I hope I am explaining this properly.

My front door has a metal plate installed underneath the door, that is
mounted to the floor. I call it the threshold, and I hope that is the
proper term for it. Anyway, last year I mixed some powdered concrete
mix, and pushed it in underneath the threshold.

Now the cement is cracking, and I removed it in hopes of putting
something else besides concrete underneath the threshold plate. This is
the plate everyone walks on when entering my home.

Does anyone have some ideas for me?

Many thanks.

Kate