I should have said "dry out before it has cured to spec".
73,
Dave AB7E
On 10/27/2010 1:42 PM, David Gilbert wrote:
>
> That's probably true for large volumes of concrete like a tower
> foundation, and I stand corrected.
>
> It is NOT necessarily true for smaller volumes of concrete, especially
> here in Arizona, where the concrete can indeed dry out before it has
> cured. I've seen it happen more than once.
>
> In any case, damp ground does not make concrete cure more slowly.
>
> 73,
> Dave AB7E
>
>
>
>
> On 10/27/2010 11:47 AM, kr7x1@frontier.com wrote:
>> 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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