This will make a small dent in the 7.5% at scale.
If we create half as much concrete waste as demand, that 7.5% could drop by half.
https://www.homedepot.com/c/ah/how-to-dispose-of-concrete/9b...
It is hard to imagine it being cost effective to transport it to recycling centers.
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.
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.
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.
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.
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.
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.
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
That it can be made into something more expensive doesn't imply that it is also environmentally sound.
In fact, those are almost always mutually exclusive goals.
My question is about what will be used for roads, and whether acquiring that product will be more environmentally sound.
I'm not immediately opposed to the technology. I'm just at least as skeptical as all scientists should be.
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?
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.
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
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.
this is one of the reasons that green building promoters are advocating a return to lime cement for cases where it's applicable
This one is large enough for several companies to make a living. What means it's large enough to care about.