A flexible, molded, polymeric grid is embedded in a predominantly concrete mat
comprising a concrete slab having relatively thicker portions defining blocks connected
by relatively thinner portions, along which the concrete slab is breakable. The
flexible grid has two longitudinal edges, two transverse edges, longitudinally
extending members, and transversely extending members, where the longitudinally
and transversely extending members connect the blocks to one another when the concrete
slab is broken along the relatively thinner portions. The longitudinally and transversely
extending members meet at nodes, which are spaced uniformly from one another, both
longitudinally and transversely, except that, along the longitudinal and transverse
edges, each node is spaced more distantly from the nodes nearest to the node. When
the longitudinal and transverse members are disposed in an imaginary plane and
the flexible grid is not stressed, fingers, which are unitary with the grid, extend
from the imaginary plane.