stone rubble columns

When your boss asked you to build these columns did he not explain to you how to do it, or doesnt he know. Its a bit hard to tell by the content of your question. As no one else has given any suggestions, I will tell you how I would do it. Depending on the diameter of the column, and wether they are load bearing you are going to need some good foundations, if we said the column is 600mm/900mm across I would put in some rebar into the concrete, for a circular construction you are going to have to cut your stone, bed your stone on, if you dont want cement joints showing ie, looking like dry laid then back bed the stone. You can probably get to a height of about 900mm depending on your bed size then back fill gently with concrete. You dont want to be going to high as the pressure of your infill concrete will push your wall out. If you have several to work on then do a section on each of them, and continue next day. Your rebar wants to go full height, if using short sections then use tying wire. If this is the wrong description, then you will have to re,edit your post with more info. If this is the right info, and you can do it, ask your boss for a rise this week.

Yes, that is a tried and tested way of getting some additional strength into the column. Be sure to let the stonework set properly before filling with the concrete though.