This article was originally published in Chemistry & Industry on soci.org on the 13th of August 2012.
Building an Olympic stadium is astronomically expensive. The UK is not expected to get any change out of £500m. The majority of the stadium – certainly by weight – comprises the construction industry favourites of concrete and steel, as well as commodity plastics. Most of the truly revolutionary materials – nanocomposites, carbon fibres and the like – have been restricted to sports equipment or the clothes worn by the athletes.
All hands on deck
The ever-present focus on sustainability means that stadium builders are looking to reduce the amount of materials that they use: lighter, stronger materials that can live up to expectations, but are cheaper and easier to transport and install.
One example is the wood plastic composite (WPC) decking panels that have been used for the VIP platform on level two of the Olympic Stadium. The Ecodek panels were supplied by Vannplastic, based near Chester, UK.
Wood plastic composites, first developed in the US, comprise wood as a reinforcing filler within a plastic matrix. The combination of the two, when mixed properly, produces a new material that is better than either one of the components on its own. WPC panels are, for example, more weather-resistant than wood, so will not rot or warp in the rain. In the US, huge quantities are consumed for decking, siding and fencing. In Europe, where volumes are lower, they tend to be used for cladding or bench slats. Importantly, the use of such composites allows two relatively cheap components – sawdust and a commodity plastic like PVC or polyethylene – to produce a tough, long-lasting product.
‘Our product is 55% recycled HDPE,’ says Alex Collins, Vannplastic’s technical director. The HDPE (high density polyethylene) is sourced mainly from recycled milk bottles. Wood fibres – post-industrial beech hardwood from a sawmill in northern France – account for about 40% of the mix. The rest is additives: pigments, UV stabilisers and the coupling agents that help to bind everything together.
‘Lots of companies skimp on the additives, but we invest a lot in them,’ says Collins. He is also particular about the quality of the main ingredient – the plastic. He pays around 75% of the price of virgin material to ensure that he gets the material he wants. ‘The formulation that we use for these boards is fairly standard, as was the contract, but for one element,’ says Collins.’ The Olympic Delivery Authority (ODA) take safety very seriously, and the standard design means there is a small gap between the boards when they are installed, which allows debris to fall through and is therefore a potential fire hazard.’ Working with Olympic Stadium designer Populous, the company redesigned the edges so that they were ‘S’ shaped – allowing an overlap. This closed the gap to debris and litter, but still allows rainwater to drain through. ‘We had to do lots of physical testing,’ says Collins. ‘I was pleasantly surprised that our boards performed so well.’
In fact, Vannplastic won the contract partly because of its use of recycled plastics, and because it has promised to buy back the decking if the stadium is dismantled after the Olympics, but predominantly because the company outperformed competitors when the products were tested. Its one-month production surge produced 110t of decking, which covers 4000m2. The decking area can clearly be seen at one edge of the stadium, accounting for around 10% of the circumference.
Living it up
For the duration of the games, competitors will live in one of the 11 apartment blocks in the Athletes’ Village. One supplier to the Village was Polypipe Terrain, which manufactures and installs pipes made from a variety of plastic materials. The company supplied HDPE piping to three of the 11 apartment blocks. ‘The organisers chose HDPE for its longevity and robustness,’ says Ian Crickmore, technical manager at Polypipe Terrain. The aim was to ‘fit and forget’ the pipes: there is no access to the majority of the drainage pipes, and the organisers wanted to avoid service cupboards. For this, they needed absolute confidence in the performance of the pipes. ‘HDPE is virtually indestructible,’ says Crickmore.
Another important factor behind the material choice was the ease of installation. When pipes are fitted, they are normally supplied in separate lengths, which have to be joined together. In the case of HDPE pipes, two sections are fitted with a ‘collar’ that contains a coil. Passing a current through the coil, for around one minute, causes the collar to soften. This ‘electrofusion’ joins the two pipe ends together, creating a homogeneous joint.
Other materials, explains Crickmore, were considered, but rejected: metal pipes, for instance, would need to be joined with inferior rubber joints; and PVC, another common pipe material, was rejected mainly because of stringent environmental rules. There are PVC pipes elsewhere in the complex, however, in applications such as waste pipes.
Polypipe also fitted a less common pipe – made from polybutene – as part of an underfloor heating system within the Village. Polybutene can withstand higher temperatures than HDPE and is often specified for this type of application. These pipes supply ‘low grade heat’ to the rooms, as an alternative to traditional radiators.
Crickmore says that fulfilling the contract was a huge challenge – mainly in terms of production planning and logistics. ‘Most people don’t realise that those 11 apartment blocks would usually take five-to-seven years to build,’ he says. ‘These have been put up in about two-and-a-half.’
