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Carbon-negative concrete

Offset CO2 from concrete production
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Concrete production is one of the major contributors to anthropogenic CO2 emissions. It’s unavoidable, it’s right there in the chemistry. Roughly 180kg of CO2 per tonne of concrete, equivalent to 50kg carbon.

Concrete incorporates cement, sand and aggregate (gravel). Adding 50kg per tonne of Biochar/carbon might have a minor effect on strength and curing, but this will be small and might even be positive (as a result of microstructure/surface area effects)

Most concrete structures are massively over-strong anyway.

Even accounting for carbon emissions in producing Biochar, the result would be concrete that was a net sink of atmospheric carbon, as opposed to a net source.

Some research into mechanical and curing behaviour required.

Frankx, Oct 16 2019

Alternate chemicals for cement https://qz.com/1123...ing-it-heres-a-fix/
magnesium oxide and wollastonite [discontinuuity, Oct 17 2019]

Concrete made from iron and glass https://www.greenbu...cled-glass-concrete
"An experiment with silica and rusty iron led this researcher to what some are saying could be the first really promising low-impact substitute for Portland cement" [discontinuuity, Oct 17 2019]

Plastic waste in concrete mix https://phys.org/ne...tainable-india.html
"Waste plastic in concrete could support sustainable construction in India" [discontinuuity, Oct 17 2019]

[link]






       Yes, but why put the biochar into the concrete? It is of no benefit to the concrete, and is potentially deleterious. Much better to plough the same 50kg of char into poor soils - you lock up as much carbon, don't weaken the concrete, and improve the soil.
MaxwellBuchanan, Oct 16 2019
  

       ^ 'struth.   

       Activate the charcoal to make bio-char and create terra preta which binds up carbon for a thousand years providing the teensiest of niches for bacteria to produce mega rich top soil several feet deep.   

       Figure out how to make tiles out of bound carbon and you've got a winner.   

       It seems to me that as long as there is a single coal mine still in operation, making biochar for the purpose of sequestering carbon (or probably just about any other carbon sequestration method) is a complete waste. It would be far better to leave the coal buried deep underground where it was formed and just burn the biomass for energy. It appears that in the US there are 178 biomass power plants (total 6374.75 MW), though maybe half to three quarters of these are currently running off of municipal solid waste.   

       Interesting note: according to google, the cost of coal is $39 per ton and the cost of biochar is about $2580 per ton. If just 2% of the cost of Biochar is going to pay for the energy to shred, transport, heat, etc, it may be that you're releasing more carbon than you're sequestering. Or maybe the supply/demand is just really messed up right now.
scad mientist, Oct 17 2019
  

       My first thought was that you were going to put diamonds in as part of the aggregate.
scad mientist, Oct 17 2019
  

       Totally agree about using Biochar in the soil. $2580 doesn’t sound like a real price. In the UK you could make Biochar for around £100/tonne.
Frankx, Oct 17 2019
  

       //UK you could make Biochar for around £100/tonne//   

       Biochar has problems with low density, it could migrate in the mix, it's porous with inconsistent gas pockets and can contain varied mineral deposits. Instead, use a nice Anthracite coal. Crystaline, high-strength, high carbon, relatively pure, much cheaper and the carbon is biologically sourced from the atmosphere before a careful ageing process.
bs0u0155, Oct 17 2019
  

       If burned properly retort the off gas could be collected and burned for fuel as it once was before finding natural gas deposits.   

       It's completely retorted...   

       Why not just construct buildings out of wood instead of concrete ?   

       The downside is that wooden buildings burn really well.   

       However, the upside is that wooden buildings burn really well ...   

       <Sniggering/>
8th of 7, Oct 17 2019
  

       //wooden buildings burn really well ...//   

       Providing a supply of biochar...
bs0u0155, Oct 17 2019
  

       Yup. <Evil chuckling/>
8th of 7, Oct 17 2019
  

       There have been several proposals to make cement out of other chemicals in order to absorb CO2, including magnesium oxide, iron oxide, and the mineral wollastonite (see links). None have had commercial success. There have also been attempts to add plastic waste to concrete.
discontinuuity, Oct 17 2019
  

       //as long as there is a single coal mine still in operation [etc.]//   

       You're assuming some sort of global unity of human purpose; it's a bit like arguing that no-one should fight fires so long as there are arsonists, isn't it?
pertinax, Oct 18 2019
  

       // arsonists //   

       What if it wasn't intentional ? What if it's just a case of playing with matches or a lighter, and maybe a can of butane gas, and some kerosene, and it all got a bit out of hand ? No intent to do harm just a craving to see the gorgeous golden-yellow flames curl and dance, a beautiful coruscating ballet of light and destruction ...
8th of 7, Oct 18 2019
  

       // You're assuming some sort of global unity of human purpose; // No I'm saying that if there's a coal power plant in some other city, state, or foreign country, if you GIVE them money to build a new power plant, the money will be much better spent there than building a biochar plant big enough to compensate for the coal power plant. Even if they object to loosing all those coal mining jobs, offer to buy all their coal production and rebury it. That sounds wasteful, and stupid, right? But it's less wasteful than burning the coal at a 37% efficient utility scale power plant, then producing biochar to compensate at a presumably even worse efficiency.   

       //it's a bit like arguing that no-one should fight fires so long as there are arsonists, isn't it?// No because you can't pay arsonists to stop setting fires. I haven't heard of anyone who wants to keep coal power plants in operation for any reason besides economics. If you offer them enough money to switch, they will. Okay, maybe North Korea would be resistant, but if you can get the money to them in some way that they can save face and brag about their new modern power plants, I'm sure you could make that work too.
scad mientist, Oct 19 2019
  

       // maybe North Korea would be resistant, //   

       Not if you offered them free nuclear powerplants...
8th of 7, Oct 19 2019
  
      
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