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Pykrete is a composite material made of 14% wood pulp and ice, invented by Max Perutz and proposed during World War II by Geoffrey Pyke to the Royal Navy as a candidate material for making a huge, unsinkable aircraft carrier, Project Habbakuk, actually more of a floating island than a ship in the traditional sense. Pykrete has some interesting properties, notably its relatively slow melting rate (due to low thermal conductivity), and its vastly improved strength and toughness over pure ice, actually closer to concrete. Pykrete is slightly harder to form than concrete, as it expands whilst freezing, but can be repaired and maintained from the sea's most abundant raw material.
History
Pyke managed to convince Lord Mountbatten of the worth of his project some time around 1942, and trials were made in two locations in Alberta in Canada. Blocks of Pykrete were attacked with various explosives and it was found that a charge corresponding to a torpedo warhead would have made only a minor dent in the planned Habakkuk carrier.
At the Quebec Conference of 1943 Mountbatten brought a block of Pykrete along to demonstrate its potential to the bevy 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 the other was Pykrete. He then drew his service pistol and shot at the first block, and it shattered and splintered. Then fired at the Pykrete to give an idea of the resistance of this kind of ice to projectiles. The bullet ricocheted off the block, grazing an admiral and ending up in the wall. The Admiral was impressed by Mountbatten's unorthodox demonstration. Thus a small pilot project was given the go ahead but the main Project Habakkuk was never put into action. The funds simply were not available due to other WWII projects (such as the atomic bomb).
Pykrete experiment
As a bit of fun, Pykrete can easily be made in small quantities by shredding bathroom tissue in water (or you can use sawdust) and moulding it in, say, an ice cube tray. As an experiment, vary the volume fraction of pulp to water, and freeze it. One could bang on it with a hammer to see how resistant it is to impact loading. However it should be noted that such a small piece of Pykrete will melt in about the same time as an ice cube of the same size. Thermal conductivity will only slow melting appreciably on much larger pieces of Pykrete.
Durability
If a ship were made of pykrete, it would be unsinkable; torpedoes could hit it and do little damage. Pykrete has a crush resistance of greater that 3,000 pounds per square inch. A 1-inch column of pykrete can support an automobile. The wood pulp also makes the pykrete extremely stable at high temperatures. If a .303 caliber bullet is fired at the pykrete, it will penetrate only 6.5 inches.
Project Habbakuk
http://www.combinedops.com/Pykrete.htm
References
- Collins, Paul (2002). The Floating Island (http://www.cabinetmagazine.org/issues/7/floatingisland.php). Cabinet Magazine, Issue 7, Summer 2002. Retrieved Jul. 23, 2004.
- Perutz, M. F. (1948). A Description of the Iceberg Aircraft Carrier and the Bearing of the Mechanical Properties of Frozen Wood Pulp upon Some Problems of Glacier Flow. The Journal of Glaciology, 1 (3), 95–104
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