Jack,
Unfortunately, I cannot provide you with a legitimate answer to your question via this electronic venue. Your questions require on-site evaluation. What I can tell you is that plugging the holes (foam, concrete, etc.) is generally NOT recommended - cause more harm than good. I would seriously question anyone who recommends such treatment. Generally, we do nothing for such "holes", and allow the tree to compartmentalize the wound naturally.
Yes, pouring concrete around the base of a tree is going to cause problems. However, an on-site evaluation would be needed for comments and suggestions :-)
Therefore, you will need to contact a professional tree care specialist (e.g., certified arborist). Your local yellow pages should contain a list of certified arborists.