So what will they use for roads if they run out of rubble? It has to come from somewhere?

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.

Curious about the downvote.

Do you believe we should blindly trust corporations not to lobby?

Do you believe that government doesn't respond to lobbying?

Do you believe that good intentions always cause good results when without research and education?

What exactly is there to not like about asking questions?

This is a real request for explanation. I can't see the other side of this argument. From my view, without explanation, I have no choice but to imagine that the downvoter is literally out to produce negative results for human kind and loves money more than all else. Such a person deserves to sit in prison, to my perspective.

Open to hear the other side of the argument.

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…

My question was directed at the downvoter.