[TowerTalk] Rebar base for new 18HT installation?

[Patrick Greenlee]

In general, for standard mixes, as concrete cures it achieves 90% of its 
final strength in 28 days.  Depending on the safety factor inherent in your 
design, your concrete may be adequately cured sooner than that. Keeping the 
concrete wet as it cures is a good thing.  In summer it is a good idea to 
use a water mist to keep the concrete from overheating due to its heat 
production.  In winter at below freezing temps the heat keeps the concrete 
from freezing but may require straw or other insulation over it to keep more 
heat in.

If you get professional help in pouring concrete beware the inclination of 
the concrete guy to add too much water.  More water makes the mix runny and 
super easy to pour but reduces the strength of the final product.  Stiffer 
mixes retain more of the theoretical strength of that mix. Sometimes 
concrete is referred to as 5 bag or 6 bag or...  This is the number of bags 
of concrete added per cubic yard.  You may also hear concrete quality 
related in PSI as 4000 PSI or 5000 PSI concrete or...

There is also "slump."  A conical cup is filled and dumped out to see how 
much the test sample slumps.  Less slump is a stiffer mix.  Too much slump 
and your final product is not as strong as it would have been if it slumped 
less.

Concrete design engineers specify the desired/required mix and slump but if 
too much water is added so the concrete can be "poured" rather than having 
to be "placed" the strength will be compromised.

There is a way to make concrete more mobile and easy to pour without 
reducing the final cure strength and that is to add a water reducer 
plasticizer.  These work well but have a short pot life so they need to be 
added shortly before pouring the concrete.

Patrick AF5CK





-----Original Message----- 
From: Tom Anderson
Sent: Monday, January 21, 2013 2:10 PM
To: towertalk at contesting.com ; Allen Brier N5XZ
Subject: Re: [TowerTalk] Rebar base for new 18HT installation?


Allen:

I would use some extra rebar if its possible.

When I poured the base fpor my W51 crank up tower I put some extra sections 
of rebar in the hole, usually attached to the base.  You can buy pre-cut 
rebar at most home improvement centers like Lowes or Home Depot.  I just 
used the same twisted wire recommended by folks who poured streets made of 
concrete.  I also used a heavier mix of concrete than what was specified.  I 
used what they call "6 sack mjix" suposedly the same mix they use in pouring 
interstate highway bridges.  My W51 base is still there, no cracks and 
nothing wrong with it either.

Also, while the base is curing, take a hose a lightly sprinkle the concrete 
top and sides several times a day for a week or more. Be sure and do it 
lightly, no deluges.  Curing concrete is exothermic and gives off heat while 
curing and the water will help the concrete cure evenly.  I did it with mine 
and so far no cracks in the base installed in 1992, etc.  I let my base cure 
for a month before attaching the tower to it and pulling it up.

Hope that helps.

Tom, WW5L


--- On Mon, 1/21/13, Allen Brier N5XZ <n5xz at earthlink.net> wrote:

> From: Allen Brier N5XZ <n5xz at earthlink.net>
> Subject: [TowerTalk] Rebar base for new 18HT installation?
> To: towertalk at contesting.com
> Date: Monday, January 21, 2013, 11:19 AM
> I'm wondering if I need to install a
> rebar base for my new 18HT tower, or go with the standard
> "base tube assemblies" per the installation manual. The
> manual does state: "For extra security, steel reinforcing
> rods can be added to the base before the concrete is
> poured."
>
> Tower will be installed in sandy soil (Texas Gulf Coast) and
> I am not currently planning to guy it.
>
> Recommendations from the group?
>
> Allen Brier N5XZ
> _______________________________________________
>
>
>
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