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Concrete Slump/Pumping

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I have experience in pumping concrete over 200 lineal feet horizontal and another 30+ feet vertical.  This enormous length was required for reaching newly constructed river piers without the added hassles of loading and unloading concrete trucks on barges and transporting the barges out to the pier.

On to the question...The slump will decrease.  This is due to the friction developed between the walls of the pipe and the concrete.  For the case I've mentioned, we used 5" slump ( this was a variance in the specifications) to produce a workable 3" slump at the discharge.  In addition, we had flyash and revised the mix design for a different sand which would also help with the flow.  The pipe is lined with a special material but as time goes on it becomes worn and adds to the problem.  Also, when priming the pump, a grout is run through the pump to line the interior of the pipe.

When testing the concrete for quality control, we did all testing at the pump rather than the discharge.  This was chosen with the idea that if the added water would delay the set and lower the strength, we wanted to know about it.  As it turned out, all went well and the concrete cylinders broke well above what was expected.  In some cases, tests were taken at the discharge for comparison.

I hope this helps.  You can usually talk with the pump manufacturers for specific technical questions.

John Finke, P.E., S.E.