Frozen Solid

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The demands on a coating for low temperature environments are rarely as challenging as on the Halley VI research station, now sitting on the 130 metre-thick Brunt Ice Shelf in the Antarctic Weddell Sea.

Typical winter temperatures range from -20°C to -55°C. The ice shelf flows slowly out onto the Weddell Sea, where chunks of ice ‘calve’ off as icebergs. For 105 days of the year there is 24-hour darkness and residents are completely isolated from the outside world, with only a nearby colony of emperor penguins to keep them company. Visibility is reduced to a few metres, as strong winds pick up dusty surface snow.

Five previous versions of the research station perished over the years as they were gradually buried under the snow or pushed to the edge of the ice, so when the British Antarctic Survey asked for designs for number six, one key requirement was that it be re-locatable. A design life of 25 years also had to include reliable protection against the worst the Antarctic could throw at it, for the safety of 70 staff in summertime and around 16 who would stay through the winters.

Coatings choice

In September 2006, a £22 million contract was signed with builders Morrison Falkland Ltd, now part of Galliford Try, for design and construction of Halley VI and demolition of the former Halley V. Architects Hugh Broughton Associates prepared the design with help from Engineering consultant Faber Maunsell (now AECOM). Hugh Broughton describes the construction as a ‘loose fit semi-monocoque’. Its fibre-reinforced plastic (FRP) envelope was subject to extensive structural analysis to ensure it would not distort the steel superstructure under wind loading, and pressure testing was conducted on trial modules. Coatings were applied in the factory and the station delivered in kit form for construction on site. The station, built by Galliford Try over a period of five years, features adjustable hydraulic and telescopic legs with ski pad feet to cope with the rapidly changing snow and ice terrain.

Glazing and paint were used to coat the panels. Broughton says: “We used an automotive polyurethane acrylic semi-matt paint system which is resistant to UV degradation. This is spray applied to the gelcoat of the GRP. The paint is 75 microns thick and manufactured by Plascon (of South Africa). The glazing is triple glazed with a U-value of 1.0W/sqm degK and has a high level of solar control coating to reduce glare from reflections off the ice surface. The panels were manufactured by MMS Teknologie of Pretoria in South Africa – they were responsible for the whole cladding system. The acrylic top coat was applied to an etch fill primer applied to the gel coat.”

Moving snow

Approximately 1.2 metres of snow accumulates each year on the Brunt Ice Shelf and buildings on the surface become covered and eventually crushed by snow. This part of the ice shelf is also moving westward by approximately 700 metres per year. Construction on-site was limited by a summer weather window, and by the difficulty of transporting heavy units across the ice from the nearest unloading point.

Broughton says the reasoning behind his choice of materials benefited from the experience of other architects: “To start with we planned to use timber structural insulated panels finished with a painted aluminium architectural over-skin – the same system that had been used by Ferraro Choi Architects at the new US base at South Pole.

However, after winning the design competition, we held a peer review with Patrice Godin of the French Antarctric Survey. He had just completed the construction of the new French-Italian base at Concordia using composite GRP panels and advised that we change to this system because it would reduce time on site, as panels could be bigger and would offer enhanced thermal performance. Also, GRP performs excellently in cold climates and is a poor conductor of heat compared to metal or even timber based systems. We investigated further, prepared a complete analysis of the possible systems and eventually BAS agreed to the change to a GRP based system.”

GRP provides advantages over other materials, including a very low coefficient of thermal expansion, ensuring stable joints between the panels. The cladding panels measure up to 10.4 metres high by 3.5 metres wide, and are 210-220mm thick. They were formed under vacuum, with resin-infused cross fibres running diagonally between the inner and outer skins to prevent delamination under windloading (wind speeds at the Antarctic site can surpass 100mph). The FRP inner skin has an intumescent paint finish, achieving Class-0 surface spread of flame. The panels are designed for temperatures down to -57 °C and incorporate triple glazed vision panels.

