I have a small cabin that has half of it supported by treated 6x6 posts. The posts are under the soil by about 2 feet. They are rated for soil contact but when I replaced 1 post that was split it seems that what was underground was looking a little extra worn.I was thinking of digging out the posts and forming them inside concrete to above grade. Is this a good thing to do in regards to putting concrete around wood. I heard it can rot it out also. If not any suggestions?

I used 4x4 treated posts in concrete for my decking but put a heavey coat of roofing tar on the portion of the posts that contacted the concrete. Let it dry for a few days too. Deck and posts are now 20 years old and solid as a rock!