I’m not sure if you’ve already seen this, but It looks promising! Cambridge developed a process to reactivate the Portland by sending it through an electric arc furnace to recycle the individual materials in concrete. Their hope is to have a furnace running off of renewables to create a very low carbon material and they’re in the process of scaling it up now.
https://www.nature.com/articles/s41586-024-07338-8
They’re still prototyping the process, but it looks promising.