Bacteria and sand engineered into living concrete | Hacker News Reader

Bacteria and sand engineered into living concrete

eurekalert.org

79 pointshhs22 comments

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.

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.

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

sounds worse than lime plaster

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 ?

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.

This reminds me of the JG Ballard story Venus Smiles, which I found whimsical and scientifically ridiculous at the time of reading, where an artist creates a living sculpture which basically makes a hell of a racket and grows itself out of control. Panicking, the owner has it cut up and sold for scrap, only to start hearing the same noises start when he is in new buildings - the tainted metal has been used in construction projects from the melted down scrap and is proliferating - "The whole world will be singing."!

Reading this news story it seems that one could retrofit a bacteria based scientific explanation - perhaps not so outlandish after all. What an amazing futurist he was!

https://en.wikipedia.org/wiki/Venus_Smiles

Can it use desert sand rather than riverbed sand?

Not really, desert sand and riverbed sand have different characteristics with regards to smoothness and grain size, etc.. You really can just use desert sand.

I elsewhere read much concrete is made with rare, far away, environmentally damaging illegally dredged riverbed sand, because desert sand (or other more available less environmentally precious substitutes) were unsuitable.

All sorts of stuff can be used for agregate, but not all of it produces concerte of the same quality. Also, the problem is local availability... most of the sheer mass of our construction projects is the aggregate for the concrete, so getting the aggregate from a distant source would be almost like constructing the whole building there and then transporting it to its final location!

There is essentially an endless supply of aggregate on this planet, it's the transportation costs that are prohibitive (both in terms of money and of course the environmental costs of transportation).

that's great and all but it's the sand part that's making concrete expensive. The type of sand to use is becoming harder and harder to source

> The brick needs to be completely dried out to attain the maximum structural capacity (i.e., strength), but at the same time, drying stresses the bacteria and compromises its viability. To maintain structural function and ensure microbial survivability, the concept of optimum relative humidity and storage conditions is critical. Utilizing the humidity and temperature as physical switches, the researchers can control when the bacteria grow and when the material stays dormant to serve structural functions.

So it can't get wet.

> they use light from the sun to grow and proliferate with very little exogenous material needed for their growth

Do the bacteria just die after the initial nutrients run out?

To both comments, not really.

It can get wet, but just not too wet. And it doesn't necessarily die when the initial nutrients run out as long as more naturally enter. The solution is to deal with sub-maximal strength and provide a slow nutrient drip(or possible occasional soaking with a nutrient slush).

Sorry, maybe it's just me, but what is the main motivation for this? What problems does it solve? What secondary problems does it create?

> and concrete also releases CO2 when it cures.

As it cures, Portland cement ABSORBS "nearly a quarter" the CO2 used to produce it.

https://www.sciencemag.org/news/2016/11/cement-soaks-greenho...

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