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The important thing here is that it only recycles concrete. Most of the 7.5% emissions are from new concrete constructions - new roads and new buildings - as we

The important thing here is that it only recycles concrete. Most of the 7.5% emissions are from new concrete constructions - new roads and new buildings - as we increase the total concrete in use. Very little is from old buildings/roads being destroyed and then replaced by something else. This will make a small dent in the 7.5% at scale.

marcosdumay 2y ago
Once you solve energy producing and handling, 100% of the remaining is composed of tiny little problems. This one is large enough for several companies to make a living. What means it's large enough to care about.
s1artibartfast 2y ago
I dont understand your point. Are you saying there isnt enough recyclable concrete to meet the demand for new construction? If we create half as much concrete waste as demand, that 7.5% could drop by half.
- trimethylpurine 2y ago
  Home Depot seems to suggest that old concrete is already in high demand. If we need it for roads and we can't get it because concrete is more valuable, now we have to go find road building materials. Is the manufacture of road building materials cleaner than concrete? https://www.homedepot.com/c/ah/how-to-dispose-of-concrete/9ba683603be9fa5395fab90139b31d64 https://www.homedepot.com/c/ah/how-to-dispose-of-concrete/9b...
  - s1artibartfast 2y ago
    I dont think that suggests there is a high demand for used concrete. It does however highlight the fact that there may be insurmountable transportation and handling costs for recycled concrete. It is hard to imagine it being cost effective to transport it to recycling centers.
    - XorNot 2y ago
      But it's already transported. You can't demolish an old concrete structure and just leave the rubble there. Old concrete is already moved to sites to crush it down to gravel for re-use in other applications. The issue is whether the extra transport would offset any benefits - which I'd say is unclear. i.e. even if you had to truck this stuff to ports and put it on ships...that could be worth it, because we already truck every component of concrete around.
      - szvsw 2y ago
        Using demolished concrete rubble in roads is pretty much the lowest form of recycling possible. Up-cycling it so you can make new cement and ultimately new concrete which can be used structurally at a huge carbon advantage is far more valuable - most certainly from a carbon perspective and likely from a financial one as well.
        baq 2y ago
        So what will they use for roads if they run out of rubble? It has to come from somewhere?
        aDyslecticCrow 2y ago
        Road grit has basically no constraints. They put in whatever is cheap to dilute the expensive cement or asphalt as much has possible. Old concrete is used because it's cheap, not because it's special in some way. If old concrete can be turned into new cement, that is extremely valuable compared to using it as grit. There are some logistics and energy questions, though. Transporting old concrete to the nearest steel plant could be too expensive to be worth it. And arc-furnace steel plants are still the exception, not the rule.
        trimethylpurine 2y ago
        My question about these things is always, "what are we not thinking about?" There's a lot more to environmental responsibility than just carbon. Killing all the fish to reduce carbon isn't an answer. Of course we're not talking about doing that, but aren't we? How do we know? History tells us that government has repeatedly destroyed ecosystems while trying to repair or preserve them. The Grand Canyon, African elephant, countless small lakes and canyons around the US. All of these were well meaning projects to preserve, protect, and repair ecosystems. Responsible environmentalism is far more important than reducing carbon, is my point. So let's do both by asking questions.
  - kragen 2y ago
    old concrete is not in high demand. unfortunately, when i try to follow your link it just says 'fuck you, wetback scum', like every home depot page, so i'm not sure what your evidence is. are they offering you money for your old concrete? how much are they paying? something like 15% of the material that gets carted to landfills is old concrete generally speaking, old concrete is used in new concrete as (very) coarse aggregate. alternative coarse aggregate is mostly angular crushed stone, like the track ballast you see around railroad tracks. this is made by dynamiting deposits of limestone, granite, or basalt and feeding it through a rock crusher. while this sounds violent and energy-intensive, it's nothing compared to running a cement clinker kiln. most of the cost of coarse aggregate is from the cost of shipping it, not the cost of the energy needed to crush it; as wp says > Large stone quarry and sand and gravel operations exist near virtually all population centers due to the high cost of transportation relative to the low value of the product. Trucking aggregate more than 40 kilometers is typically uneconomical
