Need a leveling/patching compound

I have an outdoor patio slab, concrete and partially sheltered. I need to level out and waterproof a number of depressions in the concrete where 8"x8" wooden posts are imbedded in the concrete. The depressions are about 1" deep and 1 sqft wide.
Since the wood and the concrete have slightly different expansions, I would need a material that is not completely brittle. I am trying to avoid water infiltration around the post and potential for dry rot.
Epoxy, what kind? Dense urethane Foam? Cementitious patch with caulk around wooden posts?
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