Infilling Suspended Slab Voids Around Pipes

[JC456]

Does anyone have any details or guidance on filling small voids around services through suspended RC slabs?
other than any fire collars etc what maximum sizes of voids would be suitable with mass concrete infill or particular mortars.
The infill would not be structural as such as the slabs designed with the small rectangular holes as already cast. Just a matter of a suitable infill being used.

 

[DETstru]

I've always seen those filled with some sort of rated firestopping. Sometimes if the opening is too large they use some gauge plate on the bottom to support the material though I'm not sure if that's the "official" way it's supposed to be done.

I don't think I'd be comfortable with putting concrete around the pipes. There's no positive attachment and you're only relying on the bond. Don't get me wrong, you can do a lot with bond, but plumbing lines can move a lot, your building moves, they get bumped into (if exposed), etc. This can degrade whatever chunk of concrete that you've mashed in there.