Fractured concrete - how to repair

When my wood-frame apartment was built 20 years ago, lightweight low-strength concrete about 2" thick was poured on the plywood subfloors in each suite as a fire barrier.
The concrete has now fragmented and fractured in many places and makes crunching noises as the pieces grind against each other when someone walks on the floors.
Would anyone know of a simple and permanent way to rebond or secure the fragments and fractures so that they become a solid slab?
Thanks in advance for your helpful replies.
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I've got a catalog at work that is all about floor repair & maint products.
Gypcrete is not a verys trong product but it is widely used in multi-unit const fro fire & sound proofing.
If installed (mixed) correctly it shouldn't bust up like that but once it does you've got somewhat of a problem on your hands.
Epoxy or polyester resins won't be cheap; depending on amount required you might be in the $'s per ft^2 range. Short of complete R&R you need something to penetrate & consolidate the material.
All depends on cost........R&R might be cheaper
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I wonder if non shrink grout would do it.

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