Durability of hydraulic cement under pool floor

[Sq1873]

Hi,
So I have these spots under my liner where vermiculite seems to have gone (or was never applied properly? not sure). I was thinking filling that in with hydraulic cement following someone's suggestion. I looked a bit into hydraulic cement durability and it seems like it usually isn't a very permanent solution due to it not being very strong structurally. Given that this patch would remain under pressure from the water above, would it be actually better because it is being held in place or worse because it will put strain on it and eventually crack?
If anyone had their pool repaired this way, how long did that fix last?
Thanks!

 

[ajw22]

@jimmythegreek how would you patch a vermiculite floor?

 

[jimmythegreek]

Patch with actual pool vermiculite. If you cant source it mix half Portland half sand. Just damp and tacky like peanut butter not wet like concrete

 

[Sq1873]

Thank you!