[lisivka]

Why not just use straw, instead of carbon fiber, in concrete? Straw is comparable to steel. Chopped straw is used for stucco, but it can be used in reinforced concrete too. It is hard to calculate amount of straw, which is necessary to reinforce concrete, because it strength varies, but it cheap, so just triple amount of straw.

[abduhl]

Straw could probably be used effectively for lightly loaded structures (slabs, bearing walls in nonseismic areas) the same way that fiber is used currently. It is essentially for crack control and provides nominal flexural capacity which is generally hard to quantify but there are some formulas which are accepted.

Using straw for anything that is loaded in flexure will be a disaster. Reinforced concrete theory relies on the reinforcing to act as a crack stopping mechanism which will yield in a ductile manner. Straw's variable strength and inability to place it at critical sections means that it cannot perform the function of reinforcement as it will be possible to encounter localized weak reinforcement which will not prevent cracking and loss of section leading to progressive and sudden failure.

[guard-of-terra]

Straw is biodegradable. It will degrade.

[lisivka]

When straw/wood is enclosed in concrete with some lime, it does not rot. I saw video[1] of remains of houses built by German prisoners in Siberia using "soft concrete" - concrete with wood chips (cement bonded particle board, AKA Arbolite, fiber reinforce concrete, Papercrete, etc.). They are looking good after about half of century without any maintenance of houses, even in broken walls without roof.

From my own experience, I saw that wood rots quickly for about 1cm (1/2") when it contacts with concrete or cement stucco, but remains intact when enclosed in cement-lime mix. IMHO, lime is important to save wood/straw from rotting.

[1] https://www.youtube.com/watch?v=iAiT6IRVgTE

[2] https://en.wikipedia.org/wiki/Papercrete