A Computational Approach to Estimating a Lubricating Layer in Concrete Pumping

When concrete is being pumped, a lubricating layer forms at the interface of the inner concrete and the wall of the pipe. The lubricating layer is one of the most dominant factors in determining the pumping capability, yet no study has endeavored to quantitatively estimate the thickness and rheological properties of the layer. Recently, there has been a growing demand for large-scale construction under extreme conditions, such as high-rise buildings and super-long span bridges. This demand has heightened the need for more accurate predictions of pumpability.
A possible mechanism that contributes to the formation of the lubricating layer is shear-induced particle migration. That is, particles of suspension in the shear flow move from a region with a higher shear rate to a region with a lower shear rate. This study uses computational fluid dynamics to analyze the pipe flow of concrete under conditions of shear-induced particle migration. The analysis shows how the particle distribution as well as the plastic viscosity and yield stress vary throughout a particular cross section. The analysis results are used to estimate the thickness and rheological properties of the layer.