What is Cement Really?

It is basically powdered rocks that you turn into Rocks or boulders or mountain size rocks that are sometimes reinforced with metal for extra strength especially during earthquakes.

How could you replace this industry worldwide with something else?

I suppose you could use 3D Printers with lasers and turn actual dirt into Glass or obsidian instead reinforced with metal pieces too but unfortunately for some uses Glass or obsidian would be too brittle like for bridges and some roads or tall sky scrapers maybe.

So, at least for now I'm not seeing a replacement for Cement in building things worldwide at least at this point (unless people want to move underground) and even then you likely are going to want cement and reinforced concrete in case there are earthquakes while people are living underground too.

So, at present I don't really see a  perfect replacement for cement at this point in time. But, even if you replaced cement with glass or obsidian you are going to have gases that come from using lasers that people might not want to deal with either when you turn dirt into glass or obsidian with lasers.