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Heating by electricity is not a problem. But both production and setting of concrete chemically produce CO2.

Hydraulic cement does not produce CO2 during setting. Non-hydraulic cement actually consumes CO2 while setting.

Doesn't it essentially just re-absorb the same co2 it emitted when it was made?

Yes. I was replying to parent's comment that concrete produces CO2 when setting, which is clearly not the case for hydraulic cement.