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Experts revive ancient techniques to make concrete more sustainable

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Re: Experts revive ancient techniques to make concrete more sustainable

#61

Post by quickthrowman »

cm2187 wrote: post #36
foobarian wrote: post #35

Earlier quoted context omitted.

European acquaintances often poke fun at our North American wood frame construction, noting their concrete houses are stronger and "will last for centuries." Are they wrong? I know there are a lot of stone buildings that had excellent longevity but those are made of large stone blocks instead of reinforced concrete. And that's just walls, floors in old houses are usually spanned by wood beams (there goes the wood aga…

I think a lot of houses are made of bricks, not necessarily reinforced concrete. Appartement blocks on the other hand is all reinforced concrete I believe.

> Appartement blocks on the other hand is all reinforced concrete I believe.

Five-over-one is probably the most common new residential apartment building variant in the US today, it’s a single story of concrete (commercial space or common areas) with 4-5 floor of stick built (wood-framed) apartment housing on top. Developers only build apartment towers when the land is expensive enough to force them to.

https://en.m.wikipedia.org/wiki/5-over-1

Re: Experts revive ancient techniques to make concrete more sustainable

#62

Post by toss1 »

joelegner wrote: post #57
cm2187 wrote: post #10

I was a bit shocked when I learned that reinforced concrete only has a lifespan of about 100 years. That means that if you buy a condo in a building built in the 1970s, the building will become unsafe and need to be demolished in your life time. I don't know if people are pricing this consideration. It also means there will be pretty much nothing left of our architecture, all those appartments, offices, museums, brid…

Where did you hear that reinforced concrete has a lifespan of 100 years? As a structural engineer, I can tell you this is not correct as a general rule, but is true for structures subject to chlorides, especially marine structures like bridge piers. One of my now-retired professors at the University of South Florida studied concrete durability for FDOT. He told me FDOT is now using a 100-year design basis for bridges…

What baffles me (as someone working in Advanced Composites) is why not simply get rid of the steel, the steel-concrete interface, the chloride ion and corrosion problem altogether — by instead using rebar made of composites?

Rebar of fiberglass, carbon fiber, basalt, and other combinations is all redily available and has known properties.

The key issue is that steel will corrode, then expand and put the concrete in tension (which concrete sucks at reacting), causing the concrete to crack, then spall off. None of the composites do this.

Yet, despite composites being available for years, and even being cheaper than steel [0], they are being picked up at remarkably slow rates.

It seem blindingly obvious to me that everyone should have just switched some time ago. Yet, this has not happened. Why?

[0] https://ernestmaier.com/is-fiberglass-rebar-more-affordable-...

Re: Experts revive ancient techniques to make concrete more sustainable

#63

Post by Qem »

cm2187 wrote: post #10

I was a bit shocked when I learned that reinforced concrete only has a lifespan of about 100 years. That means that if you buy a condo in a building built in the 1970s, the building will become unsafe and need to be demolished in your life time. I don't know if people are pricing this consideration. It also means there will be pretty much nothing left of our architecture, all those appartments, offices, museums, brid…

Probably a lot of buildings will hit the end of the lifespan just as we're going through the other hard bumps of climate change and mass population ageing, compounding the problems.

Re: Experts revive ancient techniques to make concrete more sustainable

#64

Post by scythe »

rowanG077 wrote: post #45
scythe wrote: post #34

Earlier quoted context omitted.

Also in Japan, there has been an increasing use of aluminum (!) in construction, since it will generally be melted and re-used after the structure is no longer useful. https://www.acsa-arch.org/chapter/toyo-itos-second-age-of-al...

What's the problem with aluminium? I would always build structures out of aluminium if aluminium would be strong enough. It has extreme corrosion resistance, it's cheap, it's easy to handle, you can easily make almost any imaginable shape with it, you can cheaply reuse it, it's very light.

Aluminum is generally much more expensive than other construction materials, but less obviously, it has practically no fatigue limit, meaning a structure made of aluminum will eventually fail under repeated loads.

Re: Experts revive ancient techniques to make concrete more sustainable

#65

Post by scythe »

hef19898 wrote: post #51
rowanG077 wrote: post #45

Earlier quoted context omitted.

What's the problem with aluminium? I would always build structures out of aluminium if aluminium would be strong enough. It has extreme corrosion resistance, it's cheap, it's easy to handle, you can easily make almost any imaginable shape with it, you can cheaply reuse it, it's very light.

Aluminiums corrosion resistance is mostly myth so.

Aluminum's corrosion resistance is decent, but it's particularly weak to alkali, and cement is alkaline. So.