    - CyberDildonics 2y ago
      Every link to homedepot.com calls you a racial slur?
      - defrost 2y ago
        It rejected my advances as a corked hat wearing kangaroo chaser ... it appears to be heavily geofenced and insular.
        VagabundoP 2y ago
        It rejected me like the potato eating stout drinking bare knuckle fighter that I am.
        defrost 2y ago
        mar ná beidh ár leithéidí arís ann
  - szvsw 2y ago
    Putting old concrete into roads loses almost all of its value and is a pretty atrocious form of downcycling; notice that the linked article is literally about “disposing” of concrete, not re-using it meaningfully. Most of concrete’s primary use case is as a structural material in buildings/infrastructure - beams, columns, slabs, etc, and we unfortunately have very little by way of re-using concrete structurally, partly due to demolition processes, documentation, rebar etc etc. While pre-cast concrete is potentially more up-cyclable, again, it’s not really designed for disassembly, re-assessment, etc, and there are very few actual use-cases/projects that have done anything of the sort, though some very cool research is being done on this at places like MIT and EPFL, including novel pre-cast concrete systems specifically designed for dis-assembly and re-use. Part of what makes the article and methodology linked here interesting is that it a) uses waste heat which b) is already theoretically able to come from renewable sources and c) can be used to to support manufacturing of structural components further upstream in the lifecycle of cement/concrete.
    - trimethylpurine 2y ago
      >Putting old concrete into roads loses almost all of its value Because roads can be made from something cleaner? If so, what, and why aren't we already using that something? Value wasn't really the question. Environmental care costs more. It typically means doing something that is in opposition to monetary value in order to make gain towards an environmental goal. Although, rarely, those are also in alignment to be mutually beneficial. Is this such a rare case? I'm skeptical.
      - szvsw 2y ago
        By value, I meant, broadly, engineering/environmental value, not financial. Its value as a material from an engineering perspective is that it (a) functions fantastically in compression and with the addition of (usually) rebar, it can function in tension and bending as well, and (b) it is generally speaking easy and cheap to build structures (of all sorts) with it. This comes from a beautiful interaction of materials - cement, sand/aggregate, steel - all working in concert together. In fact, turning concrete into gravel on roads does precisely what you suggest is a bad thing (and which I agree is bad!) - pursing an economically valuable form of recycling which is less environmentally valuable than the significantly more challenging pathways towards proper structurally valuable reuse. All sorts of things can go into aggregate for roads: various forms of sand, stone, concrete, etc. anything you can make gravel out of really. If you can instead somehow reclaim the concrete and/or the cement within the concrete for structural use rather than use as aggregate, you can displace more carbon emissions by preventing the manufacture of new cement/concrete.
colechristensen 2y ago
One of the problems with calculating CO2 emissions from concrete is the process involves cooking off the CO2 out of a carbonate mineral, but when you actually use it to construct something, the chemical reaction to make it involves pulling that same CO2 back out of the atmosphere into the concrete as it cures. A big chunk of it in the first few days of curing, and in theory all the rest in a long tail of curing which takes decades (in practice not actually all of it). So how do you account for this – temporary – CO2 emission when doing your calculations? Often it depends on the story you're trying to tell... lying with statistics and all.
- kragen 2y ago
  this is true of lime cement, but it is not true of portland cement. portland cement absorbs much, much less carbon dioxide from the atmosphere than the lime used to make it released when it was calcined. (i think the figure i heard was 15%?) this is one of the reasons that green building promoters are advocating a return to lime cement for cases where it's applicable

