Papercrete

Papercrete is made with cement and paper pulp. When done right, it is fire resistant, water resistant, decay and vermin resistant, structurally sound, provides excellent insulation, has excellent acoustics, and is cost competitive. It's been the 'done right' part that most people have had trouble with.
I built a half yard blender, some racks, and some forms, and built one room on my house, but I gave it up when I started losing too many batches. Two hours time, two gallons of gas, and two bags of cement shot to hell when something in the paper completely blocked the cement from curing. Finding plain paper was a major hassle.
Cardboard works well and is plentiful, but doesn't shred well in a blender. Cardboard needs to be pre-shredded dry.
In order to be fire and water resistant and maintain accurate dimensions, papercrete should be about two thirds cement by dry weight of paper and needs to be compressed a bit while the cement cures. If you do blocks, you need forms and racks. You'll need forms with perforated top and bottom to squeeze out some of the water. I'm using old store shelves. Because you need to leave the blocks in the forms for two days, it takes a lot of forms and racks to achieve much production. Blocks can be stored outside, uncovered, in any weather. You can still make them when it's freezing hard every night. They're surprisingly impervious to freezing, even when fresh and wet.

So far I've just done blocks, but the problem with blocks is a lot of labor and a lack of bond strength of the mortar joints. Prefabed wall sections would be much faster and stronger. Papercrete is carbon intensive [cement], so it's not for frivolous use, but it seems quite durable, which makes it environmentally economical for some uses.
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