Make a concrete Tent, a BIG tent over a few hours time.
Concrete Tent: http://www.concretecanvas.co.uk/index.html
It uses a concrete canvas technology. Simply put it in position -- in this case inflate the tent. And then moisten the canvas. Let it dry and you have a hardened shelter. Put sand around it, and you have a hardened bunker.
Look at the video with ~1.5m facebook <likes>...
Winner of a whole bunch of innovation awards including a couple awards from insurance companies and:
- 2011 Most Innovative Product, MIP Expert's Choice
- 2005 World Changing Idea Award, Saatchi & Saatchi
- Material Connection's 2011 Material of the Year Award