Don't rush! I'd wait the full 28 days.
With my LM470 after 3 weeks, we installed the raising fixture, but
didn't raise the tower until after 6 weeks.
IOW, no stress on the concrete for 6 weeks after the pour.
I would have done it at 4 weeks, but it took two weeks to get help, but
I was quite willing to wait a couple weeks for volunteers.
We had very little frost except for a really cold spell at the end of
winter, so the yard was soft and the hole was dug by hand (couldn't
believe how fast those guys dug a 4 X 4 X 7' hole,(came out a bit
oversize) set the wood frame and the base with the rerod cage. All
concrete was moved with wheelbarrows. The ground was still cold, but
most of the hole would have been the year round 50 some degrees. The
contractor was concerned about the heat from curing, because they
didn't want it speed curing. The concrete supplier said the 5 yards
shouldn't be a problem. Just give it plenty of curing time.
When raising the tower from horizontal there is a lot of stress from the
raising fixture. With the 1300# tower, the raising fixture applies
several tons to the base legs. At a couple of weeks the concrete is at
different cure states from the center to the outside edges.
Even lowering the tower straight down, that is still a fair load/stress
for concrete not fully cured, or at least almost cured. The last few %
takes a long time.
They stressed that with concrete, let it cure properly and don't rush!
73
Roger (K8RI)
1-207-476-00
On 7/25/2015 12:30 AM, Matt wrote:
This topic has come up before and I'm sure you will get a lot of answers, but
here's mine:
Most conventional concrete mixes will typically achieve about 50% of ultimate
strength within 7 days, and will develop about 75% of ultimate strength after
14 days. To answer your question, I have tilted up many crank-ups 2 and 3
weeks after the pour without any incident. I would be reluctant to try in
only one week.
Since the foundation functions as ballast, the main stresses occur in the vicinity of the
anchor bolts, so if you are using a raising fixture, you can actually achieve some pretty
good loads on the anchor bolts while in the process of tilting it up. If you are using
a crane or "cherry picker" to pull it up into place, there really is not much
load imparted on the anchor bolts.
Hope this info is helpful to you. Good luck on your project.
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Chris
Wynn via TowerTalk
Sent: Friday, July 24, 2015 10:25 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Concrete Pad for U.S. Tower TX-472
I am in the process of putting up a TX-472. So far, I have been relatively lucky and
things have gone pretty smoothly. I dug the hole using an excavator and
"slightly" over dug it by a few feet. From my initial calculations, I should
have needed just under 8 cubic yards, but ended up pouring 16 cubic yards (32 tons and
$2k more)! So far the concrete has sat for 7 days curing in the Georgia sun. I have been
pretty cautious to keep water on it, and covered pretty well. I know that the specs call
for that concrete to cure for 28 days. However, how early can I raise this tower? Does
anyone have any experience with cheating the 28 day curing period? I was kind of hoping
to raise it at the 21 day point. I guess the last real job is to trench from the tower
back to the shack. Therefore, I plan on spending the next couple of weeks burying
hardline.....
Thanks y'all and see you in the pile ups!
73's es CUL,
ChrisN4XFA
Christopher L. Wynn
Attorney-at-Law
Christopher L. Wynn, ESQ., P.C.
6716 Church Street, Suite B
Douglasville, Ga., 30134
(770)942-8661 (Landline)
(770)577-1626
chris@chriswynnlaw.com
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73
Roger (K8RI)
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