marcosdumay 2y ago

Once you solve energy producing and handling, 100% of the remaining is composed of tiny little problems. This one is large enough for several companies to make a living. What means it's large enough to care about.

s1artibartfast 2y ago

I dont understand your point. Are you saying there isnt enough recyclable concrete to meet the demand for new construction? If we create half as much concrete waste as demand, that 7.5% could drop by half.

trimethylpurine 2y ago
Home Depot seems to suggest that old concrete is already in high demand. If we need it for roads and we can't get it because concrete is more valuable, now we have to go find road building materials. Is the manufacture of road building materials cleaner than concrete? https://www.homedepot.com/c/ah/how-to-dispose-of-concrete/9ba683603be9fa5395fab90139b31d64 https://www.homedepot.com/c/ah/how-to-dispose-of-concrete/9b...
- s1artibartfast 2y ago
  I dont think that suggests there is a high demand for used concrete. It does however highlight the fact that there may be insurmountable transportation and handling costs for recycled concrete. It is hard to imagine it being cost effective to transport it to recycling centers.
  - XorNot 2y ago
    But it's already transported. You can't demolish an old concrete structure and just leave the rubble there. Old concrete is already moved to sites to crush it down to gravel for re-use in other applications. The issue is whether the extra transport would offset any benefits - which I'd say is unclear. i.e. even if you had to truck this stuff to ports and put it on ships...that could be worth it, because we already truck every component of concrete around.
    - szvsw 2y ago
      Using demolished concrete rubble in roads is pretty much the lowest form of recycling possible. Up-cycling it so you can make new cement and ultimately new concrete which can be used structurally at a huge carbon advantage is far more valuable - most certainly from a carbon perspective and likely from a financial one as well.
      - baq 2y ago
        So what will they use for roads if they run out of rubble? It has to come from somewhere?
        aDyslecticCrow 2y ago
        Road grit has basically no constraints. They put in whatever is cheap to dilute the expensive cement or asphalt as much has possible. Old concrete is used because it's cheap, not because it's special in some way. If old concrete can be turned into new cement, that is extremely valuable compared to using it as grit. There are some logistics and energy questions, though. Transporting old concrete to the nearest steel plant could be too expensive to be worth it. And arc-furnace steel plants are still the exception, not the rule.
        trimethylpurine 2y ago
        My question about these things is always, "what are we not thinking about?" There's a lot more to environmental responsibility than just carbon. Killing all the fish to reduce carbon isn't an answer. Of course we're not talking about doing that, but aren't we? How do we know? History tells us that government has repeatedly destroyed ecosystems while trying to repair or preserve them. The Grand Canyon, African elephant, countless small lakes and canyons around the US. All of these were well meaning projects to preserve, protect, and repair ecosystems. Responsible environmentalism is far more important than reducing carbon, is my point. So let's do both by asking questions.
- kragen 2y ago
  old concrete is not in high demand. unfortunately, when i try to follow your link it just says 'fuck you, wetback scum', like every home depot page, so i'm not sure what your evidence is. are they offering you money for your old concrete? how much are they paying? something like 15% of the material that gets carted to landfills is old concrete generally speaking, old concrete is used in new concrete as (very) coarse aggregate. alternative coarse aggregate is mostly angular crushed stone, like the track ballast you see around railroad tracks. this is made by dynamiting deposits of limestone, granite, or basalt and feeding it through a rock crusher. while this sounds violent and energy-intensive, it's nothing compared to running a cement clinker kiln. most of the cost of coarse aggregate is from the cost of shipping it, not the cost of the energy needed to crush it; as wp says > Large stone quarry and sand and gravel operations exist near virtually all population centers due to the high cost of transportation relative to the low value of the product. Trucking aggregate more than 40 kilometers is typically uneconomical
  - CyberDildonics 2y ago
    Every link to homedepot.com calls you a racial slur?
    - defrost 2y ago
      It rejected my advances as a corked hat wearing kangaroo chaser ... it appears to be heavily geofenced and insular.
      - VagabundoP 2y ago
        It rejected me like the potato eating stout drinking bare knuckle fighter that I am.
        defrost 2y ago
        mar ná beidh ár leithéidí arís ann
- szvsw 2y ago
  Putting old concrete into roads loses almost all of its value and is a pretty atrocious form of downcycling; notice that the linked article is literally about “disposing” of concrete, not re-using it meaningfully. Most of concrete’s primary use case is as a structural material in buildings/infrastructure - beams, columns, slabs, etc, and we unfortunately have very little by way of re-using concrete structurally, partly due to demolition processes, documentation, rebar etc etc. While pre-cast concrete is potentially more up-cyclable, again, it’s not really designed for disassembly, re-assessment, etc, and there are very few actual use-cases/projects that have done anything of the sort, though some very cool research is being done on this at places like MIT and EPFL, including novel pre-cast concrete systems specifically designed for dis-assembly and re-use. Part of what makes the article and methodology linked here interesting is that it a) uses waste heat which b) is already theoretically able to come from renewable sources and c) can be used to to support manufacturing of structural components further upstream in the lifecycle of cement/concrete.
  - trimethylpurine 2y ago
    >Putting old concrete into roads loses almost all of its value Because roads can be made from something cleaner? If so, what, and why aren't we already using that something? Value wasn't really the question. Environmental care costs more. It typically means doing something that is in opposition to monetary value in order to make gain towards an environmental goal. Although, rarely, those are also in alignment to be mutually beneficial. Is this such a rare case? I'm skeptical.
    - szvsw 2y ago
      By value, I meant, broadly, engineering/environmental value, not financial. Its value as a material from an engineering perspective is that it (a) functions fantastically in compression and with the addition of (usually) rebar, it can function in tension and bending as well, and (b) it is generally speaking easy and cheap to build structures (of all sorts) with it. This comes from a beautiful interaction of materials - cement, sand/aggregate, steel - all working in concert together. In fact, turning concrete into gravel on roads does precisely what you suggest is a bad thing (and which I agree is bad!) - pursing an economically valuable form of recycling which is less environmentally valuable than the significantly more challenging pathways towards proper structurally valuable reuse. All sorts of things can go into aggregate for roads: various forms of sand, stone, concrete, etc. anything you can make gravel out of really. If you can instead somehow reclaim the concrete and/or the cement within the concrete for structural use rather than use as aggregate, you can displace more carbon emissions by preventing the manufacture of new cement/concrete.

colechristensen 2y ago

One of the problems with calculating CO2 emissions from concrete is the process involves cooking off the CO2 out of a carbonate mineral, but when you actually use it to construct something, the chemical reaction to make it involves pulling that same CO2 back out of the atmosphere into the concrete as it cures. A big chunk of it in the first few days of curing, and in theory all the rest in a long tail of curing which takes decades (in practice not actually all of it). So how do you account for this – temporary – CO2 emission when doing your calculations? Often it depends on the story you're trying to tell... lying with statistics and all.

kragen 2y ago
this is true of lime cement, but it is not true of portland cement. portland cement absorbs much, much less carbon dioxide from the atmosphere than the lime used to make it released when it was calcined. (i think the figure i heard was 15%?) this is one of the reasons that green building promoters are advocating a return to lime cement for cases where it's applicable