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?
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.
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.
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.
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.
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.
What? It’s extremely unclear what your concrete (ha) questions are. Your questions (while clearly well-meaning and well-intentioned, and probably from a perspective that most people in this discussion generally agree with, including myself) seem generally too broad and disconnected from the more detailed discussion of materials. You mentioned you can’t see the other side of the argument, but it’s unclear what exactly you are arguing for or against in relation to reclaiming cement from concrete versus down cycling concrete into roads. It’s unclear to me what environmental concerns you are talking about that directly relate to the discussion above.
There are all sorts of ecological/environmental/social concerns at various stages of the concrete lifecycle, but certainly at a global scale one of the most significant effects is the contribution to climate collapse associated with cement production for concrete (around 10% of global emissions). Concrete however is certainly not going away though as it is one of the primary structural materials in most of the world, especially in parts that are rapidly expanding the building stock, and so doing everything we can to mitigate the resulting carbon emissions is essential, as those emissions pose a dire threat…
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.
>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.
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.
It's interesting that the alternative things you listed that can go into roads are all incredibly expensive and also produce high amounts of carbon. I happen to live in a mining capital. Looking around, I'm convinced that there is nothing clean about sand, stone, concrete, or anything else they make gravel out of. Hence my skepticism.
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
no, i am saying that the only real market for old concrete today is to replace some of the crushed stone used in making new concrete, for example for making roads, but that old concrete is in so little demand for this purpose that most of it ends up in the landfill
it's possible i'm misunderstanding, but you seem to be asking whether making crushed stone is more or less environmentally damaging than recycling old concrete. the answer is that neither of them results in significant environmental damage in itself, but trucking them to construction sites does
also can you elucidate which goals you meant to say were usually mutually exclusive? it isn't clear from context
also, i asked two questions in my previous comment that you haven't answered: are they offering you money for your old concrete? how much are they paying?
I meant that we typically need to choose between two goals. Profit and environmentalism.
They are offering money. As for how much, I imagine it depends on the area. All things gravel and stone are expensive at the moment. People are getting caught stealing sand, that's the world we're in today.
i see, thanks! it sounds like you haven't attempted to take them up on the offer
it's not true that gravel, crushed stone, and sand are expensive, by most definitions of 'expensive'. they cost pennies per kilogram. yes, that's enough for people to make a profit from stealing
at greater length, what it says is 'Access Denied
You don't have permission to access "http://www.homedepot.com/c/ah/how-to-dispose-of-concrete/9ba..." on this server.', as it always does when you access a homedepot.com page from argentina; i summarized it for your benefit
https://www.homedepot.com/c/ah/how-to-dispose-of-concrete/9b...