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Pykrete is a frozen composite material made of approximately 14 percent sawdust or some other form of wood pulp (such as paper) and 86 percent ice by weight (6 to 1 by weight). During World War II, Geoffrey Pyke proposed it as a candidate material for a huge, unsinkable aircraft carrier for the British Royal Navy. Pykrete has some interesting properties including its relatively slow melting rate (because of low thermal conductivity) and its vastly improved strength and toughness over ice; it is closer in form to concrete. Pykrete is slightly more difficult to form than concrete, as it expands during the freezing process. However, it can be repaired and maintained using seawater. The mixture can be moulded into any shape and frozen, and it will be extremely tough and durable, as long as it is kept at or below freezing. ==History== Geoffrey Pyke managed to convince Lord Mountbatten of the worth of his project (actually prior to the invention of pykrete) some time around 1942, and trials were made at two locations in Alberta, Canada. The idea for a ship made of ice impressed the United States and Canada enough that a -long, 1,000-ton ship was built in one month on Patricia Lake in the Canadian Rockies. It was, however, constructed using plain ice (from the lake), before pykrete was considered. It took slightly more than an entire summer to melt. Plain ice proved to be insufficiently strong. Pyke learned from a report by Herman Mark and his assistant that ice made from water mixed with wood fibres formed a strong solid mass—much stronger than pure water ice. Max Perutz later recalled: Perutz would later learn that Project Habakkuk was the plan to build an enormous aircraft carrier, actually more of a floating island than a ship in the traditional sense. The experiments of Perutz and his collaborators in Smithfield Meat Market in the City of London took place in great secrecy behind a screen of animal carcasses. The tests confirmed that pykrete is much stronger than pure ice and does not shatter, but also that it sags under its own weight at temperatures higher than . Mountbatten’s reaction to the breakthrough is recorded by Pyke's biographer David Lampe: Another tale is that at the Quebec Conference of 1943 Mountbatten brought a block of pykrete along to demonstrate its potential to the entourage of admirals and generals who had come along with Winston Churchill and Franklin D. Roosevelt. Mountbatten entered the project meeting with two blocks and placed them on the ground. One was a normal ice block and the other was pykrete. He then drew his service pistol and shot at the first block. It shattered and splintered. Next, he fired at the pykrete to give an idea of the resistance of that kind of ice to projectiles. The bullet ricocheted off the block, grazing the trouser leg of Admiral Ernest King and ending up in the wall. According to Perutz's own account, however, the incident of a ricochetting bullet hitting an Admiral actually happened much earlier in London and the gun was fired by someone on the project—not Mountbatten.〔Perutz, 2002〕 Despite these tests, the main Project Habakkuk was never put into action because of limitations in funds and the belief that the tides of the war were beginning to turn in favour of the Allies using more conventional methods. According to the memoirs of British General Ismay: Since WWII, pykrete has remained a scientific curiosity, unexploited by research or construction of any significance. New concepts for pykrete however crop up occasionally among architects, engineers and futurists, usually regarding its potential for mammoth offshore construction or its improvement by applying super-strong materials such as synthetic composites or Kevlar. In 1985, pykrete was considered for a quay in Oslo harbour. However, the idea was later shelved, considering pykrete's unreliability in the real-world environment. Since pykrete needs to be preserved at or below freezing point, and tends to sag under its own weight at temperatures above , an alternative was considered that would guarantee effectiveness and public safety.〔 In 2011, the Vienna University of Technology successfully built a pykrete ice dome, measuring in diameter. They improved on an original Japanese technique of spraying ice on a balloon by utilizing the natural properties of ice and its strength. This structure managed to stand strong for three months before solar radiation started melting the ice, rendering the structure unreliable.〔http://www.livescience.com/11704-austria-imbibe-ice-dome.html〕 In 2014, the Eindhoven University of Technology worked on a pykrete architecture project in Juuka, Finland, which included an ice dome and a pykrete scale model of the Sagrada Familia. Their attempt to build the largest ice dome in the world was partially unsuccessful when the dome collapsed within a few days of it being open to the public. Due to human error, the plug to a compressor that kept the balloon inflated was pulled, leading to the balloon deflating. The team of Dutch students quickly re-inflated the balloon, and resprayed the part of the dome that had collapsed. They continued with their progress, and eventually opened the dome to the public, where within a matter of days the roof caved in. Luckily, there were no visitors on the site during this time.〔http://yle.fi/uutiset/maailman_suurimman_jaakupolin_katosta_romahti_pala_juuassa/7056718〕 In Japan, ice domes have been built using a construction method in which water is sprayed onto a balloon. Researcher Johann Kollegger of Vienna University of Technology thinks his team's new method is easier — for instance, when spraying water onto the balloon, the ice sprays back at the workers. To build their freestanding structure, Kollegger and his colleagues first cut an 8-inch- thick (20 centimeters) plate of ice into 16 segments. To sculpt the segments to have dome-like curve, the researchers relied on ice's creep behavior. If pressure is applied to ice, it slowly changes its shape without breaking. One of the mechanisms by which glaciers move, called glacial creep, functions similarly, the researchers say.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pykrete」の詳細全文を読む スポンサード リンク
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