They were expansion joints. Replace them with redwood, fiberboard, or
even tar.

Rick

AndyPaul wrote:
perhaps not entirely a garden question, but it is near my garden. i have wood
barriers between slabs of sidewalk concrete, not the fiber boards, but actual
wood. i have some that are rotting away from the elements and bugs. what are
those pieces of wood call, or better, what do i look/ask for at home depot?

thanks for any help

andrew