hillpc wrote:
I'm making a home tennis court out of an asphalt paved area. I've
already bought the net and posts. The specified concrete footing for
each tennis net post is a 30" square at the bottom, tapering up over a
height of 42" into an 18" diameter circle at the top. A drawing is at
http://sportsbuilders.org/page.php?id=96&from[]=11&from[]=12&from[]=13&.
Could I use 3/4" plywood to make a form strong enough to contain this
much concrete without blowing out or breaking? I think the bigger job
may actually be cutting out a big enough square out of the asphalt
(32"?) so I can then rent a 30" auger to dig 42" deep, cut the corners
out to a square with a shovel, and then drop the empty form in, and
somehow hold it down while pouring the roughly ton of concrete into
each one. After stripping the form, backfill with dirt and repair the
asphalt. Any suggestions for me? I'm thinking readymix concrete for
the little over 1 cubic yard I need to avoid all that mixing, and it's
probably cheaper than buying eighty 80" bags of concrete mix.

Is there a reason you can't use the hole as the form? I'd use a Dingo
with an 18" auger, then switch to a 12" auger and/or a post hole digger
to finish. That avoids all the problems associated with trying to
backfill, compact the soil, and fix the asphalt (and then fix it again
after the disturbed dirt settles).

If you really want to have fun, you can get a cement mixer attachment
for the dingo. It'll mix and pour 200lb (dry) batches.