Title: Using Slump to Predict Pumping Pressure: A Scientific Fact or a Historical Coincidence?

Author(s): Dimitri Feys

Publication: Web Session

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Date: 10/23/2022

Abstract:
Pumping nomograms have been developed to predict pressure during pumping of concrete. These pump design figures include equivalent pipeline length, diameter, desired flow rate and a concrete workability parameter: slump. Recent research findings on more modern concrete mixtures have shown that pumping pressure is rather influenced by concrete viscosity and the capacity to form the lubrication layer near the pipe wall, compared to yield stress or slump. New nomograms were proposed replacing slump as a workability input. The slope of the pressure-flow rate relationship of the SLIPER, a device developed to measure flow resistance during pumping, works well in those nomograms. In this presentation, the relationship between pumping pressure and viscosity, SLIPER results and slump will be highlighted. When all other factors remain constant, there is a relationship between pumping pressure and slump, but its importance is relatively small compared to concrete viscosity. So, why did a pressure prediction based on slump work in the past? This is because highly efficient chemical admixtures were not yet developed. As such, concrete producers had limited tools to alter the mix design: w/cm, aggregate content, aggregate gradation and SCMs. And for most of these parameters, viscosity, and yield stress, and thus slump, are influenced simultaneously in similar fashion. With the development of these new chemical admixtures, the industry now has the opportunity to control viscosity and yield stress independently. As such, predicting pumping pressure based on slump is rather a historical coincidence.