Mesostructure-Enriched Constitutive Modeling of Fresh Concrete

The study aimed to develop a mesostructure-enriched constitutive model for fresh concrete. This required determination of an accurate means of computing the mesostructural strain because existing formulations proved inadequate due to the large deformations induced by the flow. A mesh-free smooth particle hydrodynamics–based strain that relies on mesostructural information computed from an underlying discrete-element method (DEM) solution, was developed. The mesostructural stress and strain, along with a mesostructurally determined yield stress, were then used to determine a suitable macro constitutive model. At strain rates up to 10 s−1, the Bingham model was seen to be accurate and yielded realistic estimates of the initial viscosity for mixes of low, moderate, and high flowability. The constitutive modeling also yielded insight on the role of mesogeometry in determining yield stress and viscosity. While the yield stress was found to increase with reduction in maximum aggregate size, it was much more sensitive to changes in aggregate angularity. The viscosity, while relatively insensitive to changes in aggregate size in the range of flowable concretes considered, showed a sharp increase with angularity. The role of mesoscale material parameters in determining yield stress and viscosity was explored. While an increase in mesostructural damping led to higher viscosity as expected, this was found to be true only up to a threshold. Further increases led to a sharp increase in the yield stress. A material fabric–based explanation for this phenomenon, which has also been observed in experiments on the effect of viscosity-modifying agents on flowable concretes, was found.