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Comment by frandroid | Hacker News Reader

We already have slow-curing low-emissions concrete, which has existed for centuries. Fast setting is a core feature of modern (Portland) concrete, and any "replacement" which doesn't do that is not a replacement at all. Companies want to build their 40-story towers in 6 months, not 6 years.

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We use a lot of cement blocks these days for building foundations and pavers. I dunno how many private residences it takes to equal a mile of new highway or an office block, but it’s not nothing.

A lot of concrete is used for making standardized "pre-molded" parts (blocks, panels, structural elements) and those can absolutely by made using a much slower process, stocked and then rapidly assembled during construction.

I'm often dumbfounded when I see building with cast cement only to be broken down with cranes later. Is it stupid (unstable) to make cement blocks and build by stacking most of them (maybe keep pillars and floors cast). So you can reuse them.

As a counter, do you want to buy a brand new Tesla made with "100% recycled parts from former cars!"?

I'd buy a refurb at a refurb price. My car is 10 years old and still running great so I can't imagine a refurbished newer vehicle running any worse.

There are no refurb skyscrapers. Noone wants a transmission with 185,000 miles on it in a "new" car, just like a developer doesn't want a concrete form that supported 40 floors above it for 20 years in his "new" construction.

But I meant blocks that were mostly under simple compressive load, not slabs. Would they still age bad ?

I agree, > Utilizing the humidity and temperature as physical switches

sounds worse than lime plaster

Our modern concrete has not existed for "centuries"... Portland cement was invented about 150 years ago, and steel-reinforced concrete started being used just over 100 years ago.

I'm talking about lime-based cement, which predates Portland cement and steel-reinforced concrete. Portland cement is a huge source of CO2 emissions.

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