Is it acceptable to put deck support posts into the ground with concrete around the posts?

I am concerned about termites, but the builder says the cocrete will protect the wood.

That is how I did mine.

That would be the lazy way of installing the posts. What could happen is water could soak into the wood then freeze (depending where you live) which could crack the concrete. the post will loosen and possibly start sinking into the ground under the concrete.
i would fill the hole with just concrete, and use 12 inches of cardboard tubing above ground to build the concrete up atleast 12 inches above grade. then install a post mounting plate of some kind. I use square plastic platforms that screw onto the bottom of a 4x4 and uses a threaded rod in the concrete and 4x4 to keep it from kicking out.
treated wood will keep away the termites and the concrete will keep away the water. just make sure it's dug below the frost line.

You must dig hole's and they must be below the frost line if you live in a cold climate area and put post holders in the concrete! As for termites, they will build hollow mud tunnels up to where their looking for food and shelter so look for these if they are exposed and also termites like a moist location so try to build in the sun and in a dry location as much as possible!

If there are termites, they will attack the wood above, as well as below, the ground. I always use concrete in the post hole but not for termite control/repelling. It makes the deck structurally sound.

Check with the lumber supplier. Treated wood has changed considerably with the treatment processes in recent years. Some treated lumber is rated "ground contact" and some has "in ground" ratings. Treated lumber is treated to protect against termites; not the acids that concrete creates. We have always dug the post hole and put some dry sack concrete in the hole. It hardens over nite from the ground moisture and then the wood sits on the concrete; not in it. Lots easier to remove if you want to later.

i always dig the hole and fill concrete inside of silo tube. put bracket on top of concrete and attach post to bracket. if post is put inside of concrete, moisture can get between concrete and post. when temp freezes concrete will crack. water between concrete and post can rot the post.

Or you can use post fix, it is much easier

http://www.ultimatehandyman.co.uk/diy/de...

The concrete will do exactly that. It will keep the wood from rotting and will also keep the termites at bay.