I was watching the History Channel today - Modern Marvels was on. In a segment about ice, they mentioned Pykrete:
Pykrete is a composite material made of approximately 14 percent sawdust or some other form of wood pulp (such as paper) and 86 percent ice by weight. Its use was proposed during World War II by Geoffrey Pyke to the British Royal Navy as a candidate material for making a huge, unsinkable aircraft carrier. Pykrete has some interesting properties, notably 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.
Yes, the various Canadian, British and American militaries were considering using it to make a sort of crude self propelled aircraft platform not unlike an aircraft carrier to help fill the gaps from submarine losses during WWII. But, with the advent of long range bombers, radar and sonar keeping the Wolfpack at bay, the need was less pressing, and the idea dropped.
Still interesting, though.