My concrete driveway butts up against my foundation for about 40 feet in the side and rear. Over the years, movement of one or the other or both has resulted in a large separation... Up to 3 or 4 inches in spots. About ten years ago, I hired somebody to fill it when it wasn't as pronounced, and they used a hardening sand compound. That lasted, but now it needs filled again. Any ideas on how to fill it and with what?