[TowerTalk] Tower base concrete work

[K7LXC at aol.com]

In a message dated 5/6/03 7:36:59 AM Pacific Daylight Time, 
davidgreer73 at yahoo.com writes:

> Can an
>  almost concrete-work novice (me) expect success in
>  pouring the base and doing the finishing work of
>  getting it all level, etc. for the T-base? Anything to
>  watch for in particular?

    Well, it's not brain surgery so you can't screw up too badly.

    Get a backhoe or other piece of equipment to dig the hole. I always like 
to assemble the rebar cage on the ground and then have the backhoe lift it 
into the hole; the danged thing might weigh a couple of hundred pounds so you 
can't really do it yourself. 

    BTW I don't care for the typical UST hole designs - they're narrow and 
deep and difficult to dig. I use a PE to re-design it for me so that it's 
shallower and wider; it might use more concrete but it's much easier to dig 
and deal with. 

    I always have the anchor bolts and base fixture available before the 
tower arrives - that way you can pour the base and then the base is ready for 
tower installation when it arrives. In any case, bolt the anchor bolts to the 
T-fixture or template and take them to your local welding shop. Have them 
weld some scrap metal pieces to the anchor bolts top and bottom so they don't 
move when tying the anchor bolts to the rebar cage and pouring. That way you 
don't have to have the T-fixture attached since it's real heavy and a pain to 
deal with when the anchor bolts are attached. Dropping the tower onto these 
anchor bolts is a slamdunk fit. 
>  
>  I will buy a dense grade mixture of concrete, as per
>  Sam's advice the first time, and have it delivered.
>  The installation site is on a slight incline so I have
>  to build the concrete form to compensate.
>  
    Concrete is HEAVY so do a real substantial job of building and anchoring 
your form. You don't want it bursting just as you get finished pouring. Use 
several wooden stakes or pieces of rebar to hold it in position. 

>  I have studied several web sites showing tower
>  installations. K4ZZR's site is particularly good. But,
>  as he says on his site, any mistake is one you have to
>  live with forever when it involves 4 cubic yards of
>  concrete. 

    In this case, it will be "cast in concrete" - hi. As long as the anchor 
bolts stick up above the top of the form an adequate amount, you're good to 
go.

>  Obviously, the leveling nuts under the
>  T-base can make up for some imperfection in how level
>  one gets the top of the base once poured. How much
>  compensation can those nuts provide? 
>  
    Lots. Almost level/plumb is fine - the tower can be leveled a bunch (a 
couple of inches) with the nuts. I tape the threads so that when I take the 
tape off, the threads are clean and usable as opposed to having concrete in 
the threads. 

    Use a concrete vibrator from your local rental shop to move the concrete 
around in the hole. Use it sparingly as it'll vibrate the rock to the bottom 
of the hole if used too much. 

    You can finish the top of the pour or leave it rough - the tower doesn't 
care. 

    You need a NON-SHRINK GROUT to go between the top of the concrete and the 
bottom of the base fixture. Mix it so it's pretty stiff and pack it in the 
whole space. It's supposed to take some of tower forces along with the anchor 
bolt nuts so it is a structural part of the installation and required per the 
manufacturer's specs. 

    I have trouble finding non-shrink grout and buy it from my local masonry 
supply house. The big box hardware stores don't typically have it and the 
clerks have never heard of it. It's less than ten bucks a bag so it's not 
expensive but you need the right stuff. 

Cheers & GL, 
Steve      K7LXC
TOWER TECH -
Professional tower services for commercial and amateur