First concrete is considerably less dense than granite, so you need a larger mooring block.

Second, cement takes a lot of energy to make, granite is already here.

Third, it takes less than an hour to change a staple on the mooring barge at the mooring location starting with straight bar stock. If you use a pre-bent staple the process takes less than 30 minutes. You only need a sledge to knock the old staple out of the block. You don't need a sledge to put the new staple in.

I will stick with my granite block