Question

Red Oak #15  

Red Oak #18   These are photos of roots/base of tree

Answer
It looks like the tree is dying--the foliage is thin and sparse looking. I would recommend that you take the tree down.You can try fertilizing it and this might give it some life. But I would not expect much. I could not tell what is damaging the tree from the photos. But it looks like it has a problem. It really would take a on the ground visit to ID the problem. You might call the State Forestry agency and ask one of their Foresters to come take a look. This is a free service in most states. Sorry!