If anyone ever wants to get serious & build an ice wall -- e.g., on a frozen outer planet/moon/asteroid -- they'd be far better off using *pykrete*. I wonder if the creator of "The Martian" ever considered using pykrete in his story? https://en.wikipedia.org/wiki/Pykrete 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. ... [Lord] Mountbatten's reaction to the breakthrough is recorded by Pyke's biographer David Lampe: What happened next was explained several years after the war by Lord Mountbatten in a widely-quoted after-dinner speech. "I was sent to Chequers to see the Prime Minister and was told he was in his *bath*. I said, 'Good, that's exactly where I want him to be.' I nipped up the stairs and called out to him, 'I have a block of a new material which I would like to put in your bath.' After that he suggested that I should take it to the Quebec Conference." The demonstration in Churchill's steaming bath had been most dramatic. After the outer film of ice on the small pykrete cube had melted, *the freshly exposed wood pulp kept the remainder of the block from thawing*. ... [Lord] 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. --- * Not the most novel concept: the ancient Romans included straw in their cement & concrete; the Meso-Americans included straw in their sun-dried adobe bricks. --- Of course, due to global warming, pykrete is now completely impractical on Earth.