I claim the ornamental design for a concrete block mold, as shown and described.
FIG. 1 is a perspective view of a concrete block mold.
FIG. 2 is a front view of the divider plate of FIG. 1, shown apart from the surrounding walls of the concrete block mold for clarity of disclosure.
FIG. 3 is a top plan view of the concrete block mold of FIG. 1.
FIG. 4 is a rear view of the divider plate of FIG. 1, shown apart from the surrounding walls of the concrete block mold for clarity of disclosure; and,
FIG. 5 is a side view of the divider plate of FIG. 1, shown apart from the surrounding walls of the concrete block mold for clarity of disclosure, the opposite side being a mirror image thereof.
The dashed lines in the drawings represent unclaimed portions of the walls of the mold and form no part of the claimed design.