You could glue a 3/4 inch block of wood to the concrete with construction glue, then mount the bracket on that.
Or you could use tapcon screws to fasten the bracket directly to the concrete, if there is not enough highth room for the blocks.
Sometimes two screws into a stud, and a dab of silicone works too if you don't want to drill tile or something. If it's a bare slab, you may want to use the blocks to be sure the doors will clear finished floor covering. ( high pyle carpet)
If it's on carpet, glue down a 3/4" wood block. If on concrete hard floor, screw to wall, & glue small block just a little wider (1/8-1/4 ea side) bigger than the pivot guide. Then glue inside & short screws. Screws will work loose, glue don't.
Plywood/MDF/K3 block with Pl or premium 400 to the concrete is the way to go and once the door is in line when they close just put and drop in the bottom track to stop lateral movement. Save fooling around with drill & anchoring into concrete specially if there is in-floor radiant heating in the slab.
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