I have had a huge ant problem ever since moving into my house a few years ago. Usually, I use Ant B Gone to get rid of it (liquid drops in a tiny red bottle). I found it to be sort of effective...
Now, I also have a brick path and I knew there were a ton of ants under it because I could see all the holes (and the ants).
The absolute best solution for such a situation is the new spray foam they sell now ($6 at Home Depot). It's a can that sprays foam through a tiny nozzle hose that you ram down into the the ant colony.
It is so satisfying.
Sometimes, you spray and the foam comes right out...that's not considered a good hit...
The good hits are when you ram the hose down a hole, press the trigger, and it just keeps on spraying...seconds pass...and then you see the foam pop up another hole a few feet away....then you go "Ahhhh" and get a smoke
This spray doesn't work as well with holes in dirt, though...harder to get the hose into the hole. With bricks, the ants need to make the hole straight for a little bit.