusion principle is comparable with a continuous press. Normally 24,000 parallel
filaments are pulled through the impregnated bath, formed into strips under heat, and
hardened. These strips are uni-directional; the fibers are oriented only in the
longitudinal direction. Correspondingly, the strip strength in this direction is
proportional to the fiber strength and, thus, very high. Strips are produced with
strengths of approximately 3,000 MPa in the longitudinal direction, and with a thickness
of up to 1.5 mm and widths of up to 150 mm. |
 
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In order to achieve an optimum
composite action, the preparation of the bonding surfaces of the strip and concrete is
critical. The strips must have the outermost layer of their bonding face, normally
matrix-rich, removed to expose the fibers. Just before the bonding, the bonding surface is
carefully cleaned with acetone. The concrete surface is treated by sand blasting, high
pressure water jets, stoking, or grinding. Shortly before the bonding, it is cleaned with
a vacuum cleaner. Concrete must be at least 6 weeks old, and have a minimum tensile
strength of 1.5 MPa. Highly filled epoxy resin adhesive is used for the bonding. |
The Benefits
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CFRP laminate reinforcing technology provides
a solution for strengthening problems of concrete structures. It provides great strength,
high modulus of elasticity, and outstanding fatigue resistance It is a very lightweight
non-corrosive material, that requires minimal preparation of laminates, and it's alkali
resistant. It is an economic method that requires very short contract times. |
Status
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Based on the worldwide research and
development work, the use of CFRP strips to rehabilitate structures is already routine for
many firms in Western Europe and Japan. In the U.S., Sika has introduced Sika CarboDur,
which is a CFRP laminate used to strengthen concrete, steel, or wooden structures. CFRP
materials will not replace traditional construction materials, but will be used
increasingly to supplement them as needed. A research
team led by Dr. Abdul-Hamid Zureick, Professor of Civil and Environmental Engineering at
Georgia Institute of Technology, Atlanta, GA, has performed an integrated field/laboratory
approach to rehabilitate the Lee Road Bridge over Interstate 20 in Douglas County, GA,
using CFRP. This project is funded by the Georgia Department of Transportation (GDOT) in
cooperation with the Federal Highway Administration (FHWA). The project took workers less
than a day to complete what could have taken several weeks to do traditionally and, so
far, laboratory tests have determined that CFRP can make bridges 30 to 40 percent stronger
than the original design. |
Barriers
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Although this technology has been used
successfully in Japan and Europe, the usage of composite materials like CFRP is still not
widely recognized in the industry. The lack of knowledge of the technology and the
simplicity of it will make some people hesitant to use it. |
Points of Contact
- SIKA
Corporation, Central Region, 2190 Gladstone Court Suite A, Glendale Heights, IL 60139
USA, Phone: (630) 924-7900, Fax: (630) 924-8509
- Dr. Abdul-Hamid Zureick, School of Civil and Environmental
Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0355, Phone: (404)
894-2294, Email: azureick@ce.gatech.edu
References
- Alexander, J.G.S. and Cheng, J.J.R. Field
Application and studies of using CFRP sheets to strengthen concrete bridge girders.
Advanced Composite Materials in Bridges and Structures, ed. El-Brady, M., The Canadian
Society for Civil Engineers, Montreal, Canada, pp. 465-472
- Chajes, M.J.,Thomson, T., Finch,W.W., and
Januszka, T. 1994. Flexural strengthening of concrete beams using externally bonded
composite materials. Construction and Building Materials,Vol 8., No 3, pp.191-201
- Sanders, J.M., Rehabilitating Bridges,
Research Horizons, Georgia Institute of Technology, Winter 1999, pp. 12-13
Disclaimer Statement
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Neither the Construction
Industry Institute nor Purdue University in any way endorses this
technology or represents
that the information presented can be relied upon without further investigation. |
CHC05/MA |
