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Hi AD,
I also had to create a pier approx. 3m tall. I dug a 2 cubic metre hole (=1.26m/side) and filled it with steel reo and concrete. (I achieved 1% steel by volume). I figured that I could not pour the concrete column at the same time, since the concrete might flow out the bottom of the 457 mm dia formtube. The professional advice that I received was that to get a good bond between the concrete block and the column (apart from using reo bar), roughen up the top surface of the block (where the column will be later poured) and use bondcrete on it as well. I used a wire brush to roughen the surface. I poured the column a week or two later and it is as "solid as". I used 8 off 20mm reo bars in the column, and these were a long "L" shape and fixed into the block both at top level and halfway down the block.
The concrete column stands about 2.2 m above the block, and I have used a steel pipe, approx. 1 metre long, on top of the concrete pier.
I'm happy to supply more details if you wish, and I've attached a few pics.
Cheers, Chris
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