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Re: [TowerTalk] Concrete, etc

Subject: Re: [TowerTalk] Concrete, etc
Date: Mon, 31 Jul 2006 19:23:16 +0000
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Phil and list:

Phil I agree with you and this is not directed at your comments but an attempt 
to get people to the best information on the subject.

I have actually posted several times a basic concrete primer to this list, but 
for those who missed them please go to ; then cement & concrete 
basics page; then to frequently asked questions. You will find most of the 
answers you need there. The site is a terrific starting point for  more in 
depth research if you need it.

Concrete cures asymtotically to its mix design strength. The rule of thumb is 
60% after 7 days. My concrete specs allow stripping of forms and construction 
loading of major loaded elements after 14 days. For a tower base 7 days would 
be a good conservative number. Mix design strength is stated at 28 days cure. 
It reality the actual strength achieved is somewhat variable and hardly ever 
meets the mix design exactly, usually a litte lower or higher but within a 
statictical derived limit.

Concrete is poured in forms in the ground to minimize the amount of concrete 
used, to compenstate for unstable soil or to create specific geometric shapes 
as required by the design. It is not poured in forms, in the ground, to 
eliminate weak points due to soil contact. It is poured in forms above ground 
for the obvious reasons as it needs to comform to some final shape in the air. 
Proper mix, placing and consolidation determine the quality of the final 

The water cure of concrete place in the ground, especially a single tower base 
foundation is not a bad idea. The sophisticated admixtures and continuous 
curing is used mostly for slabs and flat work and very large surface area 

Another web site to research ( american concrete institue). They 
publish the concrete building code.

Lonberg Design Group, Ltd.

H.S. Lonberg, P.E.,S.E. / KR7X
-------------- Original message -------------- 
From: (Phil Camera) 

> I'm no expert but have over 25 years of capital project experience and have 
> had 
> contractors pour all sorts of concrete for me for various reasons (slabs, 
> footings and foundation wall, slabs, pedestals, floors). 
> Some musings on the recent subject matter: 
> Guys around the Chicago area just use diesal or kerosene sprayed on the forms 
> after the forms are made, usually while waiting for the cement truck to 
> arrive. 
> Never have seen any sticking problems. 
> Forms are used in holes in the ground to keep the surrounding soil from 
> caving 
> in, not to make the shape of the concrete. From the pictures, it looks like 
> you 
> have good soil and no forms would be needed. I totally agree with the 
> warnings 
> about "properly" compacting backfill around a structural pedastal like what 
> you're building. If not done so, you may have a leaning tower. 
> In the hot weather or if exposed to sunny conditions, most lay a sheet of 
> plastic across the top and/or water underneath it a couple of times. The 
> first 
> week is crucial. 
> The concrete would be setup with a week but I would never start applying any 
> real load, like erecting a tower, until at least 3-4 weeks (that 28 days) is 
> up. 
> Concrete is continuosly curing, reaching 90+% of it's strength within that 28 
> days. Then it will completely cure to 100% in a few years (at least that's 
> what 
> I remember reading in the Concrete Construction handlbook we had back in the 
> Engineering library). 
> Phil KB9CRY 
> _______________________________________________ 
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