Avocados are not particularly destructive as tree roots go, but keeping ANY tree as far as possible from all concrete and masonry is always wise.

Also, avocados are quite thirsty trees. That's one reason Avocados are fairly expensive--the water needed to grow them. You might want to wait until next year and see if the drought finally breaks this fall and winter.

This is quite a good article on the root system of avocado trees, and well worth a read:

avocado root system