Effect of material fabric on gravity flow in fresh concrete

The paper investigates the influence of material fabric on gravity flow in fresh concrete. A discrete element method (DEM) based approach is developed: polyhedral particles of random shape and size are used to model the coarse aggregates. This enables the effect of meso-geometry to be studied. A meso constitutive model appropriate for fresh concrete is proposed. The DEM model is experimentally validated, and used to simulate gravity flow. The results shed light on the role of fabric anisotropy, whose history is found to be crucial in determining the rate of slump and spread. The history of the flow is seen to be separable into a pre-peak fabric-dominated regime, where there is a sharp build-up in anisotropy, and a post-peak momentum-dominated regime, where randomness is restored to the fabric. The evolution of fabric anisotropy also provides information on the stability of the mix: a large drop in anisotropy in the post-peak regime is seen to coincide with a tendency for the larger particles to separate, contributing to slower spread. The overall conclusion is that gravity flow in a dense two-phase system such as concrete is sensitive to the interplay between fabric anisotropy and the intensity of the contact-driven constraints impeding flow.