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Re: Concrete Mix Design Variations

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A possible short list includes:

Permeability (needs testing to confirm)
Air content - bubble characteristics (needs petrographic testing) - this is
probably irrelevant in your area, however.
Dusting

Strength may be a poor factor for decision making in a hot environment. The
28 day strength may reflect an equivalently longer curing period compared to
ACI assumptions in the specifications due to your hot weather. Consider
longer curing times to determine strength conformance.

James Cohen, PE
James Cohen Consulting, PC
http://expertpages.com/jccpc

----- Original Message ----- 
From: "Paul Blomberg" <blomberg_az(--nospam--at)yahoo.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, August 20, 2004 05:59 PM
Subject: Concrete Mix Design Variations


> I have a concrete supplier that is less than accurate
> when batching ready mix products.  The concrete
> suppliers water-cement ratios vary considerably and he
> loves to add water (beyond the ASTM tolerances) to
> achieve his desired slump.  When non-conformances are
> issued for the mix and the contractor goes ahead and
> places the concrete at his own risk, the usual
> performance measurement of 28 day strength is the
> governing factor.
>
> Any thoughts on what other critical characteristics
> are effected by higher water cement ratios.  I keep
> discussing shrinkage cracks and perhaps other
> durability issues but am trying to collect other
> opinions.
>
> The subject building is a cast in place concrete
> structure in the Phoenix, Arizona area (hot weather,
> mixes approaching the 90 deg. temperature limit when
> delivered).
>
> Appreciate your thoughts.
>
> Paul Blomberg
> Phoenix, AZ
>
>
>
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