List readers:
Please go to the PCA (Portland Cement Association) or ACI (American Concrete
Institute) web sites and read the FAQs on concrete.
Concrete once mixed with water does not need additional water to assist the
exothermic reaction (generates heat) that allows the mixture to harden. The
reason you cure the exposed surfaces with water is to help to draw away the
heat and assisted in the limiting of shrinkage cracking at the exposed surfaces.
A mix designed for 2500 psi is a specification that it should develop 2500 psi
compressive stress strength in 28 days. It actually continues to cure to a
higher strength after that point but at an asymptotic rate where it would take
many years to get to some significantly higher strength value.
I typically specify 2500 psi concrete strength when designing amateur tower
foundations. I do so to avoid special inspection requirements by some
jurisdictions, as this is in the building codes. This allows for just about any
method of placement by any yahoo.
The "rule of thumb" is that after 1 week the concrete mix typically cures to
about 2/3's of its design strength, value whatever that is.
Keep your facts straight by doing some research. If you can post here, you
should be able to use "google" or another search engine.
Regards
Lonberg Design Group, Ltd.
H.Lonberg, P.E.,S.E. / KR7X
President
----- Original Message -----
From: "David Gilbert" <xdavid@cis-broadband.com>
To: towertalk@contesting.com
Sent: Wednesday, October 27, 2010 10:07:25 AM
Subject: Re: [TowerTalk] Concrete Strength
Concrete actually >cures< faster when damp. Concrete needs water to
form the chemical reaction that gives it strength, and without moisture
present it merely dries out.
73,
Dave AB7E
On 10/27/2010 6:36 AM, Mike wrote:
> It cures more slowly in the damp ground which is good, wait the recommended
> month.
>
> Mike, K6BR
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Dan Bookwalter
> Sent: Wednesday, October 27, 2010 5:18 AM
> To: towertalk@contesting.com
> Subject: [TowerTalk] Concrete Strength
>
> I seem to recall from about 8 years ago that concrete is up to 75% of its
> strength in 72 hours or something like that. UST calls out 2500 PSI concrete
>
> after 28 days , so that i don't have to wait a month i was going to use 4000
> PSI
> concrete and put the tower on it after a week or so , thoughts ?
>
> Dan N8DCJ
>
>
>
>
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