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RE: Concrete slump

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The slump test is not really an "accurate" test of anything, but it does
serve two purposes: 1) it gives a general indication of workability; 2) when
tested under similar conditions (e.g. at the point of discharge from the
delivery truck), it gives an indication of consistency in concrete being
supplied. Slump loss, as well as loss in air content, can occur during
pumping of concrete. Since the "solid" ingredients are the same going in and
coming out, it would seem that only the air in the concrete changes during
pumping. Generally a concrete mix used for transport and placing by means
other than pumping would need to be modified to be appropriate for transport
by pumping. 

ASTM C94 provides for testing at the point of discharge from the delivery
truck - this is to confirm that the concrete supplied by the batching plant
meets the specified requirements. The batching plant cannot control effects
on concrete properties after that point. Several requirements in ACI 301
require concrete testing "at the point of placement" - this is the point at
which the Engineer wants certain properties for placeability (slump) and
durability (air content). It becomes a tricky question as to where to test
the concrete being supplied and whether it meets spec or not. 

> -----Original Message-----
> From: James Allen [mailto:allen(--nospam--at)]
> Sent: Thursday, October 05, 2000 10:14 AM
> To: 'Structural Eng List Server'
> Subject: Concrete slump
> Does anyone have experience or know of technical resources 
> that address the change of concrete slump during placement by pumping.
> I have been told that the pumping process changes the concrete slump.
> 1. Is this correct?
> 2. If pumping does change the slump does the slump increase 
> or decrease?
> 3. Without additives, i.e. plastizers, water reducers, etc. 
> isn't  the slump test basically a measure of the relative 
> water content in the mix?
> 4. If the slump changes where does the additional water come 
> from if the slump increases or where does the water go to if 
> the slump decreases?
> 5. If the pumping process changes the slump, what is the 
> slump? Is it the slump of the design mix prior to pumping or after?
> Thanks for your assistance.
> James Allen, P.E
> Homer, AK