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RE: Large block of concrete

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I have specified low heat of hydration cement for mat foundations with
pours bigger than yours and have had no problems. These were pretty
heavily reinforced mind you, and I am not sure if yours has any. I
suppose another thing you could do is to use a low cement/high
pozzolan/large aggregate mix design. There are numerous other strategies
that can be used including:

cold water & cold aggregates
embedded cooling pipes
steel forms

The whole point is to minimize the temperature differential throughout
the structure but the above might be more for exotic items like dams.
Now wasn't there related problems at the Three Gorges Dam in China?


On Sat, 19 Jul 2003, Padmanabhan Rajendran wrote:

> Harold, the concrete guru:
>
> In the refinery and pipeline industries, often a large concrete block
is provided to support equipment such as a pump or a compressor skid.
>
> Let us say that one such block is 16' wide X 50' long X 8' deep. I
believe that the heat of hydration will be pretty large and the thermal
gradient may take years to get dissipated.  Thermal gradient would cause
microscopic cracks throughout the concrete. I have not seen any special
requirement called out in a typical concrete specification or in the
notes on the drawing. What are your thoughts? Should low heat cement be
used? If ues, what are the implications? Is there any other strategy to
lower thermal gradient? Staged construction may not be acceptable
because these clients are typically in a great hurry!
>
> I have come across thousands of dollars spent in repairing old
concrete block foundations for compressors. Papers that have been
published by agencies recommending and/or performing such repairs point
out that the concrete damage arose from the machine vibration. I wonder
if the problem was initiated by the microscopic cracks from thermal
gradients and susequently, machine vibration took advantage of the
weakened concrete.
>
> Thanks.
>
> Rajendran
>
>
>
>
> ---------------------------------
> Do you Yahoo!?
> SBC Yahoo! DSL - Now only $29.95 per month!


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