Jim,
Why fill it with concrete? I think I would fill it with gravel and pour a reinforced slab on top. They should also cut some openings in the old one (above the water table) to permit drainage.
If you pour 4 feet of concrete it will take a long time to cure and will crack sometime in the future. You do not want the surface slab to be a part of that mass.
If, for any reason, you end up needing new walls for the pool, I recommend stainless steel panels that I have worked with on several projects. Unlike many of the gunite jobs that get put in without much of any engineering analysis, these are designed for the specific loads involved.
Richard Hess, S.E.
562 799 9787
-----Original Message-----
From: Jim Wilson [mailto:wilsonengineers@yahoo.com]
Sent: Wednesday, September 19, 2007 5:59 AM
To: seaint@seaint.org
Subject: Swimming pool concrete fillA client intends to fill a 9' deep pool with 5' of concrete to make a wading pool for the elderly. Are there any particular concerns with the mix design to mitigate chemical reactions between pool chemicals and components in the mix? If not, would a simple 3000lb or 4000lb mix suffice? I am thinking that they should place the final 6" in a separate lift to reduce cracking and facilitate finishing.The client expects to have a cold joint around the perimeter that will need to be sealed. They intend to drain and repaint the pool every year, so maintenance of the joint will not be too great of an issue.Jim Wilson, PEStroudsburg, PA