Concrete pipe structures - GIF

[neilbourjaily]

[QUOTE=BuffaloJohn;257559]Why not build them out of cardboard?
Actually corrugated paper.
Corrugate has many uses beyond its intent. I can use, say, a dryer box flat on a concrete floor as an anti-fatigue mat. Yes, fire hazard is something to be conscious of not fear. S-l-o-w-l-y over time the flutes give way, ie crush, softening the feel of the concrete beneath the sheet. It works as well as the kick pallet but can cover a larger area. Over a long time, months even, it crushes and becomes useless. And since it is a recyclable, most warehouses are happy for you to take them for free rather than the recycle expense they have to pay.
If corrugate were to be made of other materials than paper, say, something weather resistant or proof it could do as BuffaloJohn says without wrappings. Air cells are wonderfully adaptable and useful.