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Heading: 1.1slump loss through slick line pump
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I have a Ready Mix customer who is looking for any literature / publications / technical bulletins that explain why concrete looses slump when pumped. My customer is going to be pumping his mix through a slick line pump for a long distance and the contractor is nervous about slump loss. There seems to be some disagreement between my customer and the contractor as to the causes of slump loss through a pump. I have looked in the usual places and haven't found much written about the subject. Any information you can share would be greatly appreciated.




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John Cherne


John,
There are several reasons why concrete loses slump with time, e.g. loss of water due to:

• aggregate water absorption
• evaporation (a function of temperature, humidity and wind speed)
• chemical reaction with the cement.

Additionally, slump is lost during pumping because concrete is partially compacted as it moves through a pumpline. (It’s easy to envisage the effect of compaction on slump – just imagine measuring the slump of a concrete as it is being discharged from a truck then remeasuring it after the concrete has been compacted or partially compacted.)

However, pumps are often consider as being as being good quality control devices as a concrete mix is generally considered to be satisfactory, in terms of workability, if it can be pumped. And remember that slump does not measure workability; rather, it is a measure of consistency, useful in detecting variations in the uniformity of a particular mix.

Loss of air content in pumped concrete is normally considered more important than loss of slump – see NRMCA CIP 21.

See ACI 304.2R Placing Concrete by Pumping Methods for a more comprehensive understanding of the properties of pumpable concrete.


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Alan Kirby
 
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