The concrete patio at my father's house in Albuquerque, NM was built approx. 50 yrs ago. The redwood expansion joints have rotted, and are "raising up" above the concrete surface, creating a tripping hazard. I have removed the offending boards. I am trying to decide what is the best material to use to allow for expansion, but not present a tripping or slipping hazard for my parents who are in their late 80's.