Re: [TowerTalk] Rohn 25G clone born few minutes ago...

[Patrick Greenlee <patrick_g@windstream.net>]

The rule of thumb is 28 days to achieve 90% of final cure strength but 
this is modified by temperature of the air and ground, sunlight, 
available moisture (do you mist the surface frequently the first day or 
two if ambient temps are high), any additives to speed or slow the cure, 
and so on. Here in Oklahoma my PE soils engineer consultant supervised a 
pour done at 0200 local and within an hour or so they spread tarps over 
the surface and flooded the pour to a depth of a couple inches with 
water to reduce heat buildup. This was a quite large commercial building 
floor slab thickened in areas of loading.
Caution doesn't hurt in deciding when enough is enough, especially for 
hobby projects as a wait period likely is not costing BIG BUCKS EVERY 
HOUR. You can't wait too long but you can wait too little. I prefer to 
err on the side of caution (but  not ridiculously so.) Consider the 
ramifications of "messing up" the concrete and "losing" whatever you 
stuck into it, physically and monetarily.  Compare that to the, perhaps 
anxious wait of a few days.
In my personal concrete work I try to go by the book as to incremental 
cure strength, never approaching too close to the limits with my loading 
and then toss in a little extra wait time because I don't want to "mess 
up" and incur all the associated negatives of the downside.  I am not a 
concrete professional but I do own 3 cement mixers, two electric and one 
PTO powered for the 3 point hitch on the tractor and I admit to pouring 
way more concrete than the average bear.
My best advice is to take all the extant factors into consideration and 
add a safety margin that makes you feel comfortable. Remember all the 
outside advisers and their opinions, including mine, are not connected 
to any liability so don't let any of us get you into trouble.
Patrick        NJ5G


On 1/11/2016 11:08 PM, DALE LONG wrote:
> For most purposes 7-10 days should be enough to begin building a tower.  No 
> need to wait one month unless you are building a monster tower.
> Dale - N3BNA
>   
>
>        From: Ed Sawyer <sawyered@earthlink.net>
>   To: towertalk@contesting.com
>   Sent: Monday, January 11, 2016 11:12 PM
>   Subject: Re: [TowerTalk] Rohn 25G clone born few minutes ago...
>     
> Congrats Douglas!
>   
>
> The Concrete manuals say that concrete will reach 75% of its 28 day rated
> strength in 7 days.  Almost 90% in 14 days.  For tower building, 14 days is
> already overkill.  7 days is plenty.  Obviously, the other question is what
> was the specified mix strength.  If you have 5000PSI concrete, then its
> already stronger than typical building foundation concrete after only 7 days
> of cure.
>
>   
>
> Ed  N1UR
>
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