> For steel the possibilities are hydrogen or electrolysis, both are being tested by some companies.
We already have steel recycling plants today that shift ~100% of emissions to thermal energy source, with a hot enough nuclear reactor (G4 MSR, maybe something in fast spectrum, maybe fusion) you can effectively eliminate the majority of steel emissions globally.
> Cement is the biggest "we don't really have any good alternative, at least not any time soon"-issue.
Bill Gates posted about this recently [1,2]
[1] https://www.gatesnotes.com/Energy/Buildings-are-good-for-peo...