Comment by fpaboim | Hacker News Reader

Comment by fpaboim | Hacker News Reader

I'm a civil engineer. This is bullshit. Reinforced concrete uses much less concrete because, well, you have rebar to take care of tensile stresses and concrete does well with compression so it's much more efficient, which is basic. Also, and a very important point, reinforced concrete (in general) tends to fail in non-catastrophic ways making it safer to use and easier to spot conceptual errors in the project and building process. Reinforced concrete can also be recycled, the concrete becomes structural blocks (I even worked with these before) and the rebar is steel so thats easily recycleable too. In the end, it's cheap and affordable so you can build much more with reinforced concrete than with concrete reinforced with carbon fiber which would last forever but would cost a fortune (this can also be used to reinforce reinforced concrete...) making housing unaffordable to a large part of the world. Do you also really want to spend that much more to make a project to last 500 years without using reinforced concrete? You know that goes into the equation when engineers project strucures right? Oh well, clickbait.

The point is that longer-lasting structures should be cheaper, but because we don't factor in environmental harm and lifecycle cost into the price of things we end up with cheap buildings that exist to generate ROI ASAP.

As an aside, fiberglass (similar to carbon fiber) is used frequently (but still not much, relative to steel) in many applications. We use it extensively in underground applications.

The problem with fiberglass reinforcement is that it does not undergo ductile failure like steel does. Steel will yield and, in addition, has strain hardening behavior. Fiberglass just fractures and that's that. Extra precautions must be taken when using fiberglass in failure critical members.

Steel and concrete also have similar moduli of thermal expansion. This means that as the temperature fluctuates, there is minimal internal stress owing to the similar strains.

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.

Straw is biodegradable. It will degrade.

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

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.

Just moved into an apartment that's 116 years old.

I'm just so happy that people had different perspective back then.

It's sad that we don't understand - unsustainable growth, scaffolding and prototyping phase is long overdue.

People didn't have a different perspective back then. It's just survivorship bias. People built plenty of crappy disposable buildings 116 years ago, you just don't see them because they were crappy disposable buildings built 116 years ago.

My house, currently not there but still own it, is 173 years old. Though that's common in eastern US.

Mine is just under 200 years old--also in the eastern US. It would be pretty silly though to view my house as this incredible structure that a farmer built 200 years ago to last for the ages. The fieldstone foundation is original as are various posts and beams. But the house has been expanded, rebuilt, updated, etc. in all manner of ways since it was built.

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