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RE: Concrete slump

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For what it's worth, I've been told that one of the main reasons contractors
have problems with pumping a mix is skip grading of the course aggregate.
Because certain fractions are often reserved for asphalt, you tend to be
missing the middle sizes. Often, just by doing some modification to the
gradation, the pumpability improves dramatically.

-----Original Message-----
From: James Allen [mailto:allen(--nospam--at)]
Sent: Thursday, October 05, 2000 9:14 AM
To: 'Sturctural 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