Is there anything that common house ants won't burrow through?
The best treatment is to remove the things that attract the ants. If that is your cat's food dish I suspect that eventually, no matter how many cracks you seal up, that the ants will figure out how to come around the end of the slab and over to what they find attractive as a food source. 

So maybe you want to start a regimen with your cat. Put down its food for say half an hour at each feeding and then take it up. Cats can learn to eat on a schedule. But at the same time they will also remind you of the schedule each and every day.