Wouldn't something like BubbleDe
ck be prior-art for that?
The picture in the link shows a slab before
pouring the concrete with plastic balls in between the steel reinforcing meshes
acting as void formers so that less concrete is used.
In general, the
benefit of this kind of system is that the slab will be lighter than if it were
solid concrete yet the flexural strength won't be too much lower than for a
solid slab[1] because the voids are located at the middle of the slab (and hence
the neutral axis), and it is the extreme edges of the section that provide the
most flexural resistance[2] .
This kind of system isn't necessarily
always a win though - a notable disadvantage is a reduction in fire resistance
compared to a solid slab.
I first heard about these in 2005 (and they
probably existed long before then), but we didn't use them for our project
because of the reduced fire resistance - which was a particular concern to that
project, no doubt they are fine in other situations.
[1] - The reduction
in flexural strength will be offset by a reduction in the self-weight of the
slab, and depending on the ratio of self-weight to live loading this reduction
might not be significant.
[2] - This is why steel beams typically have an
I-section profile; that cross-section makes efficient use of the steel used for
the bending resistance it provides. (Castellated sections are an even more extreme example.)
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