Re: Experts revive ancient techniques to make concrete more sustainable

#66

Post by kwhitefoot »

foobarian wrote: post #35
cm2187 wrote: post #10

I was a bit shocked when I learned that reinforced concrete only has a lifespan of about 100 years. That means that if you buy a condo in a building built in the 1970s, the building will become unsafe and need to be demolished in your life time. I don't know if people are pricing this consideration. It also means there will be pretty much nothing left of our architecture, all those appartments, offices, museums, brid…

European acquaintances often poke fun at our North American wood frame construction, noting their concrete houses are stronger and "will last for centuries." Are they wrong? I know there are a lot of stone buildings that had excellent longevity but those are made of large stone blocks instead of reinforced concrete. And that's just walls, floors in old houses are usually spanned by wood beams (there goes the wood aga…

We have wooden houses here in Norway that are considerably more than a hundred years old and wooden churches from Viking times nine hundred years ago. My house is timber frame, built in 1952, and there is no reason why it should not last until the end of this century. But many US timber frame houses are built on the assumption that they will be demolished after only forty or fifty years and built accordingly.

Re: Experts revive ancient techniques to make concrete more sustainable

#67

Post by kwhitefoot »

sudobash1 wrote: post #53
foobarian wrote: post #35

Earlier quoted context omitted.

European acquaintances often poke fun at our North American wood frame construction, noting their concrete houses are stronger and "will last for centuries." Are they wrong? I know there are a lot of stone buildings that had excellent longevity but those are made of large stone blocks instead of reinforced concrete. And that's just walls, floors in old houses are usually spanned by wood beams (there goes the wood aga…

On the west coast of America, I would much rather be living in a wood frame house when an earthquake hits. Depending on construction, the house may not survive, but I probably will. Cement, stone, or brick all seem much riskier to me in an earthquake zone.

Properly built concrete will protect you much better. But that is assuming that it is built in accordance with the regulations regarding earthquake resistance.

Re: Experts revive ancient techniques to make concrete more sustainable

#68

Post by hef19898 »

scythe wrote: post #65
hef19898 wrote: post #51

Earlier quoted context omitted.

Aluminiums corrosion resistance is mostly myth so.

Aluminum's corrosion resistance is decent, but it's particularly weak to alkali, and cement is alkaline. So.

And to salt, and to contact corrosion woth, e.g., steel. Especially the last one is quite often ignored. Even by people at VW and General Dynamics.

Re: Experts revive ancient techniques to make concrete more sustainable

#69

Post by joelegner »

toss1 wrote: post #62
joelegner wrote: post #57

Earlier quoted context omitted.

Where did you hear that reinforced concrete has a lifespan of 100 years? As a structural engineer, I can tell you this is not correct as a general rule, but is true for structures subject to chlorides, especially marine structures like bridge piers. One of my now-retired professors at the University of South Florida studied concrete durability for FDOT. He told me FDOT is now using a 100-year design basis for bridges…

What baffles me (as someone working in Advanced Composites) is why not simply get rid of the steel, the steel-concrete interface, the chloride ion and corrosion problem altogether — by instead using rebar made of composites? Rebar of fiberglass, carbon fiber, basalt, and other combinations is all redily available and has known properties. The key issue is that steel will corrode, then expand and put the concrete in t…

Alternative reinforcement is an area of ongoing research. There are issues with cost and stiffness of the more exotic types. Research is probably slower because of the need to at all times be confident our structures are safe. We cannot freely experiment with exotic reinforcement in the built environment. It needs to be proven, first analytically then in the laboratory, then in pilot projects, and then in the legal and political forum before adoption in life safety critical applications like bridges and buildings.

Re: Experts revive ancient techniques to make concrete more sustainable

#70

Post by toss1 »

joelegner wrote: post #69
toss1 wrote: post #62

Earlier quoted context omitted.

What baffles me (as someone working in Advanced Composites) is why not simply get rid of the steel, the steel-concrete interface, the chloride ion and corrosion problem altogether — by instead using rebar made of composites? Rebar of fiberglass, carbon fiber, basalt, and other combinations is all redily available and has known properties. The key issue is that steel will corrode, then expand and put the concrete in t…

Alternative reinforcement is an area of ongoing research. There are issues with cost and stiffness of the more exotic types. Research is probably slower because of the need to at all times be confident our structures are safe. We cannot freely experiment with exotic reinforcement in the built environment. It needs to be proven, first analytically then in the laboratory, then in pilot projects, and then in the legal a…

Yes, I certainly agree that validation research needs to be done, and done absolutely solidly before wholesale switching .

Yet in this case, the existing tech is known bad (although TBF, the how-bad is well-characterized), and the new technologies are already qualified to fix this bad tech, e.g., carbon-fiber re-wrap of disintegrating steel-rebar bridge columns [0,1,2].

Certainly seems that applications like road-bed construction that require rebar, where the worst-case is a part of the road gets potholes prematurely, vs abridge or building collapsing, should already be mandated to use composite rebar. That would significantly increase the data set that can be used for real-world aging studies, with minimal risk?

[0] https://www.hj3.com/blog/dot-bridge-column-repair

[1] https://www.advancedfrpsystems.com/how-to-repair-concrete-co...

[2] https://hydratechllc.com/resources/case-study-dot-bridge-con...

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