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[TowerTalk] AN-W HD-80 in CA, progress rpt. (long)

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Subject: [TowerTalk] AN-W HD-80 in CA, progress rpt. (long)
From: "JC Smith" <>
Date: Sat, 2 Sep 2006 14:16:59 -0700
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Greetings fellow TTers,

The tower project has gone slower than I hoped, but it is progressing.  We
poured 11.5-yards of concrete ($1650) for the foundation last week.
Pictures can be seen at: (Best way to
view is to click on the slideshow button, then you can start and stop and
change the interval between slides.)

In the live and learn (but not the hard way) dept, I avoided potential
disaster on Tuesday when the guy with the concrete pump showed up early and
advised that my forms didn't look strong enough.  Fortunately, I was able to
reschedule the concrete before they started filling the truck.  I've
included a couple pictures of the original forms so you can see my errors.
They were actually staked down a little better than the pictures show, but
they weren't any stronger in terms of not blowing apart from the pressure of
the concrete.  As you can see, they are made of 1/2" OSB, covered with 6-mil
plastic and braced with 2x4s.  There's nothing wrong with OSB, at least not
if it's covered with plastic, but it needs a lot of bracing.   According to
the guy with the concrete pump (21 years experience) it can absorb moisture
and get real soft if it's used uncovered.  I had the plastic already, left
over from another project.  If not, I would have purchased plywood instead
of the OSB.  I wish now I had just gone ahead and spent the extra bucks for
3/4" plywood.  Would have made things simpler but I still needed more

The form upgrade included extra studs and there are 5/16? lag bolts in
addition to the #8 & #10 deck screws used in the original version.  There
are also 7/16? all-thread rods running completely through the studs and
forms from side to side.  The ends just gets cut off before the forms are
removed, and obviously most of it becomes a little extra steel in the
concrete.  With the beefed up form, the long 2x4 top braces that were
supporting the form in the hole were not strong enough to hold the extra
weight so those were changed to 2x6s.  Even the 2x6s had quite a bit of
side-to-side bend to them so kickers were added between the bottom of the
form and the sides of the hole on the two sides susceptible to that problem.
I was also planning to add long 2x4s bolted perpendicular on edge, parallel
to the 2x6s to stiffen the top of the forms but the guy with the pump said I
probably didn?t need that at the top.  The pressure on the sides of the form
increases with depth, just like water pressure increases as you go deeper,
only with the weight of concrete compared to water, it increases much
faster.  That was taken into consideration when bolts and all-thread were
located in the form.

I rented a concrete vibrator ($40) to help the stiff, 4000-psi (6-sack, 3/4
agg.) mix flow into all the nooks and crannies.  It was very helpful.  We
obviously poked at the mud with a long 2x4 but that would not have been
enough.  The tower base plus all the rebar and the all-thread made it hard
to work the 2x4.  Even with all that poking and vibrating, the guys handling
the concrete hose didn?t move around enough (can?t blame them too much, that
hose full of concrete in incredibly heavy) and they got too much concrete in
some places and not enough in others.  That required a lot of work pushing
it around and it ended up shifting the top of the form about 3/4? to one
side (I should have installed those extra, two long 2x4s after all).  The
kickers kept it from moving at the bottom, and I built the forms 2? oversize
(4? of concrete covering the steel instead of the minimum 3?) so I still
ended up at the top with 3-1/4? of concrete on the thinnest side (and 4-3/4?
on the thick side).  You almost have to measure it to see it but if you look
close in the one picture of the finished block of concrete you?ll see that
the leg on the right is a little closer to the edge of the block than the
one on the left.  It doesn?t look like it in the picture but the spacing in
the other direction is right on.  There was no play in that direction due to
the way the form was constructed.  One thing that really went well was the
rock-solid stability of the tower base.  The only way it was supported was
by the concrete blocks it was sitting on, but the added ratchet straps that
secured the bottom of the legs to 3? stakes (scrap rebar, sharpened on a
grinder and drilled to accept three loops of heavy wire at the top) to the
bottom of the hole really did a job.  Not only did they hold the base
rock-solid, they were also useful in fine-tuning its level.

There are other things I could have done to prevent that 3/4? form shift.
Kickers at the top would have helped, or I could have run ratchet straps or
cable pullers or something else from the sides to stakes out in the lawn.
Those would have been in the way, however.  As it was, we had two near-falls
into the concrete (one of the hose handlers and me).  The best thing would
have been those extra 2x4s.

One other minor lesson involves the plastic covering over the OSB.  It did
its job but the guys with the hose kept putting their feet on the edge of
the form and dragging the hose over it.  That eventually tore the plastic in
one place and when we were using the edge-trowel while finishing the top,
that torn plastic got into the concrete so when I stripped off the forms the
top of the ?slab? had a rough corner in that spot.  You can also see
impressions in the concrete where the creases were located in the plastic
(It comes folded and rolled).  Those are only cosmetic things and this is
after all just a tower foundation, not a work of art.  (My wife says I?m a
perfectionist with OCD.)

Speaking of stripping the forms, I did that as soon as we finished cleaning
up.  They ended up pumping too much concrete in the hole and it partially
covered the outside of the bottom of the forms.  This was from pumping too
much, not from the concrete flowing out of and up around the bottom of the
form as I had feared.  It chopped out fairly easily at that point.  If I had
waited until the next day (as I sorely wanted) it would have been three
times the job.

The cleanup took almost as long as the pour.  The pump and hoses had to be
cleaned out and flushed and the concrete truck also had to clean out.  Of
those 11.5 yards of concrete, only about 11 ended up in the hole.  The rest
is in small piles, which will be gradually fed into the garbage.  It also
took a long time to clean off the asphalt driveway.

I now have to wait 28 days for the concrete to cure to 4,000 psi before I
start erecting the tower.  I have the hole around the pier filled with water
and I?m keeping the top wet, to slow the curing and, hopefully, prevent any

So much for ?Concrete-101.?  I will continue to post pictures and updates as
the project progresses.  When it is complete I will compile all my postings
into a digest of sorts, so others can get ideas and learn from my
(hopefully) few (hopefully) minor mistakes.

73 ? JC, K0HPS


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