Producing the extra volume of pipe was one challenge. But fitting it – given the peculiar conditions of the site – was something else. Crickmore explains that enormous ‘holding areas’ were used to store components such as pipes. Contractors had to book installation slots 48 hours in advance, and there was high security – including sniffer dogs – on site. ‘But it’s all been built on time, and on budget, with these security constraints; the person who planned it all must be a genius,’ he says.
For now, Polypipe’s Olympic adventure is over – but it is not necessarily the end of the company’s involvement in this site. Once the athletes have moved out, the whole ‘legacy’ issue kicks in. The apartments will then be used for accommodation – but are not currently fit for that purpose. ‘The Village consists of more than 2500 apartments with no kitchen facilities,’ says Crickmore. ‘They will have to be fitted out – and that’s a lot of piping.’
Also largely hidden from view – but vital for bringing the event to the outside world – are the miles of broadcast cables within the Olympic complex. If you think they might escape the attention of the ‘green police’ at the Olympics, think again: they have also been chosen for their sustainable qualities. ‘Indoor cables must be flame retardant, and we’ve developed a bio-based additive to do that,’ says Damian Polansky of Dow’s electrical and telecommunications division. The additive, Ecolibrium, is a plasticiser that softens the protective cable jacket while adding flame retardancy. Ecolibrium is derived almost entirely from non-petroleum sources.
Dow claims that the material can cut the emission of greenhouse gases by 40% if used in place of the traditional di-isononyl phthalate plasticiser. As well as this hidden contribution, Dow is behind one of the most visible symbols of the stadium: the outer wrap, which comprises 336 individual panels each 25m high and 2.5m wide. It is made from a lightweight polyester with a low-density polyethylene (LDPE) coating.
Up on the roof
The roof of the stadium was built for a very specific reason – and it wasn’t to keep the rain off. Instead, it ensures that ‘wind assisted’ performances are kept to a minimum. If wind speed is too high, performances in events such as javelin and long jump are rendered ineligible for Olympic and World Records. The enormous canopy aims to minimise any swirling winds, and increase the chances of new records being set during the event.
Designer Populous ran early computer modelling tests and found that the roof would need to cover around two-thirds of the seating. This meant investigating several structural concepts, including conventional cantilevering of rigid materials. This was rejected, in favour of a ‘rim and spoke’ configuration.
The support structure for the roof comprises an outer compression truss – around the top of the stadium – which is linked, via tensioned three-inch diameter steel cables, to an inner steel ring. This transfers the whole weight of the roof – 450t – to the concrete footings, via diagonal steel columns around the perimeter. Both inner and outer rings are made from steel pipe that was originally destined for use in the Russian oil industry.
This ‘make do’ philosophy underlies a more serious point: structural steel was in short supply when the stadium was commissioned, which forced the architect to look at alternative designs. This is why the base of the stadium is sunk into the ground. And it goes some way to explain why London’s Olympic Stadium contains 10,000t of steel, just one-tenth of the amount of steel as the Bird’s Nest stadium built for the 2008 Beijing games.
But if steel keeps the roof in place, it is the 25,000m2 PVC-coated polyester canopy that keeps the wind out. Supplied by French building fabric specialist Serge Ferrari, this kind of material is commonly used for stadium roofing. Polyester fibres, while under tension, are coated with PVC to produce a fabric that maintains its shape even under high mechanical stress.
As well as numerous industrial clients, Serge Ferrari has supplied this type of fabric to the artist and sculptor Anish Kapoor, who used the material in his Leviathan work as well as earlier installations, including Marsyas.
Kapoor also played a role in London 2012 because he designed the ArcelorMittal Orbit – the 115m high tower made of tubular steel that is unique for its lack of straight edges. It uses 2000t of steel, of which around two-thirds is recycled steel. In common with other designs by Kapoor, the tower is blood-red – which required 20,000L of paint.
The Bird’s Nest stadium in Beijing cost around £250m; London’s stadium cost twice that. So, with stadium builders so obsessed with sustainability – and careful to control costs – is there a truly sustainable way of making them?
One revolutionary idea is to build a floating stadium and transport it to the site of the new Olympics every four years. In between times, it could be used to host other events. Michael Burt, professor emeritus of architecture at Technion – Israel Institute of Technology, is at the forefront of developing plans for such a structure. He has designed a stadium for 150,000 spectators, which could float alongside separate platforms for housing or offices. As part of its proposal to host the Olympics in 2028, the Netherlands has developed a similar approach – while Singapore has already built a floating platform to host sporting events.
For the foreseeable future, stadium designers will need to be as efficient as possible with available materials and – like the athletes competing at the games – squeeze the best possible performance from them.