[TowerTalk] FW: Concrete Pad for U.S. Tower TX-472

[Roger (K8RI) on TT]

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 at contesting.com] On Behalf Of Chris Wynn via TowerTalk
> Sent: Friday, July 24, 2015 10:25 PM
> To: towertalk at 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 at chriswynnlaw.com
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk


-- 

73

Roger (K8RI)


---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com