Hollow trees should not be filled with concrete.
This huge old maple tree has probably been hollow for many years. Fungi gained access to the heartwood through a wound, and rot set in. Nevertheless, the tree attained an impressive girth and height.
I don't know if the homeowners were aware of the hollow in the tree and its potential to cause damage. They were certainly fortunate that it didn't fall on their house or vehicle. It did fall onto the highway, but luckily no cars were passing at the time.
We didn't have very much wind or rain the day this tree broke, but it was enough to bring the old tree down. I know the homeowners will miss it terribly.
Just for the record, don't ever let anyone talk you into pouring concrete into a hollow tree. When the tree does eventually die and it must be removed, how can you cut up a concrete-filled tree with a chain saw? And besides that, the cement will chafe inside the cavity as the tree moves in the wind. It can accelerate the decay and seriously injure the tree.
Read more -- Tree Cavities: To Fill or Not To Fill