A meso‑structure based yield stress for fresh concrete

Abstract

Existing empirical relations for predicting the yield stress of concrete are not of general applicability and provide no understanding of the role of meso‑structure. Moreover, experimental yield stress measurements tend to vary with the type of rheometer. The study proposes a discrete element formulation to compute a meso‑structure-based yield stress that is applicable to different meso‑geometries and is valid across diverse flow regimes. The procedure relies on a mesoscale model based on stresses and displacements, which makes it easier to account for the effects of particle shape, size, and orientation. The model incorporates coupling between normal and shear damage in the aggregate-mortar bond, thus enabling reduction in bond shear strength due to excessive stretching in the normal direction. Discrete specimens are generated to simulate well-known flowability tests. The results match experiments for both elongational and shear flow. The validated model is then used to investigate the effect of aggregate angularity and size. The results suggest that viscous forces are largely responsible for the experimentally observed increase in yield stress with reduction in maximum aggregate size. The meso‑structure-based yield stress is seen to be invariant with respect to the type of test and size of the specimen simulated. The predicted yield stress values also compare well with the BML rheometer and two-point test, with the mean percentage error with respect to the BML readings being around 2 %.