What I like to use for attaching anything to concrete is lead ferrels with a sheet metal screw. I have a hammer drill and it drills perfect holes for the ferrel. The ferrel is pounded into the hole until it is flush with the surface, then the item to be attached is put into position and the screws run in with a power driver. I've use this method for flanges, electrical boxes including service panels and outlet boxes, furring strips, etc.. Holds tight, but easy to remove if necessary. Also inexpensive.