Just my opinion but embedding wood in concrete would be a mistake in at least two ways. Difference in thermal and water expansion, concrete doesn't expand much when wet, wood does swell, twist, and bend to exert considerable force, concrete is hard, brittle and cracks. Second, with the wood encased in concrete it cannot dry as it normally would in air and will encourage rot. I'm not sure what the reason would be for adding the wood, concrete has good compressive strength but posts generally use steel rebar which adds the tensile strength lacking in concrete. Hope it works out for you but as an engineer and mason I'd not do that.