From the Please Send Me a Test Unit Department, here's a concrete tent. The concept is simple: cloth containing concrete it is used to create buildings (or, frankly, anything else you want to make out of thin concrete). You just put up the cloth, get it wet, then wait. The result is a durable structure without the need for pouring concrete. To form the structure, just inflate a bag under it -- though I can see how using a plywood or other substrate could also be handy, if you don't like bag-shaped buildings. I just want to know how much this costs. (Seriously. I've got uses for this stuff. I kinda need to make a Hobbit Hole in my back yard.)
First up, a video from National Geographic showing the deployment of a concrete tent:
And here's a video featuring the materials inventors explaining it themselves. Note they mention deploying it underwater. Innnteresting.
So, who's with me? Bag End replica? Let's do this.