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.