Greetings Dennis:
No, concrete is definitely not appropriate for sealing a tree. Being a traditional dirt-forester and not not a concrete-forester like some of my former classmates, I often rely on them for their urban forestry and arboriculture knowledge.
Here is the standard recommendation when it comes to tree sealants, "Do nothing, leave it alone, and let the tree compartmentalize on its own; and the use of sealants is generally not recommended, nor warranted."
Best of luck!