Innovations in infrastructure

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Composites are finding increasing use in the rail industry – in areas other than the rail carriages themselves. Lou Reade reports.

Composites are hailed as the future of the car industry, and aircraft are using more composites than ever before – but growth in the rail industry has been much slower. There are examples of composites being used in rolling stock, but the materials are more commonly used in infrastructure projects – notably for lightweight bridges.

For instance, a composite footbridge designed by Arup has been used to span a railway track just outside Oxford station. The bridge crosses the track at Trap Grounds, which is a Site of Special Scientific Interest (SSSI). It was used to replace a level crossing – which is expected to be a common use of the technology in future, as a way of enhancing safety.

The main of advantage of the bridge is its light weight, which meant it could be assembled nearby and lifted into place by a large crane.

“It had to be done this way, because you couldn’t use any plant there,” says Simon White of Arup, who designed the bridge. He adds that the soft nature of the ground, and the restrictions on construction methods and site access, restricted the size of the foundations – meaning that a conventional bridge would have been impossible to build.

“It had to be a very light bridge, because the foundations were so small,” notes White.

The bridge was made by attaching together a series of identical, 1m-wide modules. The modules are fixed together with bolted shear connectors, and then post-tensioned.

The design of the modules was deliberately made simple, which allows the bridge to meet European building codes very easily – and stand more chance of acceptance by a customer like Network Rail.

“If you’re making something from fibre-reinforced plastic you must make the design really simple,” says White. “That way, fewer tests need to be done.”

All the materials technology – such as epoxy infusion – is well-established, as are the manufacturing methods. There is no need for autoclaving, White explains.

The idea was originally a concept called ArcoBridge, but it fitted the needs of the project perfectly so was developed into a real application. Arup has since licensed the concept to bridge supplier Mabey – which has branded its product the Pedesta Footbridge.

“This is ideal for Mabey, because they are a modular bridge supplier,” states White.

Mabey says the Pedesta Footbridge is 70% lighter than a conventional structure, making it easier to install. Spans of up to 30m are possible. Neither Arup nor Mabey actually make the bridge modules. For the Oxford project, they were made by Pipex, while Mabey is working with fabrication partners. So far, Mabey is the only company to take a licence for the technology, but White says he expects more companies to follow suit in future.

“It takes time to build partnerships, so these will happen one at a time,” he says.

Get it covered

It’s not just bridges that benefit from being lighter. Other infrastructure products, such as trench covers, are increasingly using composites – rather than steel or concrete – as a way of shedding weight while retaining mechanical properties.

“The primary advantages are increased safety and efficiency of the site where covers are involved,” says David Holmes, technical director at Fibrelite.

Fibrelite offers a broad standard range of covers, but also many custom-designed covers to meet specific customer needs.

“Anti-skid is standard on all covers while anti-static is a simple addition in the manufacturing process,” says Holmes.

Anti-skid is achieved by adding a mineral within the moulded tread pattern, while anti-static incorporates a metallised fibre into the moulding process. Products are made from a number of materials – including E-glass multi-axial fibreglass, as well as several different vinyl ester and polyester resin systems.

While Fibrelite began life in Skipton in North Yorkshire, it now has additional manufacturing bases in the US and Malaysia – and is part of US manufacturing giant, Dover Corporation.

The company supplies to a number of sectors, and its products can be seen everywhere from petrol station forecourts to rail platforms. The rail sector is a small part of its business – accounting for 3-5% – but is of growing importance. It recently retro-fitted three composite trench covers – into existing frames – at Oldham tram station, part of the Manchester Metro Link. Here, maintenance staff needed regular access to under-platform services – which was not easy with concrete covers.

The concrete covers were too heavy for one person – and tram personnel had to use lifting equipment to gain access. Fibrelite developed a lightweight composite cover – just one-third the weight of the concrete original.

“Anti-skid was essential, as the cover is located on the raised tram platform where people walk to get on trams – and a slip could be very dangerous,” he says.

In order to keep tram services running at the station, the cover was designed to be an exact fit for the existing frame – and was simply swapped for the original cover. The new FL7A composite cover can be lifted by one person, and requires very little maintenance, says the company.

Fixing the leaks

On a grander scale, a multi-partner European project to develop leak-proof composite panels for high-speed railway tunnels has won the ‘Construction’ category in the JEC Awards earlier this year.

The project, led by Acciona of Spain and including Scott Bader of the UK, involved making more than 15,000 panels, covering around 200,000m2 of tunnel with 1,700 tonnes of composites. Other project partners included Owens Corning and BYK-Chemie.

The panels were used in two 24km-long railway tunnels in northern Spain, which were experiencing continuous water infiltration on around a 7km length.

“The tunnels were letting in more than 2,000 litres/second of water – and traditional materials were not solving the problem,” says Anurag Bansal, head of composite process at Acciona.

Acciona used Scott Bader’s Crestapol 1212 resin to make the 4mm-thick panels, which measured 9.2 x 1.5m. The cycle time for each panel – which incorporated three types of glass fibre reinforcement – was 34 minutes.

Crestapol 1212 is a low viscosity, methacrylate-based thermosetting resin that is designed to run on standard pultrusion machinery, to make products with high fire retardancy performance – which is critical in applications such as this.

To meet a tough production deadline, Acciona combined pultrusion with a low-cost resin injection system and fibre impregnation chamber.

The lightweight panels were flexible enough to adapt to the shape of the tunnel – and thin enough to ensure that its internal diameter was not altered.

So, while the application of composites in railway carriages may be held up at the lights, their use in rail infrastructure – be it bridges, covers or tunnels – is steaming ahead at full pace.

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