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 -

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-nautilus/ 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/ https://www.cobiax.com/intl/produkte/cobiax-el/ similar to the "bubbledeck" technology used in Eindhoven: https://en.wikipedia.org/wiki/Voided_biaxial_slab 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 https://en.wikipedia.org/wiki/Waffle_slab