How was this concrete slab made?

[Thomas_Blekinge]

The flooring is above a basement space and above it is a deck.

Are the rectangles traces of form boards? It's a bit structured and the dimensions are 57x204 cm. Were there such boards in the 80s-90s?
Or is the flooring made up of individual concrete slabs with these dimensions? How do they connect if so?

 

[Plupp 405730]

Probably, some form of board has been reused, which has been cut from a 1200 wide board from the beginning..
Concrete companies that work with mold casting save and reuse as much of the material as they can..

 

[Thomas_Blekinge]

But why didn't they take the full width of 1200 mm then?

 

[Plupp 405730]

May be easier for work environment reasons to handle narrower boards as they will be torn down with...

 

[Thomas_Blekinge]

Hard to believe there were such rules in the 80/90s.
They must have had other plates/records underneath as the supporting part and then they placed something like tretex boards on top that left these patterns? Mysterious!