If you put the concrete in so that water does not pool around the base, a little higher around the pole and then tapering away, that helps prevent rotting. From what I understand, pooling water, water staying on the post, causes the rot.
Well, I was referring to at ground level where oxygen and moisture do their "thang." I don't know, just stuff I remember from researching the crap out of this over a year ago. I also think that as the concrete dries it shrinks as does the wood as it dries out. This creates a little gap all the way around the post inside the concrete...if that makes sense.
Absolutely, which is why local codes here (and most I gather) recommend for putting support posts (for a deck for instance) above ground on a sono tube attached with an isolation bracket to keep the wood away from direct contact with the concrete (which will draw and wick moisture).
