Pykrete is a composite material consisting of 14 percent by weight of sawdust (or other fibrous materials, such as newspaper) and the remaining 86 percent of ice.
The name is a fruit salad word from its inventor Geoffrey Pyke and concrete which in English means concrete.
Pykrete has some interesting properties compared to crystalline ice, including a marked slowness to melt (due to low thermal conductivity) and improved strength and toughness, which are similar to those typical of concrete. Compared to this, pykrete is more difficult to shape, as it expands during freezing, but is easily repaired with plain water.
During the Second World War, the use of pykrete was proposed by Geoffrey Pyke to the Royal Navy as a possible material suitable for the construction of a huge and unsinkable aircraft carrier. The idea (never realized) gave rise to the Habakkuk project and involved the construction of a sort of floating island, rather than a boat, to be used in places with a very cold climate.Around 1942 Pyke tried to convince Lord Mountbatten, admiral of the British fleet, of the great utility of the Habakkuk project (actually prior to the invention of the pykrete), and experiments were conducted in two locations in Alberta, Canada. Blocks of pykrete were tested with various explosives: it was concluded that a charge corresponding to the warhead of a torpedo would only scratch the hypothetical aircraft carrier Habakkuk.
At Patricia Lake in Alberta, the United States and Canada built a model in ice, 18.2 meters (60 feet) long and weighing 1,000 tons - it took a little longer than a hot summer to melt. Although the clearance was given to small preliminary projects, the Habakkuk Project was never completed because in reality the antisubmarine war was won with the development of sonar and advanced tactics to counter submarines.
An unlikely legend has it that Lord Mountbatten, in order to convince Winston Churchill of his usefulness, broke into his house and threw a block of pykrete into the tub where the statesman was taking a bath.
Another story relates that Mountbatten brought a block of pykrete with him to the 1943 Quebec Conference to show their potential to the admirals and generals who had arrived along with Winston Churchill and Franklin D. Roosevelt. Mountbatten showed up at the project meeting with two blocks, one of the material, the other of plain ice. Placed on the ground, he fired a bullet first at the ice, which shattered instantly, and then at the pykrete. The bullet ricocheted and grazed Admiral Ernest King's pants and then buried itself in the wall of the room. According to Max Perutz, however, the incident just described did not occur in 1943, much less in Québec, but a long time ago in London, and another participant in the project, and not Mountbatten, would have been shooting.
The useful life of a pykrete block is still under discussion, as many proportions and infinite varieties of raw materials are possible. It is normally assumed that pykrete has a tensile strength of 21 MPa, ie more than 200 kg per cm2. It has a strength 8 times higher than that of ice which corresponds to about 3.5 MPa. A 7.7 mm (.303 British) caliber bullet penetrates it by just 16.5 centimeters. Obviously the ice deforms due to pressure, but this is not affected by the presence of wood. In MythBusters' Alaska 2 special (season 7, episode 2) it was used to build a boat.
Pykrete can be easily obtained at home by using wood as a pulp, for example, newspaper or toilet paper. It is then sufficient to freeze the mixture for spe