Could this perhaps be blue concrete?

[Oliver Lindblad]

Hello! I've asked around in my circles about whether this is blåbetong or not and have received different answers. I'm unfamiliar with this area and therefore turn to you. The apartment is being renovated, and I found this space which was an old entrance to the apartment that has been closed off. Could this be blåbetong, perhaps?

 

[GoC]

If it's blåbetong, it's so porous that you can stick a screwdriver into it.
Then it probably doesn't matter much if there is a little blåbetong.

 

[Stefan N]

Looks like slag plates.