[TowerTalk] Can I incorporate existing tower base

[Alan NV8A]

On 04/16/08 10:43 am Mike wrote:

> I have an existing stand alone base for my US Tower MA-40.  I would like to
> incorporate my existing 3 x 3 x 4 foot base.  The tower I would like to put
> up is the US Tower TX-455 which requires a 5 x 5 x 6 base and 6 cubic feet
> of concrete.
 >
> So, the question is could I incorporate the existing base by digging around
> it maybe an extra two feet and go deeper to add the necessary mass of
> concrete to get to the required 6 cubic feet needed and adding more re-bar.
> 
> It is not so much about saving money, because I would have to drill holes
> for the different footprint and epoxy in new bolts.  But it would save
> having another base and having a redundant concrete slap to look at or
> remove.
> 
> I just wonder if Steve or anyone has done this before.


In a former life I worked as a humble soil tester on highway 
construction projects in VK4. From what I read and heard discussed, my 
impression was that if for any reason the pouring of what was intended 
to be a monolithic component (i.e., poured in one go -- no matter how 
many truckloads it took) was interrupted (e.g., through equipment 
failure), there were special procedures to compensate for that: e.g. 
special bonding agents to ensure an adequate bond between new and old. 
But even in that case, the rebar would still have been continuous 
between new and old. My guess would be that at the very least you would 
have to epoxy into holes in the existing slab rebar that would extend 
into the new concrete.

And it just occurred to me: is the concrete used in the existing slab of 
sufficient strength?

In short: consult an engineer.

73

Alan NV8A (long-ago VK4NDV/ZDV, VK4AFE)