When the boys that I hired built my barn, they used cement but only for a bottom in the holes. They put in about 10" of cement, went to lunch and came bach to set the posts. They would line them up, center them, check for square on the outsides of the posts and then backfill with the dirt, tamping it in as they went along. Posts are solid and there is no place for water to set in around the space that concrete will leave no matter what you do. But they did have to use water to mix with. I might want to mention, these boys also built their own barns this way, and I have seen them and they are still standing