[TowerTalk] concrete

[Roger (K8RI) on TT]

On 11/2/2013 3:27 AM, David Gilbert wrote:
>
> That (heat) is not why you should keep the concrete moist. Concrete is 
> a hydraulic cure, meaning it requires water to cure. If concrete is 
> allowed to prematurely dry out it doesn't become strong until it gets 
> wet again, and may not ever reach the strength it would have if it had 
> remained wet.  A bit of surface water will do almost nothing to affect 
> the internal heat generated by curing, but it will greatly facilitate 
> the cure itself.
>
> By the way, too much water in the mix is not a good thing either, 
> because after the cure is complete the excess water will eventually 
> depart leaving small interstitial spaces ... and air is very poor in 
> compression.  ;)  The strongest concrete is that which just barely has 
> enough water throughout the curing cycle to complete the chemical 
> reaction.  That is rarely seen in practice, though, because such a mix 
> would be very stiff and hard to work ... certainly difficult to pour.

My garage and shop aprons are excellent examples of that.  It was one of 
the hottest days of summer. They put extra water in the mix to keep it 
from drying out.  No amount of watering would fix that. It looked great, 
but after the first winter's, surface freeze and thaws the surface 
spalled off. The contractor said it was due to the salt because the 
pattern followed the tires (loosely), but that was just hydraulic 
pressure forcing water into the voids.  I eventually cleaned it and gave 
it 3 coats of epoxy, but the concrete under that eventually came loose too.

73,

Roger (K8RI)

>
> 73,
> Dave   AB7E
>
>
>
> On 11/1/2013 12:20 PM, Tom Anderson wrote:
>> Doug:
>>   One thing you might do is what I was told when I put in my base 
>> back in 1993.  Lightly water the concrete base daily.  I mean 
>> lightly, no gushers,  etc. Just a sprinkle for a couple minutes.  
>> This helps take out the heat from the curing concrete.   I mnust have 
>> worked because my 4x4x6 ft base is still in fine shape as when I put 
>> it in.
>>   Tom, WW5L
>>
>
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