Bridge Structural Repairs Using High Performance Carbon Fibre

Most bridges on Australia’s highways are constructed of steel-reinforced concrete, chosen for its load carrying ability, ease of fabrication and extended operational life. Unfortunately, after delivering sterling service, most of these structures are now several decades old, and due to the effects of ageing, corrosion and increased daily traffic, many of them are in need of repair or major rehabilitation. As a result, deteriorating bridge infrastructure now constitutes an economic burden with projected costs surpassing A$416m ⁽¹⁾. It is estimated that 42% of Western Australia’s bridges (not all of which are concrete) require strengthening or repair ⁽²⁾ and the author approximates that over 10,000 bridges Australia wide would benefit from a bridge improvement program.

Traditional techniques for the repair and replacement of bridge components can be expensive, time consuming and cause delays to road users. One effective solution is the use of carbon fibre reinforced plastics. Not only are carbon fibres 8 to 10 times stronger than steel, but they are 5 times lighter - and the reinforced composite does not corrode.

Carbon fibre composites can make bridges 30 to 60 percent stronger than the original design, thus increasing service life with minimal disruption to traffic and considerable cost savings in the long term.

The composite solution is available in a range of formats, including pultruded plates, which at only a fraction of the weight of traditional steel plates used for bridge repair, make installation easier and faster. Another popular technique consists of the external placement of fabric sheets onto the surface of the structural element to be retrofitted. The fabric sheets are primarily used to stiffen columns and beams and to repair deteriorated concrete components. In addition, the fibre sheet material has often been used as a protective coating for aging and deteriorating surfaces as a preventive measure.

The application method itself is fairly simple and because the carbon fabric is light weight, it can be used in closed areas, conforms to most geometrical changes, and can be applied very rapidly. Prior to the application of the composite, the surface of the element to be repaired is thoroughly cleaned and loose or cracked material or exfoliating concrete surface layers are removed. The entire surface is made uniform by filling of depressions with mortar/epoxy grout. The surface is then prepared by sanding. The surface is then covered with a layer of resin on top of which the fabric material is placed in a manner similar to the application of wallpaper, as shown in Figure 1⁽³⁾. Air pockets and wrinkles are removed through the application of pressure. Further layers are added as appropriate with a new layer of resin applied in between adjacent layers of fabric. Once the required number of layers is applied, with the direction of fibres varying between layers, the composite is allowed to cure. Then a top coat is applied. This layer is generically made up of a urethane, acrylic or fluorine-based resin to facilitate UV and environmental protection.

The use of carbon fibre sheet material for the strengthening and repair of bridges has been widely practiced in Japan for the last decade. In a majority of cases, carbon fibre materials have been used to either prevent further concrete cracking, to increase load carrying capacity or to strengthen the bridge deck or overhangs to enable the addition of sound walls or barriers. An example of this is in the retrofit of a road deck on the Hanshin Expressway,
Figure 2⁽³⁾, which required strengthening due to increased traffic weight. Two layers of carbon fabric were applied to the road deck in the transverse and longitudinal directions as shown in Figures 3 & 4⁽³⁾.

Carbon fibre reinforced plastics are also well-suited for repair of aging structures such as factories and buildings and applications range from use on floors and slabs in buildings to use on chimneys, tunnel linings and other concrete structural elements.

This article provided by

Dr Christian Marston, Sumitomo Australia Ltd.
Tel:+61 (02) 9335 3741
E-mail: christian.marston@sumitomocorp.co.jp

Sumitomo work closely with Industrial Composites and Engineering of WA who offer carbon fibre solutions for structural repair.

References
(1) “Working Paper 56 State Spending on Roads”, Bureau of Transport and Regional Economics, Commonwealth of Australia, 2003. ISSN 1440-9707. ISBN 1-877081-29-9
(2) “2005 Western Australian Infrastructure Report Card” Engineers Australia, 2005. ISBN 0 8582 5756 5.
(3) Examples of Repairs using Replark, Mitsubishi Chemical Functional Products Website

Disclaimer: The Warren Centre publishes articles relating to new technology and innovation that are often based on information supplied by third parties. While an editorial process is applied, we make no exhaustive investigation into the accuracy of the information, thus no liability will be accepted for its accuracy. Please note that in providing this information, The Warren Centre is not supporting or promoting any technology or company, merely seeking to inform. Interested readers should take their own steps to verify the information prior to relying on it in any way.

Contents

Water-Who's in Charge

Bridge Structural Repairs Using Performance Carbon Fibre
Innovation – do Australia's big companies get it?
Algae Bioreactor to Generate Biofuels from Smokestack CO₂
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(c) The Warren Centre for Advanced Engineering, August 2006