Experts revive ancient techniques to make concrete more sustainable • Hacker News Board

Re: Experts revive ancient techniques to make concrete more sustainable

#31

Post by chalcolithic » Mon, Dec 04, 2023, 3:37 PM UTC

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…

> if you buy a condo in a building built in the 1970s, the building will become unsafe

OTOH if I buy a condo in a building built in the 1970s....

Re: Experts revive ancient techniques to make concrete more sustainable

#32

Post by scythe » Mon, Dec 04, 2023, 3:46 PM UTC

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…

CFRP rebar has been developed with a much longer lifespan. However, it is currently considered non-economical, possibly because design lifespans are not long. Aramid FRP has been considered for rebar as well; glass fibers are attacked by cement alkali; basalt fibers have good performance dependent on the source of basalt (rocks with varying composition).

One issue with a long-lived building is that you never know exactly when it will fail. 700 years down the line, it starts to crack: now what? The evolution of biological systems has strongly preferred regular replacement to longevity.

Re: Experts revive ancient techniques to make concrete more sustainable

#33

Post by aaron695 » Mon, Dec 04, 2023, 3:48 PM UTC

adamjc wrote: post #3

> "For centuries, builders tried to cut costs by limiting how much cement they used and incorporating recycled waste materials into their concrete," says Salvatore Aprea, head of the Acm research group. "The challenge now is to revive these old methods—not for financial reasons but for the sake of our planet." I put it to you that if it was financially viable and simple ("ancient methods"), it would already be done.…

[dead]

Re: Experts revive ancient techniques to make concrete more sustainable

#34

Post by scythe » Mon, Dec 04, 2023, 3:54 PM UTC

culi wrote: post #29

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…

The oldest buildings in the world[0] are as old as they are because they use materials with lifespans of much less than 100 years. Instead they make them modular. Make it so that you can take out parts of the building to replace them without collapsing the whole thing. Instead we build our buildings in such a way that makes maintenance very hard and costly. We prefer to pretend like our buildings will last forever ra…

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...

Re: Experts revive ancient techniques to make concrete more sustainable

#35

Post by foobarian » Mon, Dec 04, 2023, 3:56 PM UTC

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 again).

Re: Experts revive ancient techniques to make concrete more sustainable

#36

Post by cm2187 » Mon, Dec 04, 2023, 4:02 PM UTC

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…

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.

Re: Experts revive ancient techniques to make concrete more sustainable

#37

Post by scythe » Mon, Dec 04, 2023, 4:07 PM UTC

p1mrx wrote: post #18

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…

> reinforced concrete only has a lifespan of about 100 years. Currently, less than 1% of rebar is made from stainless steel: https://www.youtube.com/watch?v=zn9SzyDhfj8&t=140s

Stainless steel contains a necessary 12% (often more, usually 18%) chromium, which is relatively scarce from a building materials perspective. Already 85% of available chromium is used for stainless steel; many other metals are primarily supplied as byproducts of chromium extraction because of the extensive efforts [1, 2] made to locate and exploit deposits. In fact, total rebar production is roughly the same scale (if not larger) as total stainless steel production, meaning that practically the entire world supply of stainless steel would have to be diverted to rebar in order to use it for this.

In general only the 12 or so most common elements can be used for construction. Copper is the rarest material used in major applications, but this is relatively less total mass consumed than rebar.

1: https://en.wikipedia.org/wiki/Bushveld_Igneous_Complex#Minin... (50% of world supply)

2: https://en.wikipedia.org/wiki/Ring_of_Fire_(Northern_Ontario...

Re: Experts revive ancient techniques to make concrete more sustainable

#38

Post by davidgay » Mon, Dec 04, 2023, 4:22 PM UTC

culi wrote: post #29

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…

The oldest buildings in the world[0] are as old as they are because they use materials with lifespans of much less than 100 years. Instead they make them modular. Make it so that you can take out parts of the building to replace them without collapsing the whole thing. Instead we build our buildings in such a way that makes maintenance very hard and costly. We prefer to pretend like our buildings will last forever ra…

> The oldest buildings in the world[0] are as old as they are because they use materials with lifespans of much less than 100 years.

Rather apropos counter-example: Rome's Pantheon is several hundred years older and built in part of concrete.

Re: Experts revive ancient techniques to make concrete more sustainable

#39

Post by semi-extrinsic » Mon, Dec 04, 2023, 4:29 PM UTC

culi wrote: post #27

semi-extrinsic wrote: post #8

While it's interesting to explore ancient concrete, actually scalable improvements of concrete production will be made elsewhere. For instance HeidelbergCement has successfully piloted and is currently implementing technologies that bring the CO2 emissions from cement production close to zero. The OxyCal hybrid process that they are deploying in Bulgaria and Belgium will capture >97% of all emissions from the cement…

I tried looking it up but don't fully understand. What exactly is the OxyCal hybird process?

It's their name for combining oxyfuel combustion with amine capture.

Oxyfuel is where you feed the combustion process using pure oxygen mixed with exhaust gas, instead of air. Since you're not pulling in all that nitrogen gas from the air, the exhaust is much richer in CO2, which is then easier to catch.

Amine capture is where you use an amine solvent liquid that is sprayed as droplets into a large column, where the droplets fall down and absorb CO2 into the liquid, while the exhaust gas flows up and leaves the column free from CO2. Then the liquid that collects at the bottom is moved to a stripper cylinder, where the liquid is heated up and the CO2 is released as pure gas.

Specifically for the cement process, using both of these technologies together, it turns out you can do some cool process integration where the byproduct of one is the requirement of the other, and vice versa, so you can make the whole setup a lot cheaper in both CAPEX and OPEX.

Re: Experts revive ancient techniques to make concrete more sustainable

#40

Post by foobarian » Mon, Dec 04, 2023, 4:55 PM UTC

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.

Good point - yes the walls not necessarily, but floors. There used to be a common community activity similar to "barn raising" - "building the plate" where after the homeowner DIYd the molds and rebar, the neighbors would come together and mix and pour concrete over the span of one day. Fun times.