Prediction of lubrication layer properties of pumped concrete based on flow induced particle migration

Abstract

Flow induced particle migration facilitates the formation of lubrication layer, which dominates the pumping performance of concrete. However, the properties of lubrication layer, such as thickness, composition, and rheological properties, are dynamic during the prompting process. In this study, a numerical model is proposed to model the formation of this lubrication layer from a new perspective of particle migration with consideration of wall effects which was often ignored in the past. To predict the properties of lubrication layer, diffusive flux models (DFM) of particle migration in non-Newtonian suspensions are extended to account for the wall effects. The proposed model is validated by ultrasonic velocity profile (UVP) experiments. The results show that, the wall effect induced particle migration makes a major contribution to the formation of lubrication layer, as well as the shear induced particle migration. The lubrication layer is found to be barren of aggregate but enriches in sand. In addition, the material and rheological properties of lubrication layer are inhomogeneous and not necessarily equivalent to that of mortar.