FIG. 1 is a top perspective view of a first embodiment of a concrete building block, according to the new design;
FIG. 2 is a front view of the embodiment of FIG. 1
FIG. 3 is a rear view of the embodiment of FIG. 1
FIG. 4 is a right side of the embodiment of FIG. 1
FIG. 5 is a left side of the embodiment of FIG. 1
FIG. 6 is a top plan of the embodiment of FIG. 1
FIG. 7 is a bottom plan of the embodiment of FIG. 1
FIG. 8 is a bottom perspective of the embodiment of FIG. 1
FIG. 9 is a top perspective of a second embodiment of a concrete building block, according to the new design, the portions shown in broken lines forming no part of the claimed design;
FIG. 10 is a front view of the embodiment of FIG. 9, the portions shown in broken lines forming no part of the claimed design;
FIG. 11 is a rear view of the embodiment of FIG. 9, the portions shown in broken lines forming no part of the claimed design;
FIG. 12 is a right side view of the embodiment of FIG. 9;
FIG. 13 is a left side view of the embodiment of FIG. 9;
FIG. 14 is a top plan of the embodiment of FIG. 9, the portions shown in broken lines forming no part of the claimed design;
FIG. 15 is a bottom plan of the embodiment of FIG. 9, the portions shown in broken lines forming no part of the claimed design; and,
FIG. 16 is a bottom perspective of the embodiment of FIG. 9, the portions shown in broken lines forming no part of the claimed design.