I own a office/warehouse complex with metal expansion material instead of the redwood or ceder expansion joints. The complex is about 30 years old but it has been kept up pretty well. When it rains water seeps through the expansion joints and gets under the slab. When a heavy vehicle drives over the joint water and soil come out of the joint. After a period of time the concrete settles a little because the soil washes out underneath. I use a piece of equipment to fill the expansion joints which is a hot melt tar pit. It pours hot tar in the cracks like you see done on highways. The problem is that the tar dries out eventually and cracks allowing water to get through the tar. Any suggestions as to how to get either the tar to stick or a material I could use to seal the expansion joints? When I get too much wash out the concrete breaks up and I have to replace the concrete in that area.