Drain grate falling to drain on concrete driveway

[fvl2212]

I'm thinking of trying to fix this up on my own. The issue, as you can see in the pictures, is that the edges that the drain grate normally sits on is wearing out, causing this grate to fall into the drain. This issue is slowly starting to show on the other sections as well. 

I'm not too sure what to get between these two

https://www.bunnings.com.au/dunlop-5kg-ardit-rapidset-repair-mortar_p0760262

https://www.bunnings.com.au/dingo-10kg-fast-set-hi-strength-concrete_p0760509

Would appreciate any tips, tricks or insights