Discrete-element modeling of shear-induced particle migration during concrete pipe flow: Effect of size distribution and concentration of aggregate on formation of lubrication layer

The paper seeks to better understand the particulate mechanics giving rise to the lubrication layer (LL) in flows with wide particle-size distributions (PSD) typical of concrete pumping applications. The study uses a soft-sphere discrete element method (DEM) to simulate the shear-induced particle migration (SIPM) mechanism of formation of the LL. To provide realistic understanding of SIPM and rheological heterogeneity of concrete, three wide PSDs (fine, medium, and coarse) and three different concentrations (10 %–40 %) of five spherical-particle subclasses (1–17 mm diameter) were investigated. The radial evolution of concentration and particle distribution was simulated over time and the LL formation was successfully simulated. The predicted LL thicknesses compared well with experimental values. The coupled effect of PSD, concentration, and mean diameter of particles on wall effect, SIPM, and rheological heterogeneities across the pipe was evaluated. Higher rheological heterogeneity across the pipe was obtained for higher concentration and coarser particle size distributions.