It is rather common for slabs to be made lighter by embedding in the concrete pipes (usually either plastic or metal/tin) or actual "pockets" (think of large - usually plastic - largish and squarish containers). Here is a photo of a commercial solution:

https://www.geoplastglobal.com/en/products/slabs/new-nautilu...

There is also an as well already available commercial solution using "balls":

https://www.cobiax.com/intl/produkte/cobiax-el/

similar to the "bubbledeck" technology used in Eindhoven:

https://en.wikipedia.org/wiki/Voided_biaxial_slab

Anyway these are basically an evolution (involution?) of "waffle slabs":

https://en.wikipedia.org/wiki/Waffle_slab