The main problem with concrete screws loosening is usually over-tightening, which introduces an angular stress (twist) into the anchor, steel being slightly flexible, which slowly untwists itself after use, leaving it loose next time. I usually tighten it up fully to make sure the thread is cut, then turn it back a quarter-turn to remove the twist and then tighten it back up 'just enough'. Generally it'll stay in place after that. We used fixed rigging on these every weekend for three years and never had one loosen after the procedure above. And as Mark points out, there is nowhere for resin to go, as the screw fills the hole completely.