Hi @Ryan1980,
This is a concrete expansion gap which is typically filled with Sika 600ml Concrete Grey Sikaflex 11FC Purform.
If the gap is deep, then you should start by pushing some foam filler rod into the gap. This will stop the sealant from seeping down into the gap and greatly reduce the amount of sealant you'll need to use. You can then apply the Sikaflex 11FC Purform over the filler rod to seal the gap.
These materials are flexible, so they allow the concrete to expand and contract as it would without them, while still sealing the gap from things like leaves, dirt and water, as well as making things look much nicer.
It's not the same scenario, but check out How to fill a joint in a concrete slab for some further guidance.
Let me know if you have any further questions.
Jacob