Thermal shock

The extreme challenges of temperature, ice abrasion, UV, and a degree of flex would push any coating to its limits. Broughton continues: “The paint system had to withstand all of these factors. A particular issue is thermal shock: surface temperature can change from +20 °C when the sun is shining on a surface to -25 °C as it moves off the surface in a very short time, ie seconds. Another important factor is abrasion resistance from wind born ice crystals (known as spindrift) and the high levels of UV resistance required (due to spring time ozone depletion over this part of Antarctica) posed significant challenges.

“The paint selected therefore had to be proven through a series of tests developed especially for the project and conducted both in the factory of MMS Teknologie and at testing houses in South Africa. As part of this process MMS Teknologie actually made its own cold testing facility that could go down to -50 °C, as we could not find any reasonably priced testing facility which worked to that level in South Africa. R&D for the project was extensive and took over a year before panels went into production. The degree of testing was necessary because there was no previous installation that had performed to similar standards.”

Ozone hole

Halley VI is the world’s first re-locatable research facility. It provides scientists with state-of-the-art laboratories and living accommodation, enabling them to study pressing global problems from climate change and sea-level rise to space weather and the ozone hole. In fact the ozone hole was first discovered at an earlier version of the station in 1985.

After seven years, Broughton says the buildings, and their coatings, are holding up well: “The coatings still look fantastic. The station recently featured in a BBC Horizon TV show called Ice Station, hosted by the weatherman, Peter Gibbs, and looked as if it had just been completed. The design life of the station is 25 years and the design life of the paint system was 15 years. It looks like it will easily meet this requirement.”

Small areas of damage can be repaired on-site if needed – but only during the summer months – otherwise it is far too cold for this kind of work. The building is carefully inspected each Austral summer, and so far no significant paint repairs have been necessary.

During construction, PVC laminated vinyl fabric encasements were installed on six of the seven units, and then removed when the FRP panels were installed. These were used as a temporary cover to the steel frames before the panels could be installed, but lasted brilliantly for 18 months.

Red, White and Blue

Broughton explains that the colour of the coatings was significant: “The colour selection was important. Class 1 resistance to Surface Spread of Flame of the paint finish was an important part of the overall fire strategy. We chose the two principal colours to aid route finding in white out conditions. Darker colours are also good because they do not reflect as much solar glare onto the ice surface – this could cause local melting of the ice around the skis which could exacerbate risk of differential settlement. That’s also why the skis are painted white – to minimise solar absorption – in their case we want to reflect the sun away from them. After all this science we then coincidentally found we had created a red, white and blue building – the same colours as the Union Jack, which is of course a good thing for a British research station!”

Timely move

The re-locatable design of Halley VI proved its value when satellite measurements from 2012 to 2015 showed that a large crack in the ice shelf had started to grow, just 8 km away from the base and extending in the direction of Halley VI at a rate of 1.7 km a year. The main concern was that the chasm would grow so much that it would become impossible to relocate the base in the future, and a move was initiated.

The move is a complex operation involving bulldozers brought in by ship, which will tow the station to a safer area. The modules are so heavy that even small slopes pose an issue, so the route must be carefully chosen.  The move project is planned to complete in 2018.

Further success

A long string of awards for the station include the AIA UK Excellence in Design Awards Winner 2013,the RIBA International Award for Architecture 2013, the BCI Awards International Project of the Year 2013 and the Institute of Structural Engineers’ Structural Awards Sustainability Award 2013.

Moving on from their success with Halley VI, Broughton Associates now have an impressive portfolio of jobs for similar environments. “The largest building we had designed before winning the RIBA international design competition to design Halley VI back in 2005, was a small building in south west London for Girl Guides which cost £160,000! (RIBA Award 1999), says Broughton. “In the competition, British Antarctic Survey were looking for fresh ideas backed up by experience – we were the ‘fresh ideas’ and AECOM (the engineers) provided the experience, so we presented an ideal team.

He told PCE-International; “Since working on Halley however we have become the world’s leading experts on the design of buildings for polar research and have designed a new base for Spain on Livingstone Island, a laboratory for the US National Science Foundation on the Summit of the Greenland Ice Cap and been invited to prepare designs for polar research bases for Korea and India. More recently we have expanded our horizons to design buildings in other remote locations – most recently a healthcare facility for Tristan da Cunha, the world’s most remote inhabited island in the South Atlantic.”

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