I was concerned that the expansion board used on my concrete drive and sidewalk had rotted out and this Sashco Pre-Caulking Filler Rope Backer Rod Roll, 50' Length x 1" Width, Grey allows me to add a filler and seal the gap to prevent water from getting into the gap and damaging my concrete's base material and result in expensive repairs in the future.  This works well and will last a long time.